Help converting house lights to DMX

[Esoteric]

Originally Posted by D.R.HADDOCK

I was referring to the the wiring between the dimmers and the lights,
I think he said there where over 100 lights, all with a common neutral,
It doesnt really matter how many lights there are, the electrical principle is the same weather there are 100 lights or 10 lights.
With seperate actives and a common neutral,
Because the dimmer is always in the active line, you can dim them individually
even with a common neutral,
If you follow the wiring in any dimmer rack you will see that the neutrals are all commoned to one main neutral point, and the triacs are in the active line.
Unless I am miss understanding something,
I still maintain that only one common neutral line is required between the dimmers and the house lights.

Okay, if we don't clarify then some people are going to get very confused and I am afraid they are going to act on bad advice.

Here is the deal. Straight from ETC.

In application note 104-2:

In non-dimmed applications, branch circuits are often installed with three circuits sharing a common neutral conductor, where each of the three circuits is on a different phase. This is known as a “multiwire” branch circuit arrangement. It is used to save costs because only four total conductors (three hot, one neutral) are used to feed three branch circuits.

This type of multi-wire branch circuit arrangement is not recommended for use with phase-control dimmers on new installations because it can cause voltage-drop interaction between the three branch circuits, as well as neutral conductor overloading.

In a new development, the 2008 NEC section (210.4), adds a new condition requiring multiwire branch circuits to be fed from a multi-pole breaker, or three single-pole breakers with a handle-tie identified for the purpose. This essentially eliminates new installations or retrofits using common neutrals on branch circuits fed from dimmer racks, because the handles of single-pole breakers in the dimmers cannot be mechanically tied together. The exact wording of the 2008 NEC is:

2008-210.4(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

So, where are things getting confused here? When you crack open your dimmer rack, there are two bars. A hot bar and a Neutral bar. When you put your dimmer blade into the rack, it makes contact between the two and vio la you have a completed circuit with SCR dimmers.

Now each circuit (usually a circuit either eequates to a plug or an individual light, but it does not have to) must have a hot and a neutral. Here is where things get a little confusing.

BOTH the hot and the neutral define a dimmer. For example dimmer 1 and dimmer 2 can NOT have different hots and share a neutral. This is not only against the installation specifications of the dimmer, but it is against code. But if this were able to be done, then yes, DR would be correct that you could then dim dimmer 1 and dimmer 2 separately. But this is NOT the case because in an SCR system the neutral can be a load carrying line.

What actually happens is that dimmer 1 has hot 1 and neutral 1. Dimmer 2 has hot 2 and neutral 2. So dimmer 1 and dimmer 2 are dimmed individually.

Now where we can get a little different (and be sure to check with local codes to make sure) is when we have multiple plugs or lights connected to 1 dimmer.

For example I have houselights 1-8. I divide them into two groups 1-4 and 5-8. I put lights 1-4 on dimmer 1. They all get hot 1 and neutral 1. Now when you do this each light has to get its own hot and neutral and they are tied together outside the rack in a gutter, but you can put more than one light on a dimmer. Then light 5-8 are on dimmer 2. They get hot 2 and neutral 2. They can NOT get hot 2 and neutral 1. This is against the installation instructions (which will void your warranty) and against code. So now we have lights 1-4 (on dimmer 1) that dim together and lights 5-8 (on dimmer 2) that dim together. But we have two groups that dim separately. This is how houselights are commonly wired. Technically lights 1-4 "share" a neutral (of course they also "share" a hot). But dimmers can NOT, should NOT, EVER share a neutral.

This is why you should always hire a licensed electrician with experience in dimming systems to do your installs.

Hope this clears things up.

Mike

[D.R.HADDOCK]

But electrically all the dimmers in the rack do share a common neutral!
Grab a multi meter and put it on ohms, and check any dimmer rack( turned off, of course), i will bet that all neutrals are connectted together to one point.
No matter what type of dimmer you use, if you have seperate actives and one common neutral, between the dimmers and the house lights you can still control/dim each light individually.

As for three phase power systems, this is another issue, and depends on many variables, such as star or delta configurations, and balanced loads, all these things will
effect the currents in the neutral line, these things are the domain of the power authorities and designing electrical engineers/electrians.
whilst I do understand these issues, I rarely have to worry too much about them
as the electricain that designs the instalation has sorted these out.

[Esoteric]

You are correct that electrically all the neutrals eventually terminate in the same place, but this IS NOT the same as running a common neutral to the lights.

I can not stress enough that you SHOULD NOT run a common neutral out to your fixtures. Not only is it against code, but it is against the manufacturers installation instructions and will void the warranty on your system.

ALWAYS hire engineers, designers, and electricians that are familiar with entertainment wiring.

Mike

[EBAC LD]

Instead of putting your dimmer near your wall switches, why not put it at the breaker panel, and run the wiring for the lights into the dimmer. I would imagine your dimmer is already near the panel anyway? This of course would only work if your lighting circuits are not shared with anything else that you wouldnt want dimmed.

[D.R.HADDOCK]

My point was meant to be that, with a common neutral to the house lights ( as theatre for JC ) mentioned, you can still control/dim the lights individually because they will have seperate active lines.
My point was not meant to be that I recommend using only one common neutral,
but if you already have just one (as theatre for JC) mentioned,
individual control is still possible!
I think we drifted off the main subject a little.