I have an electric Power generator and have a manual transfer switch to use a Power generator when the utility power is out. So the electric power generator is used as is with bonded neutral when used stand alone, but must be set to floating neutral when connected to the transfer switch, per the instructions from the manufacturer. I originally installed a switch to the screw on the case, but it is rated to 250V 20 Amps, but my generator has a max of 240V 50 Amps 9KW.

It is difficult to find a small enough switch for 240V 50 amps AC that can fit inside the generator housing. I was thinking if I can use an isolation switch like those used for car batteries that are rated at 500 amps, but at 12 DC Volts.

The bonding cable is the top right white cable screwed on the casing. bonded cable on generator

Battery isolation switch Battery cut off switch

The transfer switch has the neutrals connected along with ground to the home.

  • Have you considered running the wiring outside the case (through a strain relief/water proof connection), to a larger, easier to find isolation switch, then back into the case (through the same connection point would be ideal)? This would eliminate the need to find a small switch to do the job you're after and give you more opportunities. The new switch would need to be installed into an appropriate box and affixed in a safe way/place to the generator, but it could make your life much easier.
    – FreeMan
    Jun 17, 2020 at 13:34
  • @FreeMan because both of you were editing at the same time. NBD. Jun 17, 2020 at 13:42
  • @FreeMan What type of water proof isolation switch would you recommend?
    – Rick
    Jun 17, 2020 at 15:34
  • While it doesn't say explicitly, @Rick, the one you linked in your OP appears to be reasonably weather proof. When used in racing, these are mounted on the outside of the vehicle where rescue workers can reach them and disconnect the battery after an accident to ensure the car isn't energized. If mounted to a water-tight box with the electrical connections inside, and silicone sealant applied liberally to the mounting screws, I'd think this one may well do the trick. YMMV. If not, an internet search for "waterproof switch" should turn up a few options.
    – FreeMan
    Jun 17, 2020 at 15:59
  • @FreeMan Would that same isolation switch work? SInce it is rated at 12V DC 500 Amps
    – Rick
    Jun 17, 2020 at 16:21

1 Answer 1


The root problem is you are modifying an appliance that is UL-listed, thus, voiding the UL listing. And further, you create a situation that Code really does not like, where a procedure is essential to safety. Code wants interlocks to be mechanical.

Assuming this thing has an internal GFCI to keep you honest, the problem is on the other side: when you've disconnected it from the house and are now using it portable, and you forget to restore the N-G connection. Again the internal GFCI will protect you here, if it exists and works - but not every outlet has GFCI. In fact the company has a page on how to disconnect the N-G bond for powering a refrigerator (which often trip GFCIs).

I am a huge fan of "permanent wiring done temporarily", so I would just bolt on a small box and put the appropriate wrenches in that box, and simply follow the factory procedure for removing/reapplying the N-G bond.

If you had to use a switch, I agree, a 12V switch is probably insufficient. Your best bet that's readily available is 30A snap switches intended for water heaters etc. If it's 2-pole, parallel it. (still a codevio, but more suitable for the service).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.