Wiring portable generator as a backup

[jim1450]

I have a Generac GP3250, I wanted something I could take to the race track easily and use @ home in an emergency.
I want to instal a power inlet in my garage instead of using extension cords http://www.homedepot.com/p/Reliance-Controls-30-Amp-Power-Inlet-Kit-PK30/202216490 and also have a Square D Homeline panel & interlock HOMRBGK2C.
I have a 4 conductor #10 cord made up to connect the generator to the inlet but haven't ran the wires from the main panel to the garage.

I have been reading every thread I can find on on how to do this and initially thought it was a straight forward project but then saw some threads discussing how some portable generators have the neutral bounded to the ground which mine does.
Basically as I understand it you do not want the neutral and ground bonded in the main panel & on the generator. I've seen recommendations to separate them @ the generator for back feeding & connect them for portable use, don't like the idea of switching it back & forth.

Is there a good way of making the connection?

Since you only have 3 wires into the house and I remember the old electric stove & dryer plugs were only 3 prong I was wondering about running 3 wires from the panel to the generator inlet.

 

[RickP]

You could add a switch on the generator to disconnect the neutral for home use.

Your house has 4 wires, not 3. You'll need a transfer panel in the garage with 4 wires to hook up that generator, to avoid backfeeding the house. This is not a small project - make sure you know what you're doing before you start it.

Edit: Jim - Did you mean "3 wires [from the generator] into the house" ? I didn't get that the first time I read your post. If you only bring 3 wires from your generator into your house, you'll need to follow sands35 post below.

 

[sands35]

I've been thinking this through too. Found this:

http://www.imsasafety.org/journal/ma03/ma5.htm

The key seams to be that you need to know if the neutral on the generator is bonded to ground or floating. It it is bonded, then you need to switch neutral as well (3 pole transfer switch). If it is floating, then you can just switch the mains. (2 pole switch)

You can remove the bonding jumper for hookup to the house - but it needs to be bonded if you use the genny as a full stand-alone unit.

 

[RickP]

^^^ good reference. So using a portable generator with extension cords is easy, but if you hook it up to the garage outlets, the transfer switch needs an interconnected neutral?

 

[sands35]

Genny ground and neutral bonded = switch neutral at transfer switch and add separate ground system
Genny ground and neutral floating = don't switch neutral

Portable generators are covered in Section 250.34 Portable and Vehicle-Mounted Generators. This section allows the generator or vehicle frame to serve as the grounding electrode when:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.

Caution-Generator Neutral Grounding
Generators will often have the neutral conductor bonded to the generator frame. This is commonly done on small portable generators supplied with receptacles. [Illustration 3]
Larger generators with a cord supplied pin and sleeve connector typically do not have the neutral grounded to the frame. There is no industry standard for when the neutral is or is not grounded, however it seems to be dependent on the generator having receptacles mounted on the frame, as then the neutral is grounded to the generator frame. The generator user needs to know if the neutral is grounded or not.

If the generator neutral is grounded then the generator can only be used with a transfer switch that transfers the neutral, or as a stand alone generator for a carnival or special even, and then ground rods are required.

 

[RickP]

Genny ground and neutral bonded = switch neutral at transfer switch and add separate ground system
Genny ground and neutral floating = don't switch neutral

I guess my post should have included a little more detail - I was pecking away in a mobile browser, so I didn't type the next sentence...

So using a portable generator with extension cords is easy, but if you hook it up to the garage outlets, the transfer switch needs an interconnected neutral? (Since the OP's generator has a bonded ground/neutral, he would need to disconnect the neutral for home use, because it seems that connecting it to a ground rod for occasional home use would be a PITA.)

 

[sands35]

yes - that is my understanding of how the codes are written (not a code inspector or a licensed electrician!)

 

[442stu]

Hmm, seems a bit to complex. The OP stated he is using an interlock kit with backfeed breaker in his panel. The main and backfeed breakers only switch the 2 poles, and GND and Neutral are bonded in the panel, so it would make sense to have them bonded in the generator as well.

 

[sands35]

The explanation that makes sense to me (remember what I also said in post #7):

Ground is ground and neutral is neutral. They serve difference purposes even though they are bonded back at the main panel. You only want them bonded at one spot, not two. Unexpected things can happen if the potential is different at the ends of what becomes a ground loop if they are bonded at both ends. Really long runs or areas where there is different soil resistance or pH can really cause problems with ground loops.

Granted, the % something bad happening is really low, but the consequences are potentially dire (shock, house fire, etc.).

The simple way to do it is to simply take out the neutral-ground jumper in the genny and use it for dedicated in the home service only (or put a switch on it or something). The portables are not really intended to be plugged into a house like a stationary one is anyway even though people do it.

If you are messing with the house wiring, probably 95% of the US population falls under municipalities that require following the building codes. The codes are there for a reason, sometimes they sound excessive, but a reason none the less.

 

[RickP]

Hmm, seems a bit to complex. The OP stated he is using an interlock kit with backfeed breaker in his panel. The main and backfeed breakers only switch the 2 poles, and GND and Neutral are bonded in the panel, so it would make sense to have them bonded in the generator as well.

Okay, I see what you're saying -- I missed that interlock kit in the first post. So because the generator isn't feeding anything else in the house (except through the main panel) the Neutral and Ground would simply be bonded at both ends of the feed wire. Does that meet code?

 

[jim1450]

Okay, I see what you're saying -- I missed that interlock kit in the first post. So because the generator isn't feeding anything else in the house (except through the main panel) the Neutral and Ground would simply be bonded at both ends of the feed wire. Does that meet code?

From what I've read ground & neutral should not be bonded @ both the generator & panel. I did consider the switch as mentioned in #2 but if anyone else would use the generator it could be dangerous.
Since its portable & does not require an additional ground I was curious if I needed to run a ground wire to the main panel.
http://www.generac.com/SpecSheets/0196590SBY_GP3250_Model_5982.pdf

 

[sands35]

200 amp three pole double throw switches are 2-400 off ebay. Pick up a 20-30 spot sub panel and move the circuits you want to run off the genny there. Put the DP switch between them and you are good to go. (obviosly requires some wall space to do it...)