208 lights fed from a 3 pole breaker

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copper123

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I have been looking at a lighting job the last couple of days and have been having questions about how the over current protection is working.

The building has three separate bays in it. Each bay has 7, 400 watt metal halide fixtures in each bay. They have a FLA of 2.4 each. They operate at 208 volts single phase.

Here is the issue. All three bays of light fixtures are fed off of a three phase, 30 amp breaker. Each bay has a 3 pole lighting contactor controlling the light for the area. They bring all three legs into the contactor and then split the three phases up in each one of the bays. I am not sure how the load is distributed. The contactors are controlled with a 120 volt coil and they use a different phase of the three phase power for the control ckt to each bay.

If you do the math for the 30 amp 3 phase ckt, you have a VA of 10,800. 30 amps x 1.73 x 208. You surely can?t use this number for the load calc. My biggest question is how this can be code. I understand that the NEC is not a design manual, and was wondering if anybody has seen this before. Can you use a 3 pole breaker and evenly distribute the load for single phase 208? And, would you not have a total load for all 21 lights of 8400 VA? But wouldn?t you use the ballast rating of 2.4 amps apiece and come up with 50 amps?
Thanks for all the help
 
Re: 208 lights fed from a 3 pole breaker

Copper, this is common and is not a code violation.

Balance the single phase loads across the 3 phase feed.

You have 21 fixtures which works out great.

7 hooked up to A and B

7 hooked up to A and C

7 hooked up to B and C

The load calculation must use the ballast input current as you said.

2.4 x 21 = 50.4

50.4 x 208 = 10,483

Your 3 pole 30 amp breaker provides 10,795

This installation is fine as long as the load is not continuous.

If the entire load is continuous there is a violation of 210.19(A)(1).
 
Re: 208 lights fed from a 3 pole breaker

Thanks Iwire.

I was thinking that at some point, you would need three, two pole breakers. Even though you can distribute the load among all three legs of the three pole breaker, the breaker was not being used in the manor that it was made. I looked in the code for awhile and of course I could not find anything. I guess I had the thought that it should be more isolated and clean as far as the distrubution and design should go. So this is done a lot? 3 phase power and they slam a 3 pole in and run a large portion of lights with it? I am still pretty young, but all the work I have seen is more isolated with two pole breakers. Also, with the three pole, its all or nothing. You have to shut down the entire operation to work on the lights.
 
Re: 208 lights fed from a 3 pole breaker

Thanks Iwire.

I was thinking that at some point, you would need three, two pole breakers. Even though you can distribute the load among all three legs of the three pole breaker, the breaker was not being used in the manor that it was made. I looked in the code for awhile and of course I could not find anything. I guess I had the thought that it should be more isolated and clean as far as the distribution and design should go. So this is done a lot? 3 phase power and they slam a 3 pole in and run a large portion of lights with it? I am still pretty young, but all the work I have seen is more isolated with two pole breakers. Also, with the three pole, its all or nothing. You have to shut down the entire operation to work on the lights.
 
Re: 208 lights fed from a 3 pole breaker

Are your lighting contactors 2 pole or 3 pole? Connecting light fixtures phase to phase does occur in some US installations but is prohibited by Canadian rules.

If your lighting contactors are 2 pole then 25 amp or 30 amp 2 pole circuit breakers are required. Just remember that if you use the existing conduit for the 6 wires you must derate the wire ampacity 80% because of the conduit fill.

If your contactors are 3 pole AND using all 3 poles you would be better off using a subpanel and running a 50 amp feeder.
 
Re: 208 lights fed from a 3 pole breaker

Also remember to use circuit breakers rated HID which means that they have some extra silver in the contacts so that inrush current and breaking the circuit does not wear them out.

Also, breaking up the system into 3 branch circuits keeps all of your lights from dying if there is a short circuit or if you are doing deenergized maintenance.

I have had to take down 400 watt HID fixtures ( both HPS and metal halide ) because it takes 3 people to wrestle the bulb out of the socket. That is 1 extra person than what is allowed in a standard high reach. If the bulb breaks off from the base then digging the base out creates fine glass particles that tend to get into alledged safety glasses if you try to do that with the fixture in place. In other words, every once in a while ( about 1 out of 8 times ) the fixure is going to be a pistol to relamp.
 
Re: 208 lights fed from a 3 pole breaker

Originally posted by mc5w:
I have had to take down 400 watt HID fixtures ( both HPS and metal halide ) because it takes 3 people to wrestle the bulb out of the socket. That is 1 extra person than what is allowed in a standard high reach. If the bulb breaks off from the base then digging the base out creates fine glass particles that tend to get into alledged safety glasses if you try to do that with the fixture in place. In other words, every once in a while ( about 1 out of 8 times ) the fixure is going to be a pistol to relamp.
Click to expand...
Mike what the heck are you talking about?

It takes 3 people to change a lamp?

No wonder you have a hard time finding work. :D
 
Re: 208 lights fed from a 3 pole breaker

MCW5:
The 25 or 30 amp breaker that you have talked about, is this if you use a 30 amp contactor?

The installation is three, 3-pole lighting contactors fed of a three pole 30 amp breaker, installed for three different bays of lighting. Why would it matter if I broke out the ckts, put a two pole 20 for each 7 lights, and then just reused the existing lighting contactors that are there. I can not find any code reference to having to use a 25 amp breaker for use with a 30 amp rated contactor. Also, I have not found anything wrong yet with using two poles of a three pole contactor, but i am still digging. This is really the problem with going in and trying to fix stuff that is already installed. You really need to get down and dirty with the code. You are trying to use gear that is allready on the wall, but there are so many issues. But also, i sure do agree with you on the design element of the lighting job. I would never think about putting all my lights on a three pole breaker, especially for three different bays. Really no way to truly isolate just one bay. You could cut the control ckt to the contactor, but in this instance, they are using a leg of the three pole to drive each one of the lighting contactors!

[ June 09, 2005, 02:05 PM: Message edited by: copper123 ]
 
Re: 208 lights fed from a 3 pole breaker

just did the numbers on a two pole 20 with 7 - 2.4 amp lights.

It will not work at 208 at 1.25% Thought I better say something before I got blasted!
 
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