3-pole and 4-pole lighting contactors 3

[tricard]

Hello all,

I am wondering if there are any advantages to using a 4-pole contactor when switching 3 single phase loads that operate phase to ground. I have a lighting circuit branch that is fed by a contactor. The lights are connected phase to ground on a 600V three phase system (e.g. lights operate 347V). From each contactor is a 5/C #10 cable, where three of the conductors feed the lights at 347V (phase to ground, one for each phase), one conductor is the neutral return and one conductor is the bonding wire. I know that a circuit like this would typically just be connected to a 3-pole contactor and the neutral would be brought back to a neutral bus in the panel, however would there be an increase in safety or any advantage if the neutral was completely switched off with the phase circuits via a 4-pole contactor instead of a 3-pole?

Thanks for the help

 

[davidbeach]

Safer to only switch the phases and leave the neutral connected. And it’s less expensive as well.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[tricard]

Thanks for the fast response!

So, why would it be safer to just keep the neutral connected? Because the neutral provides a reliable path to ground?

 

[waross]

I agree with David commpletely.
But your last question;
It doesn't make a lot of difference as long as nothing goes wrong.
Switching the neutral adds to the number of possible things that can go wrong and a lot of things get worse when there is a problem with the neutral switching.
One possibility, the neutral pole of the contactor fails to close when the other poles do close. You may lose almost half your fixtures due to over voltage if the neutral goes open.
Why would you pay extra for a four pole contactor to add a new and expensive possible failure mode?
I have had to clean up the carnage a couple of times when a neutral went open.
And the AHJ may have a word.
If the neutral is switched, the contactor must either make and break all poles simultaneously, or have an early make, late break on the neutral pole.
Contactors with early make, late break are available, they have an application in some Automatic Transfer Switches, but they cost even more than a standard four pole and there is no guaranty against failure.
Then comes the AHJ.If he asks for documentation that the contactor does indeed make and break all poles simultaneously, good luck with that.
While it is assumed that a contactor makes and breaks all poles simultaneously, I have never seen a contactor certified to do so.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[tricard]

Thanks Bill for the added information!