Help with wiring new shed

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Old 02-10-20, 09:40 AM
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Help with wiring new shed

I'll be helping a family member wire his new garage/shop, which is metal frame construction and will be unfinished (no insulation or drywall) and unconditioned. The plan is to use metal boxes and MC cable. My experience has been with wood frame construction, Romex, and plastic boxes. How much different is it to run MC with metal boxes? A couple unknowns for me are what are best type of boxes to use and how best to secure/strap the MC cable to the metal studs. I'm assuming in addition to clamping the MC inside the boxes (using the integrated clamp) that I'll also need to bond the ground to the box using a green screw, correct? The garage/shop will not be insulated or finished (no drywall), so I want to be sure everything is nice and secure. My experience with metal studs is in residential construction and I remember hating them because they twist and the boxes flop around. However, the walls of this garage/shop are nice and rigid so I don't anticipate this being an issue.

The garage is about 1000 sq ft (maybe slightly more) and I plan on using 12/2 MC. All outlets will be GFCI protected. How many 20A circuits should there be? Does it make more sense to use GFCI breakers or GFCI outlet, or does it simply come down to cost?
 
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Old 02-10-20, 10:44 AM
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Definitely buy a MC cable cutter. There are tricks for using a hacksaw or diagonal cutters, but this nifty little tool will save you a lot of time.

But otherwise, it's all about the same to install. There are special clips that can snap over the steel studs and hold the cable in place. And you need to use those little red bushings at the end of each cable before it gets fed into the box.
Also remember that MC cable still needs to be protected from damage. So this may include using EMT for sleeving where it could be damaged.

As for number of circuits, you'll need to consider how many people will be working together and using what kind of tools. For a one-man shop, 1 or 2 circuits is plenty since how many tools can you possibly use at once. But for multiple people in the shop, need to start thinking about areas and who's going to be using what.
For that size shop, you'll probably also want to consider larger tools too. Welder, table saw, dust collector, compresor, etc... they all could use their own circuits, and sometimes more than 20A.

GFI protection is fine either way. I like the receptacle GFIs as they are less expensive and quicker to see when one trips. But there's something to be said about keeping all the breakers (and protection) in one place.
 
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Old 02-10-20, 11:05 AM
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Great. Thanks for the tips. What about strapping vertical runs of MC along the metal studs, horizontal runs along rafters, perpendicular to rafters, etc? And what are the best type of self-tapping screws for securing boxes, straps, etc?
 
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Old 02-11-20, 02:56 AM
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Myself I go overboard on installing outlets just because it is a one time cost. Even then, what is a 70 cent outlet and some extra wire compared to being 2 feet short with an electrical tool when you want to do something? In my opinion, just not having to fetch an extension cord is worth putting in extra outlets.

On shops, I put an outlet in every 4 feet.
My house has them every 6 feet.
My barn has them every 8 feet.

I also install 20 amp outlets on shops, GFCI's on the first outlet in the run, and never put more than 6 outlets on a circuit,
 
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Old 02-12-20, 02:24 PM
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Myself I go overboard on installing outlets just because it is a one time cost. Even then, what is a 70 cent outlet and some extra wire compared to being 2 feet short with an electrical tool when you want to do something? In my opinion, just not having to fetch an extension cord is worth putting in extra outlets.

On shops, I put an outlet in every 4 feet.
My house has them every 6 feet.
My barn has them every 8 feet.

I also install 20 amp outlets on shops, GFCI's on the first outlet in the run, and never put more than 6 outlets on a circuit,
That's smart. Thanks.

What about strapping the MC to metal studs, rafters, etc? Are bushings required where MC passes through holes in the studs?
 
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Old 02-12-20, 04:42 PM
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I'm assuming in addition to clamping the MC inside the boxes
I would recommend using 1900 (4x4) boxes and with mud rings or industrial covers. Do not use the boxes with internal clamps. You can get boxes with brackets welded on the side for easy attachment ( https://www.homedepot.com/p/Steel-Ci...-25R/202592840 )or use other brackets like a B-line BB4 or BB4-6

There many connectors available for MC cable. I typically use Arlington fittings so I know their numbers. For singles, I use 4010AST connectors. Doubles I use 404010AST. These are designed for MCAP cable which is similar to the MC with a ground wire but has a full-sized bonding wire in contact with the cable armor so the cable armor is ab approved grounding path. This saves time and wire count in the boxes. Other connectors are ones that use a locknut.

When passing MC cable through metal studs it is not required to install bushings. The same rules apply as with NM cable keeping the cable 1 1/4" away from the stud face. Strapping can be as simple as a 3/8" single hole strap. https://www.homedepot.com/p/Halex-3-...-206126680-_-N or you can use other straps like Colorado Jim's https://www.homedepot.com/p/CADDY-9-...3A%7B1%7D%3Anf
 
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Old 02-13-20, 11:52 AM
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I would recommend using 1900 (4x4) boxes and with mud rings or industrial covers. Do not use the boxes with internal clamps. You can get boxes with brackets welded on the side for easy attachment ( https://www.homedepot.com/p/Steel-Ci...-25R/202592840 )or use other brackets like a B-line BB4 or BB4-6

There many connectors available for MC cable. I typically use Arlington fittings so I know their numbers. For singles, I use 4010AST connectors. Doubles I use 404010AST. These are designed for MCAP cable which is similar to the MC with a ground wire but has a full-sized bonding wire in contact with the cable armor so the cable armor is ab approved grounding path. This saves time and wire count in the boxes. Other connectors are ones that use a locknut.

When passing MC cable through metal studs it is not required to install bushings. The same rules apply as with NM cable keeping the cable 1 1/4" away from the stud face. Strapping can be as simple as a 3/8" single hole strap. https://www.homedepot.com/p/Halex-3-...-206126680-_-N or you can use other straps like Colorado Jim's https://www.homedepot.com/p/CADDY-9-...3A%7B1%7D%3Anf
Awesome. Just the info I was looking for. Thank you.

Why do you use the 404010AST for 2-gang boxes? So if there are more cables than knockouts you don't have to come in through both the top and bottom of the box?

Are you supposed to insert those red bushings inside the end of the armor termination to prevent chaffing?

Do I use these for mounting the devices? Then regular wall plates to cover them? Walls will not be finished, so I want it to look nice.
https://www.homedepot.com/p/Steel-Ci...-5-8/207172963

Reminder that the walls will not be finished. Will the type of boxes you recommend be nice and sturdy without any wall covering to aid in keeping them in place?

If I use MC cable without the bonded armor, I'd have to bond the ground conductor to the box using a green screw, correct?
 

Last edited by mossman; 02-13-20 at 12:42 PM.
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Old 02-13-20, 12:13 PM
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I used to order out Jiffy 125 one hole straps for small MC cables. Jiffy 105C copper plated one hole straps are ideal for a Grounding Electrode Conductor.

https://www.minerallac.com/products/...e-hole-straps/
 
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Old 02-13-20, 03:25 PM
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Why do you use the 404010AST for 2-gang boxes?
That is for two cables into a single 1/2" KO. The 4010AST are for one cable in on 1/2" KO. You don't need to use them if you have enough KO's available. Just giving options.

Are you supposed to insert those red bushings inside the end of the armor termination to prevent chaffing?
MC you are not required to use red bushings. You can use them if you want.

Then regular wall plates to cover them? Walls will not be finished, so I want it to look nice.
If it is all going to be exposed I would recommend industrial covers. https://www.homedepot.com/p/4-in-Squ...4402/204609726 or https://www.homedepot.com/p/4-in-Squ...4422/204609728 or https://www.homedepot.com/p/4-in-Squ...4404/204609713 etc.

type of boxes you recommend be nice and sturdy without any wall covering to aid in keeping them in place?
The ones I posted earlier. https://www.homedepot.com/p/Steel-Ci...knQKmU5Tyl4Rg0 There are also brackets that span between two studs.

If I use MC cable without the bonded armor, I'd have to bond the ground conductor to the box using a green screw, correct?
Yes.

 

Last edited by Tolyn Ironhand; 02-14-20 at 04:22 PM.
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Old 02-13-20, 08:38 PM
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Got it. Thanks again! By the way, stud spacing is 4ft O.C.
 
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