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I have a firman t07571, I followed this post to convert this generator to floating neutral.

I have a 200 amp main panel and a 125 amp sub panel. Generator breaker is installed in the main panel. I am just looking to turn on my well water pump and few lights and a refrigerator in the house to turn during a power outage.

I am using 50amp 2 pole breaker with interlock kit to back-feed the generator. Used a 6awg wire from generator inlet to main breaker panel with junction box, because wire i had was not long enough to go all the way to main panel, so added a junction box.

I turned off the main breaker, turned off back-feed 50amp breaker in the main panel, turned off all the other breakers, started the generator, hooked up the nema-14-50 plug to generator and other end of wire hooked up to generator inlet. Generator have 30 amp breaker, when I turn on the breaker on the generator, it trips immediately.

All the breakers on the main-panel are off including 50 amp generator backfeed breaker, but the when I turn on breaker on the generator (not breaker on the main panel, which is still off), generator breaker trips immediately.

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@Triplefault suggested to check the clamps of junction box, this is what i found in the picture below, fixed the junction box and issue is solved.

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    Verify that the generator operates as expected when its breaker is turned on while the feed cable to the house is disconnected -- that's a basic check to confirm nothing is miswired inside the generator. Also, keep in mind that the neutral and ground do not go through the turned-off backfeed breaker. If either of neutral and ground is mistakenly swapped with a hot somewhere in the generator or hookup cord, it'll be a dead short despite the backfeed breaker being off.
    – Greg Hill
    Commented Nov 25 at 2:20
  • I disconnected the feed cable from the generator inlet, kept it plugged into generator, started the generator and turned on the generator breaker, it did not trip, everything was fine. I checked everything 10 times to make sure hot and ground are not swapped.
    – cody
    Commented Nov 25 at 2:25
  • Re-visit the orientation of the wires into the plug in your top image. Every termination for 14-30 plug I have ever seen the hots are opposite sides of plug and neutral and ground the other opposite sides just like the blade layout. I cant imagine the plug crosses those blades internally.
    – NoSparksPlease
    Commented Nov 25 at 3:37
  • @NoSparksPlease That's what I thought too. But it turns out OP is using 14-50 at the generator (standard) to SS2-50 at the inlet. Why? I have no idea. But that explains the strange orientation.
    – manassehkatz-Moving 2 Codidact
    Commented Nov 25 at 3:39
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    @mdfst13 that image you are referring to is the main culprit for the short i believe, i am going to fix that and check other wires as well. Hopefully this will solve the problem.
    – cody
    Commented Nov 25 at 4:11

2 Answers 2

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That the breaker on the generator trips as soon as you turn it on, while the 50 amp backfeed breaker is off, means that you have a short in the wires leading from the generator to the backfeed breaker.

Everything appears to be wired correctly by color in the places shown in the photographs. The plug at the generator is not shown: a miswire there could cause the breaker to trip. Here is the proper wiring for a NEMA 14-50:

NEMA 14-50 wiring

source

Also, I do see that you don't have the cables properly clamped in the junction box with the big black connectors. The black sheaths of the cables are not under the clamps and poking into the junction box. If these cable clamps have been tightened, it could be possible that the threads of the clamp screws have cut into the inner wires' sheaths and shorted out the electricity from the generator.

While the 50 amp back-fed breaker is OFF, disconnect the NEMA 14-50 plug from the generator and measure resistance across the plug's 240V pins, and from each 240 pin to the neutral pin and ground pin. There should be infinite ohms between any power pin and any of the other pins. If you get anything other than infinity, you have a short, which will trip the breaker.

I'd try getting proper-size cable strain relief glands for those cables to the junction box, and any other places such partial clamping have taken place. The whole outside sheath of the cable needs to be under the clamp.

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  • Generator cable feed to inlet, I bought it from amazon and that feed cable pluged into generator and not connected to inlet, the generator breaker did not trip. So cable and nema-14-50 plug is fine. I will measure the resistance tomorrow. Regarding black sheaths, I will change the junction box and will use a bigger box, this box is very tight, I will make sure the sheaths are under clamps, I will update you on this when I make these changes.
    – cody
    Commented Nov 25 at 2:29
  • You were right, I checked the junction box clamp and one of the screw bit into hot wire, causing the shot. I will fix that in a day or two and test again.
    – cody
    Commented Nov 25 at 3:12
  • I added picture to the post causing short.
    – cody
    Commented Nov 25 at 3:17
  • Excellent, @cody ! That was probably it. Try using "strain relief" cord clamps, like this: homedepot.com/p/…
    – Triplefault
    Commented Nov 25 at 12:22
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    Thanks @triplefault, i removed wires from junction box and connected directly to test the generator, it worked like a charm, everything else is working fine. I ordered bigger junction box and the strain relief clamps. Thanks a lot!!!
    – cody
    Commented Nov 25 at 16:59
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Original answer deleted - it was based on my erroneous assumption that this was all 14-50. It turns out the house connection (inlet and one of the cord) is SS2-50 while the generator is 14-50. Not sure why, but that's what is being installed.

Interlock and breaker connections look OK. The junction box looks OK, though I am not sure why there is a junction box and not just a single cable run from panel to inlet.

Which leaves testing the extension cord and the receptacle wiring with a multimeter as the next steps. If the generator runs by itself (others already suggested checking that) then the remaining possibilities are:

  • Extension cord - miswired or internal short
  • Inlet - miswired or internal short (unlikely because OP tried two different inlets
  • Junction box - looks OK but some testing wouldn't hurt. And fix up the open cables outside the box.
  • Breaker/panel - looks OK, but again testing wouldn't hurt.

Most of this testing should be done using a multimeter to check resistance/continuity with the generator off for safety. If/when you find a problem and resolve it, then put everything back together and try the generator again.

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  • I checked with multimeter, those connections seems correct. I bought another inlet from a different company, which had red and black colors coded receptacles. I was having the same issue where generator breaker was tripping.
    – cody
    Commented Nov 25 at 2:40
  • What is the model # of the inlet in the picture?
    – manassehkatz-Moving 2 Codidact
    Commented Nov 25 at 2:42
  • And are you using an off-the-shelf extension cord or was it built-to-order (whether you did it or someone else)? Have you checked to make sure the extension cord is wired correctly by testing all connections end-to-end (each pin connected correctly and no shorts)?
    – manassehkatz-Moving 2 Codidact
    Commented Nov 25 at 2:44
  • I am using this generator extension cord amazon.com/dp/B0BV1SQKMP?ref=ppx_yo2ov_dt_b_fed_asin_title
    – cody
    Commented Nov 25 at 2:46
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    I ordered the AC works again and will use that. @Triplefault suggested to look at the junction box clamps, because they were not looking proper. I looked into and it turns out one of the screw of the clamp bit into black hot wire, I think that is what was causing the short circuit. I will replace the inlet with AC works and use a new and bigger junction box in few days and will let you guys know. Thanks for the help! I have added picture to the post, which show the issue with hot wire
    – cody
    Commented Nov 25 at 3:15

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