Somebody please explain...


Active Member
Would somebody please explain why the 20amp breaker on the dimmer hasn't tripped when they have been running over 33amps on 3 of the dimmers for over 2 years? I mean... I know breakers don't trip right at the rating to allow for surges like when you turn on a light... but they are running 4000watts on 2.4Kw dimmers....
faulty dimmer maybe? just a guess.

i would be thankful that it hasent set fire to the building yet, or that it hasent failed at some important moment.. kinda sounds like these are house lights (just another guess) but that would kinda be a bad things to lose at a nadom moment
"They are rated in terms of their maximum load; the most common are 1.2kW and 2.4kW. A dimmer rated at 1.2kW means that you can put 1.2kW worth of load on the dimmer, e.g. one 1000 W PAR can or two 500 watt Fresnels (you'll usually want to give yourself a bit of headroom, particularly with older dimmers)." - from a google search

so i am going to assume that the 20 amp breakers in there can then take a load of 2400 watts

ship or someone else with more electrical experience can you please explain this as i am currious as well
A stab in the dark:

Perhaps the dimmers are not being run at 100%. A 1000 watt PAR running at 50% only uses 500 watts. The board we have at school has, buried deep in its menus, an option to limit sliders so if the slider can move in the range 0%-100% it only outputs 0%-90%, for example (that was really badly explained). You limit the sliders output to a maximum value. Perhaps your board has been set so that channel can never be moved above 60% which is 2400 watts, hence the breaker does not pop.

I might be totally off the mark here, but it’s possible.

come to think of that we do that too w/ our house lights, but we limit the dimmers rite at the rack. i would check the control module to see if thats the problem
While what everybody has said above is possible, could it also be possible that it is a 20 Amp 240v breaker that is feeding the dimmer? If that is the case, then you would have 4,800 watts of available power and not the 2,400 watts that you think you are limited to. I am not claiming any advanced knowledge of electricity, but this is how I understand things to be.

I certainly invite Ship to put in his opinion because his knowledge far exceeds mine, but the above was just my $.02 on the question.
Well, first off, it doesn't sound safe, so I would change it ASAP, before something bad happens.

Taking a stab in the dark, is this a 240v system? If you are running 240v thru a 20 amp dimmer, you will get 4800 watts of power available. Of course, if this were the case and you were to put normal 120 volt lamps in the fixtures, the lamps should drop like flys.

More likely, it seems like the breaker is broken. This is bad, because if something happens and the breaker should trip, and doesn't, well.... the building could burn down, you could get electrocuted, or other bad things could happen.

SO: get someone to look at the dimmers, or at the very least make it so nothing is overloaded.

Of course, this is all a stab in the dark. Other, smarter people will comment on this soon I believe.
Well are we talking about a dimmer module like one from a sensor rack, or are we talking about what I refer to as a dimmer pack or like a set of 4-12 dimmer circuts all enclosed in one box that is fed from one power input?

In the case of a dimmer pack, I don't think you are having any problems or electrical phonomena. The dimmers that I have at school run on two legs of power a.k.a. 240v and we use regular 120v fixtures and in my years at the theatre, we have never had a fixture explode. To explain this, when power enters the dimmer it is usually split in half so that one leg feeds half the channels, and another leg feeds the other half of the channels. In my case one leg feeds 3 channels at 2.4 Kw each thus requiring 60 amps, then the other leg feeds another 3 channels requiring an additional 60 amps. This doesn't however mean that I need a 120 amp breaker, I just need a 60 amp 240v breaker because that delivers 60 amps per leg. If you don't believe me, follow the "signal" path. Look at a schematic for a dimmer on how to connect the power cable and you will see that there are two separate legs that feed the 2 halfs of the dimmer each running at 120v each.

What I am curious about is how many channels this dimmer is considering that it only runs on 20 Amps. If I ran the numbers correctly, you would only have 2 channels at 2.4Kw being fed by 240v.

If I am wrong about you using only a dimmer module, then certainly listen to what the people who posted above me have to say because it sounds like in the case of a dimmer module that you would have something seriously wrong.

Once again I claim no amazing knowledge of electricity or lighting, my primary job is as a sound tech as my signature says. I just study electricity because it seems to be becomming common that everybody expects the sound personel to deal with power and know how to wire things correctly. Plus its always good to be well rounded when you work in the theatre industry, or any industry for that matter.
How to tell

First step is to look at the breaker and see if it is a single or double pole breaker (for instance is it like 2 breakers with the handles joined together by plastic or is it just a single one). If it is a 120v breaker then it will be a single pole breaker.

120 volt electricity consists of a hot wire and a neutral. The hot wire carries 120v. The neutral allows a return path. The potential between hot and neutral is 120v.

240v electricity is actually two 120v legs. A way to think about it (though not exactly scientifically correct) is to imagine that one leg is 120v and the other is -120v (don't think negative like lack of...just imagine a number line). Neutral is in the middle (at 0). The potential difference between neutral and either leg is 120v. The potential between the 2 legs is 240 volts.

So you could have a system with a 240 v breaker that was actually a 120v dimming system. If that were the case, however, the one breaker would have to control 2 dimmers. which doesn't make much sense.

It would be a good guess that you're using a 120v dimming system with a single 20A breaker...240 is not as easy to dim (not as fluid, noisy, etc) and most systems are designed for 120v

If you find that you have a 120v dimming system the next step is to check your actual load. If you happen to have ETC sensor racks then go into dimmer check on your board and get the actual will tell you. Or you can use a clip on load meter...clip the ring around the cable and it will tell ya the number of amps you are drawing (do this with the lights on of course...)

If it was just one dimmer and one breaker i would think it was a bad breaker...but since it's three of them i think breaker or dimmer problems can be ruled out.

I will guess...and this is only a guess...that it is a combination of a smaller load (lamps may not be drawing their rated wattage) than you think you have and a tolerance in the breakers that is allowing a little bit more power through than the 20 A they're rated for.
Before an answer of meaning can be offered, I have to ask, how have you determined there is a 33 amp load on a 2.4k dimmer?

What is the brand and or model of the dimmer?

Could they actually be 3.6k dimmers, LMI used to make such a 6 pack rack.
They are Strand CD-80 PACKS

Its 4000w on each dimmer at 120v... therefore... 33.3 amps approx.3

And right there I just answered the other question... everything is 120v (but actually its more like 115v)
i would get that looked at very quickly. that does not sound correct. i have use many cd80s and have had them trip every time i went over. I am wondering if your lamps are no longer pulling the full wattage and taht is how it is not tripping or if you have it limited so that it is ok to put that on based on current load.

again i dont claim any advanced electrical knowledge
What type of lamp are you using on each dimmer? I would be quite surprised if you were using 4 kW lamps on each dimmer.

Also, can you please describe how you know it's the same 120V leg for all three dimmers?
mbenonis said:
What type of lamp are you using on each dimmer? I would be quite surprised if you were using 4 kW lamps on each dimmer.

Also, can you please describe how you know it's the same 120V leg for all three dimmers?

There are 4 1kw scoops (why we have those damn scoops instead of real cyc lights I don't know) on each dimmer.

I believe its only one leg feeding the dimmer because there's only one breaker for each one of our packs... wouldn't there be 2 if there were 2 legs? But the question the way I see it has nothing to do with the legs feeding the dimmer. I am asking why the 20amp breaker on the dimmer pack for each of the 12 dimmers in each pack doesn't trip when a 33amp load is applied.
are you positive they are 1000w? for our scoops we use EGJ's but one had a BTL in it
koncept said:
is the 33 amp load per dimmer or over the whole pack

there are 12 scoops, 1Kw each, divided on 3 dimmers...
there are 3 dimmers with ~33amp load on them each...

are you positive they are 1000w? for our scoops we use EGJ's but one had a BTL in it

Yes, they all have 1kw lamps. I've already put in the order for the 500w lamps.
750w lamps? 6Kw dimmers? Shunt system? Lights are not left on long enoug to heat the breaker sufficiently to trip?

Otherwise, bad circuit breakers by now will have effected your dimming curve and wiring. CD-80 packs are good but not that good.

If you know for sure you have 4x 1Kw fixtures on a 2.4Kw dimmer, and have had it as such for a while, you might find it wise to not do so and have the dimmer and wire feeding such fixtures professionally insepected for problems.

Users who are viewing this thread