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 <----
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
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
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
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...
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
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
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 ;D
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
Quote from: mike90045 on December 21, 2011, 05:05:46 PM
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
QuoteIf 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.
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 :D
2) windows paint:
I use the old windows 2000/xp version.
Me and Ronmar have our "MASTERS" degree in Paint sketching ;D
Cheers
Veggie
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.
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
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 (http://www.amazon.com/Leviton-1282-Maintained-Industrial-Grounding/dp/B0033PSG5A/ref=pd_sxp_grid_pt_1_0)
veggie
And the data sheet....
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
Interesting....
In the schematic that came with the switch, it shows both L1 and L2 being switched.
---> click on picture to enlarge <----
I look at that drawing and I just have to say "Huh?".
Casey
Quote from: Ronmar on December 21, 2011, 08:01:19 PM
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
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?
Quote from: veggie on December 21, 2011, 09:11:06 PM
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...
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
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
Quotehttp://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.
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.
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
Quote from: veggie on December 22, 2011, 08:39:13 AM
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?
Quote from: veggie on December 22, 2011, 11:51:49 AM
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.
Quote from: fabricator on December 22, 2011, 05:07:49 PM
Quote from: veggie on December 22, 2011, 11:51:49 AM
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
Hi Veggie,
QuoteI 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?
Quote from: LowGear on December 22, 2011, 05:58:26 PM
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
Quote from: veggie on December 22, 2011, 05:46:09 PM
Quote from: fabricator on December 22, 2011, 05:07:49 PM
Quote from: veggie on December 22, 2011, 11:51:49 AM
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
OK got ya.
Quote from: LowGear on December 22, 2011, 05:58:26 PM
Hi Veggie,
QuoteI 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?
Generators connected to the wiring from the mains power MUST not have their own ground rods, there can be only one ground in the system, the ground bonded to your main panel, that section in the NEC is very clear.
A receptacle wired 120 cannot carry 240, no matter what you do to it.
Careful with that...
In Ontario, a "split receptacle" - such as one in a kitchen, where each single receptacle of a duplex device is connected to a dedicated circuit - can indeed be a source of 240 volts, and 30 amps...
The small breakaway tab connecting the 2 single receptacles is what makes this possible.
If one were to jerry-rig a device that plugs in to such a split receptacle and reconnects the 2 hot wires, you can get 240 volts. Seen it done by roadies. Not legal, but doable.
But I'm sure most already knew that.
Found this article on the web regarding Generator Grounding....
May be of some help.
QuoteA receptacle wired 120 cannot carry 240, no matter what you do to it.
The receptacle (Broken Tab) in the second drawing first page (AB 50 & AB 60) sure looks like its set to deliver 120 different phases to me.
QuoteIn Ontario, a "split receptacle" - such as one in a kitchen, where each single receptacle of a duplex device is connected to a dedicated circuit
I think this two different circuits on one split (Tab Broken) receptacle on the kitchen counter is the code in Washington State and that both circuits come off the same leg inside the panel so you don't have 240 floating around the kitchen counter tops.
Casey