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I connected a Predator 9000 generator to an Intermatic pool subpanel through a 2 pole 30 amp breaker to backfeed the main panel through another 2 pole 30 amp breaker. There is a GFCI receptacle on the subpanel but was inoperable and its breaker was off.

When all breakers are off in the main panel including the main breaker I flip on the generator feed breaker in the subpanel then the breaker in the main panel that feeds house circuits. Either the the breaker in the subpanel trips or the breaker in the main panel trips or generator bogs down then they trip.

I converted the generator to floating neutral and it still happened. enter image description here

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  • You might want to edit your post to include the output specs of your generator instead of expecting people to go look them up. It may help you get an answer a little more quickly. – FreeMan Sep 4 '20 at 11:25
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    How are you handling transfer? There needs to be some mechanical means that physically blocks the main from being connected at the same time as the system is hooked up to the generator.... – ThreePhaseEel Sep 4 '20 at 11:45
  • If you want to feed the house the generator must connect to the house panel via an interlock or transfer switch, or to a panel that supplies the house panel, (again connecting to it via an interlock or transfer switch) That will not solve your problem, but it is important for your safety and the safety of others. The problem is probably that you have too many loads in your house, you will need to turn off some circuits, but first fix your generator wiring. – Jasen Sep 4 '20 at 12:05
  • @BMitch How is that not an answer? – Jasen Sep 4 '20 at 12:58
  • It sounds like you have another load you don’t know about a photo of the sub panel wiring may be helpful , I can caution this will never be a code compliant connection. Unless you install an interlock kit that you have to shut the main off to energize the back feed from the sub. – Ed Beal Sep 4 '20 at 21:56
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Frame challenge:

You need a generator interlock. Full stop.

You need a mechanical device that positively ensures the generator cannot backfeed the power grid.

You cannot replace this with a checklist, or with "being super smart". The rest of us need to do that, and you are not smarter than the rest of us - especially not during a power failure when you're running around trying to get the lights back on, in the dark, in the rain.

If you doubt that, consider the difficulty you're having solving this problem, in good conditions. You are not Superman and you CAN make mistakes. The interlock's job is to ensure those mistakes don't kill someone. And it is mandatory.

So the idea of backfeeding your pool subpanel is Right Out, because it makes the proper interlock impossible. You are either going to have to

a) lay a new cable, or b) "permanently" re-task the pool supply cable to be the generator supply cable, resulting in the pool ONLY being powerable off the generator.

Yes, I'm aware that's exactly what you're trying to avoid. The rest of us don't get to do that, neither do you.

I say "permanently" because there is nothing wrong with doing permanent and proper wiring seasonally, as long as it is proper and to Code.

Now, if you get us some information about your main panel, we can guide you to some good choices in generator interlock. (We're not normally a shopping site, but we can give some guidance).

Why?

Because power flows both ways, as you well know from your efforts to backfeed the pool sub. It also backfeeds out onto the neighborhood grid. It also backfeeds through transformers. When you energize the 120/240V side of a 120/240--9600V transformer, the high side of the transformer energizes at -- anyone, anyone, Bueller? Correct, 9600 volts.

And that's how you kill linemen with a Harbor Freight generator.

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  • The voltage depends on the actual location in cities it is lower because of the density , in the country it is higher due to the distance to reduce the voltage drop. – Ed Beal Sep 5 '20 at 19:10
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The problem is probably that you have too many loads in your house, you will need to turn off some circuits.

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  • seems I have to ignore the elephant in the room. – Jasen Sep 4 '20 at 20:19
  • With all the breakers in the house off? – Ed Beal Sep 4 '20 at 21:58
  • Yes Abosolutely! OP needs to turn some of house circuits off breakers off before OP flips "the breaker in the main panel that feeds house circuits" – Jasen Sep 5 '20 at 0:34
  • Did you read the op turned ALL of the breakers in the main panel off? Maybe this is why your original answer was deleted? – Ed Beal Sep 5 '20 at 1:23
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    You also missed the elephant in the room. No proper answer can ignore that. Hint: interlock – Harper - Reinstate Monica Sep 5 '20 at 17:40
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New here but I have some possibilities:

First have to say you definitely can't do this without an interlock!

Taking the your statement at face value - that all breakers are off (and not defective) suggests one possible scenario: The generator could have a miss-wired cord/socket, or plug. If the neutral is switched with a hot pole, it would feed the system ground with 120V (through the bonding or ground rod systems). Although this would not explain the breaker tripping in the main panel.

I think here should be a ground rod for the pool. If the resistance of the grounding system(s) is less than 4Ω, and you have a wiring fault, it would draw more than 30A. I am wondering if the breakers tripped immediately when the neutrals were tied, and tripped slow and loaded the generator when you isolated the generator neutral?

Check all your plugs and sockets' wiring for proper wiring. Try volt checks to confirm they are right; THEN, try and see if there are any sneak loads you missed...

Bottom line is something is not exactly as described; actual connections must diverge from what you think it is, or a faulty device somewhere. It could not do what it is doing, if it is actually as described (or has a wire shorting or miswired or a device fault).

[EDIT]: Thinking this through more thoroughly, a ground loop would not explain the breakers tripping if the generator was wired wrong. This only leaves a load you overlooked, or a fault in the wiring. (speaking practically). Make sure you don't have a main lug feed (terminology?) coming off the main panel buses, and connected to a load you missed.

If all your wiring checks out, the I would not move wiring too much or you may loose the fault you are trying to pinpoint (the problem could 'go away', only to appear again sometime in the future!). I would check the main panel buses and pool box breaker for voltage first (for safety), to be sure everything is off/isolated; then ohm all ways to see if there is a fault somewhere.

The only other (unlikely) possibility is if there is a defective breaker that does not open (shut off). You stated you are using double pole breakers (not 2 singles), so it should not be possible to stab them on the same poles...

[I would not rule out a main breaker that did not open one pole; however unlikely it could be possible]

Check and double-check...

Again, I emphatically second with Harper - Reinstate Monica and others have stated: You MUST have an interlock method!

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  • I just found out that some Hot Tubs can be wired for 240V OR 120V, involving putting one of the hot feeds on the neutral instead. Check that one of the 240V feeds is not switched to the neutral bar! Normally should be done in the appliance, but here it could have been done incorrectly at the main panel. Not clear if your 'pool subpanel' mean a hot tub, a pool, or something else (or connected to nothing). – troubleshooter Sep 21 '20 at 17:12

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