MEP-003A hook up question

[drjconley]

This has been incredibly helpful and informative. Thanks for all the help it is appreciated. I want to say thank you to all off you that helped with this thread.

Jim

 

[Isaac-1]

Speddmon, you are the electrical professional here and I know the NEC is constantly changing, when it comes to unbonding the neutral and grounding the generator frame I am just going by what I have been told by multiple generator professionals as well as what is published in the backup generator installations guides published by both Kohler and Generac.

Ike

 

[Speddmon]

Ike, I am not disagreeing with you. Unbonding the neutral from the ground is a safe way to do it....if you are driving a ground at the generator itself. Also, the NEC is supposed to be the basic rules for any electrical work, if manufacturers or localities want to go above and beyond the NEC that's fine, and we must comply. However, If you drive a ground at the generator itself and DO NOT unbond the neutral, then you are in violation of the NEC because there are now two paths for the neutral current.

I'm simply saying, as long as you run a seperate grounding conductor along with the other three wires back to your main panel, then you are safe for that installation, and NEC compliant. Does this mean that in inspector will not make you drive a saperate ground rod? No! Over the years I've found that a lot of inspectors think they know more than the people doing the actual work, but since they are the final word, and you cannot complete the installation without their OK, we as electricians must do as they say. Right or wrong. I'm sure that the requirements for becoming an inspector are different in all locations. But here it is pretty easy to become an inspector without having much working knowledge of the NEC.

 

[Isaac-1]

Speddmon, as I said you are the professional on the topic, no disagreement on my end, just going by the publications which seem to go against the current NEC rules.

Ike

 

[Speddmon]

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.

 

[cranetruck]

I have been following this with interest, thanks for posting guys!
It's very much like laying out printed circuit boards for analog (op-amps) circuitry where ground loops must be avoided.
Perhaps a couple of illustrations are in order at this point...

 

[Speddmon]

I'll work on a few in a little while.

 

[lavarok]

Regarding the bonding of L0 and the frame, how are they bonded?

I have a second ground rod for my frame, but wasnt aware of a bond between L0 and the frame.

 

[Speddmon]

L0 is bonded to the frame where the two groups of wires come out of the generator head itself, they go into the lower control panel on the left, but one of those wires also swings back around and bonds L0 to the frame...that's the one that should be disconnected and isolated. This is a picture I took a while back for someone else, but it shows the bonding wire.

 

[jbk]

is that the wire from rear connector j2 thats connected to the back of the ground lug?

 

[coyotegray]

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.

My head hurts now....

Could you put in a cut over switch of some kind to break/reconnect the frame to neutral bond at the gen as needed..?

Andy..

 

[Speddmon]

Andy, I am not aware of any specific code prohibiting it, but I highly doubt that you would pass any kind of an inspection simply because there would be no way to ensure that you couldn't possibly have the switch in the wrong position at any given time. That's the whole point of having the transfer switches, and some other codes in the NEC relating to disconnecting means used in industrial installations...They want the stuff to be as fool proof and safe as posssible.

is that the wire from rear connector j2 thats connected to the back of the ground lug?

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.


Here are some pictures that Bjorn asked for.

To clarify the differences of the two types of systems, the generator, the load center and the main service have nothing to do with whether it is a Separately Derived System or not. The deciding factor is whether or not your neutral wire remains electrically connected to the main service entrance from the power company. If it remains connected, then you have a Non SDS, and no ground rod should be driven, as well, the wire in the connectors coming from the generator head that ties the neutral to ground should be disconnected and isolated from the frame (wrap it in electrical tape if necessary, but this wire should not be touching the frame for a proper installation)

You’ll notice in the first picture of a SDS, the generators’ neutral wire is bonded to the frame of the generator, and the generator is grounded via a separate ground rod.

In the second picture of the Non SDS, you can see how the neutral remains electrically unbroken throughout the entire circuit. Also, that the generator neutral conductor is not bonded to the generator frame. The generator frame ground is still tied together with all of the other grounds in the system, but there is not a separate ground rod.

 

[Isaac-1]

Speddmon, to address Andy's potential question of switching back and forth (assuming we are talking about a situation where the generator would be connected to the house for backup power by a pin and sleeve connector as you suggested and might also be used to power 3 phase shop tools, etc. at other times) It seems like a simple solution would be to add another pin and sleeve outlet at a junction box with a ground rod connected to the neutral, then said tool/shop connected to this box.

It is my understanding that the NEC only applies to electrical systems connected the power grid, I am not sure about local regulations that may mirror the NEC, so even if this system is not NEC friendly it may still be legal, and fairly safe.

Ike

 

[Speddmon]

NEC Article 90.2 Scope (from the 2008 McGraw Hill NEC Handbook)
“ (A) Simply stated, the code applies to all electrical work-indoors and outdoors-other than that work excluded by the rules of part (B) in this section.”


The NEC in Article 100 defines a Separately Derived System as:
Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system

So, even though the separate switch would not be part of the utilities electric supply, it is still covered by the rules/regulations of the NEC because it is a separately derived system. That being said, Yes, Andy could put in a separate switch and ground rod. That’s a little different than what Andy had mentioned, he wanted to just switch the neutral/frame ground bond for use as a stand-alone unit.

 

[cranetruck]

Thanks, the images complete the picture.

 

[woodyNla]

Wow! What a very insightful thread! I finally got the good 003a genset on a trailer and was looking for answers about hooking it up as stand by and to use as a stand alone. Many thanks guys for so much GOOD information!

 

[cranetruck]

Ref Isaac-1 post #3 above.

Looked at the wiring on the 10kw genset today and compared my findings to the above referenced post, no biggie, but anyway...
On the mep018a, the load connections are to L2 (not L1 as stated above), L3 and L0.
I'll post this and reread Isaac's post in case I missed something.

 

[lindyp38]

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).

thank you...as i will be firing up the mep 803a shortly..and i wanna be sure ill be doing this correctly and safely.......

 

[lindyp38]

im missing this fuse.......what does it look like....?
ITS MARKED ...F U 1
thanks

 

[Speddmon]

not a great quality picture, but that looks like a standard fuse holder (missing the fuse and cap of course) for a glass automotive (old style automotive) fuse.