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#87138 - 01/25/04 03:34 PM barn or detached garage  
Wirenuttt  Offline
Member
Joined: Nov 2002
Posts: 267
Massachusetts
What are some of the requirements for installing a sub-panel in a detached garage as far as grounding is concerned? Is it just a 4-wire isolated netral at the sub panel? What about an additional ground rod? Have any of you done these installations and how did it go with the inspector?

~Andy


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#87139 - 01/25/04 07:07 PM Re: barn or detached garage  
mj  Offline
Member
Joined: Jun 2002
Posts: 186
meriidian, ms
if only one branch circuit is connected to the building, no ground rod is required.


#87140 - 01/25/04 07:46 PM Re: barn or detached garage  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Two code options for running a feeder to a separate structure, both require ground rods and any other electrodes present to be used.

1)3 wire feeder with neutral bonded to ground at the added panel.

This method is only allowed if there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved.

In other words no parallel paths for neutral current.

2)4 wire feed with isolated neutral bar and bonded grounding bar.

Look at 250.32(B)(1) and (2)


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#87141 - 01/28/04 06:08 PM Re: barn or detached garage  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
the 3 wire/4 wire argument goes round in circles with those opposed to 3 wire pointing to even acidic soil, and those that advocate it pointing to standard poco installs

the 'one circuit' exception forgoing the G-rod ends up inevitably w/3 ph multiwire circuits, or an OCPD as definitoinal benchmarks.


#87142 - 01/28/04 09:35 PM Re: barn or detached garage  
russ m  Offline
Member
Joined: Feb 2003
Posts: 169
Burbank,IL,USA
Bob:

Is it your contention that this is a "feeder" going out to the garage, and not a branch circuit(multiwire), because it is fed from a circuit breaker that is not the final overcurrent device.
The final overcurrent device being the branch circuit breakers in the panel that's in the garage.

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlets.

Russ

[This message has been edited by russ m (edited 01-28-2004).]


#87143 - 01/28/04 09:50 PM Re: barn or detached garage  
Ryan_J  Offline
Moderator
Joined: Aug 2003
Posts: 1,374
West Jordan, Utah, USA
Russ: The original post asked about installing a panel at a detatched structure. This would require that a FEEDER circuit be installed, since the panel contains OCPD's, not outlets.


Ryan Jackson,
Salt Lake City

#87144 - 01/28/04 10:08 PM Re: barn or detached garage  
russ m  Offline
Member
Joined: Feb 2003
Posts: 169
Burbank,IL,USA
Thanks Ryan

I was just try to word it so we all understood it, I was a bit confused at first.


#87145 - 01/29/04 05:41 PM Re: barn or detached garage  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Thanks for the assist Ryan and yes that was what I was going for.

A single branch circuit including a multiwire branch circuit you could forget about the ground rod, I know I would. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#87146 - 01/29/04 05:43 PM Re: barn or detached garage  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Oh and if someone could explain the reason one circuit does not need a ground rod and two circuits require a ground rod I would really like to know.

Sparky, what have you heard for this? [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#87147 - 01/29/04 07:00 PM Re: barn or detached garage  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
Quote
Sparky, what have you heard for this?


usually the converstaion turns to the technicalities of making a G-rod GEC onto a single pole switch...

at which point conceeding to the branch circuit exception seems reasonable

~S~


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