Neutral in a transfer switch

[wayne123]

I am installing a service on a house that is 400 amps. The customer bought a 400 amp manual transfer switch to supply power from a generator when the power goes out for extended time. I mounted a 400 amp meter can, then the TS then two 200 MBP. The transfer switch has an isolated neatral block in it. my question is since the neutral is bonded to the ground in the meter how do I go about grounding the transfer switch? The panels are connected together with pvc that leads to a trough under the TS and the 2-200 amp panels.Also there are no metal water pipes in the house and the AHJ told meto just drive two ground rods, so the ground I am speaking of is that.

 

[Ed MacLaren]

Re: Neutral in a transfer switch

First you will need to determine whether this transfer switch is suitable for the job. You may need one that switches the grounded (neutral) conductor.

That will depend on whether the generator winding center-tap (neutral) is bonded to the frame or not. Diagrams below.

Is there a service disconnecting means, other than the transfer switch?

Ed

 

[bob]

Re: Neutral in a transfer switch

Wayne
You have the choice whether the neutral is switched. Ed has the drawing for the 2 choices.
If you do not switch you need to remove the bonding strap from the neutral to frame on the generator I suggest you do not switch the neutral. It seems to be a simpler installation.
The question I always have is does removing the bonding strap void the warranty?

 

[don_resqcapt19]

Re: Neutral in a transfer switch

Wayne,
Is the transfer switch listed "as suitable for use as service equipment"? It is the service disconnect if you install it between the meter and the 200 amp panels. 250.28 will require that the main bonding jumper be installed in the transfer switch. Bonding of the grounded conductor in the panels is not permitted. In this case it is not possible to have the transfer switch switch the grounded conductor, so the grounded conductor bond, if there is one, at the will have to be removed. Equipment grounding conductors will be required from the transfer switch to the panels and generator.
Don

 

[wayne123]

Re: Neutral in a transfer switch

Don, are you saying that the N will have to be isolated from the TS can and since the TS is the main disconnect and the N and the ground in the 2-200 amp MBP are seperated. The N and the driven ground are bonded in the meter can and the TS is rated for service equip.

 

[don_resqcapt19]

Re: Neutral in a transfer switch

Wayne,
The neutral must be bonded in the TS and not in the 200 amp panels.
Don

 

[wayne123]

Re: Neutral in a transfer switch

Thanks Don, I believe I see what you are saying now. It's not everyday that I install 400 amp TS's on houses. Throwing a TS this big on a house is pretty much unheard of around here but with our bout with mother nature last winter when we lost power two seperate times for over a week, people around here want to be prepared for this winter. If it doesn't stop raining soon this promises to another icy winter too. Better get me a TS for my house, if I can find time to install it.
Thanks for your help,
Wayne