Generator and Circuit grounding

[LowGear]

Ronmar,

And from my garage sub-panel, as per your assessment, the four wires run out to MEL (Menehune Energy Lab) inside 200 feet of conduit to the inverter through another sub-panel there.  That sub-panel does have two ground rods at least 9 (?) feet apart.  If the inspector checked anything on the roof it was that every stinking piece of racking and every panel had a ground wire which fed through the inverter, shut-off switches and into the sub-panel bonded ground bar.  It was also designed by a Hawaii licensed Electrical Engineer besides floating through the permits office.

This is where I learned that too much lubricant on a 180 foot conduit pull is far better than almost not enough.  I'm sure you can figure out how I learned this.  "Three feet?  Are you shitting me?"  I think the people three farms away heard this exchange.

Casey

[veggie]

Interesting....
In the schematic that came with the switch, it shows both L1 and L2 being switched.

---> click on picture to enlarge <----

[LowGear]

I look at that drawing and I just have to say "Huh?".

Casey

[Lloyd]

Yes, just like the ground, the neutral runs and is bonded, and just like the ground it is never switched.  It is a safety thing, so that path of least resistance to complete the circuit is always available, or at least you get 2 shots at it:). They run around the contactors in ATS's also, just like they run around the main breaker in your home service panel.  I see no problem with connecting that ground where you indicate on the drawing.  Does a sub panel in a garage have an independent ground? Not usually, the sub usually has a 4 wire connection to the main panel, two hots to the breaker buss bars(via a disconnect) and a ground and neutral connecting from the sub panel buss bars directly back to the main panel ground/neutral buss bars.

Veg, and Ronmar

On boats we do switch the neutral, sometimes the ground if the generator doesn't have a ground switching relay. Remember all sources of power should have the neutral bonded to the earth at one place, not 2 different.

Also by not switching the neutral you set up a couple of hazards, 1. if you have the generator running while the main panel is hot, and a back feed develops on the neutral...poof there goes the magic smoke. 2 since the neutral is considered a current carrying conductor, if a lineman was to work on a downed mains and the generator was running they could find themselves at the end of a live circuit theoretically. That's why all back up gen installs require a lockout on the generator to meet code.

Lloyd

[Ronmar]

I service 8 remote communications and RADAR sites and none of them switch the neutral.  Don't know much about 120 with neutral on a boat.  All the "boats" I have worked on were all split 60:)  Pretty sure ground was never switched, only the hots...    I think in the OP's case, Neutral and ground are only bonded at the main panel. I am pretty sure the utility also bonds it to ground back at the center tapped step down transformer at the pole:)   His application is more akin to a light switch, and again, only the hot is ever switched.

How exactly does a "backfeed" develop on the neutral?

[Ronmar]

Interesting....
In the schematic that came with the switch, it shows both L1 and L2 being switched.

---> click on picture to enlarge <----

Spec sheet says it is a 120/277VAC capable.  L1 and L2 denote the 2 hot leads associated with the higher voltage capability...  A 120 application would only use one pole of it, just like a light switch only has a single pole...

[veggie]

Lloyd,
Thanks for that info.
I forgot about boat systems. The Ship/Shore switch operates in the same manner as what I'm proposing.

Ronmar,
Good point about the 240 volt, L1-L2 application of the switch.
Switching only the hot leads is not a problem. What I don't yet understand is what happens when you bond the white neutral lines of two separate power sources. (Generator and Mains)
When one source is in-active, it's neutral is still connected to the live system.
What if someone is working on the in-active system? Is there any feedback potential ?

veggie

[DanG]

What have you against a standard manual changeover sub-panel? There is the Sportsman's Guide outlet store near here that has scratch'n dent ones for $75, the 120V only one I have came from Northern Tools outlet store for $25 so they are available cheaper than that linked toggle switch.

If you are anywhere near a greenhouse (wet feet, water around metal) a system with ground-fault and/or residual-current beakers is probably code - and maybe both power sources separately protected giving possibilities of nuisance tripping on the unenergized side, and maybe a set of arc-fault breakers inline too since the generator is being run in an unattended mode.

A

http://www.interlockkit.com/

might be a way to sneak an end run around new hardware if your sub=panel is listed.

Just looks like you are volunteering for trouble, I think I'd have a 4-pole transfer switch in that mix.

[LowGear]

I'm with DanG,

I'd bite the bullet and use a 4 wire generator transfer switch too.  When I pass on to the big generator in the sky the poor mortals left behind already have enough "custom" - "brilliant" thinking "stuff" to figure out besides throwing both switches to transfer power out to the green house.  That's before they sell the complicated generator for $17.95.

I'd replace both breakers with a GFI as well.  That's the one in the panel and the one that serves the generator. 

Casey

PS:  The inverter on my system doesn't have a neutral wire anywhere near it.

[veggie]

Hi Casey,

I don't think this classifies a "brilliant thinking stuff".
It's just a standard wiring addition.
I ran it by two electricians and they don't have any problem with it. (Provided I switch the neutrals also).
Components are all approved and standard code is being followed.

cheers,
veggie

[Ronmar]

Lloyd,
Thanks for that info.
I forgot about boat systems. The Ship/Shore switch operates in the same manner as what I'm proposing.

Ronmar,
Good point about the 240 volt, L1-L2 application of the switch.
Switching only the hot leads is not a problem. What I don't yet understand is what happens when you bond the white neutral lines of two separate power sources. (Generator and Mains)
When one source is in-active, it's neutral is still connected to the live system.
What if someone is working on the in-active system? Is there any feedback potential ?

veggie

Yes, the neutral is still connected to the live system, but it is also connected to ground at the same point. It has no reason to go to the inactive system...  I think what you are missing is thinking of the configuration as a complete circuit.  lets start with the main panel conected to a 240VAC center tapped line transformer out on the pole.  Either end of the transformer windings(hots) come in thru the main breaker and feed the hot bussbars. Neutral comes in and connects to the neutral bussbar which is connected to the ground bussbar.  A 120V breaker connects one of the hot bussbars to a wire out to a load(black)  Along with that wire is a neutral wire(white) connected directly to the neutral bussbar. There is a ground wire, connected to the ground bussbar(and the neutral).  Lets say this is feeding a switched light.  The black wire goes thru the switch, the white wire goes around the switch, and the ground wire connects to the ground lug on the switch.  At the light the black wire connects to the fixture, the white wire connects to the fixture and the ground connects to the light casing.  When you turn on the light switch, current flows from the circuit breaker thru the black wire, thru the switch, thru the load and returns thru the white wire to the panel.  The only time you have current on a neutral wire is when the load is being fed.  Anything that causes the hot to connect to a case completes the circuit via the ground wire instead of the hand/body that may possibly come into contact with those casings. 

Now if you look at the added neutral leg to a generator, do you see any way for current to flow out there, when the path of least resistance is back to the panel where the power source it is referencing is located...    Since you are only working with 120, switching the neutral is not so much of a problem.  The real issue would be if you were feeding 240, then the possibility exists of winding up with 240 across multiple circuits if they loose their neutral reference. 

I guess another way to look at it would be like this.  You use 2 electrical outlets, one connected to the generator, the other connected to the commercial electric panel breaker.  The line to the greenhouse has a plug on it.  Want comm power, plug into that outlet, want generator power, plug into that outlet:) Looking at it this way, you are breaking the neutrals when you switch, but the ground plug being longer, insures teh safety is in place before current can reach a possibly shorted load...

Is this generator connected back to the main panel in any other fashion?

[fabricator]

Hi Casey,

I don't think this classifies a "brilliant thinking stuff".
It's just a standard wiring addition.
I ran it by two electricians and they don't have any problem with it. (Provided I switch the neutrals also).
Components are all approved and standard code is being followed.

cheers,
veggie

Switching the neutrals makes no sense to me, so you switch from the mains to the generator then you have no earth bond on the generator side.

[veggie]

Hi Casey,

I don't think this classifies a "brilliant thinking stuff".
It's just a standard wiring addition.
I ran it by two electricians and they don't have any problem with it. (Provided I switch the neutrals also).
Components are all approved and standard code is being followed.

cheers,
veggie

Switching the neutrals makes no sense to me, so you switch from the mains to the generator then you have no earth bond on the generator side.

If I am understanding your comment correctly....
The generator is earth permanently bonded direct to the garage panel with a grounding cable.
(See the second version sketch of the system a few posts back)

Veggie

[LowGear]

Hi Veggie,

I don't think this classifies a "brilliant thinking stuff".

I don't think it's rocket surgery either.  But those that follow might.

I keep forgetting that the switch is ganged - one toggle w/ two sets of contacts.

Are generators suppose to have ground rods.  Will the GFIs (switches or breakers) work with out a ground reference for the neutral and the ground or does it just look for differentials?

Casey

I've reconsidered.  I'd plug the puppy in, tie the grounds together at the "arrow" and see what happens.  What are you worried about smoke testing.

Addendum:  You realize that 120 receptacle on the generator (tab broken) has 240 volts on it?  That meets code?

[veggie]

Addendum:  You realize that 120 receptacle on the generator (tab broken) has 240 volts on it?  That meets code?

Hi Casey,
Can you elaborate on that please...

veggie