Wiring with MC and metal boxes questions

[ACDNate]

My steel building is up and now its time for electrical

http://www.garagejournal.com/forum/showthread.php?t=252685

I initially planned to sub out the electrical. My foundation costs ended up going substantially over budget so I'm looking to save some cost by doing the electrical myself. I've done residential wiring before but not with mc, metal boxes and not in a steel building so I have some questions.

I will be using 12/2 MC cable that includes an insulated ground in the cable. 14/2 would certainly work but the differnce in cost for a 250ft roll is $8, so it's not worth having 2 different cables on hand to me.

On to the specific questions:

1. Boxes will be attached to girters in the building. Is there a particular type of screw I should be using to attach? I have a metric **** ton of screws left over from the sheating, are those ok?

2. I see there are boxes with brackets and those w/o. I can't figure out how the brackets would be beneficial in this case. Am I not seeing this clearly?

3. Looking at the metal boxes I notice they have a threaded spot to tie in a ground to the box. With the wire already having a ground, should I also tie a ground to the box?

4. Looking at MC/punch connectors I found some snap in connectors, and the clamp type connectors. I've read that the clamp types, if you aren't careful can puncture the MC. Whats the preferred connector?

5. Stumbled across a press fit wire connector by Ideal. One of those things where you say "why didn't I ever think of that". Anyway, sure they're a bit more expensive than nuts but the space saved looks to be impressive. Anyone have any experience with these?

6. I understand that in addition to the ground from the panel, I need to ground the building itself as well. Same 8' grounding rod and lug connectors? How/where should I attach to the building?

7. My outlets must be GFCI protected as it's an accessory building. How many down line outlets can one 15amp GFCI protect? Is there a limit to run length from the GFCI?

Thanks for any advice/help that can be provided.

 

[aka Larry]

I'm sure the electrical gurus will chime in, but I thought MC could only go 4' unsupported, which is why I went with EMT in my shop.

Edit: Just looked at your pics and I see you have a way to support the MC as required. Carry on!

 

[ACDNate]

I'm sure the electrical gurus will chime in, but I thought MC could only go 4' unsupported, which is why I went with EMT in my shop.

Edit: Just looked at your pics and I see you have a way to support the MC as required. Carry on!

Most of my mc will be running along the girts, purlins and along the main structure for vertical runs. Shouldn't be an issue like you said.

 

[ACDNate]

Here's another question I've thought of while replying to Larry's post.

If I run my wire along the girters behind the up rising part to hide it, can i penetrate the girts to allow wire to run the box from behind? Or is that a bad idea?

 

[Charles (in GA)]

The only advise I can give is to use no boxes smaller than a 4x4 that is 2-1/8 deep. Run EMT and pull THHN wires. Looks 1000 times better than sagging MC running here and there. Self drilling hex head screws work fine for mounting boxes to wall girts. I ran conduit along the top of girts, to junction boxes and dropped down to other boxes where the receptacles are. Thus, all of my receptacles are pigtailed off the main runs. Down each wall I ran a conduit with two circuits in it, and each box has two receptacles, on on one circuit and one on the other circuit.

Once you get going, bending conduit is fairly easy, yes, you waste a section or two here or there, but you usually can salvage some of it for something.

You will notice in some of my pics, I have a junction box on the top of the girt and it appears to have another box on top of it. I got stupid and thought I could use shallow 4x4 boxes for the junctions. While it did work, and I think the fill was even legal, it was packed, and I opted to add an extension box on top and then a cover, and pull the wires up some to make some room between the wirenuts and wire groups. Had I used tall boxes, I would not have done this. I now use tall boxes for everything.

Charles

Charles.

 

[ACDNate]

I will definitely be using the deep boxes across the board. Not a significant cost difference and will be easier to work with.

I just noticed looking at your pics, my girders are installed the opposite direction.

 

[Crimson558]

If it is gonna be where something could hit it as it is running down a girter then I would def run emt up the girter and into a 4 square box and splice the MC and wires going into EMT there. Not only would it look better but will save you the hassle of replacing damaged MC later, and besides EMT is very affordable.

As far as connectors I have never been a fan of the clamp on connectors and main reason is they are a pain to get off if you ever need to. They make a connector that has a set screw that you just tighten down onto MC and I have always preferred those. Also the connectors should come with some red sleeves that you will slide between the cable and the MC jacket prior to putting the connector on.

If you are gonna be running primarily 120V for outlets or whatever then a hex/pan head self tapping screw will be fine. If you are gonna have any 480V outlets I'd probably tap the girter and use a bolt.

AS far as grounding the box if you have some extra wire then it can't hurt. But not always required depending on your local code.

Not sure on the limit on outlets protected by a GFCI. Something worth looking at if you are wanting your outlets protected by a GFCI is installing a GFCI breaker. That just depends on your preference, but i am sure someone could answer that question or there is always Mr. Google haha

 

[ACDNate]

If it is gonna be where something could hit it as it is running down a girter then I would def run emt up the girter and into a 4 square box and splice the MC and wires going into EMT there. Not only would it look better but will save you the hassle of replacing damaged MC later, and besides EMT is very affordable.

As far as connectors I have never been a fan of the clamp on connectors and main reason is they are a pain to get off if you ever need to. They make a connector that has a set screw that you just tighten down onto MC and I have always preferred those. Also the connectors should come with some red sleeves that you will slide between the cable and the MC jacket prior to putting the connector on.

If you are gonna be running primarily 120V for outlets or whatever then a hex/pan head self tapping screw will be fine. If you are gonna have any 480V outlets I'd probably tap the girter and use a bolt.

AS far as grounding the box if you have some extra wire then it can't hurt. But not always required depending on your local code.

Not sure on the limit on outlets protected by a GFCI. Something worth looking at if you are wanting your outlets protected by a GFCI is installing a GFCI breaker. That just depends on your preference, but i am sure someone could answer that question or there is always Mr. Google haha

The idea was to run the MC behind the girder Z. The way my girders are put up the up standing side is on the inside. Very little of the MC will be exposed to contact.

No 480v all 120 and 240.

Yeah I believe I will likely use a ground jumper to the box. Better to have extra ground points I figure.

 

[Aceman]

Are you planning on sheeting the inside walls at all? MC cable can't be installed where it's subject to physical damage. Running it on girts at 4' off the floor is going to be the inspectors call on whether he thinks it is or not. Around here we consider anything over 8' safe from damage. But, since you're running behind the face of the girt even at the 4' level, you might be alright. I would strongly advise you asking first before doing it though.

1. Boxes will be attached to girters in the building. Is there a particular type of screw I should be using to attach? I have a metric **** ton of screws left over from the sheating, are those ok?

We usually use self drilling panheads 10x3/4, but it's not a requirement.

https://www.platt.com/platt-electri...ltiple/1034SQPTKSJAR/product.aspx?zpid=427858

2. I see there are boxes with brackets and those w/o. I can't figure out how the brackets would be beneficial in this case. Am I not seeing this clearly?

I would use regular 4 square deep boxes, no bracket. I would drill a 1 1/8 or 1 3/8 hole through the face of the girt. Then I would use these duplex connectors to go in and back out of the box with your circuit.

https://www.platt.com/platt-electri...rs/Arlington/4040AST/product.aspx?zpid=511683

For the most part all we use are these insulated pop in connectors. We never use the set screw or clamp type except for the certain situations where we need a threaded connector for hub, etc.

3. Looking at the metal boxes I notice they have a threaded spot to tie in a ground to the box. With the wire already having a ground, should I also tie a ground to the box?

Install a ground screw in the box. When you strip the outer sheath off the mc cable make sure you have at least a foot of wire sticking out. Take the ground wire from one of the cables, put your stripper on it as close to the connector as possible. Slide the insulation down the cable 2-3 inches. Take the stripped portion of the wire next to the connector and loop it around the ground screw and tighten it down. Now take ALL your wire and cut them to length, I shoot for 5-6 inches from the FACE of the box. Use some scrap wire and make some 12" long pigtails. Strip all your wires(black, white, and green) and use your linesmans to twist them all together including the pigtails. Wirenut them together, push them back in the box, with your 3 pigtails sticking out. Again cut these wires 5-6 inches from the face of the box. These will land on your receptacle when you're ready to install them.

4. Looking at MC/punch connectors I found some snap in connectors, and the clamp type connectors. I've read that the clamp types, if you aren't careful can puncture the MC. Whats the preferred connector?

See above.

5. Stumbled across a press fit wire connector by Ideal. One of those things where you say "why didn't I ever think of that". Anyway, sure they're a bit more expensive than nuts but the space saved looks to be impressive. Anyone have any experience with these?

We use ideal tans and reds exclusively for MC. We do use those Ideal ground crimps on Romex though, where the ground wire is bare.

6. I understand that in addition to the ground from the panel, I need to ground the building itself as well. Same 8' grounding rod and lug connectors? How/where should I attach to the building?

If this building is fed from another panel, isolate the neutral from the panel. You will also need a ground bar attached to the panel. Take the #4 bare copper run from one 8' ground rod to the other 8' ground rod at least 6' away from the first and on into your panel on the ground bar.

To ground the building you can take a second #4 bare to the closest metal surface you can hit. Girt, beam, post, it doesn't matter. Drill a hole, grind the paint off under the lug and bolt the lug on.

7. My outlets must be GFCI protected as it's an accessory building. How many down line outlets can one 15amp GFCI protect? Is there a limit to run length from the GFCI?

I always install GFCI receps at every location. I don't want my customers working at the far end of a building tripping a GFCI at the other end because I line-loaded the entire circuit through one GFCI next to the panel.

Also, MC cable must be strapped every 6' or less and within 12" of boxes.

 

[ACDNate]

Are you planning on sheeting the inside walls at all? MC cable can't be installed where it's subject to physical damage. Running it on girts at 4' off the floor is going to be the inspectors call on whether he thinks it is or not. Around here we consider anything over 8' safe from damage. But, since you're running behind the face of the girt even at the 4' level, you might be alright. I would strongly advise you asking first before doing it though.

I'm not planning on sheathing at this point. Good point I'll check on that with the inspector.



We usually use self drilling panheads 10x3/4, but it's not a requirement.

https://www.platt.com/platt-electri...ltiple/1034SQPTKSJAR/product.aspx?zpid=427858



I would use regular 4 square deep boxes, no bracket. I would drill a 1 1/8 or 1 3/8 hole through the face of the girt. Then I would use these duplex connectors to go in and back out of the box with your circuit.

https://www.platt.com/platt-electri...rs/Arlington/4040AST/product.aspx?zpid=511683

Ah excellent. Keeping the wire behind the girt all the way will look much better. Hadn't noticed that style of connector. That will beat multiple punch outs and connectors.

For the most part all we use are these insulated pop in connectors. We never use the set screw or clamp type except for the certain situations where we need a threaded connector for hub, etc.



Install a ground screw in the box. When you strip the outer sheath off the mc cable make sure you have at least a foot of wire sticking out. Take the ground wire from one of the cables, put your stripper on it as close to the connector as possible. Slide the insulation down the cable 2-3 inches. Take the stripped portion of the wire next to the connector and loop it around the ground screw and tighten it down. Now take ALL your wire and cut them to length, I shoot for 5-6 inches from the FACE of the box. Use some scrap wire and make some 12" long pigtails. Strip all your wires(black, white, and green) and use your linesmans to twist them all together including the pigtails. Wirenut them together, push them back in the box, with your 3 pigtails sticking out. Again cut these wires 5-6 inches from the face of the box. These will land on your receptacle when you're ready to install them.



See above.



We use ideal tans and reds exclusively for MC. We do use those Ideal ground crimps on Romex though, where the ground wire is bare.



If this building is fed from another panel, isolate the neutral from the panel. You will also need a ground bar attached to the panel. Take the #4 bare copper run from one 8' ground rod to the other 8' ground rod at least 6' away from the first and on into your panel on the ground bar.

To ground the building you can take a second #4 bare to the closest metal surface you can hit. Girt, beam, post, it doesn't matter. Drill a hole, grind the paint off under the lug and bolt the lug on.

Building will have it's own 200amp service. Ground it back to the panel or direct to the rod?



I always install GFCI receps at every location. I don't want my customers working at the far end of a building tripping a GFCI at the other end because I line-loaded the entire circuit through one GFCI next to the panel.

The cost difference is pretty dramatic. under a $1 vs $10+ per outlet. If I'm understanding it correctly the GFCI breaker and standard outlets would meet the requirement? I'm looking at 4 circuits with multiple outlets, would be cheaper to spend $30 extra on a breaker as opposed to $10 extra on 6 outlets.



Also, MC cable must be strapped every 6' or less and within 12" of boxes.

See replies above. I appreciate all the help.

 

[Charles (in GA)]

The cost difference is pretty dramatic. under a $1 vs $10+ per outlet. If I'm understanding it correctly the GFCI breaker and standard outlets would meet the requirement? I'm looking at 4 circuits with multiple outlets, would be cheaper to spend $30 extra on a breaker as opposed to $10 extra on 6 outlets.

If you are buying receptacles that cost less than a dollar each, you are buying pure junk. Even with discounts and quantity, I'd expect to pay $2+ for decent receptacles, if not more. I have a bunch of Hubbell spec grade backwire receptacles I bought at the flea market, and I paid a dollar each there! I bought the Hubbells after my shop was wired. Wished I had found them years ago, I spent about $4 each on Leviton commercial grade backwire for the shop. If you are wrapping wire around screws, you are wasting time. Backwire works much better, insert wire, tighten screw.

Charles

 

[ACDNate]

Garden variety Cooper Wiring 15amp outlets with he back slide in and clamp run around a buck when bought in 10 or 25 packs at HD/lowes.

Electrical Supply house has them for less in larger quantities.

Maybe pricing is regional?

 

[Charles (in GA)]

That would be a new one one me. I've searched and searched, in person and online, and cannot come close to $2 each, let alone $1 for commercial or spec grade devices with backwiring. I can find cheap builder grade **** for close to a $1 each or less, but not the good stuff. And of course, on residential property, it is supposed to be tamper resistant also.

Charles

 

[ACDNate]

That would be a new one one me. I've searched and searched, in person and online, and cannot come close to $2 each, let alone $1 for commercial or spec grade devices with backwiring. I can find cheap builder grade **** for close to a $1 each or less, but not the good stuff. And of course, on residential property, it is supposed to be tamper resistant also.

Charles

Thankfully tamper resistant hasn't been adopted in my area (yet). I'm not a fan...

 

[Aquamoose]

Just to warn you, Canadian code allows for the ground wire to be semi-looped at the ground screw in each box before joining to the outlets, etc. US codes don't permit that.


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[ACDNate]

Just to warn you, Canadian code allows for the ground wire to be semi-looped at the ground screw in each box before joining to the outlets, etc. US codes don't permit that.


Sent from my iPhone using Tapatalk

"semi-looped"???

 

[Aquamoose]

As in one continuous ground wire that loops around the Vic's ground terminal before feeding to the out let's ground terminal.


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[Charles (in GA)]

Just to warn you, Canadian code allows for the ground wire to be semi-looped at the ground screw in each box before joining to the outlets, etc. US codes don't permit that.


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Which is what Aceman is describing in his post above. It is quite legal in the US, nothing in the NEC to prevent it.

Install a ground screw in the box. When you strip the outer sheath off the mc cable make sure you have at least a foot of wire sticking out. Take the ground wire from one of the cables, put your stripper on it as close to the connector as possible. Slide the insulation down the cable 2-3 inches. Take the stripped portion of the wire next to the connector and loop it around the ground screw and tighten it down. Now take ALL your wire and cut them to length, I shoot for 5-6 inches from the FACE of the box. Use some scrap wire and make some 12" long pigtails. Strip all your wires(black, white, and green) and use your linesmans to twist them all together including the pigtails. Wirenut them together, push them back in the box, with your 3 pigtails sticking out. Again cut these wires 5-6 inches from the face of the box. These will land on your receptacle when you're ready to install them.

 

[Aquamoose]

I was quoted by a friend who brought out his massive 3 ring binder. He was an electrician for 30+ years. It was one of those "odd" rules but its there in black & white.


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[ACDNate]

Ah gotcha

 

[Aceman]

I was quoted by a friend who brought out his massive 3 ring binder. He was an electrician for 30+ years. It was one of those "odd" rules but its there in black & white.


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There is no such code article, it IS perfectly legal. I haven't been an electrician for 30 years like your friend, but I do know my way around a code book and use it on a regular basis.

If your friend is around to ask, I'd be interested to know which code article he's basing that statement on.

 

[Beemer533]

The only advise I can give is to use no boxes smaller than a 4x4 that is 2-1/8 deep. Run EMT and pull THHN wires. Looks 1000 times better than sagging MC running here and there. Self drilling hex head screws work fine for mounting boxes to wall girts. I ran conduit along the top of girts, to junction boxes and dropped down to other boxes where the receptacles are. Thus, all of my receptacles are pigtailed off the main runs. Down each wall I ran a conduit with two circuits in it, and each box has two receptacles, on on one circuit and one on the other circuit.

Once you get going, bending conduit is fairly easy, yes, you waste a section or two here or there, but you usually can salvage some of it for something.

You will notice in some of my pics, I have a junction box on the top of the girt and it appears to have another box on top of it. I got stupid and thought I could use shallow 4x4 boxes for the junctions. While it did work, and I think the fill was even legal, it was packed, and I opted to add an extension box on top and then a cover, and pull the wires up some to make some room between the wirenuts and wire groups. Had I used tall boxes, I would not have done this. I now use tall boxes for everything.

Charles

Charles.

Some nice looking work!

I'm curious as why you seem to have a cover on one of the outlets in each picture? Unless I am seeing things!

 

[CoopVA]

There is no such code article, it IS perfectly legal. I haven't been an electrician for 30 years like your friend, but I do know my way around a code book and use it on a regular basis.



If your friend is around to ask, I'd be interested to know which code article he's basing that statement on.

I agree... Don't know of a code issue with doing it that way. I personally prefer to use a ground tail on the box though... Been an Electrician for over 25 years....


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[Charles (in GA)]

Some nice looking work!

I'm curious as why you seem to have a cover on one of the outlets in each picture? Unless I am seeing things!

Thank you. The box in the pic has covers on all four receptacles (simple child safe covers). One is opaque, the other three are translucent. I have covers on virtually all of the unused or very infrequently used receptacles. The reason is dirt daubers/mud wasps. They love to build in the ground pin holes. I plug my extension cords together and my air hoses too. Still, they seem to build in the craziest places. The open screw holes in the corners of the boxe covers are apparently a little too small for them, as they never try to go thru those (look for the mud trails).

Charles

 

[ACDNate]

Thank you. The box in the pic has covers on all four receptacles (simple child safe covers). One is opaque, the other three are translucent. I have covers on virtually all of the unused or very infrequently used receptacles. The reason is dirt daubers/mud wasps. They love to build in the ground pin holes. I plug my extension cords together and my air hoses too. Still, they seem to build in the craziest places. The open screw holes in the corners of the boxe covers are apparently a little too small for them, as they never try to go thru those (look for the mud trails).

Charles

Damn things are like that here as well. Take over the place if you let them.

 

[Norcal]

Mud daubers & leaf cutter bees are a pain, but we all know that.

 

[Charles (in GA)]

My steel building is not so tight as to keep them out. I need to install better seals in some places and at the top of the large garage door install a seal where then never has been one. But even at that, in the summer I open the building all day on days when I am mostly at home doing things. It just gets too hot otherwise.

They are persistent buggers. I heard one building under the step of an aluminum ladder one day. I carried the ladder out and hosed it off. within an hour it was back building again in the same place. This went on for several times that day before it gave up and went elsewhere. They love the recessed screw holes of plastic housing tools such as my leaf blower.

Charles

 

[Beemer533]

Thank you. The box in the pic has covers on all four receptacles (simple child safe covers). One is opaque, the other three are translucent. I have covers on virtually all of the unused or very infrequently used receptacles. The reason is dirt daubers/mud wasps. They love to build in the ground pin holes. I plug my extension cords together and my air hoses too. Still, they seem to build in the craziest places. The open screw holes in the corners of the boxe covers are apparently a little too small for them, as they never try to go thru those (look for the mud trails).

Charles

Ahh, makes sense!

I guess I should be grateful I don't need to worry about those things up here!

 

[ACDNate]

I find them all over the brick mortar on the house for some reason. Seems like an odd place to camp out but they seem to like it

 

[ACDNate]

Got the building wired up this weekend. Took a buddy (apprentice electrician) and myself half a day Friday, full day Saturday and about 2 hrs this morning to get everything up and done.

MC worked out pretty well. The girts/purlins hide it well for the most part.

My hands are absolutely thrashed. More cuts and scrapes than I can count. I'm wore out like nobody's business. Kudos to those of you who do this kind of work 5 days a week.

 

[bmxer883]

The only advise I can give is to use no boxes smaller than a 4x4 that is 2-1/8 deep. Run EMT and pull THHN wires. Looks 1000 times better than sagging MC running here and there. Self drilling hex head screws work fine for mounting boxes to wall girts. I ran conduit along the top of girts, to junction boxes and dropped down to other boxes where the receptacles are. Thus, all of my receptacles are pigtailed off the main runs. Down each wall I ran a conduit with two circuits in it, and each box has two receptacles, on on one circuit and one on the other circuit.

Once you get going, bending conduit is fairly easy, yes, you waste a section or two here or there, but you usually can salvage some of it for something.

You will notice in some of my pics, I have a junction box on the top of the girt and it appears to have another box on top of it. I got stupid and thought I could use shallow 4x4 boxes for the junctions. While it did work, and I think the fill was even legal, it was packed, and I opted to add an extension box on top and then a cover, and pull the wires up some to make some room between the wirenuts and wire groups. Had I used tall boxes, I would not have done this. I now use tall boxes for everything.

Charles

Charles.

Where did you get your switch box that's 5 or 6 gang ? And cover

 

[wyliesdiesels]

this thread is nearly 10yrs old