Generator and Circuit grounding

[veggie]

Hi All,

I need some advise on the the ground bonding side of my project.

I am extending my 120 volt AC garage outlet circuit outside the wall to the greenhouse.
I am also interrupting the extended section with a simple DPDT transfer toggle switch which will allow me to run the greenhouse equipment (battery bank charger, lights, pumps, heaters, controls, etc..) from the generator if needed.

My DPDT toggle can divert power to the greenhouse from (A) the mains garage power or (B) the generator power.
Easy so far.....

All of the 14/2 wire in this system has a ground bonding wire, including the 120 volt cable from the generator.
My question is whether it's ok to connect the generator ground to the Mains ground in order to have a grounded circuit regardless of which power supply I select with the switch.?
The sketch below should illustrate this problem more clearly.

Can (should) I connect the ground wires at at the point of the RED question mark ?

If it helps, also shown below is a wiring diagram of my generator head which does have an external ground connector if needed.
The external case of the generator head is currently not grounded but I was intending to run that connection to a code compliant grounding rod(s) outside the garage.

Thanks all
veggie

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

[quinnf]

When I asked the same question of real, papered, employed 'lectrical engineer, he said the genny should be grounded to the building ground, no separate ground rod is necessary or desired.  But I've heard others say different things; perhaps that reflects local differences in practices or code requirements.  On the one hand, suppose there's a break in the ground wire between your genny and the building ground at the service entrance.  You're left with no ground except through the white wire which is grounded at the panel.  So you should stil be safe.  But if you drive a ground rod at the genny, you're running the possibility that differences in ground conductivity and resistance of the ground wire will allow a voltage difference between the building ground and the genny ground.  And now any ground faults will go all the way to your genny ground rod.  Do you really want that?  And then there are folks who want everything grounded everywhere 'cause of lightning.  For my money, I'll follow the EE's advice and ground at the building ground/service entrance only.

Quinn

[veggie]

Hi Quinnf

Thanks for for the input.
What about connecting the generator cable ground wire to the circuit grounds (red arrow in the sketch).?
Any problem with that ?

veggie

[mbryner]

FWIW, my ST/Listeroid was signed off by the county when I built the powerhouse and my gen head case ground was bonded to the house (whole system) ground.  Multiple electricians have looked at it.

Marcus

[Ronmar]

Well at first glance, you are only dealing with 120 right?  If so, you have one too many switched wires there...  For 120 you have a hot, a Neutral and a ground.  Neutral and ground are never switched, they are both hard run.  The only thing that gets switched is the hot.  Same goes for a 240 installation, L1 and L2, both the hot wires would run thru the switch, the neutrals and grounds are run past the switch and always connected.  Lifting a neutral in a switch can caus you issues...

[LowGear]

Hi veggie,

I think you need a qualified local electrical contractor to look at your drawings.  I think they're wrong.  How much more would it cost to pull a permit and do this totally to hoyle?  Or should I write NEC?

I don't see the need to switch the neutral (white) wire?

It also kinda looks to me like your all of the receptacles on your generator are wired to 240 volt.

Hey nice drawing.  I don't suppose it's some simple to use - cheap to buy program?

Casey

[veggie]

This is a preliminary discussion to get ideas.
I agree about the neutral, so I can change it so that only the hot wire gets switched.
Thanks for that.
What about connecting the generator's cable ground to the mains cable ground. (At the RED arrow) ??

cheers,
veggie

[veggie]

The sketch below shows the revised ground wire running from the gen head to the mains box as discussed by Marcus and Quinnf.

Romar, you suggested that the neutrals for the supply cable do not get switched.?
If only the HOT wires are switched, and all the neutrals are tied together, then the Generator neutral will be connected to the Mains neutral all the time ?

veggie

PS: Casey, the sketch is done using "Windows Paint". Very low tech 

[mike90045]

Be careful if using a "toggle switch" instead of a household  switch. Some toggles are
MAKE-BEFORE-BREAK and you can imagine what that will look like, just be sure to test that it is
Break- before - make

[veggie]

Be careful if using a "toggle switch" instead of a household  switch. Some toggles are
MAKE-BEFORE-BREAK and you can imagine what that will look like, just be sure to test that it is
Break- before - make

Hi Mike
yes, its  a break-before-make.
3 position center-off switch.    ON .. OFF .. ON
Ul/CSA approved for switching AC loads up to 15 amp.

Thanks
Veggie

[LowGear]

If only the HOT wires are switched, and all the neutrals are tied together, then the Generator neutral will be connected to the Mains neutral all the time ?

Yup!  You've thought it out better than me.  And that means the neutrals and ground will be bonded together at the breaker box.  Oh what a big happy family you'll have.  I go back to my first suggestion.  Ask a qualified electrician or two in your jurisdiction.

So do factory generator transfer switches do all three wires?

I've played with paint and you are good.  You must be using a pre Windows 7 version.  I went to use it the other night and almost puked it was such a cheesie imatiation of the old paint I used to complain about.

Casey

Addendum:  It might be interesting if one of the switches failed or was forgotten too.

[veggie]

Hi Casey

1) qualified advice:
There are a lot of qualified people on this forum so I'm hoping the get some further input.
Others may have had similar experience.
If theres any electricians, lets get there take on it.
Its not like Im re inventing the wheel with this small circuit  

2) windows paint:
I use the old windows 2000/xp version.
Me and Ronmar have our "MASTERS" degree in Paint sketching 

Cheers
Veggie

[Ronmar]

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.

[veggie]

Ronmar
You are correct. The panel in the garage is grounded by the 4 conductor cable from the house.
Thanks for clearing up the neutral question.

Veggie

[veggie]

For anyone who's interested, here is a DPDT 120 volt, 15 amp switch made for switching light loads like pumps, fans etc...
http://www.amazon.com/Leviton-1282-Maintained-Industrial-Grounding/dp/B0033PSG5A/ref=pd_sxp_grid_pt_1_0

veggie

And the data sheet....