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I have been in our new house less than 1 year. Yesterday we had a a prolong power outage so I decided to test the generator I got for hurricane season to the house existing generator inlet. I turned off main line breaker engaged interlock to isolate back feed breaker.

I turned generator while generator breaker and all other breakers are off I connected the 240/120 50 AMP cord to the outside inlet all good. I turn on AC breaker on generator all good. When I get the to house main panel and attempt to turn on the panels back feed 50 AMP breaker the AC breaker on the generator trips off.

House has the following:

  • Duromax XP10000EH with floating neutral system connected with Generator Power Cord to 240/120 (I don't know what prior owner had)
  • Reliance PB50 Inlet box wired through 4 wires (Red, White, Green, Black) Green connects to Inlet bolt.
  • Reliance MB125 Indoor 50-Amp Meter Box into (4 wires from inlet red, black, white and copper). White and copper connect to neutral bus on panel, red and black connect to Q-Line Breaker.
  • Main panel with Interlock with GE 50 AMP - Q-Line 50 Amp 1 in. Double-Pole Circuit Breaker (thin).

Any ideas? At first I thought it was the generator but this generator has a floating neutral. I am not sure if there is a fault somewhere or the breaker may not be appropriate for the generator.

Panel: Panel

Inlet: Inlet

Inlet wiring: Inlet Wiring

Generator Cord: Generator Cord

MB125: MB125

Generator cord: Generator Cord

Panel with back feed breaker removed: Panel with backfeed breaker removed

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    Do you mean the ground bond in the generator has been lifted to prevent a parallel current path! Lifted or not if the connections are correct it will not matter. – Ed Beal Jul 20 '20 at 21:28
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    Oh boy I think I see a huge mistake. I need you to unplug the Ginny and turn off every breaker in the panel. Including the main. Now I need you to set your meter to resistance and measure between the red and black screw on the back feed breaker this must be the only breaker that is on. Do you get zero ohms? – Harper - Reinstate Monica Jul 20 '20 at 22:14
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    Oh, that’s the wrong answer. Assuming generator unplugged, that should be infinity. Found your problem! – Harper - Reinstate Monica Jul 21 '20 at 1:54
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    Good thing you decided to test this now instead of waiting for hurricane season. Much better to figure this out now than when you're wet, wind blown, and all the stores are closed! – FreeMan Jul 21 '20 at 11:35
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    This is a well-asked, very well-illustrated question. Kudos to you. – Eric Hauenstein Jul 21 '20 at 15:34
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Found it! It’s the breaker.

It’s in the wrong place, because somebody really worked to defeat the keying meant to force it into the right place.

This is going to take a little explaining, though.

Note your interlocked breaker. Normal 2-pole breakers are two complete breaker spaces wide. Each row of spaces has the opposite pole of power in it, so being 2 spaces wide means it is able to grab both poles, for 240V.

Read more about spaces, poles, and double-stuffs here - but GE’s double-stuffs are special and that article doesn’t fully apply.

Q-line does a fairly unique trick

Your GE Q-line breaker is 1” wide. At first glance, it looks like a duplex, but it’s not. GE uses a totally unique scheme (well, shared with Crouse-Hinds and FPE) where they don’t force you to get balky quadplex breakers, they sell actual half-width breakers. The 1-pole breakers are 1/2” wide and occupy half a space.

Their 2-pole breakers (i.e. yours) are particularly special: They ‘straddle the line’ between two spaces: So half the breaker is in space 1, and half the breaker is in space 2. That lets them grab both poles. That also leaves an empty half-space above and below them, which you’re supposed to fill with 1-pole 1/2” (1/2-space) breakers.

  • Or, if you prefer, you can have another 2-pole breaker immediately below the first 2-pole, grabbing the bottom half of space 2 and the top half of space 3. Rinse wash repeat, as tall a stack as you please. You finish the stack with a 1/2-space 1-pole breaker.

This means that GE 2-pole breakers must straddle two spaces. It can never occupy a whole space, since then, it could only access one pole. And in fact, the breakers and buses are keyed to make this sort of mis-positioning impossible.

And your breaker is in the wrong place.

Note how your generator interlock breaker is crowded up against the top edge of the panel. There is no half-space above it, as we know there must be. That means the entire breaker is in space 1 - both legs - and that means both legs are on the same pole, which means they are a dead short to each other. No wonder the gen breaker trips!

Since the breaker is keyed to be unable to go there, I bet if you pull the breaker, you will find someone used a Dremel or Skil Saw to cut a notch on the breaker, to let it slide over the bus stab. Or just hammered it into place and it fits poorly.

That’s because whoever installed it, realized their interlock kit was made for full-size 2-space breakers only, and would not work with this double-stuff. They were under time pressure to get a signoff and a check, so they horked it just like this, and had no idea how badly they screwed it up.

There’s another possibility: the generator crew might’ve Done The Right Thing, and then somebody else came along to add a circuit, and went “Oh hey, I can double-stuff this generator interlock breaker...”

Fixing it

You can try placing the breaker correctly - 1/2 of a space downward; merely swap it with the 1-pole half-space breaker directly beneath it. However, I suspect the design of the interlock won’t play nice with that 2-pole double-stuff, even if it was placed correctly. So I think your only option is to install the “classic” full-size 2-pole breaker, such as this.

That will displace 2 double-stuffs; they will simply have to go somewhere else. If you’re crunched for space, it’s subpanel time. You should never tolerate being out of breaker panel spaces; because it causes a huge amount of problems in shortcuts, hacks and bad work. You should have maybe half your spaces unused.

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    Thanks for the very thorough and informative explanation. I will go to home depot and see how that 2 pole double breaker fits and plays with interlock, if it doesnt play well I will get a license electrician out here to replace interlock and breaker to address the condition to appropriate standards. I added a picture of the slot after I pulled the breaker. – Ron Jul 21 '20 at 4:33
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    Oh yeah, confirmed! It’s exactly what I said above. You’re looking at 1 “space” and the 1 bus stab in that space, and the little cruciforms are how GE’s half width breakers grab on. – Harper - Reinstate Monica Jul 21 '20 at 4:39
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It seems like you have a wiring problem. First try turning everything in your panel off!

Start your generator and turn it on to feed power to the panel.

Now with everything off, turn on your back feed breaker and see if the breaker on the generator trips.

If the breaker doesn’t trip, turn one breaker on at a time and verify that load is working.

My guess is you have overloaded the generator and it is tripping.

== OR ==

One of your hot conductors is swapped on the generator cord or inlet. If the generator trips when the back feed breaker is energized and all other breakers, a hot and neutral wire are reversed. It could be on the plug or the inlet. Just because it worked with another generator doesn’t say it was wired correctly beforehand.

You may have to leave a few things switched off in your panel. I turn the electric oven off and the pool, but other than that I can run the rest of my house on a 50 amp.

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  • Thanks! I added some pictures hope it helps. The generator trips the 2nd the Gen breaker is turned on all other breakers. I can connect an extension cord to generator no issues. The generator site FAQ says duromaxpower.com/products/… "Question: Is a ground wire required for the XP100000EH or the XP13000EH unit? Answer: Yes, both of these generators are set up on a floating neutral system which will require a ground wire for safe operation." – Ron Jul 20 '20 at 21:40
  • This is the breaker that the inlet connects to homedepot.com/p/… – Ron Jul 20 '20 at 21:41
  • The generator cord only has one way to enter the inlet and then it twists lock – Ron Jul 20 '20 at 21:43
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    I am mot sure from your response are all other breakers turned off? , do you have an ohm meter – Ed Beal Jul 20 '20 at 21:54
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    Ok that points to your cord not being correct as I mentioned. With everything turned off and only the generator breaker turned on it trips the breaker a hot is on ground or neutral. What I would do now back feed breaker off. start the generator go in to the panel using voltage ac and measure red to black , measure black to white, measure red to white measure green to white, green to black and green to red . This will tell if a wiring issue the back feed breaker off and the generator on and running black to red should be 240v black to white should be 120v, red to white should be 120v – Ed Beal Jul 20 '20 at 22:20

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