My head hurts now....I know this thread has gotten off track quite a bit from the original post, but I feel I need to clear a few things up for ya’ll. This may clear them up, or it may confuse you even more. This all deals with the NEC language, and even after all of these years dealing with it, I still get confused, as you will see as you read this long explanation. Thanks to Isaac-1 for questioning this and forcing me to dig deeper into the NEC and research the answer.
When to drive a ground rod at your generator? There are a few different answers to this question, and they all relate to the type of installation you have. The only time you are required to drive a ground rod at your generator is if the generator is considered a “separately derived system” (SDS) by the NEC….in general, most all residential generator hook-ups are NOT separately derived systems. The definition of a SDS is one in which the neutral wire is broken at the transfer switch...meaning there is no solid path back to the generator by any current carrying conductor (all three lines should be broken by your transfer switch, both hot lines and the neutral) However, you should still be using 4 wire cable so you have a ground running with the others as well.
Non SDS (which are the most common) have a solid neutral bus in the transfer switch for connecting the neutral. As is the case for many of us that use the back-feed method using a double pole breaker in our main panel, we are creating a Non SDS because the neutral wire has a permanent complete path back to the generator. This means that no ground rod is to be driven at the generator if your neutral runs unbroken (electrically) back to your generator.
Clear as mud right??? Now, here is where most of the confusion comes into play with our beloved MEP generators…the neutral wire on the generator is bonded to the frame of the generator. If you have a SDS, meaning the transfer breaks the neutral as well as the hot wires when you throw the switch, you are fine. Leave everything hooked up as it was when you bought the generator and make sure you drive your ground rod, because you have the SDS in its purest form. However, if you, like most of us have a NON SEPERATELY DERIVED SYSTEM, then you must
A)NOT DRIVE A GROUND ROD!!!!
B)UNHOOK THE NEUTRAL (L0) BOND AT THE FRAME!!!
Now that clears it all up, right??? Wrong. Now, what if you have a hook-up where you have a cord running to your house going into a pin and sleeve connector at your transfer switch and your transfer switch is set up to be a non SDS system. In that case you must not have a ground rod driven at the set, and you must have the neutral un-bonded from the frame….but what about if you want to use the generator as a stand-alone unit to run some equipment in your shop, like a welder or something by itself and not have it hooked up to your house….now the generator is back to being it’s own power source like the military used them for and must have the neutral bonded again and have the ground rod driven.
So, to save yourself the hassle and confusion of all of this, use a transfer switch that switches the neutral wire as well as the hot wires, drive a ground rod at the generator and leave the generator frame/neutral bonding just as it was when you bought it. If you want to use it as a stand alone generator, then you are covered; if you want to use it for your house when needed, you’re covered.
I know this was long winded, and you probably still are confused about this all, as I said, I was confused as well. Dealing with the NEC is very tricky business and requires a lot of research. I am sorry if I misled any of you with my earlier posts.
It's actually J10 in that picture (the lower, innermost connector on the back side of the AC reconnection box) . The neutral bond wire is the one that has the funky black polygon drawn around it. It actually bonds to the frame on the inside of the ground splitbolt in the picture.jbk said:is that the wire from rear connector j2 thats connected to the back of the ground lug?
thank you...as i will be firing up the mep 803a shortly..and i wanna be sure ill be doing this correctly and safely.......andy and the rest of you guys. I would have jumped into this discussion earlier, but i have been out of town.
Grounding!!!!!!!!! You do not need to disconnect the neutral ground of the generator. You also do not need to drive a ground rod at the generator! As a matter of fact, you should not drive a ground rod at the generator. The nec states that only one earth ground shall be installed. This was done at your main service panel when your house was wired and built. You do not drive a second ground rod at the generator, the military does this because these sets are the main power source out in the field. They are not the main power source in your home.
To install them properly, you should be running 4 wires from the generator to the transfer switch/hook-up spot in your house. Two of those wires should be the two "hot" legs of the generator, one wire should be the "neutral" from the generator, and the last wire should be a continuous unbroken ground going back to the grounding bus in the main panel. You could also do as ike suggested and isolate the neutral bond at the frame of the generator and then drive a second ground rod. This is safe to do, but depending on your electrical inspector you still may have a tough time getting it to pass muster, because as i've stated the nec specifies only one (1) ground rod shall be driven!
The reason for only havine one ground rod is this. If you look at your main electrical panel you will notice that the neutral buss and the ground buss are bonded together, they are essentially (electrically) the same buss. If you drive a ground rod at the generator and do not remove the neutral bond, you now have two (2) pathways for the neutral current to get back to the generator, the neutral wire and the earth ground because of the second ground rod you drove....this is a big no no!!!! The current will parallel the two pathways and now the earth ground becomes a current carrying conductor, and as per the nec this as a violation. The ground shall never be a current carrying conductor. If you feel better doing as ike sugested, you can go to the trouble of disconnecting the neutral bond on the generator and driving a ground rod, but if you want to go according to the nec, that is still not a proper installation, is it safe? Yes!
If you have not hooked up the generator yet, save yourself the trouble and hassels, and just run the 4th wire (the ground) back to your panel and do it the easy way. If you have 4 wires going from the generator to your house already, leave the ground wire hooked to the generator frame and remove the one going to the second ground rod (just be sure the neutral bond is connected to the frame).
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