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Old 05-16-2012, 07:03 PM   #1
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Default grounding a sub panel

I am replacing a 40amp subpanel in a garage with a 100 amp subpanel.
the garage has an exsisting 1 in. conduit from the house. do i need a ground wire ran through that condiut if i am putting a new ground rod for the subpanel in the garage?

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Old 05-16-2012, 07:12 PM   #2
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Quote:
Originally Posted by mbidingerres View Post
I am replacing a 40amp subpanel in a garage with a 100 amp subpanel.
the garage has an exsisting 1 in. conduit from the house. do i need a ground wire ran through that condiut if i am putting a new ground rod for the subpanel in the garage?


depends on what kind of conduit.

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Old 05-16-2012, 07:14 PM   #3
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just pvc underground, romex in house to main panel
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Old 05-16-2012, 07:15 PM   #4
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just pvc underground, romex in house to main panel

Unless you're still on '05 code, you need it then.
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Old 05-16-2012, 07:17 PM   #5
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which means then I have to increase the conduit from 1 in to 1-1/4 in
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Old 05-16-2012, 07:19 PM   #6
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which means then I have to increase the conduit from 1 in to 1-1/4 in
maybe if you're running copper. If you're running al, you'll need 1.5"
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Old 05-16-2012, 07:19 PM   #7
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You can increase it to 1 inch EMT and not have to run a grounding conductor inside the pipe, lol.
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Old 05-16-2012, 07:23 PM   #8
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it is 1 in pvc conduit right now but only underground
under concrete driveway. I was trying to avoid digging that up
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Old 05-16-2012, 07:24 PM   #9
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I am running copper # 2
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Old 05-16-2012, 07:24 PM   #10
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Id make it a 60a if I could.

99% of the time even the 60a is overkill.
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Old 05-16-2012, 07:27 PM   #11
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Customer needs a 100 amp
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Old 05-16-2012, 07:44 PM   #12
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Customer needs a 100 amp

http://www.electrician2.com/calculat...alculator.html

Looks like your conductors work if you use #3 cu
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Old 05-16-2012, 09:11 PM   #13
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Quote:
Originally Posted by mbidingerres View Post
I am replacing a 40amp subpanel in a garage with a 100 amp subpanel.
the garage has an exsisting 1 in. conduit from the house. do i need a ground wire ran through that condiut if i am putting a new ground rod for the subpanel in the garage?
The ground rod would be for lightning...you still need the equipment ground from the main panel to the second building.
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Old 05-16-2012, 09:42 PM   #14
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You could use a wire with a higher insulation tempature rating like a Z or a TFE. Then your conductor size would shrink you could use the same size pipe and be code compliant. However it is probally going to cost about a dollar more per foot or so.
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Old 05-16-2012, 10:10 PM   #15
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most pvc is rated 90c. Also the terminations are still 75 or 60 c rated. Does it need a full size neutral? What is the calulated load?
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Old 05-17-2012, 01:02 AM   #16
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First of all, you need to look in chapter 9 of the NEC for the correct size area of conduit.

Then you need to determine the size of the conductors you'll be using, and compare them to the size conduit you have.

Third, you're going to need a lot of lube to pull (2) #3 coppers, (1) #6 copper, and (1) #8 copper equipment grounding conductor.

Fourth, don't forget about your ground rod (required) and the (6) disconnect rule.
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Old 05-17-2012, 12:12 PM   #17
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Well It is only 25 ft and one 90 and it is fed from a 100amp breaker from the main panel so if i an right i shouldn't need a main in this panel
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Old 05-17-2012, 12:58 PM   #18
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Quote:
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Well It is only 25 ft and one 90 and it is fed from a 100amp breaker from the main panel so if i an right i shouldn't need a main in this panel
The issue is if you have more than (6) circuit breakers a "main" circuit breaker must be installed.

NEC 225.33 Maximum Number of Disconnects.
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Old 05-18-2012, 12:12 AM   #19
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Quote:
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The issue is if you have more than (6) circuit breakers a "main" circuit breaker must be installed.

NEC 225.33 Maximum Number of Disconnects.
Not if it's a sub panel like the OP was talking about changing. That only applies to the main service
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Old 05-18-2012, 12:30 AM   #20
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Quote:
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Not if it's a sub panel like the OP was talking about changing. That only applies to the main service
If the sub-panel is in a different structure with over 6 disconnects, you'll need a main disconnect.

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