ECN Forum Forums Code Related Discussion NEC & other Code issues Generator question??

Modified image posted for dfe

dfe take the generator and the ATS out of the picture.

Now put the same fault on a circuit.

The result is the same, removing the bonding jumper or neutral at the service will be dangerous.

By using a Neutral switching ATS switch all that will be accomplished is moving this potential problem from the normal power bonding jumper to the bonding jumper that will be installed at the generator.

I see one location as safe / dangerous as the other.

Just My Opinion, Bob

Thanks Bob for posting that "Graphic" make things easy to follow, "A picture is worth a 1000 words" I think we verify that??

You are correct one location would be as dangerous as the other if you open the ground or neutral. However I would think that the electrician would be aware of the generator running and would not open this under a load at the genaerator or xfer switch.( "2nd, In my opinion, anybody opening the nuetral has a death wish..." words of wisdom from Ryan_J )
With a 4 pole ats he could upgrade the main service and not be in danger from the leakage current on the ground and neutral ( bonded at generator X0). On the other hand he may not be aware of this danger if a 3p ats is used and is using the main service bond. Many times the customer will not want the generator(s) disable while we are working ( computer rooms, medical refrigeration, food storage ).

Maybe if a 3p ats is used a nice sign at the main service may warn about this danger and protect the installer in a injury lawsuit but I don't know. What do you think??

The original question appeared to be a compliance issue. I believe IWIRE is correct. The generator may be connected to the premisis wiring with either a 3 or 4 pole transfer switch.

If a 3-P switch is installed the NEC does not allow the generator neutral to be bonded at the gen or transfer sw.(XO). Additionally the non-current carrying metal parts (frame etc.)must be grounded per section 6 (VI) of article 250 by a method listed in 250.118.
If a 4-P sw. is used the generator is a seperately derived system and grounding and bonding are required per. 250.20 and 250.30 to mention a few.

Either way all eq. grounding eventually ends up at the premisesis supply main bonding jumper. (Generally)

A ground fault with the 3-P sw. may raise the voltage to ground through the Eq. Grounding Conductor.
A ground fault with the 4-P sw. may seek the main Bond through a connection at the transfer sw as well as the Neutral at the gen. Depends how the Code is applied.

No doubt an open neutral is trouble.

Back feed (so to say) at the gen during maintenance addressed in section 445.18.

I liked the idea about additional signage at the MDP.