Transfer Switch & Neutral

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wireman

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I searched the site to see if this was asked before but didn't see the exact question, so here goes:

At my house, if I put in a transfer switch to change between the utility feed and a portable generator, does the neutral need to be switched along with the hot wires? I'm talking about a single phase 120/240 3-wire system.

I was planning on grounding the generator neutral.
If the neutral is not switched, what are the problem that mayl occur when the utility power comes back on and I am still running on generator power.

Thanks,
 

iwire

Moderator
Staff member
Location
Massachusetts
Bond the neutral at the generator and you must switch the neutral at the transfer switch.

Don't bond the neutral at the generator and you do not switch the neutral transfer switch.
 

Lcdrwalker

Senior Member
Location
Columbus, Ohio
Your generator N can be switched or unswitched. Usually I don,t switch the N and take advantage of the existing grounding and bonding. If the N is switched your generato becomes a seperately derived service. This would mean that the transfer switch would have to be rated for service entrance or a rated disconnect would have to be installed. As far as the N when utility power is restored, I hope that your system is solidly grounded.
 

bob

Senior Member
Location
Alabama
wireman said:
At my house, if I put in a transfer switch to change between the utility feed and a portable generator, does the neutral need to be switched along with the hot wires? I'm talking about a single phase 120/240 3-wire system.
No. You would buy a switch that does not transfer the neutral.
I was planning on grounding the generator neutral.
If the neutral is not switched, what are the problem that may occur when the utility power comes back on and I am still running on generator power.
Thanks,
You won't ground the generator neutral. You will removed the bonding conductor from the neutral terminal to generator frame. You will connect the home electrical system neutral to the generator neutral terminal. In addition you will connect the home equipment grounding conductor(green conductor) to the generator frame. You may install a ground rod and bond it to the generator frame but it is not necessary. When the utility power returns the transfer switch will switch back to the utility power source.
 

dwcaveney

Member
transfer switch

transfer switch

If I buy a 600 VAC rated transfer switch.
What amerage does the switch need to be.
My rated load is 27,600va/240=115 amps.
Can I use a 27600watts/600VAC=46 amp x 1.25 = 57.5 (60amp 600vac rated) transfer switch? If not.... Why not?
 

dwcaveney

Member
Thanks for the response

Thanks for the response

4000 watt generator.
Back feed breaker is 30 amp.

I guess my real question is: I know breakers are rated for amps at a certain voltage; Aren't switches rated for watts?
I saw a transfer switch which said rated 600VAC, 60 amp.
So I multiply 600 VAC x 60 amps = 36,000 watts.

My 125 amp 120/240 is capable of 30,000va.
The transfer switch cost $65.00 brand new. Will be installed behind a 125 amp 22kAIC main breaker.

How about it?
 

ron

Senior Member
Switches are rated for amps and volts. You cannot exceed either rating individually.
The transfer switch needs to be rated to carry the maximum eapected current. If the current on both sources is limited to 30A (sub panel only), then the switch can be 30A. If your switch transfers between you utility service and the gen, then you need the switch to be rated at the amperage of your service 125A.
 
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dwcaveney

Member
Thank you Ron

Thank you Ron

When I look at the knife switch bars, they are twice as thick as the bus bars on the main panel.

I guess you are telling me I don't know how to rate a switch.

Not to argue with you, but what is the theory behind that? I can see where exceeding the voltage could be a problem.

Could you explain it to me with the numbers, or refer me to a code section?

EDIT: Thanks Ron, I ran it by an EE, PE Licensed. He sort of explained it to me and as you very well know, you are right!
Please excuse me, No offence meant, hope none taken.
All the best,
dwcaveney
 
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dwcaveney

Member
What about Generator Interconnect Kits

What about Generator Interconnect Kits

Interconnect kits are real pricey, if you need GE.
Square D has better pricing.
Found one (Interlock Industries) on the internet for a GE TLM 1212 C Panel (GE does not make one) It is UL listed and complies with California H & S Code Section 119075 et sec.

EDIT: Found a GE OEM that fits my panel (I think), it's a THQLLX1.

It gives me the option of using any of the circuits on my main. I am only using 4000 watt BU Generator (Abeit some manual switching required. What else are you going to do when the power is out?) Easy install, safe and versatile.

$149.00 for a four once piece of stainless steel? Probably take me two days to make one and it wouldn't work right.

I guess I'll bite the bullet. Have to use L1430s so as not to be permanently connected.

When the neighbors are all half frozen, we'll be sitting FAT.
Liked that post iwire made regarding neutral (bonded or not bonded).
Pretty sure I've made my decision, only took three weeks. (big deal eh)
Thanks
 
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