Parking Lot Lights / GFPE Service

[George Stolz]

I got a question from a guy, not quite sure what to advise; I told him I'd ask here.

There is a 1600A 480V service with GFPE protection, supplying a panelboard with a 277V single pole 20A breaker which supplies parking lot lights. The feeder run from service to panel is an average length, and the circuit length of the parking lot lights is probably around 400'.

A head in a parking lot light faulted (presumably to ground) and tripped the service GFPE. The equipment is Square-D, installed new five years ago.

When the event occurred, the display on the GFPE read "44" or something, and on the second occurrence read "49" or something like that; I've slept since then.

It took three attempts for the circuit breaker of the circuit to trip, and I believe the GFPE triggered the third time in concert with the branch circuit breaker.

So the question is, is the trip setting of the GFPE wrong? Is the GFPE defective? Is the branch circuit breaker defective? For Square D to come out and verify the settings on the equipment at this point would be $500, and the foreman does not believe that to be necessary at this time, just isn't certain exactly what went wrong here.

Please do not launch into a string of comments about resetting circuit breakers without testing, and what have you. I do not know all the details, and trust the competency of the foreman who posed this question to me.

 

[bobsherwood]

The business school here on campus. A/C guy reset a breaker for radiant heat and the entire building tripped off. There was a shorted radiant heat panel. The Main is a GFCI, the 20 amp QOB was not. The rec center does the same thing... One of the electricians re set a 20 amp single pole and the feeder to the panel was protected with GFCI. Found a shorted fixture on the front steps. It's a good thing and it's not such a good thing. I like the protection but, I do not like to lose the entire building!

 

[jim dungar]

The GFPE is always shipped from Square D at the minimum settings. The minimum settings will not coordinate with a 20A breaker.

Someone needs to determine the proper settings for coordination (it is usually possible to coordinate to around 70A branch devices).

It is unlikely that you need to "test" your GF equipment, although it is probable you need to check your branch circuits.

 

[zog]

So the question is, is the trip setting of the GFPE wrong? Is the GFPE defective? Is the branch circuit breaker defective? For Square D to come out and verify the settings on the equipment at this point would be $500, and the foreman does not believe that to be necessary at this time, just isn't certain exactly what went wrong here.

Only way to know if it defective is to test it, I wouldnt use square D, look for a 3rd party testing company so your results are un-biased. Or test it your self, just need a current source, a mulitmeter, and an understanding of GF systems.

Please do not launch into a string of comments about resetting circuit breakers without testing, and what have you. I do not know all the details, and trust the competency of the foreman who posed this question to me.

Is that aimed at me? Will...try...to resist...urge to ...quote ....1910.342.......

 

[jim dungar]

The Main is a GFCI, the 20 amp QOB was not.

In the US, the mains do not have GFCI. Yes, they can have GF, or GFI, or GFPE but definitely not GFCI. GFCI is a term, Ground Fault Circuit Interrupter, reserved for personnel protection (6mA trip for class A devices). Most main GF devices have settings beginning at 100A.

Now back to George's problem. Testing the existing GF settings will not do much for you if they are not the correct ones. After you have decided on which setting to use, you may want to have the GF tested. Unlike Zog, I do not feel that a 3rd party tester will always give you an 'unbiased' answer, after all most of them also sell repairs and upgrades just like manufacturers do. Go with a testing company you trust and feel comfortable working with (just like with vehicles, do you go to a dealer, an independent mechanic, or DIY in the backyard).

 

[Pierre C Belarge]

There is a 1600A 480V service with GFPE protection, supplying a panelboard with a 277V single pole 20A breaker which supplies parking lot lights. The feeder run from service to panel is an average length, and the circuit length of the parking lot lights is probably around 400'.

A head in a parking lot light faulted (presumably to ground) and tripped the service GFPE. The equipment is Square-D, installed new five years ago.

We just had this same scenario occur here about 3 months ago. SQD GFPE service and all that good stuff.

SQD sent a tech and he worked on the settings of the GFPE. It has not occurred since then.

 

[hillbilly1]

I had one large customer that wanted all of the settings turned all the way up, they didn't want the store to go down if a roof top unit compressor went out. Very dangerous. If a coordination study is not going to be done, I will only bump it up a notch or two. That usually reduces the nusiance tripping, while still giving reasonable protection. Cutting on large transformers can also trip them at the low setting, have that problem occasionally with transfer switches.

 

[brother]

I was taught it was 'good' practice/design to have each parking lot light with 'inline' fuses like some of the lighting we do in offices. This helped reduce a wide spread outage on the branch circuit (or in this case a whole building) for safety/liability reasons.

But never the less I would definitely check the settings on the breaker (coordination study) and have look at the branch circuit breakers.

 

[George Stolz]

Thanks for all the helpful replies, I will pass this thread along.

 

[zog]

Unlike Zog, I do not feel that a 3rd party tester will always give you an 'unbiased' answer, after all most of them also sell repairs and upgrades just like manufacturers do.

Thats the advantage of a NETA testing company, per the bylaws of NETA a testing company has to make 85% of thier income from testing, everything else, repairs, upgrades, engineering studies, products, etc can only make up 15% of revenue. So a NETA company is always focused on testing and not out to sell upgrades like an OEM service group. Not to mention thier techs are actually certified.