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If you're using a non-separately derived system (see Speddmon's post #25 and #32 (with the very helpful pictures)), then you need to break the connection between L[whatever] - the neutral connection point on the gen head windings and the frame ground and connect the frame ground to your meter box/load center ground rod. This is why residential generator connection cable is always four-wire: two for the hot legs, one for the neutral and one for ground.Gotcha! Thanks again. Will connection to L-0 accomplish the same thing for the ground?
So it is ok to ground frame as well in a non SDS system? This seems different advice again.unbond L0 from the frame) for safety it is best to drive a separate ground rod for the generator frame, that way if you have in internal short the frame will not be live, this is not as much of a concern on residential generators, but these MEP's do have control panels on them so people are much more likely to touch them while they are running.
Speddmon, I think this should be, will always be grounded IF hardwired to the transfer switch, if using some type of twist lock cord, etc. it may not be.
No, it shouldn't be. The only thing I might have left out is "If you have things hooked up properly, anytime you are running the set the frame will be grounded" It doesn't matter if you have it hooked up permanently to a transfer switch, through a cord and plug or as a stand alone generator out in the field, a proper hook-up will always have a ground on the frame ALWAYS!Speddmon, I think this should be, will always be grounded IF hardwired to the transfer switch, if using some type of twist lock cord, etc. it may not be.
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.
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.
This is actually the layout I want to go to (am currently using an interlock kit), mostly because it will get me a whole-house cutoff switch as a bonus.In my circumstance, I intend to place a whole house transfer switch upstream -- that is, between the meter pan (termination of Utility feed) and my main panel.
My main panel neutral buss is grounded directly via a copper wire/copper rod to earth.
In this circumstance, if I wish to have a SDS, and utilize a 3 pole switch and switch both hots plus the neutral:
1) Should I ground the generator to earth at the generator even though the Main Panel neutral buss is grounded with its own rod? Probably not, but I don't see how the SDS derivation would work if the house main is grounded as well.
2) The ground from the genset (4th wire) would get to the Main Panel via what route?
This is actually the layout I want to go to (am currently using an interlock kit), mostly because it will get me a whole-house cutoff switch as a bonus.
The principles are still exactly the same as if you were going into a sub panel or an interlocked backfed breaker on the main panel.
If you're doing it with switched hot and neutral in a switch between meter and panel then you still only have a single ground point in the house. You connect that to the fourth (ground) wire in the generator cable and that grounds the generator frame all the time just like it grounds the main panel and the neutral bar at the main panel. You have to break the generator frame ground connection as previously discussed.
- There must be only one ground point bonded to the generator.
- That same ground point must be bonded to the neutral at the one connection point (usually your main panel in the house)
- There must never be zero grounds for either the generator frame or the panel.
I don't believe code ever supports switching ground connections on equipment- it sounds like a sketchy idea anyway. I know that it never supports multiple connections between ground and neutral after the meter base.
Your other option is to do a separately derived system by disconnecting the house ground rod from the neutral bus in the switch box and connecting it to the neutral leg switch terminal on the utility service side of the transfer switch. You would then drive a ground rod for the generator, leave ground and neutral tied at the generator. That's your separately-derived ground for the generator side of the circuit. The transfer switch (and house) is always connected either to utility service (and is thus grounded by the ground bond on the service side neutral switch pole, or to the generator, and is grounded at the generator by the generator grounding rod and ground bond.
My plan is to skip this fun by doing a non-separately derived system and not switching neutral at all. That way I have one ground rod at the house going into the panel just like always and I ground the generator through the house ground. Only the hot conductors get switched between utility service and generator.
You're making this way more complicated than it needs to be.
First and foremost, unless your transfer switch is a double throw (meaning it has a center position on the handle, with no connection to anything anywhere) then you WILL need some means of service disconnect between your meter and your transfer switch. Period. You must install a service disconnect in all installations, so unless your transfer has a big sticker with it that says "Suitable as service disconnect" you cannot do as you have planned.
NOW, once you install a suitable service disconnect immediately AFTER your meter can and BEFORE your transfer switch, then just hook everything up EXACTLY as the picture I posted for an SDS system, and you're done.
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