Service Bonding

[mcnichol]

I am working on a project that provides a 480V, 3 phase, 4 wire service for a sewage pump station. We are providing the pump station with a manual transfer switch that will allow for connection to a portable trailer mounted generator. The manual transfer switch is a 4 pole switch fed from a service disconnect switch. The pump station load is connected to the transfer switch. Can we bond the grounding conductor to the neutral in the transfer switch if it is not service entrance rated? Otherwise it appears we will have to provide a separate generator disconnect switch to obtain the required neutral to ground bonding.

 

[mpd]

no you cannot do it in the transfer switch

it is also going to depend on the generator, if the grounded conductor is bonded or not in the generator, may determine what type of transfer switch you have to use

look at 250.30

 

[tom baker]

With a 4 pole switch you will need a grounding electrode system at the generator as it is an SDS,and the generator will be required to have a system bonding jumper.
If you use the same generator at another liftstation that does not have a 4 pole switch, then the system bonding jumper will have to be removed.

If your service does not have GFP, then having a 4 pole switch makes life more complicated and you will be best off with not transferring the neutral.

 

[tom baker]

Otherwise it appears we will have to provide a separate generator disconnect switch to obtain the required neutral to ground bonding.

The system bonding must be done in the generator ahead of its disconnect, I suggest you review all of 250.30 and the definitions of SDS and SBJ

 

[eprice]

The system bonding must be done in the generator ahead of its disconnect

Maybe I'm missing something, but it seems to me that 250.30(1) allows the system bonding to be done at the first disconnecting means.

 

[radiopet]

Tom is refering to this statement :

(1) System Bonding Jumper An unspliced system bonding jumper in compliance with
250.28(A) through (D) that is sized based on the derived phase conductors shall be used
to connect the equipment grounding conductors of the separately derived system to the
grounded conductor. This connection shall be made at any single point on the separately
derived system from the source to the first system disconnecting means or overcurrent
device, or it shall be made at the source of a separately derived system that has no
disconnecting means or overcurrent devices.
Where a separately derived system provides a grounded conductor, a system bonding
jumper must be installed to connect the equipment grounding conductors to the
grounded conductor. Equipment grounding conductors are connected to the grounding
electrode system by the grounding electrode conductor. The system bonding jumper is
sized according to 250.28(D) and may be located at any point between the source
terminals (transformer, generator, etc.) and the first disconnecting means or
overcurrent device. See the commentary following 250.28(D) for further information
on sizing the system bonding jumper.

 

[eprice]

Tom is refering to this statement...

So was I. That section allows the system bonding to be made at the first disconnect. (unless of course, there isn't a disconnect)