Backup Generator Problem

I have a backup generator that was installed by an electrician about 5 years ago. Everything was done to code, I have a lockout switch that prevents power from being fed back into the grid. The power cord plugs into my generator and the I have a twist and lock connection on the side out the house. Anyway, tonight the power went out and I went through the usual process of converting over to generator power. As soon as I attempted to plug the power cable into my generator, it drew down as if it were under an immediate load and popped the breaker on the generator. I double checked that all the circuit breakers in the service panel were off. Why would I be drawing a load when nothing is on? Any suggestions on what to check first? I opened the plug on the outside of the house and the service pane inside, everything looks like it should. Any suggestions would be greatly appreciated.

 

Welcome to the forums...

Same gen as before? Nothing changed from when the electrician installed it?

Is it portable gen?

Make and model please... that will help.

And what type of disconnect in panel or transfer switch?

Sounds like a ground fault issue...

 

It's a Generac 7500 exl. It's only purpose is to run backup power for the house so nothing has changed in regard to that.
I have an interlock device on my panel which makes you turn off the main breaker before you can turn on the generator breaker which is essentially back feeding the panel.

 

Check power cord for shorted wiring.

RR

 

I wondered about the cord. If the cord is plugged into the generator first it is ok. As soon as I attempt to connect it to the receptical on the outside of the house the generator draws down and I get sparks.

Could there be moisture in the receptical or would it have to be something more?

 

If you need to inspect is the lockout switch wiring or mechanism itself, unhook the generator..

In many cases the "lockout switch" is a mechanical slider or cam or lever that keeps the panel breaker (on one side) that controls the generator feed and the main utility breaker up top from being on at the same time. If the parts were not specifically designed for your panel then thisy might be too loose to provide proper protection. At any rate you should manually turn off both breaker sets that are linked by a mechanical lockout and be sure that the slider goes back and forth all the way freely before turning on the breaker set for the generator or the breaker set for utility power without using force.

In fact you should try plugging in the generator cord with the lockout (if a mechanical slider) set for the "neither" position i.e. both breaker sets controlled by the slider in their off positions.

 

If the generator struggled a bit before tripping, I'd imagine it's not a direct short (though I may be wrong on that one).

What happens if you don't turn on the generator breaker? Just run the generator plugged in, but not activated at your panel? There should be zero load, and nothing should change.

Then try turning off all the circuit breakers, then switch to generator power. Again, there should be zero load since nothing is connected.

Then turn on each breaker one at a time.

This process should narrow down where the issue lies, whether it's a wiring issue (unlikely if the wiring was done well), or something with one of the circuits. Maybe your AC was on? The electric range? Something that may pull more than the 7Kw that the generator can output.

 

You are 100% correct on that one.

You don't have a short or the breaker would trip immediately. If you're positive that all load breakers are off. That leaves a possible connection back to the electric company.

Allan described checking the breaker action above.

If you are uncertain..... call your electrician back. This could be a serious issue.

 

Well its working again but I'm not sold on why. Here is what I did. After I couldn't get the power cable to connect without drawing power. I ran a 110 extension cord to my sump pump so at least I didn't have to worry about that backing up over night. The generator ran for about 7 hours just powering the pump.

I took the cover plate off the service panel and visually inspected all the wires to the breakers, the neutral and the ground. I removed the double breaker and tested each side with an Ohm meter to see if they were functioning properly. I reinstalled the breakers and closed the panel back up.

I took the outside receptacle apart an looked it over, everything looked clean and just like new on the inside. Finally I took the power cable apart and examined both plugs. The male end that plugs into the generator had some cobwebs in there but looked ok. The when I got the twist connection apart I found that something had built a mud nest inside there. I broke it apart and cleaned it out. I thought maybe that was an issue but each contact inside the plug is walled off from the other so I'm not confident that would make a difference.

After all the cleaning and reassembly, I connected the cord again with every breaker in the off position and there was no instantaneous draw upon connection.

Its' been running all day now but I'm keeping a close eye on it.