Generator Should I change my PTO generator from Bonded Neutral to Floating Neutral?

[Hillman314]

Qapla: If you're not switching the neutral as part of the transfer from utility to generator power, then don't jumper the neutral and ground at the generator. The neutral and ground should only be bonded in one location. (You really have three panels????)

 

[JPCjr]

I appreciate your thoughts, but I'm wondering how many portable generators used for temporary emergency power are installed with a solid connection?

People violate the code all the time, but that doesn't mean it's safe to do so.

 

[JPCjr]

Many generators DO have as part of their instructions how to bond/unbond the neutral depending on how they are connected and they ARE tested that way.

Yes, I realize that. I mentioned that in one of my first posts in this thread, but it doesn't apply to the generator being discussed here. Look at the photos the OP posted. There isn't a system bonding jumper that can be removed. Also, the manual in the link he posted has no instructions for removing the bond between equipment ground and neutral. It's permanently configured as a separately derived system and shouldn't be changed. A three pole transfer switch should be used, but the OP does't want to do that. So he's left with a dilemma.

 

[daybreak1998]

There is a ground lug on the receptacle panel of my PTO generator, should I run an additional wire from it to the ground rod at my service entrance?
Seems redundant to me, as one of the four wires in my generator cord is also attached to ground on the generator panel and connects to the bonded Neutral/Ground in the breaker panel then runs to the ground rod.

Are you running a separate ground wire on yours?

Howdy,

No, I am not using any seperate ground rod. The 2/0 welding cable is 10 feet, and is my ground. This is attached to my central farm distribution. Meter with lugs which then feeds 5 other buildings.

The same thing with the generlink unit, and the interlock. All generators are portable and are only brought out and attached when needed.

I guess some people here might have a tool in their hand, and then attach a awg #6 wire to a ground rod as to not think there plug ground is adequate.

 

[Victory Pete]

As a licensed electrician this topic does get my head spinning. There are many different situations to consider. It is best to call in the local inspector for advice although sometimes they interpret the code differently. The last generator install we did we ran 1 1/2" emt as ground and neutral and 2 phase conductors. I am assuming the generator itself had unbonded neutral and ground. There was no neutral disconect in the automatic transfer switch. We installed a ground rod at the generator.

VP

 

[stonypass]

If a 120v whatever, in your house shorts to gnd

Wouldn't this just trip its own breaker in the box?

 

[Hillman314]

Wouldn't this just trip its own breaker in the box? : Only if the fault current is big enough to trip the breaker. To put it another way: Only if there is a path of low (enough) resistance back to the center tap (neutral) connection of a transformers or generator's winding, thus the circuit's loop is completed and current will be high enough that the breaker will trip. The "best fault" situation is when the fault is to something that has a grounding (green) conductor attached to it, then there's a low resistance path back to the neutral of the generator (because the grounding system and neutral are bonded in your house panel).
If there's a fault to something not "grounded" well enough that the breaker doesn't trip, then that object will become energized, and a person who touches it may become the path of least resistance.

Without a grounding (green) conductor to take the fault current back to the winding (in a "short" circuit), one is relying on earth as part of the circuit's loop back to the winding. (a "long circuit" ? that is, the path would be from that shorted object in contact with the ground, throught the ground, into the ground rod, to the neutral bonded to the ground in your panel, back to the generator's winding neutral tap. Here, the ground (earth) is not a good conductor, and the fault current in this scenario may not be enough to trip the breaker.

A couple things about grounding that most people don't realize: 1. The biggest function of a ground rod on a electrical service is to provide a 0 volt reference (period). A gound rod's function is not "to send fault current into the ground" (except for lightning strikes I suppose, but I digress) 2. The point of grounding (green) conductors connected to equipment is not to send fault current to the ground rod/earth, it is to have a low resistance path (i.e. a "short" circuit) to the neutral winding of the power source (transformer or generator) during a fault. Low resistance = high current = tripping breaker/fuse. That is why the neutral and grounding conductor is bonded in the panel. 3. The reason they are bonded in only one place so that normal neutral current does not have a parallel path on the green grounding conductor, otherwise normal neutral current (times any resistance) would = a voltage (Ohm's Law) on the various normally non-current carrying metal parts that are connected to the (green wired) grounding system.

 

[Hillman314]

^ Sorry, bit of a long-winded ramble. I'll work on keeping them short.

 

[SPYDERLK]

I hang my head and try to say this again for all to listen or ignore (Jpc gets it ) If you disconect the neutral to ground jumper on the jenny.... You loose the ground conductor from the genny to the house during a fault. QUOTE]

I don't think that is so, the neutral (aka "grounded conductor) and the (equipment) grounding conductor are bonded at the house panel, the fault current will re-enter the neutral back to the jenny's winding here.

Yes. A longer path, so some potential will develop on gen chassis -- but no alarming amt unless there is a connection or conductor fault.
...As to this stuf about low resistance paths: short and/or large wires are extremely low resistance. Small Fractions of an ohm. In any functioning setup where all 4 conductors make their respective contacts there is always a low enuf resistance current path to blow breakers and keep case potentials safely low in a fault. It is the contacts that are of paramount importance and that should be monitored if they are not bolted. Since a resistance at a contact is concentrated at a single point any significant amount will heat it enuf to cause a degrading chain reaction. That is why plug connections are frowned on. You cant trust people to be aware. However, if you are you clean, and then spot check the plug under significant 120/240 loads and assure that relative temp is 0 or very small in relation to that of the wire. And you further know that this only proves 3 out of 4. The ground contact is not proven since it is not carrying current. Best to bring a pigtail out and bolt it.
larry

 

[DarkBlack]

Wouldn't this just trip its own breaker in the box?

It might not with limited ampacity of a jenny. Also picture this: a pinhole in the enamel of your drill press's motor's stator finally conducts to the housing. It happens to have shorted 1/2 through the length of the winding. Now you have current limited potential on your ground system. The genny won't flow enough current at this resistance to trip your house breaker. Since you disconected the gnd bond at the generator, The only path to flow current to reduce this volatge is through the neutral wire of your genny cord. Now what if the plug connection of the neutral is less than great? This is a case where you would have been better to leave the gnd-neutral bonded at the genny.