Ground wires on MEP-003

[drjconley]

It is my understanding that there are four ground wires on the 003. One is the negative from the batteries, one is the generator head, one is the slave cable, and the last one comes from the panel.

If I look at the back of the grounding bolt should I see all four wires at that point?

Jim

 

[Speddmon]

no.

There are bonding wires all over the set. There is a strap bonding the engine to the frame. There is a strap bonding the control panel to it's frame, the battery negative bonds to the frame through the starter frame and a wire going to that split bolt connection

The wires attached to the back of the split bold for the ground would be the gen head L0 wire, starter frame/negative wire and slave cable negative.

 

[panic_button]

My interlock on the house panel does not have a switched ground. I understand the ground wire that goes from the house panel goes to the grounding lug on the generator. Do I need to disconnect the L0 wire to the grounding lug? Also, my generator is bolted to a pad with 4- 24" "footer bolts" thru the pad and into the ground. I would think that this would be the same as a grounding rod attached, and reading prior posts is a bad thing...

 

[Speddmon]

You will NEVER find a transfer panel with a switched ground!!!

I assume you are talking about a switched neutral wire. If you don't have a switched neutral in the transfer, then, yes you should disconnect the neutral to ground bond and isolate it by taping it off.

 

[panic_button]

Yes. I did mean switched neutral. Thanks for the info. Do I need to worry that my "hold down" bolts could causing a secondary ground like attaching a ground rod?

 

[Speddmon]

In all reality, the provisions set up in the NEC are bigtime overkill for the one in a million chance that something could happen. I don't think you would be in bad shape with the bolts.

But I gotta ask, I'm unfamiliar with "footer" bolts. Do they have some kind of rib or something on them for where they are actually in the concrete since your pad is probably not 24 inches thick. If not and it's just a smooth bolt going through the concrete, the vibration of the set could make them pull through the concrete a bit and loosen up some.

 

[panic_button]

They sell them at Lowes. They are like the "L" bolts used in concrete but are "S" shaped. They are used in FL to give extra holding power due to hurricane building code. I'll try to get a picture.

 

[panic_button]

Footer Bolt...

 

[Speddmon]

AAHHH...that's what I was concerned about. How thick is the pad you have the generator setting on?

If your pad is only about 4" thick or so, the problem being this...the "S" shape on the bottom of that bolt is in the ground, not the concrete...and only the smooth shaft of the bolt is going through the concrete. The concrete has nothing to grab onto, and since the steel of the bolt and concrete have different expansion rates, over time with temperature changes the shaft of that bolt will get loose in the concrete. I don't know what the soil is like where you live, but if it is sandy soil, the bolt will become loose over time. I doubt you'll notice it since the generator is so heavy and more than likely will never move. It's just my personal preference, but I like to use floor bolts or other concrete anchors for stuff like that, or some type of "J" bolt that the hook part will be embedded in the concrete, so it will never move or come loose.

 

[panic_button]

The pad is ~4" thick, I used a post hole digger to dig down and encased the entire bolt in concrete and put mesh in the pad so I don't think the pad will crack or bolts move in the sandy soil. It was a little overkill, but I hated carrying & mixing the 20- 80# bags and only wanted to do it once.

 

[Speddmon]

Sounds like you thought of the same concern I was having for you. GOOD plan and it soulds like a very well built mounting structure....just like your machine.

 

[Floridianson]

Im not real good at this but thought you used a meter to test your ground.
What was the problem with just driving a good 8 foot copper ground rod to begin with and test that an add more if needed to be shure of a good ground. Seems like this would be something you don't want to guess at.
Also it would seem to be on the safe side test once a year that you still have a good ground?

 

[Isaac-1]

Using traditional methods to test grounds requires driving a second known good ground rod and testing between them with a special type of meter that typically sells new for several hundred dollars. There is a new type of ground test meter that inducts a field into the ground rod to test it, but these meters are much more expensive costing a couple of thousand dollars, still probably worth it to save driving the testing rods if you do much of this sort of thing.

Ike

 

[Floridianson]

Wonder if he could call local power company and have them test the ground rod. You would think and 8 foot ground rod would be fine but?

 

[Speddmon]

James,

I assume you are refering to the conversation about the "footer" bolts and all. He's not trying to make sure he has a good ground, in fact with his set-up he really shouldn't have the generator grounded separately since he doesn't have a switched neutral. He was more specifically asking if the bolts he was using would cause a problem by creating a secondary ground.

In reality, with the surface area of the skid that the generator sits on, and if it is on nice soft moist ground you'll have a nice ground no matter what you do just through the frame. Like I told panic_button concerning his guestion, the NEC regs for the grounding of a generator are really overkill and the odds of having a problem with the secondary ground are slim.