Does the sensor for the generator/transfer get installed on the load or line side of a 2000a. 480v. GFP Service. The issue is, if the GFP trips should the generator start?

George:
You pose an interesting scenario....
Thinking about it, I would venture a "guess" (at this point) that the line side wins. Again, that's MHO, and I will bring this up with a few other AHJ's.

Where's the xfr switch connected line or load of the MCB?? Is the gen 480??

OK, put it on the load side, get a GF, MCB trips; gen starts. Put it on the line side, get a GF, gen does not start.

This will be a good debate!

Added:
OK, purpose of gen is to provide power during a utility failure; correct?
That thought said, a internal GF is NOT a utility failure, although the results are the same (darkness). I'm sticking with a LINE side reference point at this time.

John

[This message has been edited by HotLine1 (edited 04-08-2005).]

I would think you would want (be required) to have the generator take over.

The generator will have it's own GFP if over 1200 amps so it will 'take care of itself' if the ground fault is in the emergency system and is still present.

A fault in the 'normal' power distribution systems should not disable the emergency egress lighting.

JMO, Bob

Hotline1- I think I'd agree with you. Utility failure and generator takes over.

Story behind the question. - We had a bad electrical fire in a building near me and the utility main let go. There was a 480v. GFP service and the GFP never tripped. The generator started and kept the fire going. No GFP on the generator. Fire would have been less damaging if the generator would have had GFP. Fire deptartment had to shut the generator down and the sprinklers in the equipment room put out the fire. Point here is, if the GFP trips on the main and the low volt sensors on the transfer switch are on the line side of the main the generator probably won't feed the fire. I guess it's a crap shoot either way. Can't find anything in NFPA 70 on this point.

[This message has been edited by George Little (edited 04-08-2005).]

Iwire- look at 701.17 and we see that the alternate source is not required to have GFP and that's what is bothering me.

I assumed article 700 which would bring us to 700.26.

Regardless, my feeling is it is more important to provide emergency egress lighting then to be concerned with generator promoting the fire.

I look at this the same way as the fire pump rules, let it run till it melts.

JMO, Bob

How about a few more details George Little...

1)What was the purpose of the building?
2)Was there just the one 2000amp service to the building?
3)Did the generator backfeed the whole 2000amp service?
4)How old was the electric installation in the building?

Iwire, normal power or generator power, any emergency lighting wall packs and exit signs for egress have battery backup...right

shortcircuit

ShortC


Unfortantly no, that is not required.

IMO what you describe is good design.

When the utility drops you can be in darkness for up to 10 seconds until the generator comes on line.

To be clear here, if you have a building with a true Article 700 emergency system powered from a generator there is no requirement to have battery back up of the egress lighting.

Typically the emergency lighting in a building with a generator is the same lighting fixtures used for general illumination.

If you have 2 x 4 troughers lighting an area some of them will be fed from the emergency system.

If you do this in an area with HID lighting you must provide lighting that will cover the time for the lamps to cool and re strike.

The building was a place of assembly and the generator did not have GFP. I'm not sure exactly what was fed from the generator or if it fed the emergency lighting. The fact that it didn't have GFP may or may not be good. It's not required and I wonder if the fact that it could have been feeding emergency light is why they didn't have GFP. I don't have any more information on this at this time. I wasn't the inspector at the scene and there will be tons of litagation I'm sure. I agree with Bob about the good design attitude but good design cost money and I can only enforce code.

As a firefighter rather than as an electrician I would agree with Iwire on this one. Having lighting during the evacuation of a public assembly is far more important than limiting the damage to the electrical installation.
--
Tom Horne