MEP016D grounding

[stoneburner]

I had posted several months ago about my MEP016D wiring. I have a setup now that maybe others would want to use, so this question might concern any generator, not just MEP016D.

So...my MEP is located in my detached garage. Garage has separate electric service from house. I have established that L1 is hot, L2 is neutral on the genset.

I have installed a main lug load center in my detached garage, with L1 to the lug, L2 to the neutral bar. L2 (neutral) travels to the manual transfer switch neutral bar, and then to the house main load center, where it is bonded to ground.

In the separate garage (in the new main lug load center) I have a 20A single pole breaker serving a single duplex outlet in the garage (12/2 w ground) so that I can run some lights and a freezer during an outage (I will have to manually move the freezer plug to the generator-only receptacle), useable only when the genset is connected and running. I have also installed a 30A single pole breaker with 6 AWG wire (for voltage drop) to the house's manual transfer switch to serve house critical loads.

Now, the question: I have ground originating in the main lug load center cabinet in the garage, with green wire going from there, to the transfer switch cabinet, and then to the common neutral/ground in the main load center. (Neutral/ground bonded in the main load center as stated above, neutral is not switched anywhere). The three generator grounding options as I see it:

1. Should I run the genset frame ground for the 016D into the main lug load center and connect to the cabinet (where it is then travels to the trans switch cabinet and then bonded to neutral/ground rod at the house main load center)?

2. Should I ground the genset frame to a separate ground rod located at the garage?

or

3. Should I ground the genset frame to a separate ground rod AND to the main lug load center cabinet as described in 1?

I am leaning toward #3 - I can't seem to decipher the correct answer from NEC Article 250.

Anyone able to help with this?

Thanks,

Mike

 

[212sparky]

Look up separately derived and nonseparately service out will tell you what you need to know. When I get home I will look it up for you if you don't find it by then.

 

[stoneburner]

That's what I have been staring at...I am no pro at NEC requirements. I did note that in informational note #1 of 250.30, it would appear that my generator setup is not a "separately derived system" based on my non-switched neutral. But I then can't find the actual requirements. I tend to get tripped up with the circular references and terminology at times.

 

[212sparky]

What ampacity is your generator? You have a non separately derived system. What you need to do is make sure your neutral is not bonded in your gen set. You will have your hot, neutral and ground going to your main panel. Based on your ampacity you go to table 250.122 to size your equipment grounding conductor. Your ground should connect all metal parts. Your neutral is bonded in your first means of disconnect making that safe.

 

[stoneburner]

Thanks, Rob...I read that too. However, neutral is bonded to ground in my main load center - bonding neutral to ground in my first means of disconnect would be in my new main lug load center, which creates a ground loop between that panel and the main load center...which to me seems not such a good idea. Unless I am completely backwards and the first means of disconnect is actually the house main where neutral is bonded to ground. This is where I always get confused. I guess imagine that instead of a main lug load center, I simply had a generator inlet box - that neutral and ground would run separately all the way until the house main load center. Wouldn't this situation be the same? The only difference here is that I have overcurrent protection for a branch circuit.

 

[stoneburner]

Rob:

Here's a Mike Holt diagram (credit imsasafety.org) basically showing my setup - with the nonswitched neutral, the "non separately derived system" that we both agree on. The diagram shows the generator chassis ground running through the system, to be bonded at the main load center. This is how my system is set up. So, it looks like that MEP 016D chassis ground lug should run through the system like this. Do you agree? If so, I guess a clarifying question is: Is supplemental grounding of the genset frame allowed, and/or beneficial? I have #6 bare copper ground wire and a nearby ground rod that I'd like to use with this. But, if not allowed by code or not at all beneficial, then that's what I need to know...