# 3 phase dimmers on 1 phase service??



## lightingguy1 (May 22, 2011)

Hi guys,


I have been designing a local community show that has rented 2 24 Sensor dimmer racks, ETC Instruments, and a Express 250. They have turned an (make that REALLY) old african american school into a theater. 

I was talking with the somewhat head electrician the other day, and he said that the dimmers are operating on single phase power. When I went to visit the dimmer room/supply closet, I saw the 2 racks and 3 phase camlok connectors connecting power to the dimmers.

Now, why would there be 3 phase camlok connectors in a single phase system?? In the garage/shop, There is a main panel, and then off of that is a service disconnect box. 5 Cords( L1,L2,L3,Neu.,Ground) come out from there and then go on to the Dimmer room. 



I will try to get pics uploaded on monday.
Thanks!
-Lightingguy1


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## techieman33 (May 22, 2011)

sounds like the "head electrician" doesn't understand what he's talking about, or someone did some extremely creative wiring in that box.


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## lightingguy1 (May 22, 2011)

naharnahekim,

The problem with that is, these dimmers arn't the SP6 or the SP12 model. 

To all of the thread,

On the service diconnect box, I want to say that there are 6 breakers physically connected to one another, so you can't turn one off by itself.


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## mstaylor (May 22, 2011)

That definitely needs a picture. It is possible to run lights off single phase and do what they call faking a phase. It isn't a great thing to do because you are pulling two legs off one side. 
Take pictures of the disconnect and dimmer setup.


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## bishopthomas (May 22, 2011)

lightingguy1 said:


> he said that the dimmers are operating on single phase power. When I went to visit the dimmer room/supply closet, I saw the 2 racks and 3 phase camlok connectors connectting power to the dimmers.
> 
> 5 Cords( L1,L2,L3,Neu.,Ground) come out from there and then go on to the Dimmer room.



Quite simply, your janitor is an idiot.


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## David Ashton (May 23, 2011)

At this point it may be worth mentioning that all individual dimmers are single phase, the 3 phase is only the power distribution to the dimmers.You can run a 3 phase dimmer on single phase, all you need to do is triple the size of the neutral.Having said that there is one model of dimmer I worked on which took control volts across 2 phases, but as far as I know that was unique.


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## JD (May 23, 2011)

David Ashton said:


> At this point it may be worth mentioning that all individual dimmers are single phase, the 3 phase is only the power distribution to the dimmers.You can run a 3 phase dimmer on single phase, all you need to do is triple the size of the neutral.Having said that there is one model of dimmer I worked on which took control volts across 2 phases, but as far as I know that was unique.



This is true. In fact, the CEM is only concerned with which dimmers are connected to which phase leg; L1, L2, or L3. When the rack is changed from Single Phase to Three Phase, (or the other way) buss arrangement is changed. If it were set for single phase and the power was actually three phase, the phase of firing circuit for a given dimmer would be wrong and with all controls set at 0, 1/3 of the rack would be on 33% and 1/3 would be on 66%. 

However, if you took L1, L2, and L3 and connected them all to one hot leg, the three ramps would be the same for either configuration and the dimmer rack would work fine in theory. (In practice, the CEM software may flag an error, never tried it on an ETC.)

Often, when benching road racks for service, that is exactly what I would do as I didn't have three phase available in my shop. If you actually used a rack this way for a show, the big issue would be the cable sizing and OCPD size, although I have no idea why you would want to. 

Most likely, bishopthomas is probably correct! (Although it is not impossible.)


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## derekleffew (May 23, 2011)

JD said:


> This is true. In fact, the CEM is only concerned with which dimmers are connected to which phase leg; L1, L2, or L3. When the rack is changed from Single Phase to Three Phase, (or the other way) buss arrangement is changed. If it were set for single phase and the power was actually three phase, the phase of firing circuit for a given dimmer would be wrong and with all controls set at 0, 1/3 of the rack would be on 33% and 1/3 would be on 66%. ...


I've never seen dimmers output anything other than 0V when CEM phase settings are incorrect. A more common symptom is some of the dimmers (the "middle" ones, IIRC) not having dimming capability.


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## JD (May 23, 2011)

derekleffew said:


> I've never seen dimmers output anything other than 0V when CEM phase settings are incorrect. A more common symptom is some of the dimmers (the "middle" ones, IIRC) not having dimming capability.


 
Oh yea. Might be inhibited on the ETC, never tried it, but used to see it often on other systems. The ramp generator is getting ZVD at the wrong time. The dimmers that are in sync run fine, the dimmers on leg two are at 33% and go to 100% at about 2/3ds (liner) then wink out and come back up to 1/3rd at full brightness, and leg three is the same, but start at 66% etc.

The old, old analog dimmers like TTI and EDI did not have a problem because there was an individual ramp generator built into each channel card.

*EDIT: Memorable occurrence:* 
Did a club job, two stages. The other stage was being set up for Frank Stallone (brother of Sly.) About an hour before show time heard a lot of yelling coming from the other stage. Wasn't long before someone grabbed me to look into their "strange problem." Rack was set up with first generation non-analog EDI and was wired for single phase. (HHNG) About 1/2 of their lights were on even though the board was blacked out. I moved the dimmer through its range and had my "ah-ha" moment. Source looked like single phase but was actually two legs of three phase wired into a single phase breaker panel. Hadn't had much experience with digital back then, but suspected it had little to do with the digital part. Since they had sufficient capacity on their feeder, and the supply OCPD was large enough, I swapped everything onto one leg. Everything worked fine. Was their third show out and first time they ran into this. I assured them it would not be their last and told them to contact their vendor who will remain nameless.


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## mstaylor (May 23, 2011)

We have done the fake the leg trick on road racks when three phase isn't available but we do it with small rigs, 25 or 30k total. That way we don't go over our nuetral rating.


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## lightingguy1 (May 23, 2011)

Hi guys,


So I went and took some pictures of the dimmers and power situation today after rehersal. As it turns out, when I was authoring this thread at 2 AM in the morning, I was assuming that all of the Camlok connectors were connected to the racks - You know what they say about assuming things, right? - Well, The Red Camlok connector was nowhere to be found! 

......See pics below/Attached.......


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## DuckJordan (May 23, 2011)

It looks like a single phase setup to me, that or a two phase which I'm not sure its possible to use on dimmer racks I know some higher horsepower electric motors can use two phase.


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## mstaylor (May 23, 2011)

That is definitely a single phase set-up. I assume that the buses inside the dimmers can be changed to split the dimmers to two 110v legs instead of three. I know we used to do it with old TTI racks but never opened any ETC dimmers.


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## robartsd (May 23, 2011)

mstaylor said:


> That is definitely a single phase set-up. I assume that the buses inside the dimmers can be changed to split the dimmers to two 110v legs instead of three. I know we used to do it with old TTI racks but never opened any ETC dimmers.


 
I have seen the ability to do this listed on some ETC spec sheets.


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## JD (May 23, 2011)

Someone doesn't like red I guess. Usually, blue is the color left behind. Single phase it is. (or two of three)

Most packs can be set up both ways. That's why the number can usually be divided by two or three, such as 6, 12, 24, 48, 96. Although many require you to relocate feeds coming off of the pack's main lugs.


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## soundlight (May 23, 2011)

Also, those _are_ SP12 racks - the 12 refers to the number of modules. The modules are double density (2 dimmers to a module) so 12*2=24. The SP12s can be changed to single phase inside by reconfiguring the buss bars, as stated before, so that's definitely what happened if the dimmers are running properly.


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## mstaylor (May 23, 2011)

JD said:


> Someone doesn't like red I guess. Usually, blue is the color left behind. Single phase it is. (or two of three)
> 
> Most packs can be set up both ways. That's why the number can usually be divided by two or three, such as 6, 12, 24, 48, 96. Although many require you to relocate feeds coming off of the pack's main lugs.


I started to mention the blue/red thing but thought it was just me being picky.


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## JD (May 23, 2011)

mstaylor said:


> I started to mention the blue/red thing but thought it was just me being picky.


 
Yea, can't say too much on that. I am guilty of sometimes leaving black behind just because I think it is a boring non-color.


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## lightingguy1 (May 23, 2011)

Ok - Thanks guys! 

I still have a few questions that have stayed unawnsered, so here is one of them,

If it is single phase then why do we have the 2nd leg attached? And how does this Faking a leg work?


Thanks!
Btw, I never really did understand ETC's 2 Dimmers on one module thing. Thanks Soundlight!


-Lightingguy1


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## derekleffew (May 23, 2011)

lightingguy1 said:


> ... If it is single phase then why do we have the 2nd leg attached? ...


split-phase - ControlBooth

See also the thread http://www.controlbooth.com/forums/lighting-electrics/20234-more-phase-questions.html .


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## chausman (May 24, 2011)

lightingguy1 said:


> ...I never really did understand ETC's 2 Dimmers on one module thing.


 
Do you mean having dimmers 1+2 on a single module, or using dimmer doublers?

Having 2 dimmers on one module just makes things easier by going in pairs. Less moving parts by having fewer things going in and out of the rack. Less cost by having to buy fewer dimmers.

If your talking about dimmer doublers...set them down, leave them alone, and don't make eye contact...just back away slowly...no one fully understands the dimmer doublers.


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## rphilip (May 24, 2011)

JD said:


> Someone doesn't like red I guess. Usually, blue is the color left behind. Single phase it is. (or two of three)


 
This is only a guess but might the reason that red is not being use be that red is the middle color and for a split phase rack 1/2 of the middle 1/3 is moved to each of the other thirds?

ie normally it's 1-8 on black, 9-16 on red and 17-24 on blue. For split phase I'd guess that 9-12 are rebussed to the upper lug (black) and 13-16 moved down (to blue)

Philip


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## cdub260 (May 24, 2011)

chausman said:


> If your talking about dimmer doublers...set them down, leave them alone, and don't make eye contact...just back away slowly...no one fully understands the dimmer doublers.



Hey! I like my dimmer doublers!


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## lightingguy1 (May 24, 2011)

chausman said:


> Do you mean having dimmers 1+2 on a single module, or using dimmer doublers?
> 
> Having 2 dimmers on one module just makes things easier by going in pairs. Less moving parts by having fewer things going in and out of the rack. Less cost by having to buy fewer dimmers.
> 
> If your talking about dimmer doublers...set them down, leave them alone, and don't make eye contact...just back away slowly...no one fully understands the dimmer doublers.


 
Let me Rephrase that a little - I never did understand the ETC's Circuit calulation thing.

i.e. - "ETC 24 x 2.4k with CEM+ Portable Pack" - From 4wall's site

The 24 part, in my mind, is the number of modules, not the total amount of circuits available on the rack itself. Not so!


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## chausman (May 24, 2011)

cdub260 said:


> Hey! I like my dimmer doublers!


 
Never said they weren't useful, just that they are more mystical and magic then DMX...and Microwave Popcorn!


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## lightingguy1 (May 24, 2011)

As far as the Dimmer doublers go, I might have to use some! In the Current show, I am wanting to hang a few more systems of Backlight 

Or steal the Chauvet Colorado Batten 72 Tours we have in the closet down the hall!


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## derekleffew (May 24, 2011)

lightingguy1 said:


> ...The 24 part, in my mind, is the number of modules, not the total amount of circuits available on the rack itself. Not so!
> 
> See what I mean?
> 
> Btw, I'm the generation that mentally overcomplicates things


Ah, but in the case of Sensor, each module can be 2, 1, or 1/2 dimmers. So the number of dimmers and their size is really the important part. While the model number may be SP12, calling it a 24x2.4kW dimmer pack is more useful, IMO.


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## Dionysus (May 24, 2011)

DuckJordan said:


> It looks like a single phase setup to me, that or a two phase which I'm not sure its possible to use on dimmer racks I know some higher horsepower electric motors can use two phase.


 
There is no such thing as "two phase", either "single phase" or "three phase". Having one or two 'phases' present is still called "single phase". What you are referring to are separate voltages, 120v 240v and 220v (we'll ignore 347v, 208v, etc). 240v and 220v require two opposing phases, and 220v requires a neutral.

These dimmers only utilize 120v. As mentioned already each 'phase' or 'hot leg' is divided to an equal proportion of the dimmers (and sharing the same neutral), giving them each 120v.

A good example of common 'true' 240v or 220v loads would be larger electric motors or electric heating elements. They work much more efficiently at these higher voltages than at 120v.


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## tmm61 (May 24, 2011)

great pics.

the picture of the main breaker (labeled service discount) also says it all: 4 sections with a tie handle -- this has been a "standard" configuration with some manufacturers in the past for a 200amp single phase 240/120volt main panel. (two 200amp 120 volt phases).

(several posters might owe the "somewhat head electrician"/ _"janitor"_ an apology--many/most building electricians do have a basic understanding of their power systems, even if they do not understand the equipment we have rented or brought in)

no offense to anyone.


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## Chris15 (May 24, 2011)

Dionysus said:


> There is no such thing as "two phase", either "single phase" or "three phase".



Well actually... there is. It's just confined to academia becuase it has no practical usefulness. A true 2 phase system would be a sinusoid and a cosinusoid.
But zero practical use in the *real* world except possibly the aforementioned odd motor. Real motors would use 3 phase IMHO.


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## JD (May 24, 2011)

Chris15 said:


> Well actually... there is. It's just confined to academia becuase it has no practical usefulness. A true 2 phase system would be a sinusoid and a cosinusoid.
> But zero practical use in the *real* world except possibly the aforementioned odd motor. Real motors would use 3 phase IMHO.



Just ask Frank Stallone's road crew!  (see my post above http://www.controlbooth.com/forums/...phase-dimmers-1-phase-service.html#post216546 )

There's two legs there, but they're happening at different times.


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## Dionysus (May 24, 2011)

Chris15 said:


> Well actually... there is. It's just confined to academia becuase it has no practical usefulness. A true 2 phase system would be a sinusoid and a cosinusoid.
> But zero practical use in the *real* world except possibly the aforementioned odd motor. Real motors would use 3 phase IMHO.


 
lol, true enough. However I was 'ignoring' such a system, as you really don't see them in real life and talking about stuff like that just gets too confusing for most people.

lol if only all motors were 3-phase. There are so many bloody types of motors, lol.


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## bishopthomas (May 24, 2011)

tmm61 said:


> (several posters might owe the "somewhat head electrician"/ _"janitor"_ an apology


 
Sorry, Janitor Joe. You always make the best electrician in the whole wide world...


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## lightingguy1 (May 24, 2011)

Hi guys,


Let me see if I get this Bi-phase concept. 

ETC's Smartmodule 2 Dimmer Packs (Bi-phase models) and Leprecon's ULD Series dimmers (those that are the high power models), require two power connections, or 2 Hots, 1 neutral, and 1 ground wire for the ETC stuff, for operation...and we call this Bi-phase? 

But we Pros call the second line a phase?...So Phase A and B?


Thanks!
-Lightingguy1


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## mstaylor (May 24, 2011)

Two hots, nuetral and a ground is a single phase. It is 110v per leg and fire 180 degrees from each other. They are called legs when added together makes 240.


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## derekleffew (May 25, 2011)

lightingguy1 said:


> ...Let me see if I get this Bi-phase concept.
> 
> ETC's Smartmodule 2 Dimmer Packs (Bi-phase models) and Leprecon's ULD Series dimmers (those that are the high power models), require two power connections, or 2 Hots, 1 neutral, and 1 ground wire for the ETC stuff, for operation...and we call this Bi-phase?


ETC is the only source where I've seen the term "bi-phase" and only recently, on the spec sheets for the SmartModule, as you have noted.
"Single 12/4 SO cable for 120/240V single (bi/2) phase feeds"
"4 circuit SmartModule 2, Bi-phase (2 x 20A) Single Cable in, Stage Pin Out"

The phrase "split-phase" is also relatively new (~10 years old?), but more universally accepted, and needed in an attempt to avoid confusion between 1Ø 120V, and 1Ø 240V.

As said above, with 1Ø 240V, the wires are usually identified as L1, L2, N, G.


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## lightingguy1 (May 25, 2011)

This is good!

Now we're getting somewhere!! And what type of Connector would a "Bi-phase" Smartmodule dimmer require?


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## derekleffew (May 25, 2011)

lightingguy1 said:


> And what type of Connector would a "Bi-phase" Smartmodule dimmer require?


The most common for stage use is likely a NEMA L14-20:


But any UL Listed, 3P4W 20A 125/250V connector would be acceptable, which is why ETC makes the user supply his/her own.


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## TimMiller (May 25, 2011)

One trick I have done when you have two 3 phase dimmers or distros on a single phase service is alternate the legs. Leg 1 will go to line 1 leg, leg 2 will go to line 2, leg 3 will go to line 1, in the second rack leg 1 will then go to line 2, leg 2 will go to line 1, then leg 3 will go to line 1. It keeps the loads fairly balanced and also works the other way around. I don't like opening up a dimmer rack and rearranging the jumpers if I can avoid it.


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## DavidNorth (May 25, 2011)

I'm a little surprised that someone from the UK or EU hasn't joined in on this one....

ETC has decided to start calling things bi-phase [same as split-phase] for a very good reason. In the UK, for example, when you talk about a single-phase service, it is only one phase of power. In the US, single-phase usually means two phases of power at 180 degrees apart, but not always.

In order to reduce confusion and get product documentation and orders straight, while still being technically correct, we have gone to bi-phase.

So on another topic [which was mentioned earlier in the chain], not all dimming systems on the market sample each incoming phase of power to derive their firing signals. There are a few bi-phase and three phase inexpensive dimming products that require the correct phasing and phase order of power to correctly dim. Just thought I would throw that out there to chew on and be aware.

BTW, there are two-phase and four-phase systems out there. They're just not that common.

David


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## mstaylor (May 25, 2011)

Tim, your explanation left out some qualifiers. I understand what you are doing but without double cam locations on either the dimmers or distro, what you are saying doesn't make sense. You have to jump the third leg off one of the others and that is what the second row of cams are for, in this case. Also, I don't see how it will balance the load any. No matter the order, you will always be pulling two legs from one other. That means you have to stay under that leg's limit with the two combined, plus the nuetral needs to be oversized. 
I'm not saying you are wrong, just it may be unclear to someone with less experience than yourself.


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## JD (May 25, 2011)

Easiest way to tell Single Phase from two legs of Three Phase is to look at the hot-to-hot voltage:

Single Phase ~ 240 volts

Not Single Phase ~ 208 volts


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## TimMiller (May 26, 2011)

JD said:


> Easiest way to tell Single Phase from two legs of Three Phase is to look at the hot-to-hot voltage:
> 
> Single Phase ~ 240 volts
> 
> Not Single Phase ~ 208 volts


 
Definitely not always true. When you are using 3 phase 120/208 wye it is but there are buildings that have 3 phase delta. In delta you will have 120 on two legs and measure 240 between them but you will have a single hot or "wild" leg of 208. Never tap directly onto this leg unless the equipment is specifically designed for it and it IS NOT COMPATIBLE WITH MOVERS THAT STATE 208V OPERATION. Always meter all three legs of 3 phase power and between all 3 so you know exactly what you are working with.


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## David Ashton (May 26, 2011)

The joys of US power systems


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## STEVETERRY (May 26, 2011)

David Ashton said:


> The joys of US power systems


 
Err....how about we move on to the joys of grounding systems in the rest of the world?

http://en.wikipedia.org/wiki/Earthing_system

After we get done with that, US power systems look pretty simple! 


ST


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## Chris15 (May 27, 2011)

STEVETERRY said:


> Err....how about we move on to the joys of grounding systems in the rest of the world?
> 
> Earthing system - Wikipedia, the free encyclopedia


 
ST, I'm curious which particular bits of international Earthing practice you might be referring to...


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## JD (May 27, 2011)

TimMiller said:


> Definitely not always true. When you are using 3 phase 120/208 wye it is but there are buildings that have 3 phase delta. In delta you will have 120 on two legs and measure 240 between them but you will have a single hot or "wild" leg of 208. Never tap directly onto this leg unless the equipment is specifically designed for it and it IS NOT COMPATIBLE WITH MOVERS THAT STATE 208V OPERATION. Always meter all three legs of 3 phase power and between all 3 so you know exactly what you are working with.



If you are using two legs of Delta to power a lighting system then you are working off of the one center tapped leg, which is single phase. (120-0-120, 240v) We are talking in this thread about a feed that appears single phase. In this case, the rule in my post above would apply.


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## STEVETERRY (May 27, 2011)

Chris15 said:


> ST, I'm curious which particular bits of international Earthing practice you might be referring to...


 
Anything but TN-C-S.

ST


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## David Ashton (May 28, 2011)

I find it really difficult to conceptualize how dimmers can work on a delta trnsformer, I would have thought that the chopped waveform would play havoc with a "closed" system like delta, can you elucidate?


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## JD (May 28, 2011)

David Ashton said:


> I find it really difficult to conceptualize how dimmers can work on a delta trnsformer, I would have thought that the chopped waveform would play havoc with a "closed" system like delta, can you elucidate?


 
(In the USA)

A floating Delta cannot be used for lighting. (Unless you are only splitting it up to run a bunch of movers that run on 240 volts!) Each hot-to-hot measures 240 volts, and there is no hard connection to (what would be) the neutral. There are often bleeder resistors, or other drains (like MOVs) that may give you fictitious readings with reference to neutral or ground. No load can be placed there.




More common, or at least the one we would see used for lighting, is that one of the three windings is center-tapped. So, you have three windings connected end to end, giving you A, B, and C. We will say the winding between A and B is the center tapped one. As such, we are actually running a single phase system. The "center tap" is your neutral, and you therefore have 120-0-120 from your H-N-H. The third phase leg is where the other two windings come together, and is often called the "wild leg" as it is 208 to neutral. For practical purposes, this would not be used. (Or, at least, I would not want it mixed in with my feed!)

This type of Delta was common in buildings with mixed usage. All the heavy air conditioning would be run off the Delta 240-240-240, yet you would also have some 120 circuits for offices and such. Where I am in PA it has fallen out of favor. Almost everything is Wye, where you have three legs of 120v and 208 between the hots to run AC and heavy equipment.

The heavy chopping (caused by dimmers) in this circuit will occur across the tapped winding, but you are right in that the Delta is a balanced closed loop, so any sag caused by the chop is going to partially be felt on the other two windings. I am sure someone out there has done the math, but the loading to fill the sage would be fractional on the other two legs. On the bright side, since it is basically a single phase (0 / 180) circuit, there would be no neutral over current. 

_Picture credit: Random graphic found on internet _


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## lightingguy1 (May 28, 2011)

Hey guys,

Thanks for the over my head Information!

Now, I do have one of those, What would happen electrical questions.....

In theory, If someone had regular 150 amp home Service, and had 3 circuits from a regular panel, connected to, say an ETC Smartpack Dimmer. Each circuit rep.-ing a phase, with the three nuetrals for the Nuetral connection, What would happen when you went fire this puppy up?


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## mstaylor (May 28, 2011)

I'm not sure what you are asking. Are you saying you are pluging into three wall outlets in an attempt to power three phases? A household panel is 99% probably to be single phase. Now try refining your question.


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## David Ashton (May 28, 2011)

Should work fine


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## lightingguy1 (May 29, 2011)

Mstaylor,


No, thats not what I meant, but I guess thats rather the same concept.

If you installed three breakers, each rated for 40 Amps, and had the wires coming from there (Hot x 3, Neutral x 3, and ground x3 ) going over to the Dimmer Pack in this fashion:

Example,

Hot 1 = Phase 1 // Hot 2 = Phase 2 // Hot 3 = Phase 3

Neutral 1,2,3 = Neutral

Ground 1,2,3 = Ground


Make sense?


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## mstaylor (May 29, 2011)

Sure, it would work except most residential electric is single phase, two legs of power at 110v per leg. If you look at your panel you will see four wires coming in, two hot, one neutral and a ground. 
Another problem is you have to have connected breaker, a double pole breaker, to be compliant. At that point you are back to faking a leg.


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## David Ashton (May 29, 2011)

Are the 2 hot wires the same size as the neutral?


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## epimetheus (May 29, 2011)

David Ashton said:


> Are the 2 hot wires the same size as the neutral?


 
Generally speaking, yes.

Sent from my Xoom using Tapatalk


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## mstaylor (May 29, 2011)

In most cases yes.


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## JD (May 29, 2011)

David Ashton said:


> Are the 2 hot wires the same size as the neutral?


 
If you are faking three phase by running three hots off a single phase source, then two of those hots are coming off the same phase leg. Therefore, your neutral would have to be upgraded to the equivalent of twice the size of your hot lines if you are using a common neutral. H-H-H-2N-G

If you are running a simple single phase (H-H-N-G) then they would be the same gauge as long as your two hots are off opposing legs. ( 0/180 p)


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## David Ashton (May 30, 2011)

and what power system produces 2 phase with 180 degree phase difference? any 2 phases off a standard supply are going to be 120.


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## Chris15 (May 30, 2011)

David Ashton said:


> and what power system produces 2 phase with 180 degree phase difference? any 2 phases off a standard supply are going to be 120.


 
Their bi phase is a centre tapped single phase system, so yes there will be 180 degrees of phase shift...


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## mstaylor (May 30, 2011)

David Ashton said:


> and what power system produces 2 phase with 180 degree phase difference? any 2 phases off a standard supply are going to be 120.



In the US there are typically two types of multi-legged power. First is single phase, which is two legs of power(120v to ground), a neutral and a ground. Second is three phase Wye, which is three legs of power( 120v to ground), sometimes a neutral and always a ground. If you are using it for something like lighting then a neutral is needed. If you are running motors where it is always balanced then no neutral. Delta is the third type. It has three legs of power, two 120v to ground, one 208v to ground.


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## TimMiller (May 31, 2011)

JD said:


> If you are faking three phase by running three hots off a single phase source, then two of those hots are coming off the same phase leg. Therefore, your neutral would have to be upgraded to the equivalent of twice the size of your hot lines if you are using a common neutral. H-H-H-2N-G
> 
> If you are running a simple single phase (H-H-N-G) then they would be the same gauge as long as your two hots are off opposing legs. ( 0/180 p)



If you are faking 3 phase off of single phase you do not need to overrate the neutral. The neutral cannot exceed the capacity of any single leg from the single phase system. For example I have a single phase panel feeding a three phase dimmer rack. The panel has 2/0 HHN cables coming in and the main breaker has a rating of 200 amps. I have 3 100 amp breakers feeding off of the panel to the dimmer rack. Line 1 of the panel has two of the 3 legs of the dimmer rack connected. I turn on the first set of the dimmers that are all on leg 1 of the dimmer. Let's say I pull 100 amps. I show pulling 100 amps on the neutral and L1 of the panel. I now turn on the second leg of the dimmer rack also pulling 100 amps. So now line 1 and 2 on the dimmer rack is showing 100 amps each but now the neutral is showing 0 amps. Line 1 and 2 since they are each 180 degrees out of phase they are canceling themselves out on the neutral leg. Ok I now turn on all the dimmers on leg 3 of the dimmer rack. I am now pulling 200 amps on L1 of the panel and 100 amps on L2. I meter the neutral and it shows I am pulling 100 amps due to the 100 amps on L2 is canceling out 100 of the 200 amps on L1. Ok lastly I now turn off leg 2 of the dimmer rack. I now have 200 amps on L1 and 0 amps on L2. My neutral is now metering at 200 amps. I cannot exceed the rating of the neutral at 200 amps without popping the main breaker.


The numbers are for demonstration purposes only. Remember not to exceed 80 percent of the breaker or you may be sitting in the dark.


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## derekleffew (May 31, 2011)

Tim, let me see if I understand your scenario:

Feed:..........................DimmerRack:
L1 (200A capacity)........ØA (100A load)
L2 (200A capacity)........ØB (100A load)
L1 (200A capacity)........ØC (100A load)
Neutral current cannot exceed 200A. For argument's sake, let's say that all wire is 2/0, which in this application is rated for 200A.

Your example appears to negate the reasoning for a dimmer rack's double neutral [and NEC 520.53 (O)(1) ]:

STEVETERRY said:


> ... Note that a three-phase dimmer rack without internal conversion to single phase (240/120V 3W+G) requires a double size neutral terminal. Why? The assumption is that when the road electrician is faced with only a single phase 3 wire +G service, he or she is going to connect two phases of the rack to one phase of the company switch. This means that the neutral could be loaded to 2X the phase current. ...


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## STEVETERRY (May 31, 2011)

derekleffew said:


> Tim, let me see if I understand your scenario:
> 
> Feed:..........................DimmerRack:
> L1 (200A capacity)........ØA (100A load)
> ...


 
This example actually illustrates the problem well. When a three phase rack (without internal conversion) is connected to a large enough service to handle 2x the phase current of the rack (let's say a 200A single phase service to acommodate a three phase rack of 100A per phase), the neutral feeder cable and the rack neutral bus must both be large enough to handle a 200A imbalance.

ST


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## TimMiller (May 31, 2011)

If memory serves correctly in a single phase system the neutral must be able to carry the full carrying capacity of any current carrying conductor. So according to code you cannot overload the neutral. I understand how the neutral can be overloaded in a 3 phase system.


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## Chris15 (May 31, 2011)

I need to make some assumptions since I have never seen how it works in reality...

You have your 3 loads of 100A each.
You connect one to "phase" A
You connect two to "phase" B.
This connection may be made at the local switchboard when tying in via lugs.

In this instance you are still running 5 cores of feeder to the dimmer rack.

Each active will never see more than 100A load.
The neutral may see a 200A load.

Substitute 200A loads for 100A loads and I can see very quickly why duplicating the neutral would be neccessary...


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## JD (May 31, 2011)

TimMiller said:


> If you are faking 3 phase off of single phase you do not need to overrate the neutral. The neutral cannot exceed the capacity of any single leg from the single phase system. For example I have a single phase panel feeding a three phase dimmer rack. The panel has 2/0 HHN cables coming in and the main breaker has a rating of 200 amps. I have 3 100 amp breakers feeding off of the panel to the dimmer rack. Line 1 of the panel has two of the 3 legs of the dimmer rack connected. I turn on the first set of the dimmers that are all on leg 1 of the dimmer. Let's say I pull 100 amps. I show pulling 100 amps on the neutral and L1 of the panel. I now turn on the second leg of the dimmer rack also pulling 100 amps. So now line 1 and 2 on the dimmer rack is showing 100 amps each but now the neutral is showing 0 amps. Line 1 and 2 since they are each 180 degrees out of phase they are canceling themselves out on the neutral leg. Ok I now turn on all the dimmers on leg 3 of the dimmer rack. I am now pulling 200 amps on L1 of the panel and 100 amps on L2. I meter the neutral and it shows I am pulling 100 amps due to the 100 amps on L2 is canceling out 100 of the 200 amps on L1. Ok lastly I now turn off leg 2 of the dimmer rack. I now have 200 amps on L1 and 0 amps on L2. My neutral is now metering at 200 amps. I cannot exceed the rating of the neutral at 200 amps without popping the main breaker.
> 
> 
> The numbers are for demonstration purposes only. Remember not to exceed 80 percent of the breaker or you may be sitting in the dark.


 
Not sure what you are saying here. You can never assume a cancel-out as this varies with dimmer settings. You have to look at worst case scenario. So, if each of your hots is gauged for 100 amps, (assuming a 100 amp per leg OCPD) your neutral would have to be gauged for 200 amps, therefore twice the size. If you gauge everything for 200 amp you do not have a problem, but you have effectively over-gauged all of the other conductors to achieve this.


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## xander (May 31, 2011)

JD said:


> Not sure what you are saying here. You can never assume a cancel-out as this varies with dimmer settings. You have to look at worst case scenario. So, if each of your hots is gauged for 100 amps, (assuming a 100 amp per leg OCPD) your neutral would have to be gauged for 200 amps, therefore twice the size. If you gauge everything for 200 amp you do not have a problem, but you have effectively over-gauged all of the other conductors to achieve this.


I thought the same thing. Instead of oversizing your neutral for double your hot legs, you are halving the hots. This accomplishes the exact same thing...


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## mstaylor (Jun 1, 2011)

I have always made sure that I was sufficiently below the main limit to allow the neutral to be oversized. I was talking to an electrician yesterday and he claims that because you have to account for 200 amps twice that it is already taken care of. I couldn't of a counterargument. So if your main is single phase and 200 amps, the neutral is already gauged to carry 400 amps. I have never installed a panel from scratch, I have done panel swithouts, I don't know that to be true.


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## lightingguy1 (Jun 3, 2011)

Hi guys,

What is the "setup" of where I have the pic of the 4 connected breakers? In official electric terms....What would you call this?



Thanks!
-Lightingguy1


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## mstaylor (Jun 3, 2011)

lightingguy1 said:


> Hi guys,
> 
> What is the "setup" of where I have the pic of the 4 connected breakers? In official electric terms....What would you call this?
> Thanks!
> -Lightingguy1


In your picture you have two hot legs, a neutral and a ground, that makes it single phase.


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## epimetheus (Jun 3, 2011)

mstaylor said:


> In your picture you have two hot legs, a neutral and a ground, that makes it single phase.


 
I don't think this is what the OP was asking. I know of no *common* reason that four poles worth of circuit breakers would be ganged together. It looks like those are 2 double pole breakers with a handle link between them.

You can get 4 pole breakers, but they are generally intended for high DC voltages (2 poles per leg) or 3 phase AC systems with a switched neutral.


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## derekleffew (Jun 3, 2011)

lightingguy1 said:


> What is the "setup" of where I have the pic of the 4 connected breakers? In official electric terms....What would you call this?





I-T-E Electrical Products EQ9685

It appears even the experienced can't agree: 4 Breakers all tied together for 120/240 single phase? .


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## lightingguy1 (Jun 5, 2011)

So in a non perfect world(one much like were living in now), If I would need to power, lets say a Smartmodule 2, for a home's backyard concert that didn't have a proper tie-in, what would I do?


-Lightingguy1


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## TimMiller (Jun 5, 2011)

lightingguy1 said:


> So in a non perfect world(one much like were living in now), If I would need to power, lets say a Smartmodule 2, for a home's backyard concert that didn't have a proper tie-in, what would I do?
> 
> 
> -Lightingguy1



If there is space available install a breaker then run the cable from the breaker to your gear. Or go to the tub of tricks and pull out the TWEECOS and send everyone away. 




Also I now see where y'all are coming from on essentially doubling the neutral. In writing up my example I left out a key component. I forgot to put in the feeders coming off of the panel to the dimmers. I stated that there was 2/0 feeding the panel. Ok for our feeders we can use 2 awg for our hots but then you will have to use 2/0 for the neutral. Due to there being 100 amps max on each hot but there is a potential for 200 amps on the neutral. I now feel like an idiot for not calculating in the feeder from the panel to the dimmers. Also you do not want to double your legs unless it is unavoidable. Just because two wires can carry 100 amps a piece does not mean they can carry 200 amps together. There is a formula to go by that I will need to look up. I have a book that mainly covers the calculations for doubling conductors. Also when using double conductors they MUST both be the exact same length. You need to lay both side by side to make sure of this. If one is longer by even a foot or two electricity will take the path of least resistance and begin to overload the shorter conductor. Thus is the reason you always meter both conductors to make sure the load is balanced.


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## David Ashton (Jun 5, 2011)

"If one is longer by even a foot or two electricity will take the path of least resistance and begin to overload the shorter conductor. "
Not that critical, a slight imbalance will warm the cable with the higher current and increase its resistance which then reduces the current, a basic feedback loop.You're going to need a pretty good meter to measure the diiference of 1' in a decent length cable.


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## JCarroll (Jun 6, 2011)

David Ashton said:


> "If one is longer by even a foot or two electricity will take the path of least resistance and begin to overload the shorter conductor. "
> Not that critical, a slight imbalance will warm the cable with the higher current and increase its resistance which then reduces the current, a basic feedback loop.You're going to need a pretty good meter to measure the diiference of 1' in a decent length cable.



And if I'm thinking correctly, this would only matter if doubling the conductors for the Neutral, the doubled hots don't matter because they aren't combined once in the dimmer so there is no path for it to cross over.


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## TimMiller (Jun 6, 2011)

JCarroll said:


> And if I'm thinking correctly, this would only matter if doubling the conductors for the Neutral, the doubled hots don't matter because they aren't combined once in the dimmer so there is no path for it to cross over.


 
That is true though there are plenty of systems out there that use doubled hots due to the excessive current (more than what a single set of 400a cams can handle) I have a cd80 rack that has a 600 amp main so when connecting it for full capacity it is a beast when it comes to pulling cam. We use a matched set of 4/0 cams.


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## JD (Jun 6, 2011)

TimMiller said:


> If one is longer by even a foot or two electricity will take the path of least resistance and begin to overload the shorter conductor. Thus is the reason you always meter both conductors to make sure the load is balanced.


 
Well, "path of least resistance" does not really work that way. Example: If you take three resistors and put them in parallel, and one is 4 ohms, the second and third are each 8 ohms, everything would travel through the 4 ohm resistor as it has the least resistance. Instead, about half the current would travel through the 4 ohm resistor, and 1/4 the power through each of the 8 ohm resistors, giving the circuit a value of 2 ohms. (1 / R = 1 / R1 + 1 / R2 + 1 / R3) If you had two feeders that were the same gauge and were in parallel, one being 100 feet and the other being 101 feet, there would be about a 1% variance in the current between them. Still good practice to keep them as close as possible.


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