Portable Generator GEC & EGC

[bennie]

Re: Portable Generator GEC & EGC

Hello Ronald, I got your message sent to the webmaster, thanks a lot.

You have submitted a good article. The ground current flow in a MGN system will also affect the GFP zero sequencing of the generator, when the neutral is not disconnected. The sensor sees this as a fault and will dump the unit off line.

This, of course is on units with GFP protection.

The transfer switch, as shown, will not disconnect the MGN (neutral).

 

[Ed MacLaren]

Re: Portable Generator GEC & EGC

Doug,

1. Does this sound right?

Sounds good to me. By using a generator with an "unbonded" neutral, and a solid neutral transfer switch, no further "earth grounding" is required at the generator. (Diagram A, Page 1)

2. Is it also safer/redundant to provide a place to hook on to this same ground rod, a connection from the generator frame?

It wouldn't do any harm, but I don't see a purpose for it, unless you think lightning might strike the generator.


hurk27,

The broken line in the SDS - (Diagram B, Page 1) is an alternative connection point for the GEC(blue). One or the other would be used.

Because Doug is using a cord-connected generator, it would be more practical to connect the GEC at the transfer switch, if his system was configured as an SDS. If it was connected at the generator, the connection would have to be made each time the generator was used.

Do you still see a path in parallel with the neutral?

Ed

[ March 08, 2003, 07:54 AM: Message edited by: Ed MacLaren ]

 

[doug glasscock]

Re: Portable Generator GEC & EGC

Wayne,
Thank you for your response. That further clarified things for me about the pump house panelboard requiring an isolated neutral so you don't get parallel current paths.

So, the pump house panelboard is 277/480-4W.
This panelboard would have to be ordered with both an isolated neutral bus and a ground bus.

Correct?

 

[hurk27]

Re: Portable Generator GEC & EGC

Posted by Doug "My generator is 125KW, 277/480 on wheels."
do they make a cord that big?

doug
you cant have the ground bar isolated as it wouldn't serve the perpose.
only the neutral has to be isolated. you could just do the bonding at the panel just like in a normal service and just keep the neutral isolated from ground in the transfer panel and in the generator this will allow you to bring the gec to the service and keep it at the same poimt of bonding the neutral but you will still have to run a ground wire with the current wires to ground the cases of the generator and the transfer switch.

Ed if the gec is bonded at the transfer switch and the neutral to case bond is done at the generator then the neutral in the cord connecting the generator would be paralleled, with the gec also connecting at the service disconnect.

In diagram "B" if you follow the path from point of the gec/neutral connection in the transfer sw then to the neutral bar in the service disconnect then back through the ground bonds to the generator you will see that the neutral is infact parralleled. but just from the generator to the transfer sw.

[ March 08, 2003, 01:15 PM: Message edited by: hurk27 ]

 

[Ed MacLaren]

Re: Portable Generator GEC & EGC

hurk27,

Yes, I see it now, thanks for pointing that out. This type of installation (generator with bonded neutral used with transfer switch) would require that the GEC always be connected at the generator to avoid that problem. I will change Diagram B, Page 1, accordingly.

By the way, this is a good reason for always using a generator with a floating (unbonded) neutral when it will be connected to a fixed wiring system by means of a transfer switch, and when it must be portable.

Sh*t, now I will have to go back and fix one I just installed last week.
The guy wanted to store the generator in his garage, and just haul it out in the driveway when needed, and plug it in.

On second thought, maybe I'll leave it as is. I used an oversized feeder cable from the service panel to the transfer switch, and the green EGC in the generator cord is the same size as the neutral.

Ed

[ March 08, 2003, 03:11 PM: Message edited by: Ed MacLaren ]

 

[dereckbc]

Re: Portable Generator GEC & EGC

Doug, I think it has been beaten to death now. Your best way for a portable generator used the way you plan to use it provided no GFP is involved:

1. Do not to bond the neutral to the frame.
2. Use a 3-pole transfer switch.
3. Use a 5-pole plug-connector at the generator P-P-P-N-EGC.
4. Forget about a ground rod at the generator. If you insist on using a ground rod you will have to bond it to the service electrode and connect it to the generator. But it just cannot float unless you completly disconnect from the service.

Good luck

 

[doug]

Re: Portable Generator GEC & EGC

Everyone,
Thankyou for all the input. This has been truely helpful.

[ March 09, 2003, 01:02 AM: Message edited by: doug ]

 

[doug]

Re: Portable Generator GEC & EGC

Wayne,
I didn't mean to say that the ground would be isolated, now that I have read my post again, I see it reads that way.
Thanks for everything.

 

[dan19403]

Re: Portable Generator GEC & EGC

i believe that i am right, please correct me if wrong, but in an industrial application -- wouldn't 2/4 SOOW cord be sufficient for say a 150' run for this generator -- not even plugged in but wired directly into the disconnect.

I know we installed a 60kVA 3 phase unit using 4/4 SOOW at a demo site and we were required to install a seperate ground.

Originally posted by hurk27:
Posted by Doug "My generator is 125KW, 277/480 on wheels."
do they make a cord that big?

doug
you cant have the ground bar isolated as it wouldn't serve the perpose.
only the neutral has to be isolated. you could just do the bonding at the panel just like in a normal service and just keep the neutral isolated from ground in the transfer panel and in the generator this will allow you to bring the gec to the service and keep it at the same poimt of bonding the neutral but you will still have to run a ground wire with the current wires to ground the cases of the generator and the transfer switch.

Ed if the gec is bonded at the transfer switch and the neutral to case bond is done at the generator then the neutral in the cord connecting the generator would be paralleled, with the gec also connecting at the service disconnect.

In diagram "B" if you follow the path from point of the gec/neutral connection in the transfer sw then to the neutral bar in the service disconnect then back through the ground bonds to the generator you will see that the neutral is infact parralleled. but just from the generator to the transfer sw.

 

[gwz2]

Re: Portable Generator GEC & EGC

Last time I looked at Diagram B, Ed had corrected as he said he would.
The Green (GEC) does not tie to the Grounded Conductor at the Transfer Switch.
The GEC is now at the Generator Common Terminal.

 

[doug glasscock]

Re: Portable Generator GEC & EGC

Crouse Hinds makes the 200amp reverse plug (with female connections) and a mounted reverse receptacle (with protected male pins) that will work for this application. Seeing the question about the availability started me digging for the answer. Still looking for a 5 conductor cable.

[ March 11, 2003, 11:25 AM: Message edited by: doug glasscock ]