I recently pulled a permit and installed a 30A generator inlet and backfeed breaker w/ interlock. However, I actually would like to install a second inlet in an alternate location and be able to select from either one, as I have two different generators and they are kept in different locations on my property.

To do this safely, I need a switch that can cut off one inlet when the other is engaged; otherwise, the inlet would be live when the other one is being fed by a generator.

To do this to code, do I need to switch neutral as well as both hots? If so, where can I get a 30A triple poll, double throw switch? Leviton and the like only seem to make DPDT switches (which would be fine if I only need to switch the hots).

  • While interlocks are code compliant. In my opinion, they are not the safest or best option available.
    – Tester101
    Jan 22, 2014 at 14:04
  • @Tester101 Perhaps if you don't know what you're doing as a user, but otherwise not overloading the generator is trivial. Also I wired in a current meter along with it in order to make sure I stay within a safe margin. I have way too many circuits to have to decide on only a handful to move over to a transfer switch. Jan 22, 2014 at 14:31
  • The problem with installing anything that requires the user to know what he's doing (especially when used during stressful/emergency events like a power outage) is that in a residential situation, it's hard to ensure that the knowledgeable user is always the one to do it -- you may be away from home (or sick in bed) and it may be your wife, child, or house sitter throwing the switch.
    – Johnny
    Jan 22, 2014 at 16:30

1 Answer 1


You're looking up parts with the wrong terms. What you want is a transfer switch. You don't need the kind that includes breakers, etc., since you're using an interlock; just a simple transfer switch.

In a transfer switch where the neutrals are bonded or overlapped during switching, the advantage is reduced arcing and transients during switching. The disadvantage of this situation is that the transfer switch can not protect your genset and other electrical system components from wiring problems, such as a neutral/hot reversal sending current along the neutral.

In your case, since you're using an interlock you will already be cutting off the electricity completely anyway before switching and starting your generator; neutral continuity is not needed. So you should use a transfer switch that switches the neutral along with the hots.

See http://ecmweb.com/content/switching-neutral-whats-controversy for more details.

  • I didn't think of this as a transfer switch application, but you're absolutely right. Jan 22, 2014 at 14:32
  • There's another question you should see, too. I couldn't find it until just now. diy.stackexchange.com/questions/8682/…
    – longneck
    Jan 22, 2014 at 14:41
  • I've looked around but can't find transfer switches without breakers in them. Can you help point me in a good direction? Feb 2, 2014 at 15:17
  • I was also thinking -- why wouldn't a DPDT toggle switch such as leviton.com/OA_HTML/… work? I was concerned earlier with switching neutral but it now occurs to me that the way the interlock kit is wired, neutral is not switched even at the panel anyway. Feb 2, 2014 at 15:19

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