# QOTD: Leaving a phase out



## Footer

STUDENTS ONLY

During the in for a tour, the head elec hands you a distro and asks you to tie it in. When you look at it, you realize it only has 4 male Cam-loks, one green, one white, one black, and one red. Your company switch has 5 cam females, one green, one white, one black, one red, and one blue.

How do you proceed and why?


----------



## 65535

My thought is that you can safely omit a phase and wire it up as the split-phase the distro was designed for with.

Other than loading the 3 phase transformers odd I don't see a problem. I know our shop uses 1 leg of the 3 phase supply to run sometimes grossly unbalanced loads at 208V transformed to 220V (ok so it's really more like 218.4V depending on how stable the phase is) for stationary saws and welders.

Considering most applications feed 3phases around the building chopped down to single phases per load. I don't see it being a problem.

The only alternative I could think of would be to acquire a 3phase 5 wire distro and balance the loads.


----------



## mstaylor

Just remember proceed doesn't necessarily mean go hook it up, it can but maybe there is something else.


----------



## esmphoto

mstaylor said:


> Just remember proceed doesn't necessarily mean go hook it up, it can but maybe there is something else.


 
Seconded.,
My first thought on reading the question was that I didn't know what the heck you were talking about. 
Given that most of the pros I get to work with undertand that I'm a student I'd probaby find someone and ask, I'd rather someone know that I didn't know than do anything wrong with three phase power.


----------



## headcrab

Just because the power is available (or the connector is there) doesn't mean you have to use it. Loading two out of three phases won't necessarily damage anything, though the POCO may hate you for it.
I'd connect as normal, matching colors on the distro to the switch, but ignore the blue phase (c?) on the company switch. It would not have anything connected to it.
When loading the distro, one would have to keep in mind that the phase-to-phase voltage is 208V and not 240.


----------



## chausman

mstaylor said:


> Just remember proceed doesn't necessarily mean go hook it up, it can but maybe there is something else.


 
Well, this might not be what Footer meant by asking the question, but for me, if I was told to do something I wasn't sure of, I would ask someone else to do it correctly (and safely), and show me how. 


Footer said:


> The biggest thing is... if you don't know how to do something ask... and don't say you can do something that you can't. If you don't understand instructions, ask.


 
I do know somewhere we've talked about not using all the Cams on here before.


----------



## porkchop

Footer should the assumption be made that the gear is from the US (i.e. US color scheme and 3 phase WYE?) or are we thinking about the wide variety of touring gear out there?


headcrab said:


> When loading the distro, one would have to keep in mind that the phase-to-phase voltage is 208V and not 240.


You're very unlikely to find this phase-to-phase voltage anywhere unless you have specific transformers for it.


----------



## epimetheus

porkchop said:


> You're very unlikely to find this phase-to-phase voltage anywhere unless you have specific transformers for it.


 
I'm not sure I understand your statement here. 208V and 240V are probably the most common phase-to-phase voltages available in the US.


----------



## porkchop

epimetheus said:


> I'm not sure I understand your statement here. 208V and 240V are probably the most common phase-to-phase voltages available in the US.


 
240V is a common phase to ground or neutral voltage in lot of countries other than the US, but in the US it's hard to get 240V unless you are using both sides of a single 120V transformer. In that case you would get 240V between phases but they are 180 degrees out of phase not 120. 
That's not really useful for show power. It's done in residential and industrial installs but that's not what we're talking about here. To be honest this isn't really the point the first half of the post was the more important part.


----------



## rochem

Footer said:


> During the in for a tour, the head elec hands you a distro and asks you to tie it in.
> (snip)
> How do you proceed and why?


 

mstaylor said:


> Just remember proceed doesn't necessarily mean go hook it up, it can but maybe there is something else.



Well I mean, "say no and locate a qualified person, per the NEC to do it" seems like a reasonable answer to the question. But I don't think that's what you're looking for, is it? Or do you want an answer like "run and hide, he's gonna blow his stuff up!"? 

Not totally related, but I came across a block full of television trucks and their thousands of feet of feeder today in manhattan. Found a particularly interesting spider box on a corner, which not only had the connections into the box completely submerged under 7-10" of water, but also the electrician apparently decided he didn't feel like plugging in the ground, and it was just kinda sitting there underwater. I tried to take some photos, but they all came out blurry and obscured from the pouring rain.


----------



## avkid

rochem said:


> Not totally related, but I came across a block full of television trucks and their thousands of feet of feeder today in manhattan. Found a particularly interesting spider box on a corner, which not only had the connections into the box completely submerged under 7-10" of water, but also the electrician apparently decided he didn't feel like plugging in the ground, and it was just kinda sitting there underwater. I tried to take some photos, but they all came out blurry and obscured from the pouring rain.


Outside MSG?
Those TV trucks do some weird stuff.


----------



## epimetheus

porkchop said:


> 240V is a common phase to ground or neutral voltage in lot of countries other than the US, but in the US it's hard to get 240V unless you are using both sides of a single 120V transformer. In that case you would get 240V between phases but they are 180 degrees out of phase not 120.
> That's not really useful for show power. It's done in residential and industrial installs but that's not what we're talking about here. To be honest this isn't really the point the first half of the post was the more important part.


 
Your right voltage differences between countries and the arrangement of 120/240V split-phase, of course, but in regards to Footer's original question (and I hope I'm not giving too much away here), the most common reason someone would be in the situation of hooking a 5 wire company switch up to a 4 wire panel would be the instance of a 120/240V split-phase service.

Also, I disagree with your statement that 120/240V split-phase is not useful for show power. Though I feel I can't explain any further without totally giving away the answer to this QOTD.


----------



## porkchop

epimetheus said:


> Your right voltage differences between countries and the arrangement of 120/240V split-phase, of course, but in regards to Footer's original question (and I hope I'm not giving too much away here), the most common reason someone would be in the situation of hooking a 5 wire company switch up to a 4 wire panel would be the instance of a 120/240V split-phase service.
> 
> Also, I disagree with your statement that 120/240V split-phase is not useful for show power. Though I feel I can't explain any further without totally giving away the answer to this QOTD.


 
If it's a 5 wire company switch you're talking about 120/208V. That was my point.


----------



## DuckJordan

not to muddy the waters further but for those of you who say hook it up as is, What do you do with the now open hot?


----------



## drummerboi316

DuckJordan said:


> not to muddy the waters further but for those of you who say hook it up as is, What do you do with the now open hot?



Stand in a puddle and lick the inside?


----------



## 65535

DuckJordan said:


> not to muddy the waters further but for those of you who say hook it up as is, What do you do with the now open hot?


 
Ground it of course....

At least on our company switch and others I've seen they all had covers over the connectors.


----------



## Sony

65535 said:


> Ground it of course....
> 
> At least on our company switch and others I've seen they all had covers over the connectors.



I've seen some pretty sketchy company switches that are just basically tails hanging out of a disconnect. Not all company switches have covers.


----------



## ejsandstrom

Just curious why no one has suggested measuring the voltage? Why assume? I have had to use all of the above colors for various voltage connections.


----------



## mstaylor

As somebody that hands tails like this to building electricians and also receive them as the building electrician, there is a very basic thing that has to cleared up, what type of hook up is needed. When I hand four wires to be hooked up I tell him whether I want a single phase,nuetral and ground or three phase, three hots, no neutral and a ground. If I am recieving tails I ask what he wants, then I tell him to come visually inspect it and meter it before attaching to his gear. 
If you are hooking up single conductor cables, then you should know your tie ins and shouldn't have to meter it. If you don't already know then you don't meet the defination of qualified person. Now if you happen to be tapping a generator then absolutely check voltages. 
If you are doing a single phase tap, then either cap the spare leg or tape it off so it can't be touched.


----------



## SteveB

It's been a week and as the QotD is usually a week for students, I'll throw in my thoughts.

1) If you are not the person designated and/or the person with the skill and authority to do tie-ins, politely inform the event electrician that you will get the correct person to do the tie-in. You work for the house, so follow the rules of the house.

2) Double check that the person that handed you the tails is the person with the event that actually knows what kind of power they need. Verify what they need. 

3) Verify that the tails being provided are color coded correctly for the event equipment. If in doubt, have the person from the event hand you a Hot when asked, then another Hot, then the Neutral then the Ground. This way the event personnel are responsible for their own gear if they were in error. Big red caution lights go off in my head when I see Cam-Lok connectors that are covered in vinyl colored tape of a different color then the Cam color, makes me ask WHY ?. 

4) Connect as per color once all concerns are addressed, or connect as per the event electricians direction. If something seems amiss, be prepared to meter the tie-in at the tails. 

5) If the blue is not used, either cap it or if no capability to cap exists, open up the company switch and remove the blue feed wire from that phase lug. If the switch has live wires, switch off at the appropriate breaker, lock and tag prior to working in the disconnect. If the blue tails wire is bundled, mark it with a "Not Used and Connected" flag, white 2" gaff would be my choice. 

In truth, I run into this all the time with audio gear and simply cap the non-used tail. If it's a one-off I rarely mark it (my bad) as I'm the only electrician dealing with the tie-in.


----------



## Van

Isn't this why God invented Crutch tips? 

And if they want three wire 220 they simply are getting it out of a 3 phase 208 feed..... unless they also provide a roto-phase.


----------



## SteveB

Van said:


> Isn't this why God invented Crutch tips?
> 
> And if they want three wire 220 they simply are getting it out of a 3 phase 208 feed..... unless they also provide a roto-phase.



On a 3 phase 120/208v service, the voltage will only ever be 208 between phases - A-B, A-C, B-C. Dropping a leg doesn't get you 220.


----------



## epimetheus

Ok, now that we're past a week, let me further clarify my point from before. If an event comes in with a dimmer rack that's set up for split-phase 120/240V, it (in 99%) of cases will run perfectly normal on 2 legs of a 3-phase 120/208V system. They same would apply to a split-phase audio distro that doesn't have any phase to phase loads. The event electrician should know whether their system has any phase to phase loads. If they don't have any phase to phase loads, then 2 legs of a 3-phase 120/208V system is just as good a split-phase 120/240V system. As a matter of fact, most modern loads that require more than a 120V circuit will run on 208V or 240V. Obviously, this would have to be verified on a case by case basis. A lot of amps with switchmode poser supplies and moving lights with electronic ballasts are perfectly happy switching between 208V and 240V.


----------



## Nelson

Assuming that the equipment is happy being fed with 120/208, is it acceptable to load only two legs of the three phase service? Is it OK to have an unbalanced load?


----------



## epimetheus

Nelson said:


> Assuming that the equipment is happy being fed with 120/208, is it acceptable to load only two legs of the three phase service? Is it OK to have an unbalanced load?


 
Yes. In most cases...


----------



## ScottT

epimetheus said:


> Yes. In most cases...


 
Generally, when is it not?


----------



## epimetheus

ScottT said:


> Generally, when is it not?


 
When you're operating near the capacity of the electrical service. Circuit protection operates on a per phase basis, but it trips all phases. So, if you overload one phase, you'll trip the entire feeder. You have to be aware of how much capacity you have available when you're in one of these less than optimal situations. For example, a 3 phase 120/208V, 400A company switch is rated for 400A per phase, 1200A total. If you're only hooking up 2 of the 3 phases, you only get 800A. Of course, this a simplified example, but hopefully that paints the picture.


----------



## derekleffew

ScottT said:


> Generally, when is it not?


When using a generator. Ever had your washing machine go nuts and make that thump-thump-thump noise due to an undistributed load? Same concept.

epimetheus' concept of the issue becoming more important the closer one gets to capacity holds true for generators as well. A 100kVA unit won't care or even notice a 20A imbalance, but may well balk at 200A.

STEVETERRY said:


> There is no doubt that aiming for approximate phase balance is desirable. However, as I previously stated, if the system and its feed from utility power is properly designed, there should be no ill effects from imbalance. For a portable generator where the dimming system is a high percentage of the generator capacity, phase balance does indeed become more critical. ...




STEVETERRY said:


> ...And, if the transformer, switch gear, and dimmer rack are Listed, by NRTL and installation is done to Code [in the US, the NEC], the system as a whole can readily tolerate up to 100% phase imbalance. ...


-----

Van said:


> Isn't this why God invented *Crutch tips*? ...


Please advise where one can locate listed, by NRTL crutch tips for the purpose intended. While a clever idea and likely very safe and certainly better than an exposed contact, I don't think we should advocate such a practice, especially when the proper item exists and is readily available.


CL Female protective cap w/ 20" lanyard (black) | Marinco


----------



## Van

SteveB said:


> On a 3 phase 120/208v service, the voltage will only ever be 208 between phases - A-B, A-C, B-C. Dropping a leg doesn't get you 220.


 
Isn't that what I said ? We hold these truths to be self evident: you can't 220 out of 208.


----------



## tjrobb

This may be the third thread I've mentioned this on, but we have a 220/127V 3ph system in our building. No, really, P-G is 127V. And let's not forget the two-phase 5-wire we just RE-installed to power an old blower. Or the motor-generator providing DC power to the 1928 elevator, with mechanical relay controls. Our building excels at strange electrics.


----------



## Nelson

tjrobb said:


> This may be the third thread I've mentioned this on, but we have a 220/127V 3ph system in our building. No, really, P-G is 127V....



Sounds like some neat stuff! If I'm ever in Iowa, I'll have to come see it.


----------



## sww1235

if the distro is rated to run on 120/240 split phase, which the cam colors seem to indicate, you should be able to safely hook up the two hot cams to the first two phases on the company switch. This will cause an unbalanced load, however, but if the power supply was designed correctly, this should not matter. You may need to double the neutral cable capacity because of the unbalanced load. Since the distro needs basically 2x 120 single phase feeds this should work. If I was in this situation, I would request a distro that matched the company switch, and if it was unprocurable, I would tie the red and black cams on the distro to the first two phases on the switch, and cover the third phase.


----------



## Neil Sakaitis

Not sure if this topic is still open or being monitored by folks here, but have a question. I am faced with this exact situation in a couple of months. I have a suitcase style single phase distro that has a mix of single 15A and 20A breakers and outlets. The venue I am setting up in has 3 phase power, so my plan, as some suggested here, was to tie in my black and red, and cap or tape the blue leg. The good news in my case (I think) is that my feeder is #2 which should be good for 195A.

Here is my question, the venue has 2 CAM panels, one is rated at 100A the other at 400A. I think I read somewhere that this means each leg has that amperage rating, and not the entire feed, is this correct ?? So in the case of the 100A panel (3-phase), if I only use 2 legs I get 2 X 100A, correct ??

Even though I won't be pulling more than 100A total in gear, I am thinking that since my feeder is #2, and I don't have a main breaker in my distro, it is probably a better (not good) idea to cable into the 100A panel and not the 400A one, but again, I won't be pulling more than 100A in gear, so my feeder should be fine.

Thanks
Neil


----------



## Dionysus

Neil Sakaitis said:


> Not sure if this topic is still open or being monitored by folks here, but have a question. I am faced with this exact situation in a couple of months. I have a suitcase style single phase distro that has a mix of single 15A and 20A breakers and outlets. The venue I am setting up in has 3 phase power, so my plan, as some suggested here, was to tie in my black and red, and cap or tape the blue leg. The good news in my case (I think) is that my feeder is #2 which should be good for 195A.
> 
> Here is my question, the venue has 2 CAM panels, one is rated at 100A the other at 400A. I think I read somewhere that this means each leg has that amperage rating, and not the entire feed, is this correct ?? So in the case of the 100A panel (3-phase), if I only use 2 legs I get 2 X 100A, correct ??
> 
> Even though I won't be pulling more than 100A total in gear, I am thinking that since my feeder is #2, and I don't have a main breaker in my distro, it is probably a better (not good) idea to cable into the 100A panel and not the 400A one, but again, I won't be pulling more than 100A in gear, so my feeder should be fine.
> 
> Thanks
> Neil



The best place to ask electrical questions here is in the Lighting section of the forum.
Now here is an instance where I have to do my due diligence and say the following very loudly...

*IF YOU HAVE TO ASK THIS QUESTION YOU ARE NOT QUALIFIED TO TIE IN CAM-TAILS.*

Okay so, most of what you have asked has been already answered in several threads in the lighting area.

A 100A 3-phase, disconnect intended for typical cam-tail tie-in applications has 3 "hot" conductors, a "neutral" conductor and a "bond" or ground conductor hook-up. Each of the 3 "hot" legs is fused at 100A. With the TYPICAL setup you can hook up two of the three (along with the neutral and bond) without a problem, however this MAY not be the case (hey I haven't seen it so I can't say for sure how it is hooked up or what it is hooked up TO). Delta, Wye? etc?

You also MUST have a main breaker in your distribution panel in many cases.

Your profile says you are in Montreal, and I am not directly familiar with any local electrical code requirements for Quebec or Montreal (I am in Ontario), but the CEC parts I and II certainly still apply.

Here AHJ requires cam-lock tie-ins to be done by a "qualified" person, and to have an inspection or at least have a permit. Not that everyone follows that.

You should talk to the venue specifically regarding this. IF you have any further questions feel free to send me a message.


----------



## MikeJ

Holy super old thread, Batman!
Typically,
#2- 100a
2/0- 200a
4/0- 400a


----------



## Dionysus

MikeJ said:


> Holy super old thread, Batman!
> Typically,
> #2- 100a
> 2/0- 200a
> 4/0- 400a


Actually in Canada wire ampacity rules changed...

http://safetyauthority.ca/sites/default/files/Module1Handout2012ElectricalCodeChangesFinal_3.pdf


----------



## egilson1

For in the us 

http://www.lexproducts.com/technical-help/specification-of-feeder-cables/


----------



## MikeJ

My statement was ambiguous, I was referring to cable to be used with common disconnects.

100, 200, and 400 amp disconnects are the most common, so you choose a cable with a rating that exceeds the maximum draw.

In the U.S. Though without reading the entire link about Canada, it appears to be a document about permanent residential wiring; rules up north might be different.


----------



## Dionysus

MikeJ said:


> My statement was ambiguous, I was referring to cable to be used with common disconnects.
> 
> 100, 200, and 400 amp disconnects are the most common, so you choose a cable with a rating that exceeds the maximum draw.
> 
> In the U.S. Though without reading the entire link about Canada, it appears to be a document about permanent residential wiring; rules up north might be different.


It is a list of the CEC code changes that were made active in 2012, part of which is a change in rated capacity of conductors Changing Tables 1-4.

I think my earlier statement stands however. If you need to ask this or be told this stuff (ie how to select a conductor size) you are not qualified to hook-up cams to the disconnect. Not sure about the US, but the poster who asked is in Quebec and you are supposed to be licensed to do such connections here (not that it is always followed).


----------



## STEVETERRY

Dionysus said:


> Actually in Canada wire ampacity rules changed...
> 
> http://safetyauthority.ca/sites/default/files/Module1Handout2012ElectricalCodeChangesFinal_3.pdf



Just to be clear, the ampacities listed in Table 2 of the link refer to cables or conduits with not more than three current carrying conductors. For single conductor portable feeder cables, both the CEC and the NEC use the free-air ratings, which are much higher than Table 2.

While we're at it, how about some Canadian CB'ers getting on the case to propose updates to Section 44 of the CEC covering theatres? It is woefully out of date--it looks like the NEC did in 1980!

ST


----------



## MikeJ

Dionysus said:


> It is a list of the CEC code changes that were made active in 2012, part of which is a change in rated capacity of conductors Changing Tables 1-4.
> 
> I think my earlier statement stands however. If you need to ask this or be told this stuff (ie how to select a conductor size) you are not qualified to hook-up cams to the disconnect. Not sure about the US, but the poster who asked is in Quebec and you are supposed to be licensed to do such connections here (not that it is always followed).



I think ST cleared up the ratings. Free air rating in much higher, and is typically what we use in theater/entertainment. Ratings for overhead lines are even higher. I have a 600A service coming from the transformer on 1/0 aluminum, but it splits into (3) 2/0 cables before entering the conduit on the building. I'm not vouching for these specs, its just what the power company put in, but you can see that the more space and heat dissipated, allows for a significantly higher rating. This is conversely the same reason we de-rate socapex cables by 50% compared to individual conductors. All of that aside, I have never had an issue using 4/0 for a 400a service or 2/0 for a 200a in Canada, though you should check with the local AHJ. Really most of the difficulty is from boarder patrol holding tour buses at the boarder just to screw with them.

Even those who are qualified may not remember the exact ratings of a particular cable. That is why I posted the commonly used sizes for a given power service. Off the top of my head I might not remember what the maximum rating is for #2, however I know it is more than 100, and less than 200 amps. So when I find a ball room with 100A disconnects, I know to use #2, just as I would choose 2/0 for a 200 amp. These same rules of thumb are used all over the industry. 3/8" steel for 1-ton points, 1/2" for 2-ton. I know this to be true in most common uses, but I cannot tell you the exact rating of the steel unless I look it up. When you start to go outside of typical application then it is prudent to do exact math, but for most things, just using accepted standards will do the trick, otherwise you would have to have an impressive reservoir of numbers and equations in your head.


----------



## Dionysus

STEVETERRY said:


> Just to be clear, the ampacities listed in Table 2 of the link refer to cables or conduits with not more than three current carrying conductors. For single conductor portable feeder cables, both the CEC and the NEC use the free-air ratings, which are much higher than Table 2.
> 
> While we're at it, how about some Canadian CB'ers getting on the case to propose updates to Section 44 of the CEC covering theatres? It is woefully out of date--it looks like the NEC did in 1980!
> 
> ST



Yes indeed, There are separate tables for Free-Air and Not (Tables 1-4, 2 for copper 2 for Al), not to mention various tables for specific cable types (including K, etc), and de-rating tables for when conductors or cables are grouped together, in a warm environment, etc. There is actually a fair amount of code to sift though regarding conductor sizing.

I agree that Section 44 needs an update, and so does THE OTHER relevant section which I cannot remember the number for off hand right now (52? 48?). The wording actually needs some updating to differentiate between the two as well. I've asked 2 inspectors about some of it, and both had no clue and differed to me.

I am not ambitious enough to enact some of said changes (or experienced enough Id say) however I wouldn't be opposed in lending a helpful hand as it were.

My main point was to point out that code HAD changed for allowable ampacities in the CEC and it may not match code requirements in other regions.


----------



## STEVETERRY

Dionysus said:


> I agree that Section 44 needs an update, and so does THE OTHER relevant section which I cannot remember the number for off hand right now (52? 48?). The wording actually needs some updating to differentiate between the two as well. I've asked 2 inspectors about some of it, and both had no clue and differed to me.



Section 66 is also looking a bit out of date to me:

_Section 66 — Amusement parks, midways, carnivals, film and TV sets, TV remote broadcasting locations, and travelling shows_

_ST_


----------



## Dionysus

STEVETERRY said:


> Section 66 is also looking a bit out of date to me:
> 
> _Section 66 — Amusement parks, midways, carnivals, film and TV sets, TV remote broadcasting locations, and travelling shows_
> 
> _ST_



That would be the one. Been a while since I've actually read it. Totally needs an update. Id love to see this!

I think the worst part is that many electricians aren't even really AWARE of Section 44 & 66, and I've seen quite a number of violations based on these sections. My code teacher was totally unfamiliar with these sections (I remember referencing them in classroom discussion), and a number of inspectors are also quite un-versed in these sections (except for the few who directly generally deal with them by way of "special inspections"). So perhaps the ESA needs to get their act together a little bit on this?


----------

