Commercial lighting circuits maximum ampacity

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IL94EE

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One of the other engineers in the office has a project under construction with a problem. The contractor has completed installation of the lighting fixtures in a couple small rooms, and the breakers are tripping that the circuits are overloaded. There is a potential of the problem being much worse in a larger room which hasn't been completed yet and uses the same light fixtures. There is investigation being done into power quality, grounding, etc. to try to figure out why the ballasts are drawing more than what their nameplates say they should. At any rate, everyone is trying to find a possible quick fix, which would be increasing the breaker size, within the limits of the ampacity of the wire which is there, or replacing it with larger wire. Everyone seems to have this "feeling" that there is a restriction in the code on the ampacity/breaker size for fluorescent circuits, but none of us has been able to find it yet. It isn't so much that it's a complete limit, as it is that if you go over 20A for a circuit, you then have to have individual fusing in the fixtures. Can anyone point out where this restriction is, or are we all just so used to keeping to 20A breakers that we have a phantom limit in our heads?
 
There's no Code limit to a certain number of fixtures, just that you cannot overload the circuit with the load. Different manufacturers lights will have different amp draws, and technology keeps improving to lower the amp draws, so there cannot be a stated number as a limit.

Did anyone check the voltage of the ballasts installed against the voltage applied? In other words, did they install 277v ballasts in a 120v system, or vice-versa?
 
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IL94EE said:
It isn't so much that it's a complete limit, as it is that if you go over 20A for a circuit, you then have to have individual fusing in the fixtures. Can anyone point out where this restriction is, or are we all just so used to keeping to 20A breakers that we have a phantom limit in our heads?
Click to expand...

Check out the requirements / restrictions in 210.23.
 
iwire said:
Check out the requirements / restrictions in 210.23.
Click to expand...

I don't see where it applies here.
(A)(1) deals with cord-and-plug equipment.
(A)(2) specifcally exempts lighting.
(B) (C) and (D) are larger circuit ratings.
 
480sparky said:
I don't see where it applies here.
(A)(1) deals with cord-and-plug equipment.
(A)(2) specifcally exempts lighting.
(B) (C) and (D) are larger circuit ratings.
Click to expand...

Right (B) (C) and (D) are larger circuit ratings.

IMO the question the OP asked was about increasing the circuit rating.



At any rate, everyone is trying to find a possible quick fix, which would be increasing the breaker size, within the limits of the ampacity of the wire
Click to expand...
 
Lighting Circuits

Lighting Circuits

As mentioned you are not limited on the number of fixtures but rather by the load. Take a look at NEC 2005 210.20 (A). Your lighting load is a continuous load and your 20amp circuits would need to carry no more than 16amps. I did see a project with a simiular problem many years ago where the ballast that the manufacture provided were LPF instead of HPF and the result was the number of fixtures on each circuit resulted in a higher ampere load than the design called for. I don't know if anyone even makes LPF ballast anymore, but you may want to check the actual ballast in the field as manufactures all purchase what ever ballast they can get for the best price unless it is actually specified when the fixtures are ordered.

Grant
 
Commercial lighting circuits maximum ampacity

"Everyone seems to have this "feeling" that there is a restriction in the code on the ampacity/breaker size for fluorescent circuits, but none of us has been able to find it yet."

Section 210.23(C) does permit 40 or 50 A for lighting circuits.
Section 210.23(D) states that 50 amperes shall supply only nonlighting outlet loads.
As to why the lighting circuit is tripping:
If the overcurrent device is tripping instantly, you might check for a short circuit or ground fault.
If the overcurrent is taking some time to trip you might monitor the current to see at what level it trips you could have an overload.
 
IL94EE said:
One of the other engineers in the office has a project under construction with a problem. The contractor has completed installation of the lighting fixtures in a couple small rooms, and the breakers are tripping that the circuits are overloaded.
Click to expand...


I don't know what you call a small room but this doesn't sound right at all.

Could you give a type for the fixtures, the number of fixtures on a circuit and the operating voltage ( 120V - 277V ).

The most probable cause is operating at an incorrect voltage or just a plain old short.
 
What type of lamp/ballast is this?

I had a problem similar to this when I did my first project that was mostly T5HO lamping and we made the EC take thermal image scans of each panel to look for hot spots and tighten lugs as needed. Several lighting circuits were hot and the amp probe said it was drawing about 17 amps.

I kept thinking the EC wired something wrong. A year later I figured it out. As most people know T5HO lamps put out more light at 35 degrees C. About 10% more light vs 25C. It's not free light. The wattage also goes up about 10%. Now I put less T5HO lamps on a circuit.
 
Been out of the office the last two days, so just now seeing responses and additional questions.........

Since I'm just on the fringes of the issue, I'm not sure if the voltage applied vs. voltage rating of the ballast has been verified, but I do believe I heard discussions about nameplate data. Most fixtures seem to be coming with universal ballasts anymore, whether or not we specifically ask for them. Everything fluorescent we specify is to have electronic, 98% power factor, 10% harmonics type ballasts. But again, I don't know what ended up on site. The lamping of the fixtures is T5HO.

I don't really see article 210.23 coming into play, since this is fluorescent lighting fixed in place. I can't say I've ever heard of a "heavy duty" fluorescent lampholder before. But, I don't exactly deal with such things directly either.

Article 240.4(D) will definitely be followed, no questions asked. We have some wiggle room on homeruns because we require #10 wire in them. The branch wiring within the room may end up needing to be replaced if the breakers are bumped to 30A.

The "small rooms" in this case are a couple renovated classrooms about 25x35 with exposed laminated beams and wood deck vaulted ceiling. The "large room" is an elementary school sized gymnasium.

The problem is overloading and not shorting. They have put amprobes on, and they're drawing more than they should be. From what I'd heard at one point, it sounded like almost a 50% ballast loss. Something isn't right. The fixture manufacturer is being drawn into it, but they're sometimes less than enthusiastic about admitting and correcting a problem. We've been using T5HO fixtures for several years without problems, although the contractor bought a different brand this time from what we've had on other projects. I think this will end up having to be resolved by troubleshooting for the most part. I was/am primarily wanting to see if that internal fusing requirement is really out there hiding in the code somewhere, or if it's just a figment of people's imaginations (or maybe it was there in past versions and went away). Thanks for the responses.
 
iwire said:
Check out the requirements / restrictions in 210.23.
Click to expand...

But if you have a 30 amp circuit breaker at the panel, and a 15 amp fuse at every fixture, wouldn't the 30 Amp circuit be a feeder?

Steve
 
Specs, Shop Drawings & Circuiting

Specs, Shop Drawings & Circuiting

First I would go back & verify the specs, & then check for shop drawing approval of submitted light fixtures. Then verify what's actually out there & compare. If what was spec'd & what was installed was what was intended & approved, & you didn't overload the circuits according to mfg's data sheets, have the lighting mfg's rep get out there & see why the fixtures are drawing too much current.
 
use advance ballast!

use advance ballast!

IL94EE said:
Been out of the office the last two days, so just now seeing responses and additional questions.........

Since I'm just on the fringes of the issue, I'm not sure if the voltage applied vs. voltage rating of the ballast has been verified, but I do believe I heard discussions about nameplate data. Most fixtures seem to be coming with universal ballasts anymore, whether or not we specifically ask for them. Everything fluorescent we specify is to have electronic, 98% power factor, 10% harmonics type ballasts. But again, I don't know what ended up on site. The lamping of the fixtures is T5HO.

I don't really see article 210.23 coming into play, since this is fluorescent lighting fixed in place. I can't say I've ever heard of a "heavy duty" fluorescent lampholder before. But, I don't exactly deal with such things directly either.

Article 240.4(D) will definitely be followed, no questions asked. We have some wiggle room on homeruns because we require #10 wire in them. The branch wiring within the room may end up needing to be replaced if the breakers are bumped to 30A.

The "small rooms" in this case are a couple renovated classrooms about 25x35 with exposed laminated beams and wood deck vaulted ceiling. The "large room" is an elementary school sized gymnasium.

The problem is overloading and not shorting. They have put amprobes on, and they're drawing more than they should be. From what I'd heard at one point, it sounded like almost a 50% ballast loss. Something isn't right. The fixture manufacturer is being drawn into it, but they're sometimes less than enthusiastic about admitting and correcting a problem. We've been using T5HO fixtures for several years without problems, although the contractor bought a different brand this time from what we've had on other projects. I think this will end up having to be resolved by troubleshooting for the most part. I was/am primarily wanting to see if that internal fusing requirement is really out there hiding in the code somewhere, or if it's just a figment of people's imaginations (or maybe it was there in past versions and went away). Thanks for the responses.
Click to expand...


I dont like the universal ballast, they have been poor for a long time imho,
seen them fail many times,
 
IL94EE - In your 1st post you said the ballasts were drawing more current than labeled. Other posts explained the early checks to make. I think a last resort is to find out if those ballasts are what they say. I have experienced a 480 volt motor which had been wound with incorrect wire size, resulting in almost 10% higher current draw. I have also found a C.T. in MV switchgear which was labeled incorrectly, (300/5 and not 100/5 as labeled. These were new installations, factory errors.
 
Overloading

Overloading

You say this is an overloading issue and not a short. What you didn't say is if it is instantaneous or taking a few minutes to kick out. You said they've had amprobes on the circuit. If it's not a short and kicking out immediately, have you checked the inrush peaks?
 
Hey, just a short hijack. If you increase the breaker size to 30a, rewire the whole circuit to 10 wire, can you still use a 20a rated switch? Does the same exception for using 15a recepts on a 20a circuit (If there is more than one recept on the circuit, 15a recept is fine) apply?
 
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