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Forum topic by Matt posted 04-13-2009 05:28 PM 1258 views 0 times favorited 16 replies Add to Favorites Watch
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Matt

181 posts in 2838 days


04-13-2009 05:28 PM

I’ve got my new subpanel installed (see my blog). I’ve got the inspector coming over this week to finalize everything. I’m just now starting to plan all of my surface mounted conduit. I have a whole lot of 12/3 wire with ground.

Here is my question. Do I need to run a ground wire for all my outlets back to the subpanel or can I just ground the receptacles at the outlets? That would let me stay in code by running 2 wires for each circuit and get 2 circuits inside the 1/2 inch conduits. Everything is going to be in rigid metal conduit. (For now). I would think grounding all the way back to the panel wouldn’t be necessary.

Thanks in advance,

-- Matt - My Websites - http://www.bestinwood.com - Hand Tools :: http://www.workshopgarage.com - Small Shops


16 replies so far

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PurpLev

8523 posts in 3114 days


#1 posted 04-13-2009 05:48 PM

unless you have a ground wire that goes all the way to the panel (which is supposed to be properly grounded) OR have an iron pipe/bar that is grounded properly in the ground next to the outlet, there is no way for you to ground your receptacles. if you mean connecting the receptacle to the outlet metal box? that box is not considered (and is not) ground by code (unless you connected a ground cable to it that is properly grounded on the other side – which brings us back to grounding at the panel, or iron bar/pipe)

If I’m not mistaken, you are also not supposed to run 2 circuits inside 1 conduit by code.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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Matt

181 posts in 2838 days


#2 posted 04-13-2009 06:22 PM

My subpanel is grounded all the way back to the main service panel. Also, if I can’t run more than one circuit in the conduit why do they have ratings for number of wires you can stuff in a single conduit? Up to half a dozen for #14 in a 1/2 inch conduit. 4 for #12.

Thanks Purplev. Why does electricity have to be so confusing? hahaha

-- Matt - My Websites - http://www.bestinwood.com - Hand Tools :: http://www.workshopgarage.com - Small Shops

View sandhill's profile

sandhill

2128 posts in 3390 days


#3 posted 04-13-2009 06:33 PM

Does this help? Even 12/3 you should have a 4Th wire that is tied to the buss and connected to the green hex screw on all receptacles and switches.
http://i116.photobucket.com/albums/o13/Sandhill_01/wireRec.jpg

View Matt's profile

Matt

181 posts in 2838 days


#4 posted 04-13-2009 06:53 PM

Yes, that helps a bunch. By your diagram, it looks like you’re running two hots (red and black) and sharing the neutral (white) and ground? Is that legal? I mean, that’s an option I can do. Only 4 wires in a 1/2 inch conduit.

-- Matt - My Websites - http://www.bestinwood.com - Hand Tools :: http://www.workshopgarage.com - Small Shops

View PurpLev's profile

PurpLev

8523 posts in 3114 days


#5 posted 04-13-2009 07:03 PM

yes, you can share the ground. as long as it IS grounded in the panel.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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Matt

181 posts in 2838 days


#6 posted 04-13-2009 07:08 PM

Thank you! You guys rock!

-- Matt - My Websites - http://www.bestinwood.com - Hand Tools :: http://www.workshopgarage.com - Small Shops

View DaveH's profile

DaveH

400 posts in 3244 days


#7 posted 04-13-2009 08:35 PM

12/3 is normally run for 220v. 2 hots, 1 neutral, 1 ground. I’m not sure if code will allow you to split the neutral for 2 circuits. You can’t use a ground for the neutral. If your conduit and boxes are metal, you can use the conduit for the ground. It’s not legal to run 12/3 or 12/2 wire in conduit. I believe you can only legally use individual wires in conduit. You can run as many circuits as you want in a single run of conduit as long as you do not exceed the capacity of the conduit. I don’t believe you would pass inspection by trying to ground at the outlet. At a minimum you would need to drive a ground rod in the ground at each plug.

Sounds like you better hold off on your wiring until you talk to the inspector or an electrician or get a good book on wiring.

-- DaveH - Boise, Idaho - “How hard can it be? It's only wood!”

View Matt's profile

Matt

181 posts in 2838 days


#8 posted 04-13-2009 08:58 PM

I’ll clear up a few things. Sorry.

I’m going to run #12 on all my 20amp circuits. #10 on any larger circuits. I’m using individual conductors. (No sheathed cables) My conduit is 100% rigid metal 1/2 inch for now. (Thinking about getting some 3/4 for the larger runs to hold more wires). The code I read said only 4 wires for #12 conductors in 1/2 inch metal conduit.

It’s funny. I hired the electrician to install my subpanel but he said nothing about a ground rod. Would the close proximity to my house have anything to do with him not installing one? Now I’m worried. The guy was highly recommended by several folks. In what instances would a subpanel in a detached structure not require a ground rod?

P.S. The feeder from my main panel is buried.

-- Matt - My Websites - http://www.bestinwood.com - Hand Tools :: http://www.workshopgarage.com - Small Shops

View PurpLev's profile

PurpLev

8523 posts in 3114 days


#9 posted 04-13-2009 09:05 PM

I can only assume he grounded it with the main panel ground. best bet ? call him up and verify this. easy, quick and will calm you down.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View TopamaxSurvivor's profile

TopamaxSurvivor

17671 posts in 3141 days


#10 posted 04-13-2009 09:40 PM

Matt,

The National Electric Code requires a ground rod at each seperate building with a subpanel. I believe this requirement just changed with the 2005 or 2008 code. Many jurisdictions can be several years behind in adopting the latest revisions; ie, enforcing them. On the other hand, I have met a lot of electricians who don’t know the code very well and a lot of inspectors who don’t either.

You can put as many conductors as allowed in a conduit until you reach 4 current carrying conductors, then you have to start derating them to 80% of their rated load capacity to allow for heat. The ground is not a current carrying conductor. For example: THWN copper #12 is listed at 35 amps. That is where you start your derating, but in no case do you fuse it for more than 20 amps, except in the case of a dedicated motor circuit. If you run no more than 4 circuits with 2 neutrals in a single conduit, you should be in good shape. That only requires one ground wire if you pull it. I recommend you do even though the conduit is a legal grounding conductor. Remeber the ground is the “brakes” on the system. You wouldn’t drive without brakes, would you?

Box fill is another consideration. As long as you are going from one box to he next, you will probably be fine, but I recommend use 2 1/8” deep 4 square boxes a minimum. I would pull all the conductors which are not bieing connected at a box right on through; they cound as one wire that way insterad of two, plus you have eliminated a possible trouble point. The raised covers you mount your devices in on a 4 square box are required to be grounded in addition to the grounding of the device itself. Good luck.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View johnpoolesc's profile

johnpoolesc

246 posts in 2826 days


#11 posted 04-13-2009 09:58 PM

good advice,, but check the LOCAL codes as well.

-- It's not a sickness, i can stop buying tools anytime.

View sIKE's profile

sIKE

1271 posts in 3220 days


#12 posted 04-13-2009 10:21 PM

Go get this book at the Borg in the electrical section:

Wiring Simplified

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

View sIKE's profile

sIKE

1271 posts in 3220 days


#13 posted 04-13-2009 10:35 PM

Many times 12/3 or even 14/3 is used in 110V applications. Rooms that are pre-wired for ceiling fans normally use /3 type wire. One hot for the light receptacle and one hot for the ceiling fan. My understanding from reading that a sub-panel in a detached building should have its’ own grounding rod that “may be inside or outside the wall, but should reach permanently moist earth.”

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

View johnpoolesc's profile

johnpoolesc

246 posts in 2826 days


#14 posted 04-13-2009 10:51 PM

in sc i had to have a stand alone ground rod. i ran 12/3 to all the 110’s, i did not loops anything because i had a new 200 amp service. inspection was about 20 seconds

-- It's not a sickness, i can stop buying tools anytime.

View TopamaxSurvivor's profile

TopamaxSurvivor

17671 posts in 3141 days


#15 posted 04-14-2009 12:00 AM

johnpoolesc,

Do you feel you got your money’s worth? :-)) They charge good money for permits, lic fees, ect. They should do something for the public, shouldn’t they? I quit doing any residential work 20 yrs ago because I ran into too many homes that were illegally wired waiting for a fire to start. The last knowledgeable person is the responsibile party even if the owner doesn’t want to have it fixed.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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