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-   -   Sub-panel grounding question. (http://www.diychatroom.com/f18/sub-panel-grounding-question-16962/)

gesoneguy 02-11-2008 08:52 PM

Sub-panel grounding question.
 
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I'm installing a sub-panel in a detached garage, and I'm confused about grounding it properly. I've run #2 from the Meter Box to the sub-panel, and grounded it at the sub-panel with two grounding rods 6ft apart. It's my understanding that if a detached structure is connected to the main structure through any other cabling (ex. coax, telephone, etc), the building cannot be bonded (or grounded back to the meter box), is this correct? I'm having trouble wrapping my head around the whole bonding thing.

My other question is, if I install a GFCI breaker in the new sub-panel, do I connect the white from the GFCI to the neutral bus or the ground bus, since it's not bonded?

I've attached a picture of my work so far. Any insight would be appreciated!

goose134 02-11-2008 09:07 PM

If this is tied into the meter cabinet as you say, you'll need an overcurrent device on it. The panel you picture is a main lug only. You should only bond the neutral if there is no other metal between the house and garage (conduit, water, gas pipe etc.) Take the green screw out of the neutral. Also tag your neutral with some white tape.

Stubbie 02-11-2008 09:16 PM

Questions

1.) As goose said where is your overcurrent protection? And just exactly how did you connect at the meter? Double lugs or is there a main panel and meter combination and you are using overcurrent protection from a breaker in the meter main?
2.) How is power getting to the sub-panel buried cable or cable in conduit or overhead? It looks like SEU 3 conductor w ground coming into the sub-panel??
3.) Do you have a metallic path like goose mentioned between the House and the detached garage?

So far all I can tell you is you have the ground rods correct. And yes the gfci connects as shown

chris75 02-11-2008 09:20 PM

You need a disconnect at the detached garage as well, unless you plan on only using 6 breakers... and I hope you didnt run that SER underground... :) should have asked a few quesions before you did the job...


As far as the overcurrent device is concerned, if you boys take a look at 230.40 exception no.3 he can install the OCP in the garage...

InPhase277 02-11-2008 09:22 PM

As already mentioned, you need the panel protected by a breaker. I assume that you mean you fed it from a meter/main that has space for a couple of additional breaker spaces, right? If that is the case, you should use a 4-wire cable, remove the green screw from the neutral, and get jiggy with it.

Inside the meter/main, the ground and neutral of your new cable will be landed on the same bar, but NOT in your new panel.

EDIT: You need a disconnect or a main rated at no less than 60 amps since this is a detached building.

InPhase277

gesoneguy 02-11-2008 09:32 PM

Sorry guys.. I'm not that polished on the terminology. Yes, it's fed from a 100Amp breaker in the main/meter panel.

It is a 4 wire cable inphase277... so I should connect the ground an neutral at the meter, but not at the sub-panel? What about grounding it at the detached building itself?

Stubbie.. the only metal connections to the main building are coax, telephone, and security wire.. I assume those count?

chris75 02-11-2008 09:37 PM

I see a few problems...., I already mentioned the SER run underground, #2 SER is only good for 90 amps because you cant use table 310.15(B)(6) for a garage...

gesoneguy 02-11-2008 09:41 PM

Thanks Chris. I could be wrong on the #2 deal... was told it was rated for 100amps. Is there a way to know for sure?

gesoneguy 02-11-2008 09:41 PM

by looking at the cable?

Stubbie 02-11-2008 09:44 PM

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Gesnoeguy

4 wires is good you can't go wrong with that. Take out that green screw it is the bonding screw for the neutral to the metal of the enclosure, you do not want that. See below diagram to use as a guide.

chris75 02-11-2008 09:45 PM

Quote:

Originally Posted by gesoneguy (Post 97128)
by looking at the cable?

it should tell you the wire size on the jacket,


#2 is rated for 100 amps under certain conditions, yours not being it...

gesoneguy 02-11-2008 09:55 PM

Cool thanks Chris. And Stubbie, the diagram is PERFECT! The extra grounding rod at the detached building is what was throwing me. I thought if I grounded there, then also grounding back at the meter would somehow bond the sub-panel, since the neutral and ground are connected at the meter. But I guess not. Uggh.

Stubbie 02-11-2008 09:59 PM

In my opinion he cannot use the six handle rule for a lighting and appliance branch circuit panelboard... ie... 10% of his breakers are 30 amps or less with neutral connections serving lighting and appliances. He must use a main breaker in the sub panel or main disconnect nearest the point where the feeder enters the building.

chris75 02-11-2008 10:04 PM

Quote:

Originally Posted by gesoneguy (Post 97139)
Cool thanks Chris. And Stubbie, the diagram is PERFECT! The extra grounding rod at the detached building is what was throwing me. I thought if I grounded there, then also grounding back at the meter would somehow bond the sub-panel, since the neutral and ground are connected at the meter. But I guess not. Uggh.

You just need to understand what the wires are actually doing to understand it...

chris75 02-11-2008 10:10 PM

Quote:

Originally Posted by Stubbie (Post 97144)
In my opinion he cannot use the six handle rule for a lighting and appliance branch circuit panelboard... ie... 10% of his breakers are 30 amps or less with neutral connections serving lighting and appliances. He must use a main breaker in the sub panel or main disconnect nearest the point where the feeder enters the building.


Take a look at 408.16 (A) exception No. 1


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