# grounding a sub panel



## mbidingerres

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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## McClary’s Electrical

mbidingerres said:


> 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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## mbidingerres

just pvc underground, romex in house to main panel


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## McClary’s Electrical

mbidingerres said:


> just pvc underground, romex in house to main panel


 
Unless you're still on '05 code, you need it then.


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## mbidingerres

which means then I have to increase the conduit from 1 in to 1-1/4 in


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## McClary’s Electrical

mbidingerres said:


> 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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## jza

You can increase it to 1 inch EMT and not have to run a grounding conductor inside the pipe, lol.


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## mbidingerres

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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## mbidingerres

I am running copper # 2


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## Awg-Dawg

Id make it a 60a if I could.

99% of the time even the 60a is overkill.


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## mbidingerres

Customer needs a 100 amp


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## Awg-Dawg

mbidingerres said:


> Customer needs a 100 amp


 
http://www.electrician2.com/calculators/rf_calculator.html

Looks like your conductors work if you use #3 cu


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## RIVETER

mbidingerres said:


> 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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## fanelle

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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## mbednarik

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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## Magnettica

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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## mbidingerres

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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## Magnettica

mbidingerres said:


> 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. :thumbsup:


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## ElectricJoeNJ

Magnettica said:


> 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. :thumbsup:


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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## wendon

ElectricJoeNJ said:


> 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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## Shockdoc

You might be able to pull two #2s, one #4 and a #8 ground tightly in 1"


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## Toto

Yes to your original question. All grounds go back to the main panel. If I'm not mistaken all grounds must be connected to each other in typical residential system.


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## electricmanscott

YOu can fit 3# 3cu and 1 #8cu in 1" pvc. :thumbsup:


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## electricmanscott

Toto said:


> Yes to your original question. All grounds go back to the main panel. If I'm not mistaken all grounds must be connected to each other in typical residential system.


Not sure if you mean at the separate structure but grounding and grounded are not bonded to together at that point.


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## sparkie2010

Ok if your installing a sub-panel that is being fed from the main, then yes you would need a grounding conductor.

Do a full load calculation to make sure your service can handle the additional load.


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## Magnettica

Shockdoc said:


> You might be able to pull two #2s, one #4 and a #8 ground tightly in 1"


why are u gonna run #2 cu if you're looking for 100 amps? 

75º column, THHN/THWN, 100 amps.


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