Junction Box Grounding with 6AWG Splice

kevin1900July 2, 2013

I am running power to a barn from the service panel in the garage. It will be a 40-amp service.

I will be running copper wire to a junction box inside the garage switching to aluminum.

An electrician at the supply house pointed me to the clear taps shown in the picture to splice the aluminum to copper.

My question is now I have to ground the steel junction box and how to do it.

Maybe I should return it and get a plastic box (it's 8X8) if there is such a thing.

I'm familiar with crimping on a pigtail with a ferrule with 10-14 AWG.

Must the grounding wire be the same size as the feed wires, correct? In this case 6AWG.

Bottom line what materials and techniques should I use. Regarding the tap in the picture, is it permitted to put two wires under one screw.


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Ron Natalie

The ground wire doesn't need to be the same size as the feeder wires. You can use 10 Cu or 8 Al.

You have to make listed connections to the box following the instructions. I can almost guarantee that the connector pictured (I have no idea what it is given the ugly photo) will not allow two wires to be crammed in one terminal. Companies do make three way connectors that are approved for aluminum and copper.

You do have a grounding system going in at the barn right?

    Bookmark   July 2, 2013 at 10:53AM
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Thank-you for the response. There's nothing wrong with the photo, it's just blown up too large. If you do a search on "electrical clear taps" you will find many examples of this connector type. Maybe those photos will help. They do have them with more taps, as you say, but I'm not sure that's the solution.

The junction box does not have any instructions. It is a plain steel box with a cover, some mounting holes and a single threaded hole for a 10-32 screw. One of my questions is whether I would use that small a screw to bond the grounding pigtail to the box.

On the other end I need to bond the pigtail to the grounding wire. In this jurisdiction grounding connections must be non-reversible. On 10-14 gauge we crimp a ferrule. I don't think a screw down connection is allowed.

Thank-you for the information on the wire size. I didn't think it had to be the same size, I'm just saying that I only know what materials and techniques to use for smaller wire. The principles are the same.

I don't know what you mean by "grounding system".

What I'm thinking is drilling a 17/64 hole in the box, put a 1/4-20 bolt through the hole, use one nut to attach it to the box to make a stud, put a loop in the wire and clamp it to the stud between two washers, then run the end into the clear tap.



    Bookmark   July 2, 2013 at 5:20PM
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Ron Natalie

As I stated, Clear Tap/Unitap (which seem to be the people you are lifting the tiny pictures from) make 3 way connectors. If you were planning to use one to splice the ground I don't see why you can't use a 3 terminal one to pigtail the box ground. I don't know your local codes (we follow the NEC pretty slavishly in the two states I work in), are you sure it applies to feeders? I can understand doing a permanent connection on a branch circuit. A simple ferule is illegal for al/cu connections. The UNITAPs aren't reversible anyhow it would appear.

A grounding system: ground rods etc...

    Bookmark   July 2, 2013 at 6:54PM
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I"m not an electrician, nor do I play one on TV.

Since this is a building away from the house (detached barn), it requires its own ground. You will need to drive a ground rod in the ground near where the box is located and attach your ground wire there. IIRC, you will not need to run a ground from the house. You will keep the ground and neutral wire separate in the box.

I think.

    Bookmark   July 3, 2013 at 1:40AM
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Sorry for misinformation. You DO need to run a ground from the main to the subpanel.

    Bookmark   July 3, 2013 at 2:00AM
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Ron Natalie

You most likely need TWO ground rods and as weed has realized, in the later codes you always need to run a ground with the feeder (it used to be you could skip it if there were no other metallic paths between the structures).

Grounding and bonding is a pretty complicated but essential to safety issue (so much so that our trade schools offer a course completely dedicated to that issue when you want to be come electricians).

    Bookmark   July 3, 2013 at 9:43AM
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ronnatalie - I will go back by the supply house and check into a 3-way. I think you're right - it would not seem to apply to feeders. BTW if I wasn't clear, I would bond on the CU side so my ferrule example wasn't entirely out of line.

On the grounding system - I'm running four conductors to the outbuilding, so it seems like my electrical grounding needs are met. Are we talking about installing a grounding system *instead* or *in addition* ?

I am attaching a drawing for clarity.


    Bookmark   July 3, 2013 at 10:03AM
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Ron Natalie

You need a grounding system at each structure. There is an exception for a building with only one branch circuit in it, but your example does NOT qualify. Typically that's two ground rods (other issues involve whether there is water piping, etc... within the structure as well).

I presume the stuff you're running into the conduit is individual conductors? CPVC? Are we running listed conduit or plumbing pipe?

    Bookmark   July 3, 2013 at 10:57AM
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Thanks, good information on the grounding rods. I'll include that.

Yes, individual conductors in the conduit. Which will be listed PVC conduit

    Bookmark   July 3, 2013 at 1:43PM
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