# Hot Patching



## Mayhem (Jan 31, 2006)

In the a recent topic ship and I refer to a practice known as "hot patching" and we both (strongly) advise against it.

Coming from Australia – I hadn’t hear the term before reading here some time ago. This prompts me to ask the following questions:

1. What does the term "hot patching" refer to;

2. Why it is unsafe (or, do you think it is safe?) and;

3. What precautions and steps should be taken to achieve the same end result safely?


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## soundman (Jan 31, 2006)

1. unplugging a fixture or any part of the chain from the dimmer to the fixture while the dimmer is on.

2. Arcing can occur and will cause carbon build up over time, also an exposed arc is no ones friend.

3. User training.


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## ship (Feb 1, 2006)

Wouldn't that than be hot un-patching?


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## jonhirsh (Feb 1, 2006)

I dont know about you but i generaly dont want to see a light go out on deck and then a random light come on in the middle of a scene. Usualy hot patching is dont when the dimmer for the chanel is off. and is coordeinated so that you do not see the switching on stage. 

Hot patching is an accepted way to gain more dimmers for a show its not unsafe. its is also acctepted practice to hot swap gels from fixtures during a show. if they are in the gird and accsessible during the show. 

the only way hot patching could be dangerous to the look of your show is if you dont label properly. so its simple label, label , label. 

JH


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## soundman (Feb 1, 2006)

ship said:


> Wouldn't that than be hot un-patching?



pluging the fixture back in with the dimmer on. Sorry should have added that.


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## Mayhem (Feb 1, 2006)

Well we are getting close to an answer on part one of the question (is it limited to dimmers?). 

Anyone care to discuss parts 2 and 3?


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## AVGuyAndy (Feb 1, 2006)

Assuming you mean hard-patching things while the dimmer is on, I do it all the time. But, we have an "old-school" system, 16 dimmers and about 130 circuits. I only do it because it's a long way back to the booth when I'm doing things by myself. 

It's dangerous because you can shock yourself, since conductors are exposed which plugging/unplugging things. I always make sure my hand is towards the back of the connector. And I tell people around me "Don't do that"


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## koncept (Feb 1, 2006)

I am not sure what it means to "hot/hard patch" yet. Judging by what has been said I do it on a regular basis. I have never until now heard it is dangerous.


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## propmonkey (Feb 1, 2006)

what exactly is hot patching? is it plugging a fixture directly into an "always on" circuit and not a dimmer? or is it jsut plugging a fixture into an "on" dimmer?


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## jonhirsh (Feb 1, 2006)

All hot patching is is when you repatch the dimmers during the show to gain more dimmable circuts. 

JH


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## fosstech (Feb 2, 2006)

I've heard the term used in both instances...both plugging an instrument into a hot circuit, and switching circuits to dimmers.

Our old system that is now thankfully gone had 15 dimmers and 66 circuits. All patching was done with these sliders on the wall that would assign each circuit to a dimmer or non-dim (each circuit had its own slider). For load testing we would patch the group of circuits into non-dim 5, which was the 60A non-dim relay that had an ammeter in line. Normally we would just patch them hot right into the non-dim since the meter was at the patch board and not up at the console where the non-dim switch was. Normally this isn't a good idea since the contacts in the sliders could arc and promote carbon buildup which could ultimately result in high resistance, but we did it anyway since we knew we were getting it replaced soon.

Hot patching (plugging or patching an instrument into a hot circuit) is generally not a good idea for more than one reason. Lamps don't like to be patched like that, the resistance of the filament is different at room temperature than it is at 3000 degrees. Ship can elaborate on the actual figures, because I don't know them. This results in a current surge at the instant the lamp gets that full 120V, which can lead to the breakage of the filament. Ever notice how most of the time when the light bulbs in your house go out, they go out the instant you turn on the switch? This is exactly why. You might have gotten more hours out of that light bulb if it were on a dimmer. The second reason is what I was talking about in the previous paragraph. Hot patching, either with patch cables, sliders, or just plugs on the instruments isn't a good idea because of the arcing that leads to deterioration of contacts.


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## Mayhem (Feb 2, 2006)

OK – now we are getting there and yes, hot patching refers plugging something into a live or ‘hot’ circuit. It doesn’t matter if the power is coming from a dimmer or out of a wall receptacle.

Now think of the actual process of joining a plug to a receptacle, it is something that we do on a daily basis and most of you would actually have to stand back and think because it is something that most do as second nature.

Once you have thought about it you will be able to expand further on the dangers.

Still waiting on someone to tell me what you should do if you want to test a fixture (for example). How would you go about doing it?

Good work thus far – keep it up.


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## AVGuyAndy (Feb 2, 2006)

On the patch panel in our (old) system, there is a socket which you can plug into which goes into a breaker and a watt meter to test with.


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## koncept (Feb 2, 2006)

Mayhem said:


> Now think of the actual process of joining a plug to a receptacle, it is something that we do on a daily basis and most of you would actually have to stand back and think because it is something that most do as second nature.


dont we do that every day when ever we plug anything into a standard home outlet such as a light, hair dryer, ect??

dangers
- water -if wet location
- fingers can come in contact with the prongs of the plug


Mayhem said:


> Still waiting on someone to tell me what you should do if you want to test a fixture (for example). How would you go about doing it?



after readin what has been posted i am going to assume that we should be using a dimmer swtched outlet that way a) the power is off, b) it can be slowly increased so as not to give the lamp full power off the bat.


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## tenor_singer (Feb 2, 2006)

I had a drama student come visit after her junior year of college. She had interned at a playhouse for Pittsburgh and mentioned how they used "hot patching" as part of their lighting design. I thought... wow... this is a possible way to increase my dimmer space.

I never really got into that practice with high school. Primarily I was concerned about students getting hurt (ie- falling off of the grid as they rushed through a hot patch, getting burned as they rushed through a hot patch...). I find that high schoolers... in their zeal to be good at what they do and to make you proud of them... are prone to speed errors, so I try not to increase their chances of injury by doing something that may cause them to rush around haphazardly.


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## Mayhem (Feb 2, 2006)

koncept - with a hair dryer or a desk lamp, circular saw, drill etc, they have a switch. A PAR can, leko, Fresnel etc does not. Now consider what that means to the circuit created when plugging a switched item into a receptacle versus plugging a non-switched item in.


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## ship (Feb 2, 2006)

jonhirsh said:


> I dont know about you but i generaly dont want to see a light go out on deck and then a random light come on in the middle of a scene. Usualy hot patching is dont when the dimmer for the chanel is off. and is coordeinated so that you do not see the switching on stage.
> Hot patching is an accepted way to gain more dimmers for a show its not unsafe. its is also acctepted practice to hot swap gels from fixtures during a show. if they are in the gird and accsessible during the show.
> the only way hot patching could be dangerous to the look of your show is if you dont label properly. so its simple label, label , label.
> JH



Wouldn't that be re-patching?


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## Mayhem (Feb 6, 2006)

Surely we don’t need to give any more hints do we?


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## Diarmuid (Mar 7, 2006)

I don't think this is what you were hinting at, but if the channels were all seperated by different phase power supplys, and you tried to patch between, them, I believe things could go badly wrong, because over here (in the UK) our phases our seperated by something like 419 Volts.

Also, with a non switched Item, it will start as soon as it makes any form of contact with both live nad neutral connections, so, it may easily give u a large electric shock.

Also, to test a fixture, I normally just run a continuity test with my multimeter.


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## Mayhem (Mar 9, 2006)

Diarmuid said:


> I don't think this is what you were hinting at, but if the channels were all seperated by different phase power supplys, and you tried to patch between, them, I believe things could go badly wrong, because over here (in the UK) our phases our seperated by something like 419 Volts.
> 
> Also, with a non switched Item, it will start as soon as it makes any form of contact with both live nad neutral connections, so, it may easily give u a large electric shock.
> 
> Also, to test a fixture, I normally just run a continuity test with my multimeter.



Hot patching is plugging an item into a power point that is live. For example, if you were to plug a 1K PAR 64 lamp into a live power socket so that the lamp lit up as soon as the pins on the plug came into contact with the blades is the socket, what bad things could happen?

Voltage between phases on a 240V three phase system is 415V.


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## Footer (Mar 10, 2006)

um... you shouldnt ever touch a cam when power flowing through it.... now thats arcing....


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## Diarmuid (Mar 10, 2006)

I thought the term hot patching, also applied to patching fixtures into a live dimmer, so sorry if my answer sounded a bit strange.


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## Mayhem (Mar 10, 2006)

Footer4321 said:


> um... you shouldnt ever touch a cam when power flowing through it.... now thats arcing....



On the right track now.


Diarmuid said:


> I thought the term hot patching, also applied to patching fixtures into a live dimmer, so sorry if my answer sounded a bit strange.



Well the context in which I have heard the term is in regards to plugging into a live circuit, so this would also include a dimmer.

To be honest with you – I believe it to be more common in the US than is Australia or the UK, as out power outlets have switches on them, where the US ones do not (well not that I have seen). If the unit being plugged in has a power switch it is not a problem (but still not good practice). But grabbing a high wattage light and plugging it into a hot outlet can change your outlook on the day.

Think about the B grade horror movies where there is an old style cam switch (the big old open contact lever ones) and recall what happens as the two contacts come together. Now, imagine that wrapped in fairly thin plastic with your hands griping onto it. Ok – so you have to use your imagination a little but that is what is happening inside of the plug.


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## Chris15 (Mar 10, 2006)

"Even a single power lead with a 650W lantern running on the end will cause a decent spark inside the socket at the point of disconnection. Each time this happens, the socket and the pins get damaged. This damage causes resistance at the join – and given enough damage, that could lead to a fire. If you have ever seen someone disconnect a three phase connection under load, it is the same effect, but multiplied significantly. 

That kind of disconnection will ‘blacken’ the interior of the socket, and cause it to fail its next electrical tagging. It could even potentially ‘jump out’ and get you depending on the amount of load, age/wear of the connection etc." http://www.juliusmedia.com/cxweb/article.asp?ID=446

Electricity can jump 1cm for every 10 000 volts in dry air. When a plug is hot patched to a socket, at a point 2.4mm from contact [240V parts of the world], an arc occurs between the plug & socket. This will then lead to a buildup of carbon, you have probably seen this on plugs before. This carbon buildup introduces a higher resistance into the connection and if repeated, this will eventually lead to an intermittent or faulty connection. 

It is worth noting that the design of some connectors prevents or at least lessens the impacts of disconnection under load. Speakon connector being an example. Similarly, connectors such as Neutrik Powercon must not be disconnected under load as they are not rated for that.

Consider also that while we may be more aware of arcing in connectors, every time we flick a switch, there is a small amount of arcing occurring. This is one reason why switches can fail. Older switches can get to a point where they are not disconnecting properly and a blue arcing can be seen even through the plastic of the housing. If this occurs, it is replacement time.

It is interesting to note that circuit breakers normally contain plates to stop the ionisation of gas & arcing when they disconnect the load.

If the connection is through a dimmer and the dimmer is at a low level, the effect will not be as profound but will still occur, hence why one should not hot patch.


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## Mayhem (Mar 10, 2006)

Chris15 said:


> "Even a single power lead with a 650W lantern running on the end will cause a decent spark inside the socket at the point of disconnection. Each time this happens, the socket and the pins get damaged. This damage causes resistance at the join – and given enough damage, that could lead to a fire. If you have ever seen someone disconnect a three phase connection under load, it is the same effect, but multiplied significantly.
> 
> That kind of disconnection will ‘blacken’ the interior of the socket, and cause it to fail its next electrical tagging. It could even potentially ‘jump out’ and get you depending on the amount of load, age/wear of the connection etc." http://www.juliusmedia.com/cxweb/article.asp?ID=446
> 
> If the connection is through a dimmer and the dimmer is at a low level, the effect will not be as profound but will still occur, hence why one should not hot patch.



Well done. However, if you have seen someone disconnect a three phase lead under load, I hope that you beat them over the head with the plug. Not only is it a good way to remover yourself from the gene pool but wrecks the springs in the sockets and you cannot buy replacements any more. There is another wasted $200+

The arcing and jumping that you refer to when disconnecting underload also occurs when connecting under load. 

The other important factor to consider is that hot patching is often done to test a (potentially) faulty piece of equipment. 

Lets go back to the 650W Fresnel and imagine that you just pulled a pair from the rig because they didn’t work and threw the breaker on the dimmer (plugged into the same circuit). So, you grab one and plug it in to a live feed. 

What would happen if the lamp base had failed creating a dead short and you are now holding the plug in one hand and about to stick it into the end of an extension lead that you are holding in your other hand?


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## Chris15 (Mar 10, 2006)

Mayhem said:


> The other important factor to consider is that hot patching is often done to test a (potentially) faulty piece of equipment.
> 
> Lets go back to the 650W Fresnel and imagine that you just pulled a pair from the rig because they didn’t work and threw the breaker on the dimmer (plugged into the same circuit). So, you grab one and plug it in to a live feed.
> 
> What would happen if the lamp base had failed creating a dead short and you are now holding the plug in one hand and about to stick it into the end of an extension lead that you are holding in your other hand?



One hopes that one has an operational RCD / GFCI and /or defibrillator. What will happen is that there will be the arcing seen normally, but since there is a short and thus that arc will not have any limit imposed upon it as to the amount of current that will be drawn. Given this, it should not be long before you trip your circuit breaker / fuse but in the mean time, you have probably sustained a reasonable electric shock and hopefully have worked out that it was not a safe thing to do in the first place.


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## rustystuff (Mar 10, 2006)

When I was in high school, (back before the Earth cooled), we would occaisionally have a show that required more specials than we had available dimmers. The patch panel resembled an old fashioned telephone operator's panel, with plugs that pulled out and were plugged into receptacles. We alsways made sure the dimmer handle was at "0" before anything ws re-plugged. Admittedly not the best way; but it was making the best of a bad situation.


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## Diarmuid (Mar 11, 2006)

Would you get a electric shock from the plug, as it was shorted, and (i dont know the science behind this) but would that cause the current to be different to what it would of been, if it was flowing through the lamp, i.e. stronger or more intense and as such cause the spark inside the socket/plug to be larger, and thus have a greater chance of getting you?

Also, surely hot patching is quite a bad method of testing a fixture, for example if the lamp hadnt blown, but something in the Internally Wired Bar was wrong, is it not possible that by hot patching the light, without pre-heating the filament, the lamp would then blow anyway.


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## Radman (Mar 12, 2006)

So wait, black is ground? 

This is one more reason someone should invent wireless power cables. Or a connector with a switch that must be thrown to connect/disconnect. Probably wouldn't be viable for cams though, too much current! I admit at times I do hot patch lights sometimes, but then again I never have anyone helping me, so it would not fit into my schedule if I had to go to the board every time I plugged something in.


Come to think of it, outlets that aren't on dimmers are generally always hot, so that's hot patching every time you plug/unplug anything. Scary...


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## koncept (Mar 13, 2006)

my thought with the spagetti board patch is that if the dimmer is at 0 then there is no problem with patching durring a show like that. i do not see it as an issue.

question: could this also cause a breaker to wear out? I worked at a pool and i told them the breaker was bad because if it was off for a while it would not always flip back on with out continualy flipping it. the breaker is used as a on off switch for the main pump. it is turned off at least once a day to clean the strainer basket thingy.


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## Mayhem (Mar 13, 2006)

Hot patching is a good way to blow a lamp and I think someone already pointed out that when a lamp fails, it quite often does it when being turned on.

The risk of shock or even other damage caused by a large current draw in the material in your hands can cause other painful injuries as well.

There are plenty of connectors that have switches on them and they certainly in common use in Australia and the UK and several other countries that I have visited. It seems that the US hasn’t embraced the need for them. In my workshop all the wall receptacles have switches built into them and all circuits are breakered and protected by a RCD. I even have a pendant receptacle with a switch on it hanging over an island bench.

Having said this – how hard would it be to make up a test bench power supply that not only had a switch on it, but also a RCD and a breaker or fuse?

I don’t think that wireless power would solve the problem as some bright spark would find a way to use it in an unsafe manner!

Koncept - yep, wear and tear will do that and it is not advisable to use a breaker as a switch.


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## Chris15 (Mar 14, 2006)

Diarmuid said:


> Would you get a electric shock from the plug, as it was shorted, and (i dont know the science behind this) but would that cause the current to be different to what it would of been, if it was flowing through the lamp, i.e. stronger or more intense and as such cause the spark inside the socket/plug to be larger, and thus have a greater chance of getting you?
> 
> Also, surely hot patching is quite a bad method of testing a fixture, for example if the lamp hadnt blown, but something in the Internally Wired Bar was wrong, is it not possible that by hot patching the light, without pre-heating the filament, the lamp would then blow anyway.



In my opinion, yes. The lamp filament has a given resistance which will change slightly as heated but for this, remains a constant. Power = volts squared over resistance. Thus, with the standard mains voltage, the different resistances of the filaments will regulate the brightness of the lamp. Say, for instance, you have a 250W lamp and your mains voltage is 250 volts. P = V x V / R. Rearranging this, R = V x V / P. Now for the above example, R = 250 x 250 / 250 = 250 ohms. In this case a current of 1 amp will flow.

If there is a short circuit, the resistance is much lower, say 1 ohm or less, at 1 ohm, 250 volts, 250 amps will flow. You can see the difference in current. 250 amps will produce quite a spark. It will also trip a circuit breaker / fuse pretty quickly.

In response to the second part, have you noticed that if a lamp is going to blow in your house, 9/10 times it will be when you switch it on...


Radman said:


> This is one more reason someone should invent wireless power cables. Or a connector with a switch that must be thrown to connect/disconnect. Probably wouldn't be viable for cams though, too much current!I admit at times I do hot patch lights sometimes, but then again I never have anyone helping me, so it would not fit into my schedule if I had to go to the board every time I plugged something in.



Some nice folks down here in Australia have thought of you. Australian 3 phase sockets can be ordered with a mechanical interlink such that you have to turn off the switch to be able to insert or remove a plug. Have to specially order them but they are available from Clipsal.

Do US dimmers not have circuit breakers on the front panel. I can see no justification for plugging in hot to an Australian portable dimmer pack such as the Jands HP12. Flick the breaker on the front, connect the load, flick the breaker back on.


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## Lightingguy32 (May 4, 2006)

Hot patching as told by my lighting design text book is when any fixture is plugged into a dimmer circuit when the fader controlling that dimmer on the board has a read out anything above 0 and it is not a wise thing to do becuase it may lead to failure of equipment eventually


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## Mayhem (May 4, 2006)

Lightingguy32 said:


> ....it may lead to failure of equipment eventually



It can also lead to failure of the operator!


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## Chris15 (May 5, 2006)

Lightingguy32 said:


> Hot patching as told by my lighting design text book is when any fixture is plugged into a dimmer circuit when the fader controlling that dimmer on the board has a read out anything above 0 and it is not a wise thing to do becuase it may lead to failure of equipment eventually



Now we need to remember that even though the DMX output might be 00, many dimmers have a preheat setting so that there is a small amount of power going through the lamp so that lamps don't blow as quickly, so this can still cause arcing, since with most dimmers, the full voltage is there, just not all the time, so effectively there is less voltage.


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## Lightingguy32 (Dec 10, 2006)

Chris15 said:


> Now we need to remember that even though the DMX output might be 00, many dimmers have a preheat setting so that there is a small amount of power going through the lamp so that lamps don't blow as quickly, so this can still cause arcing, since with most dimmers, the full voltage is there, just not all the time, so effectively there is less voltage.



Yeah that is right, but remember that preheat is normally set through the control board and is usually shut off after a few minutes. Therefore, there is absolutely no power going through the dimmers at all so it is highly unlikely that the scenario above is correct.


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## koncept (Dec 10, 2006)

i disagree completely. we were doing a show and needed little lights like 3 watts so we wired about 4 of them up like we wanted to give us a 12 watt load. on a 2.4kv dimmer they lit right up bc there was no ghost load. and this was with the board set to 00 and off...on newer dimmer racks with a processor you can change settings directly on the rack and override the settings on the board.


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## Chris15 (Dec 11, 2006)

Lightingguy32 said:


> Yeah that is right, but remember that preheat is normally set through the control board and is usually shut off after a few minutes. Therefore, there is absolutely no power going through the dimmers at all so it is highly unlikely that the scenario above is correct.



Sorry, But I have to disagree. More often than not, the preheat is a setting on the dimmer rather than the desk. Let me pose this question: what use is the preheat if it turns off after a few minutes? I thought that the idea of preheat was so that the filament was warm so that if you say flashed the lamp, the filament did not have to warm up and so was less likely to sustain damage. I recall that triacs and dimmer circuits have limits. We know that they cannot go all the way to 180 degrees. Hence one of the reasons that dimmers (except in some very specific cases) are not suitable for supplying clean power. Those specific cases are where there is a setting that changes it so that it activates a relay, bypassing the triacs etc. and chokes and all that. I also recall there it is a point, maybe 5 degrees which the dimmer can't go below.


koncept said:


> i disagree completely. we were doing a show and needed little lights like 3 watts so we wired about 4 of them up like we wanted to give us a 12 watt load. on a 2.4kv dimmer they lit right up bc there was no ghost load. and this was with the board set to 00 and off...on newer dimmer racks with a processor you can change settings directly on the rack and override the settings on the board.



This is why dimmers have marked minimum loads. The preheat and the lower limitation of the switching mean that there is still sufficient power to light up small loads.


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## koncept (Dec 11, 2006)

i understand the idea of minimum loads the point i was trying to make was that current is still at the plug even if the dimmer is at 00 dmx.


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## Chris15 (Dec 12, 2006)

koncept said:


> i understand the idea of minimum loads the point i was trying to make was that current is still at the plug even if the dimmer is at 00 dmx.



I certainly did not mean to imply otherwise. I apologise if I did.


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