3 pole or 4 pole STS??

[wonderchi]

Hi,

Can someone clarify for me...when can we select a 3 pole STS over a 4 pole STS unit?

Thanks

Allan

 

[davidbeach]

When you don't need to switch the neutral.

 

[wonderchi]

To do with Tier 1, 2, 3, 4 requirements?

When dont you need to switch the neutral??

 

[alehman]

When no neutral is required? Or if both inputs are 4W, from the same separately derived source?

 

[wonderchi]

Let me rephase my question:

I am to install a STS (static transfer switch), in the upstream we only have one supply and one generator...I am planning to use a 3 pole STS instead of a 4 pole STS...(since we dont need to switch the neutral because there is only one generator)...Am I right?

Please advise

 

[waross]

The important point is not the number of generators, it is the number of connections to ground.
My preferred installation is as follows:
Supply to 3 pole transfer switch.
Generator to 3 pole transfer switch.
Solidly connected neutrals.
From the transfer switch to the main panel.
One connection from neutral to ground in the main panel.

The code only allows one connection from the neutral to ground. There are very good reasons for this.

If for any reason, there must be more than one ground on the neutrals then the neutrals must be switched in such a manner that only one at a time is ever connected.

There may be some exceptions to the "one ground connection" rule if more than one building is involved.
respectfully

 

[alehman]

I agree with waross. That means no neutral to ground connection at the generator.