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Author Topic: Help With Tripping Dimmer Breakers  (Read 8837 times)

Don Lomonaco

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Re: Help With Tripping Dimmer Breakers
« Reply #40 on: August 05, 2014, 07:20:16 pm »

The following is a reply from the Control Booth forum that bears attention.  I'm going to check into these points and report back.


Hi Don,
I think there are a few issues that are compounding your problem.
Please excuse me if I ask simple questions to better understand the situation, I do not mean anything personal by it.

This is a Unison system. Do you have the problem with breakers tripping when you use any Unison presets?
Are you able to read the Unison configuration to know what level those dimmers with 4 PARs are being driven at by Unison? (unison menu [Diagnostics]-[Dimmers])
Has the problem only been noticeable since you started using the SmartFade console?

Now, some observations.
Ohm's law is arbiter of Amperage not W=VA. 120V lamps on a system of 124.7V are drawing around 4.98A.
(Math - to find current draw of 120V lamp at 120V W=VA __ 575=120/A A=575/120 A=4.79 amps
to find the resistance of the filament I=V/R__4.79=120/R R=120/4.79 R=25.05 ohms
to find the current draw of this lamp at 124.7V I=V/R__ I=124.7/25.05 I=4.98 amps So, 4 lamps create a load of 19.92 amps.)

If the wire pulls are long, the use of 12awg wire for a 20A load is possilbly not code compliant and probably inadequate. In the lobby of my space, the 20A dimmers are wired with 10awg wire. The stage circuits are 8awg for the 20A circuits. I don't know my NEC code well enough to be sure without pulling out my book, but I think that resistance due to wire size/# per conduit/load is also increasing the current draw on the breaker of your dimmer. Dimmers are often not thought to be continuous use devices, but if a 20A load is placed on the circuit for 3-4 hours as for a lobby circuit during a performance, it really should be designed with a maximum of 80% rated capacity.

When you fix the burnouts, the breakers on those dimmers will most likely trip as well.

One 575W/115V lamp in this mix will certainly put you over the max current.

A loose hot or neutral on different circuits which causes arcing and therefore an increase in heat will increase the resistance in the cable. I know that you checked the lugs, but all terminal strips and connectors and two-fers could be suspect.

You have to be careful how you balance your load across the whole rack. This rack is being fed by single phase power and is not balanced. One leg is feeding dimmers 1-8, and the other leg feeds 9-19(or 24 if the rack was fully loaded). Nominally, you have 115A on the first leg and 100A on the second. With the feed being 150A, you are near the maximum that you would want it to be if you derate the main breaker to 80% for continuous use.)

More than an entertainment lighting company, I think you need a licensed electrician and/or electrical engineer.
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Don Lomonaco

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TJ (Tom) Cornish

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Re: Help With Tripping Dimmer Breakers
« Reply #41 on: August 05, 2014, 08:20:57 pm »

The following is a reply from the Control Booth forum that bears attention.  I'm going to check into these points and report back.


Hi Don,
I think there are a few issues that are compounding your problem.
Please excuse me if I ask simple questions to better understand the situation, I do not mean anything personal by it.

This is a Unison system. Do you have the problem with breakers tripping when you use any Unison presets?
Are you able to read the Unison configuration to know what level those dimmers with 4 PARs are being driven at by Unison? (unison menu [Diagnostics]-[Dimmers])
Has the problem only been noticeable since you started using the SmartFade console?

Now, some observations.
Ohm's law is arbiter of Amperage not W=VA. 120V lamps on a system of 124.7V are drawing around 4.98A.
(Math - to find current draw of 120V lamp at 120V W=VA __ 575=120/A A=575/120 A=4.79 amps
to find the resistance of the filament I=V/R__4.79=120/R R=120/4.79 R=25.05 ohms
to find the current draw of this lamp at 124.7V I=V/R__ I=124.7/25.05 I=4.98 amps So, 4 lamps create a load of 19.92 amps.)

If the wire pulls are long, the use of 12awg wire for a 20A load is possilbly not code compliant and probably inadequate. In the lobby of my space, the 20A dimmers are wired with 10awg wire. The stage circuits are 8awg for the 20A circuits. I don't know my NEC code well enough to be sure without pulling out my book, but I think that resistance due to wire size/# per conduit/load is also increasing the current draw on the breaker of your dimmer. Dimmers are often not thought to be continuous use devices, but if a 20A load is placed on the circuit for 3-4 hours as for a lobby circuit during a performance, it really should be designed with a maximum of 80% rated capacity.

When you fix the burnouts, the breakers on those dimmers will most likely trip as well.

One 575W/115V lamp in this mix will certainly put you over the max current.

A loose hot or neutral on different circuits which causes arcing and therefore an increase in heat will increase the resistance in the cable. I know that you checked the lugs, but all terminal strips and connectors and two-fers could be suspect.

You have to be careful how you balance your load across the whole rack. This rack is being fed by single phase power and is not balanced. One leg is feeding dimmers 1-8, and the other leg feeds 9-19(or 24 if the rack was fully loaded). Nominally, you have 115A on the first leg and 100A on the second. With the feed being 150A, you are near the maximum that you would want it to be if you derate the main breaker to 80% for continuous use.)

More than an entertainment lighting company, I think you need a licensed electrician and/or electrical engineer.
Don, with respect, you're starting to go in circles here, and more information is only helpful if it's accurate.  Reading TFM, we see that the ETC modules are "fully rated for continuous duty" http://www.etcconnect.com/Products/Dimming-Switching/Unison-Dimming/Dimmer-Modules/Features.aspx

These are not subject to 80% derating, and the whole 575w thing was designed specifically about being able to have 4 of these on a 20A circuit.

You mentioned earlier that you already have #10 wire - there isn't a problem there.  Most of this post you copy is dubious at best, and not particularly germane to the equipment you are using.  He's wrong about having 124v at the bulb (you won't - dimmer modules have a voltage drop of 4 volts or so), and wrong about de-rating the ETC breakers (though probably correct about the main breaker).

If you truly want to find out the root issue, you will need to do some measurement of voltage and current, and stop guessing.  If you just want to make the problem go away, your choices are either to lamp down to 375w bulbs (not my personal choice), or reallocate and use 3 fixtures per circuit.

I'm still suspicious that you have either a mixture of 750w bulbs or 115v bulbs, and that if you measure the current, it will be more than 20A.
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Josh Daws

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Re: Help With Tripping Dimmer Breakers
« Reply #42 on: August 06, 2014, 07:43:06 am »

i thought i wrote about de-rating somewhere....lol

anyways there is always going to be some de-rating. continuous duty means that it is designed to be able to operate at 20a continuously (see link and scroll down http://www.qualifiedhardware.com/glossary...it doesn't mean that at the lamp end that you are able to fit 20a. unless someone has installed larger breakers.

and as i've stated previously stated you should keep your loads to around 80% max, and this then allows for overdraw of the amperage due to de-rating.

however yes there is a voltage drop. 124v is a little high IMO, especially if you are using non-dim fixtures. however as long as you are reading 120v at the fixture end you are fine.

my advice is to either lamp down, or go to 3 fixtures...

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TJ (Tom) Cornish

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Re: Help With Tripping Dimmer Breakers
« Reply #43 on: August 06, 2014, 08:52:54 am »

i thought i wrote about de-rating somewhere....lol

anyways there is always going to be some de-rating. continuous duty means that it is designed to be able to operate at 20a continuously (see link and scroll down http://www.qualifiedhardware.com/glossary...it doesn't mean that at the lamp end that you are able to fit 20a. unless someone has installed larger breakers.
Josh - continuous duty 20A means that you can draw 20A forever without tripping the breaker.  This means exactly that you can you can supply 20A worth of lamps on this dimmer.  Whether the OP is over or under 20A is the issue.

Your earlier post:
Quote
has anyone considered de-rating?? a TBH im a little out of practice here as i've hadn't had to deal with this and electrical isn't my forte, but i have been taught by electricians when ive done installations and larger live event setups is to not load up more than around 80-90% of your max allowance to allow for de-rating...

for example i have a 16AWG 100ft AC cable connected to a 575w Source 4. the actual power because of distance maybe close to 650w as the current required to operate at 575w @ 120v is actually more.

but you should never load your circuit to near max.

if someone more qualified reads this and if my information is misleading or wrong, please feel free to educate me, and correct me!...
You have several errors here, and they have already been addressed in this thread.  Adding cable length does not increase the power consumption of a light bulb, it reduces it. 
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Stephen Swaffer

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Re: Help With Tripping Dimmer Breakers
« Reply #44 on: August 09, 2014, 08:18:28 am »

A $100 clamp meter would give you your answer in 30 seconds or less.  Trying to solve this without one is like stumbling around  in the dark looking for something-the first thing most people do is find a light.

If your time is worth anything, the investment will pay for itself.

Not allowing for derating should have one of two results-dimmer lamp for same output at dimmer or overheated wires in the conduit/wiring,  not a tripped breaker.  I have seen on a number of occasions where a loose connection on a breaker of fuse will cause it to blow at less than rated current, but it sounds like that possibility has already been eliminated.

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Steve Swaffer

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Re: Help With Tripping Dimmer Breakers
« Reply #44 on: August 09, 2014, 08:18:28 am »


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