Wiring a sub-panel for Aux. generator

mmcl26554November 30, 2011

My motorhome has a 7KW generator which I want to be able to connect to my home for Axillary power. I have a 4PDT manual switch for the transfer. I will put a sub-panel in my garage and move all of my 120 volt circuits from the main panel to the sub-panel which will be controlled by the transfer switch. I will run each individual 120 volt hot (black) wire now in the main panel to the sub-panel. My question is about the neutral wire (white). Can I leave those connected to the neutral buss in the main panel and run 1 wire to connect the neutral of the transfer switch to the main panel, OR must I run each neutral also from the main panel to the sub-panel? If I must run the neutrals to the sub-panel also can I connect them together in the main panel and then run 1 additional larger wire to the sub-panel. This would save the effort or running 12 separate wires through the conduit. But what about the grounds? Can they remain connected in the main panel or must I run them also, individually or bundled into 1. Sorry for the long post but I can't explain it simpler.

Michael

Thank you for reporting this comment. Undo
Ron Natalie

I'll make it even simpler. You can't do any of the shortcuts. You must run the grounds and neutrals along with the hot wires together. You can't merge them, you can't leave them terminated in the other panel.

Further you do know about the derating requirements for running multiple current carrying conductors in the same conduit?

    Bookmark   November 30, 2011 at 2:24PM
Thank you for reporting this comment. Undo
mmcl26554

I was looking at wiring diagrams for prewired transfer switches and they do exactly what I want to do. Take the hot wire off the breaker and connect it to the transfer switch which contains a breaker but they leave the neutrals and grounds where they were. So are they also wrong? I am not aware of the derating current when using a conduit but I suppose it has to do with "back emf" or eddy currents. I will have less than 15 feet of conduit and thought it easier & neater than running 12 NM cables. However I can just run 12 black(hot), 12 white(neutral) & 12 green (ground) in my 1 1/4 conduit. Or are you suggesting 3 separate conduits for each type of run?

    Bookmark   November 30, 2011 at 3:57PM
Thank you for reporting this comment. Undo
Ron Natalie

All the conductors for a circuit need to be run together. I have no idea what you're describing, I've never seen a transfer switch wired like that.
The derating primarily has to do with heat. You also can't put that many wires in the conduit. I don't know if you're running PVC or EMT or what but you're going to be limited to 14-17 #12 wires.

I

    Bookmark   December 1, 2011 at 5:18AM
Thank you for reporting this comment. Undo
stinkytiger

Hi,

I think that the connection of the (a) neutral, (b) ground, (c) transfer switch and (d) generator bonding and grounding are interelated.

Some transfwer switches switch the neutral, some do not. It is equipment and site dependent. Rather than confuse you with my expanation, here are two write ups from Cummins generators which explain the issues.

http://www.cumminspower.com/www/literature/technicalpapers/PT-6005-GroundingAC-1-en.pdf

http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

Hope this is useful.

Warmest regards, Mike.

    Bookmark   December 1, 2011 at 9:09AM
Thank you for reporting this comment. Undo
Ron Natalie

His questions have nothing to do with whether or not his neutral gets switched. The code prohibits just about everything he wants to do: not run the neutrals and grounds, merge the neutrals, run 12 (or 24) current carrying wires in the same conduit without derating, exceeding the conduit fill rules, etc...

He needs definite assistance in at least the design of what he's trying to do.

    Bookmark   December 1, 2011 at 9:43AM
Thank you for reporting this comment. Undo
mmcl26554

Thank you ronnatalie, I have learned a lot and have rethought the project. I will now use 12/2 WG for each run, no conduit. I'll feed the input of the transfer switch from a sub-panel which is now next to where I am putting this panel & has plenty of amperage available. I have learned about bonding and no bonding of the grounds in sub-panels. In fact my main panel may be incorrectly bonded because there is a 200 amp breaker at the meter. I'll check into this and make the necessary changes if needed. I guess this is what forums like this one are all about.
Michael

    Bookmark   December 1, 2011 at 11:02AM
Sign Up to comment
More Discussions
Replacing fan speed dial back to standard toggle?
I am removing a ceiling fan and replacing it with a...
onkyokoi
Reuse electrical panel
I replaced a 24 circuit Square D panel with a new 40...
zver11
ARGH! no boxes
Went over to my daughter's house to help them change...
Ron Natalie
Too much load for circuit?
I have 200 amp service to the main panel (which has...
zver11
Replacing dimmer switch: different wire colors on new switch
My DR lights, which are controlled from two switches,...
msa6
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™