Portable generator bonding.

[steve66]

Re: Portable generator bonding.

Don,
I wouldn't have thought to look for a definition of "premises wiring", but suprise it is there.

I still have to argue that a generator with receptacles mounted on it, an extension cord, and an appliance are not NECESSARLY premises wiring. The definition for premises wiring includes "permanently and temporarily installed". Just sitting a generator in the garage and plugging something in is not necessarly "installed".

I agree that if the generator supplies any other type of wiring or devices it must be grounded.

One point I would like to make is that 250.20(B) requires only things that "can be grounded" to be grounded. Assume the power goes out, and Joe runs to the hardware store and buys a generator, plops it on his garage floor, and plugs in his drill. He isn't qualified to make a grounding connection to the generator, and we wouldn't want him trying. Therefore, the code says this generator doesn't have to be grounded.

On the other hand, if Joe hires an electrician to connect the generator and install a transfer switch, then I would call this a system that "can be grounded" and I would expect the electrician to do so.

Steve

 

[pierre]

Re: Portable generator bonding.

250.34(A) Portable Generators.
The frame of a portable generator shall not be required to be grounded and shall be permitted to serve as the grounding electrode for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipmment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
Quoted from the 2002 NEC


This is quite clear that a ground rod for a portable generator used as above is not required.

Pierre

 

[pierre]

Re: Portable generator bonding.

The bonding that someone mentioned may be the bonding that is required in 250.34(A)(2)

Pierre

 

[goldstar]

Re: Portable generator bonding.

Bennie,

What I was referring to when I asked "what would happen if you bonded one side of the generator output to ground" is what would happen to the generator output in general. If one side isn't bonded to the case then both legs have an equal potential. Does it matter which side is bonded to ground ? What about in the case of the 240V output of the generator....is the casing of the generator required to be bonded to ground if it is used to feed a well pump in a residence in the event of a POCO power outage or does that float also ?

I can understand if it is cord and plug connected but Generac and Cutler-Hammer are selling breaker/disconnect panels suitable for use in this application. You can buy these panels with 10 circuits that are switchable so that there cannot be feedback to the POCO power. The panels come with a whip, prewired and adaptable to a 1 1/4' KO of a breaker panel and UL approved.

I know it's only our opinions here but I'm just curious as what the general consensus is on this.

Regards,

Phil

 

[iwire]

Re: Portable generator bonding.

Originally posted by goldstar:
If one side isn't bonded to the case then both legs have an equal potential.

If one side is not bonded, than there will be no potential between anything except between the two leads from the generator, no potential to the frame, the earth or persons.

Bob

[ September 03, 2003, 07:10 PM: Message edited by: iwire ]

 

[don_resqcapt19]

Re: Portable generator bonding.

Bob,

If one side is not bonded, than there will be no potential between anything except between the two leads from the generator, no potential to the frame, the earth or persons.

Be careful here. On small generators there will be almost no voltage between either power conductor and anything else, but on larger systems there will be, as a result of capacitance coupling. Would you say it would be safe to touch one leg of a 3 phase ungrounded delta system? The generator is the same.
Don

 

[iwire]

Re: Portable generator bonding.

Don, I assumed Phil was talking about a small generator as I have never seen a 2 wire 120 volt large unit.

But thanks I would not want any one to get blasted.

On the 3 phase ungrounded delta system, I have some questions as I can only remember one building I went in that had this system.

At the time I was a helper and the way it was explained to me at the time was the whole point of the system was personal protection.

I take it from your post that this is misinformation.

If this system does not protect me from getting a shock, what is the advantage?

Bob

 

[Ed MacLaren]

Re: Portable generator bonding.

Bob, the only advantage of the ungrounded three phase delta system was continuity of service.

Many industrial processes cannot tolerate a non-orderly (sudden) shutdown.

The first "ground fault" would not trip a breaker or blow a fuse, and production could continue.
As long as that first ground fault was located and repaired before another occured on a different phase, no power interruption resulted.

The resistance (or impedance) grounding system is now being specified for such facilities, as it has the continuity of service advantage of the ungrounded system, with none of the disadvantages.

Ed

 

[iwire]

Re: Portable generator bonding.

Thanks Ed, I am glad I did not test the info I was given with myself.

I remember this place having 6 light bulbs on the wall placed in a Y pattern, I was told if any leg of the Y went out that indicated a problem.

Is it possible that you have a drawing to show how these indicators worked?

Or was that more incorrect info?


Bob

 

[Ed MacLaren]

Re: Portable generator bonding.

The one I am familiar with had three lights, which were normally lit.

When a ground fault developed in a phase, it "shorted out" the light connected to that phase, and the light went dark.

It was often very difficult to locate the fault. You had to shut down loads, one by one, until the light came back on.

The modern "pulsing" ground fault location feature permits location of the fault, live, without shutting down any loads, using a clamp-on ammeter.

Ed


The

 

[iwire]

Re: Portable generator bonding.

Thanks Ed I would guess that they wired the two bulbs on each leg in series's with each other as they never where very bright, perhaps to make the bulbs last longer at the lower voltage.

I am confused, if this is an ungrounded system how is there potential to ground?

Bob

 

[don_resqcapt19]

Re: Portable generator bonding.

Bob,
Under normal conditions, all of the indicating lamps are dim, under fault conditions, one lamp is out and the other two are bright.
Often two 240 volt bulbs were used in series for this connection. Under normal conditions, they would see 277 volts and under faulted conditions two sets of lamps would see 480 and one set would see zero volts. This connection does not need voltage to ground, although there will always be some due to capacitive coupling and induction. The 3 pairs of lamps are connected "wye" and this places line voltage divided by the square root of 3 across each set of lamps. When one of the phases has a ground fault, this forces the voltage on that phase to zero and effectively shorts out one set of lamps (both sides of that set of lamps is now connected to ground, one side by the intentional ground connection at the wye center point and the other by the accidental ground fault). With one phase now connected to ground, the other two sets of lamps see full line to line voltage.
Don

[ September 04, 2003, 08:34 AM: Message edited by: don_resqcapt19 ]

 

[Ed MacLaren]

Re: Portable generator bonding.

(Don types faster than I do. )

Although there would be a small voltage to ground due to capacitive coupling, the circuit does not depend on the voltage to ground to operate.

The lamps would light without any ground connection, but they would not perform their indicating function.

The indicating lamps are wye connected across the line voltage. The lamp current at any instant would be in through one lamp, and out through the other two, the same as any three phase load.

When a ground fault occurs on one line of the system, it simply "shorts out" one of the lamps, thus indicating which line is faulted.

In other words, there is no voltage difference across the lamp connected to the faulted line.

Ed

[ September 04, 2003, 08:40 AM: Message edited by: Ed MacLaren ]

 

[don_resqcapt19]

Re: Portable generator bonding.

Ed,

(Don types faster than I do.

Yes, but your drawings do a much better job of explaining the system than my words do. Thanks again for all of the drawings that you post. They are always excellent and very much appreciated.
Don

 

[iwire]

Re: Portable generator bonding.

Thanks greatly to both of you I got it now, I was failing to see the path for one set of lamps through the other lamps.

Ed your last drawing made it very clear.

I like older methods always simply and reliable.

Bob

[ September 04, 2003, 04:53 PM: Message edited by: iwire ]