Generator Wiring

[McGrew 460]

OK guys, I am looking for advice on a home electrical job.  I know we have some electrical pro’s here.  I recently acquired a really nice 7000 watt Onan generator out of an RV.  I built a cart for it, and will tow it  with the Wheel Horse.  I will use it to power up critical circuits in the house (refrigerator, microwave, etc.) when we lose power, which is far too often.  The generator output has four wires, two hots, a common and a ground.  I installed an L14-30 receptacle on the generator, and bought a 25’ ten gauge cable to connect it to the house.  The L14-30 receptacle will be here tomorrow, and will be mounted in a weatherproof box on the back of my house.  

 

I just installed a new 30 amp double pole breaker for the input from the generator, but realized when I took the cover off the 200 amp breaker panel, I do not have separate ground and common bars in the box...  So, my question is this:  I have both a ground and a common coming in from the generator, but only have a single ground/common bus bar in the breaker panel.  Do I hook both to the ground/common bar, or only one?  If only one, which one?  My thinking is hook both wires to the ground/common bar, but wanted some advice from those who know.  BTW, this house was built in 1976, and must have met code at the time...  Thanks for your advice!  Danny

[Racinbob 11,044]

First things first. Are you installing an approved transfer switch? Anything less is a code violation, dangerous and irresponsible.

[Sparky-(Admin) 21,302]

  Yes, both your neutral and ground from the gen cord tie to the same buss in your main panel. 

  Are you installing an interlock kit?

 

[953 nut 55,077]

If you don't install a transfer switch to remove the incoming power while on the generator you could end up killing a lineman who is restoring your power.               Safest way to use a generator is to use a good quality 12 gauge extension cord for each load.

[McGrew 460]

Thanks guys!  Yes, interlock kit has been ordered.  I started to make my own, but it seemed like reinventing the wheel...  953, I bought a 10 gauge cable from Harbor Freight this morning.  It has the L14-30 twist lock plug and receptacle that match the generator and recessed plug that should be here tomorrow. Danny

[JoeM 7,871]

The code says ground wires can not be a current carrying conductor. This is why you need a separate ground wire. (4 wires from the main to the generator plug). At the main the reason they are tied together is because this is the starting point for the ground. 

One thing to remember, the ground wire runs nothing, it is there for protection to divert the flow of electricity in a fault condition back home in place of you. 

It sounds like you are on the right track getting that interlock. It is critical, to have the main off when the generator is in service / running.

[Sparky-(Admin) 21,302]

7 hours ago, McGrew said:

Thanks guys!  Yes, interlock kit has been ordered. Danny

 Awesome! Glad to hear your doing it right  !

[Racinbob 11,044]

9 hours ago, McGrew said:

Thanks guys!  Yes, interlock kit has been ordered.  I started to make my own, but it seemed like reinventing the wheel...  953, I bought a 10 gauge cable from Harbor Freight this morning.  It has the L14-30 twist lock plug and receptacle that match the generator and recessed plug that should be here tomorrow. Danny

Excellent! Like Sparky, I'm thrilled that you are doing it right. 

I was thinking about making one myself as well but changed my mind when I found a Square D interlock for QO breakers. Simple and inexpensive (<$20). It won't work on the Square D Homeline panels though. The nice thing is that you maintain a UL listed system but better yet you avoid any possibility of creating a very dangerous situation. 

[rmaynard 15,427]

Curiosity has prompted a question from me. If you use a manual interlock such as this, how do you know when service has been restored? I would hate to run my generator all night long if service was restored just after I went to sleep. Is there something that could be attached to the incoming service line that would sense that the current is back on and turn on a buzzer or something?

 

 

 

Edited September 10, 2019 by rmaynard

[Racinbob 11,044]

With my setup I have a separate panel feeding the items on the generator. I just leave a light that's not on that panel in the on position. When the power is restored I simply flip the interlock breaker back to the normal position and now that panel is returned to normal power. With any system something can be done to let you know the power is back on.

[Racinbob 11,044]

Let me elaborate on that hopefully to avoid confusion. Here's what I call my transfer panel:

 

 

I have 5 panels on this property. One in each garage, the main 200 amp, a panel in the addition with a 60 amp feed from the main and the transfer panel. A 60 amp feed from the main panel is connected to the breaker on the left marked 'utility supply'. A dedicated line is run from the breaker marked 'generator supply' to the garage where it can connect to the generator. The feeder to the 60 amp panel in the addition is connected to the main lugs in this transfer panel. Everything we need powered in an outage is run to the addition panel. The furnace, refrigerator and chest freezer and run to this transfer panel only because it was easier. The transfer panel and addition panel are powered through one of the 60 amp breakers you see. The interlock is a Square D QO2DTI and that's was prevents normal power and generator power from meeting. The main 200 amp panel is still connected to the power company in an outage but isolated from the transfer panel and, of course' the addition panel. When power is restored anything on the main panel will come on if the switch is on. At that point just flip flop the two breakers with the interlock and everything is back to normal. 

[JoeM 7,871]

2 hours ago, rmaynard said:

Curiosity has prompted a question from me. If you use a manual interlock such as this, how do you know when service has been restored? I would hate to run my generator all night long if service was restored just after I went to sleep. Is there something that could be attached to the incoming service line that would sense that the current is back on and turn on a buzzer or something?

 

 

 

Good question and good suggestion. Might have to look into something like that, my brother uses the lock out on his main.

We have a generator sub panel set up, like RB, so the lights in some of the house come on when the power comes back on. As a note, we usually don't run our generator continuously. I will run it for an hour then down for two. Topping off the fridge, pumping the sump or making some heat, (we have a gas furnace).

Thought about a automatic system, but the power is pretty reliable and just can't justify the cost.