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electrifier, Master Electrician
Category: Electrical
Satisfied Customers: 1633
Experience:  Electrical contractor and electrical inspector for over 24 years with phone and networking expertise
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Hooking up 240 volts - Generator to Breakerbox.

Customer Question

Hooking up 240 volts from my Generator to my Home Breakerbox. I have a Craftsman 7500 watt Generator. Electric Start 7500 Watt AC GEN Model No.NNN-NN-NNNNI am using 600v 6-3 wire. I went and got a 4 pronge plug today at Menards so I can plug this wire into my generator and feed it into my breaker box in the garage to send power from the Generator back into the house for backup power. Im using a 50 amp breaker in the garage, which is then wired to my breaker box in my basement which is also on a 50 amp breaker. I followed all wiring diagrams for the new plug to plug into the generator. White wire to bottom (Neutral) Copper wire to Top (Ground - green screw) Black wire to left side (Y) Red wire to right side (X) Garage box is wired the same with the 2 Hot leads and white&copper to bus bar. Basement box is the same exact way. I shut off the main breaker in the basement. I start the Generator up and plugin the new cord to the 240v (50 AMP) outlet on the generator and flikp the breaker on at the box oin the garage to back fedd the power into the house. A Light in the garage comes on at the ceiling, but is very dim. After a minute, I notice the exhaust on the generator is RED HOT. I shut it down right away and the exhaust back fired???!!!!! I am not gettting full power into the house. I unplugged everything from the genrator going to the breaker box. I let the generator cool off and restarted with no 6-3 wire hooked to it. I can plug a light into the 110v outlet on the generator and everything is fine, I can also use a drill. I used a volt meter at this point while the generator was running and no 6-3 wire hooked it. I turned the meter to "V~" AND SET IT TO 600. I tested the 110v outlet. Gave me a reading of 166 v. I tested the 240v socket. Here is what I did and the volts it gave me: Black probe to left hot Red probe to right Hot. Reading of 327-336v Black probe to Top (Ground) Red Probe to Left Hot. Reading of 166v Black probe to Top (ground) Red probe to Right Hot. Reading of 166v Black Probe to BOTTOM Neutral Red Probe to Left Hot. Reading of 165v Black Probe to BOTTOM Neutral RED PROBE to Right Hot. Reading of 164v What is going on? Why is my generator acting up when I plugin the 6-3 wire? No sufficiant power and the exhaust turns red hot?? Help!! I have pics that I can post on here to so you can visually see how the wires are hooked up. I know the wiring from the garage to the basement is good because I had a hot tub hooked up to it for quite some time and I use the 240 all the time. I also replaced the Power Regulater board in the generator yesterday as well as the brushes.


*** UPDATE***

I changed the plug on the end of the 6-3 wire to a 10/30 amp plug and used a different outlet on the Generator. Its the 4 way 110/240 plug. It ran power to the house and also ran my 220 ac Central air unit as well as the fridge, fans and lights. After 5 minutes or so, now NO 220 was supplied to the house to run the central air (but lights and fridge still worked fine). I thought, well maybe because I have only 30 amps max running into the house and maybe all the other stuff running, is not supplying enough to the central air to turn on. A couple minutes later....all the lights in thee house started flickering and going dim. I went out to the garage and shut down the Generator and the exhaust on the generator back fired with smoke and a little flame like a gun went off. I dont get it at all. The generator was running hot almost like it was either grounding out or there wasnt enough ground, but I rechecked all connections again to make sure. So Im lost right now.

Submitted: 4 years ago.
Category: Electrical
Expert:  electrifier replied 4 years ago.

electrifier :

Is this generator new or used before you got it?

electrifier :

First of all you MUST connect this generator to your main panel directly using a manual interlock so it is not possible to backfeed to the power company. You can not feed a sub panel such as you describe and let that feed back to the main panel. It's illegal.

electrifier :

Now, do you have a male on one end of the cord and a female on the end that connects to the house? You would use a 10/4 SO cord for this, NOT Romex as it is outside and a wet location. It is easier to just buy the proper cord than to make it. The twist lock ends are quite pricey.

electrifier :

You are correct in what you describe as red and black to X and Y but it does not matter which is which. Just make sure the ground and neutral stay straight.

electrifier :

Your generator is good for 30 amps so 50 amp wiring and breakers is not advised. Remember, this wiring goes to the main panel and not the sub panel and a mechanical interlock is REQUIRED so the main breaker can not be turned on when the generator breaker is on.

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