[Dennis H.]

Got a question about installing a generator transfer switch. I am in the process of installing a Generac 8 circuit 30 amp generator manual transfer switch, but have a couple of questions that I would like to get an answer on. I have tried to get a hold of several electricians but get no response back from them as of yet.

My question has to do with the grounding system, I had my house built in 1987 and had a professional electrician do all of my electricals. I have a 200 amp service panel and have not had any electrical issues at all since we had the house built. When I started to wire in my transfer switch, I examined my main box grounds, and found out it was wired with the neutrals and ground wires on the same grounding bus bar, (which I think was standard code in the 80's) and from what I am finding out now, it is now code that you must have an exclusive ground bar for the ground, and a separate bar for the neutrals. All the instructions I have seen show the transfer switch being wired with the grounds and neutrals separate. So I don't know which way I need to go, if it is ok to go ahead and proceed putting the grounds and neutrals of the transfer switch together into the main box bus bar as it currently set up, or does the main box have to be rewired with the separate ground and neutral bus bar isolated to current code. Would like some expert advice and opinions of anyone who is versed in this area, Thanks, I have included a picture of my main box and a picture of the transfer switch I am using.

[poncho-mike]

I am a mechanical engineer, and I work for a company that designs and builds industrial UPSs and power distribution systems.

On your house wiring, you have four wires: neutral, L1, L2, and ground. L1 and L2 are your power wires. Let's say you have your L1 drawing 70 Amps and your L2 drawing 50 Amps. The neutral wire carries the difference between L1 and L2, which in this case is 20A.

The ground wire is used to direct current in a fault condition to ground.

The neutral and ground wires are tied together at the panelboard. You must have only one location where neutral and ground are tied together, that is your main ground.

The reason why you don't want to have neutral and ground tied together at different points is to prevent ground loops. Let's say that instead of one main ground rod, for some reason somebody installed a sub-panel and installed a second ground rod. That can set up a ground loop if both ground references are not at the same potential. This will cause current to flow in a loop between the two grounds. This ground loop is eliminated if you remove the jumper tying neutral and ground at the sub-panel.

From an electrical standpoint, if the neutrals and grounds are tied to the same voltbar in the main panel board, it will not cause a problem if that is also the only point where you tie the system to a ground rod. I think the newer electrical codes probably want a separate neutral and ground, which get bonded together at the main system ground.

I hope this helps. Just for the record, I am not an electrician.

Mike

[BTCS]

I installed a Reliance manual transfer switch maybe 6 years ago at my place. It required obtaining a permit from the county and a post install inspection.

I installed the switch and it failed the first inspection due to having a shared neutral between two breakers (one in the main panel sharing a neutral with one in the MTS).

I had an electrician friend explain all this to me, added a breaker in my main panel, rearranged my configuration (split the common neutral between the boxes), and passed the inspection. The inspector then placed a decal on my main panel cover.

All in all, not a hard project - but I'm glad I had it inspected by L&I for peace of mind.

Marc

[Chris65LeMans]

Not surprised you are doing it yourself - the local Generac dealer wanted $13,000 to install mine. That didn’t even include the generator- just hooking up the gas and electric.

[West Coast GTO]

So, if you look at the instructions AND the actual wiring diagram, it shows you to connect the neutral ( white grounded conductor) and the grounding( green) conductor from the main panel to the transfer switch. The grounding ( green) conductor acts like a bond wire from the main panel to the transfer switch. Then a grounding conductor( green) is connected to the grounding buss in the transfer switch( appears to run to the power inlet box).
Instructions also state that " a grounding system and a grounding electrode shall be connected to the ground terminal on the portable generator. THIS IS A SEPARATELY DERIVED SYSTEM.
BTW, only location where neutrals and ground wires connected is the main service panel.

[Stuart]

As mentioned, the main panel is the one place where the neutral and ground wires are to be connected, so assuming there isn't any other main disconnect 'upstream' of the panel in your picture it's fine as is. The ground and neutral connections in the transfer panel need to be separate.

[Dennis H.]

Thanks for all the input, I really appreciate it. After seeing the responses to the grounding issue, I am thinking I might need to add a separate ground and neutral bar to my existing main box, and use it to wire the neutral and grounds from the transfer switch. But I might also contact an electrician, and get a feel for what they might have to offer on the best approach to go. I don't mind doing basic electrical repairs, but I do also need to make sure what I end up doing will be within code, as we hope to in the next few years to put our house on the market, and I do not want any inspection surprises at sale time.

[poncho-mike]

If the neutral and ground are bonded together in your main panel board, there is no electrical difference between connecting the neutrals and grounds into separate voltbars and then tying the two voltbars together, versus tying all the neutrals and grounds into a common voltbar. The voltbar is what we call the aluminum bar where you connect the neutrals and grounds.

The local electrical code might require separate voltbars for neutral and ground. I suspect the reason why the code may require separate voltbars is to prevent the neutral and grounds from being tied to gether at a sub-panel.

Somebody noted that the generator is a separately derived system, which is true. But since it will be tied into your home electrical system, it needs to share the same ground as your home system.

[West Coast GTO]

Dennis,
I recommend definitely getting an electrician because you may not be clear about grounding, bonding and neutral requirements for the sub-panel ( transfer switch breakers) you want to install.
If you look on the wiring diagram specifically for your transfer switch, you will see that a ground wire must be connected from the breaker switch through a junction box( power inlet box) to the generator. This bonds the transfer switch to the generator. Also note that ( on page 14) " When used in this application, a grounding electrode may be required by the local code to be connected to the generator."
A grounding electrode ( if required by local code) prevents the possibility of a ground potential between two ground paths.
Be safe and have an electrician pull a permit and wire the unit. Then,if anything goes wrong with the components, your homeowners insurance cannot deny coverage of any possible claim.

Originally Posted by Dennis H.

Thanks for all the input, I really appreciate it. After seeing the responses to the grounding issue, I am thinking I might need to add a separate ground and neutral bar to my existing main box, and use it to wire the neutral and grounds from the transfer switch. But I might also contact an electrician, and get a feel for what they might have to offer on the best approach to go. I don't mind doing basic electrical repairs, but I do also need to make sure what I end up doing will be within code, as we hope to in the next few years to put our house on the market, and I do not want any inspection surprises at sale time.