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Steve Roxberg
01-15-2008, 2:16 PM
I am going to rewire a large portion of my shop and have some questions.

My shop is in the basement and the subpanel is in the same room. The existing outlets are wired by running romex along the floor joists and then down into conduit to the actual wall boxes.

I am planning on running conduit horizonitally around the room about about 54" high and having boxes about every four feet.

Can or should I run two seperate 20amp circuits through the conduit so I can alternate which circuit is being loaded. Meaning I would alternate every other outlet to a different ciruit so that a vacuum and a drill plugged into two seperate outlets would be on different circuits?


If I run two seperate 20amp circuits Can I share the neutral or ground and run two hots? Or would I needt to run two hots, two neutrals, and two grounds?

Should I run 1/2" or 3"4 conduit?

Jim Becker
01-15-2008, 2:24 PM
You can run conductors for more than one circuit in a single conduit as long as it's sized appropriately. I can't answer the sharing question with any respect to code, but personally, I wouldn't.

Jason Beam
01-15-2008, 2:25 PM
Whether or not you should is up to you and your needs. I like the idea, myself. And I think 12/3 is perfect for what you want to do. I'm unaware of any codes that require you to run all new romex for each circuit.

Eric Haycraft
01-15-2008, 2:48 PM
I can't answer if using 12/3 meets code or not, but it will work. The two hots must be 180 degrees opposite of each other, otherwise you can easily fry the common wire..start a fire, etc. From a safety standpoint, you may want to stick with multiple wires..much easier to identify what is connected to what breaker and if someone accidentally moves a breaker in the box you don't risk a fire.

What I did was to have the top outlet on one breaker and the bottom outlet on another breaker and marked the outlet plates with marker to show what was on what breaker. That way I could have two large machines in the same outlet running at the same time. If you do that, you need to break away the metal tab on the hot side of the outlet. Again, I can't say if this meets code or not.

In general, the larger the conduit the better..especially if you plan on pulling more than 1 romex through. You may want to go with 1 inch which would let you pull much larger wire if you needed to add some larger wire for big 220 machines.

Scott Velie
01-15-2008, 2:49 PM
You can share the ground but not the neutral. (unless the wire size is twice as large).

Scott

Rob Russell
01-15-2008, 3:01 PM
Steve,

You don't say whether this is a finished or unfinished basement, but because you have access to the floor joists I'm going to interpret that as being an unfinished basement.

Based on that assumption, your receptacles must be GFI-protected (per NEC 210.8). You can't have a multiwire circuit and GFI-protect the separate parts of the circuit.

It's fine to run multiple 20 amp circuits in the same raceway (conduit). Pull (5) #12 THHN/THWN conductors for the (2) hots, (2) neutrals and 1 equipment grounding conductor. Because these are separate circuits, you can make the first receptacle on each circuit a GFI and use the "feed-through" option to protect the receptacles that are down-circuit from there.

Rob
(Addy protocol: unlicensed, homeowner electrician)

Wade Lippman
01-15-2008, 4:17 PM
Steve,

Based on that assumption, your receptacles must be GFI-protected (per NEC 210.8). You can't have a multiwire circuit and GFI-protect the separate parts of the circuit.


Of course you can; you just have to use a GFCI outlet everytime, rather than one for the circuit.
If you are saying it is a bad idea I agree, but it is possible.

Rob Russell
01-15-2008, 4:30 PM
Of course you can; you just have to use a GFCI outlet everytime, rather than one for the circuit.
If you are saying it is a bad idea I agree, but it is possible.

Wade - yeah, I guess you could do it that way. I agree with your statement that it wouldn't be a good idea.

Rob

Steve Roxberg
01-15-2008, 4:34 PM
It is an unfinished space, does code really require GFCI circuits? Do they even make a GFCI that supports 20amp, and is grey?

Joe Chritz
01-15-2008, 4:40 PM
If I read your question correctly you want to run two circuits of 20 amps each. Alternating individual outlets from circuit to circuit. That wouldn't be hard and you could pull THHN wires or two runs of 12-2w/g NM and feed through the outlet. One keeps going unbroken, the other goes to the outlet.

I am not sure you really gain that much but it is possible. It would be the same as running two conduits next to each other, as long as it is properly sized. When pulling NM bigger is better for conduit.

Joe

Tom Veatch
01-15-2008, 4:45 PM
You can share the ground but not the neutral. (unless the wire size is twice as large).

Scott

What if the OP ran one 240v 20amp circuit with a neutral (3 12ga wires, black, red, and white) and used the EMT conduit as the grounding conductor. If the 120v outlets alternated connection to the hot wires (black/red) then there would, in effect, be two 120v 20amp circuits that share the neutral and the ground and be protected by a common trip breaker. The only current in the neutral would be the difference between the two hot legs so it would not exceed the 20amp breaker rating. The only downside I see is both circuits would go down if the breaker tripped. An upside would be the availability of 240v if/when needed.

Rob Russell
01-15-2008, 4:50 PM
It is an unfinished space, does code really require GFCI circuits? Do they even make a GFCI that supports 20amp, and is grey?

Steve,

Here are snippets of the applicable section of the NEC:


210.8 Ground-Fault Circuit-Interrupter Protection for Personnel.


(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel.


(5) Unfinished basements — for purposes of this section, unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like

GFI receptacles are absolutely available in 20 amp ratings. You can get gray, but that is probably a color you'll have to get from an electrical supply house. Our local big box stores like Home Depot and Lowe's tend to carry white, almond and beige.

Rob Russell
01-15-2008, 4:53 PM
What if the OP ran one 240v 20amp circuit with a neutral (3 12ga wires, black, red, and white) and used the EMT conduit as the grounding conductor. If the 120v outlets alternated connection to the hot wires (black/red) then there would, in effect, be two 120v 20amp circuits that share the neutral and the ground and be protected by a common trip breaker. The only current in the neutral would be the difference between the two hot legs so it would not exceed the 20amp breaker rating. The only downside I see is both circuits would go down if the breaker tripped. An upside would be the availability of 240v if/when needed.

Tom,

If Steve did that, he'd need to install a GFI receptacle everywhere. It's cheaper to run another conductor and use the feed-through capability of a GFI receptacle to protect each string of receptacles.

Rob

Rob Russell
01-15-2008, 4:55 PM
If I read your question correctly you want to run two circuits of 20 amps each. Alternating individual outlets from circuit to circuit. That wouldn't be hard and you could pull THHN wires or two runs of 12-2w/g NM and feed through the outlet. One keeps going unbroken, the other goes to the outlet.

I am not sure you really gain that much but it is possible. It would be the same as running two conduits next to each other, as long as it is properly sized. When pulling NM bigger is better for conduit.

Joe

If he's running conduit, there is no reason to pull NM-cable and some inspectors will give you grief about running NM in conduit. If conduit is required, he's better off pulling THHN/THWN.

Rob

Chris Padilla
01-15-2008, 4:59 PM
Wade - yeah, I guess you could do it that way. I agree with your statement that it wouldn't be a good idea.

Rob

Right...each GFCI protected circuit requires its own neutral so keep that in mind...nearly bit me in my garage rewire. A true multi-wire system has a common neutral returing current for the black and red hot legs. That won't work in a GFCI circuit as you'll need a second neutral.

I hear they make 14/4 now and the second neutral has a red line on it.

Chris Padilla
01-15-2008, 5:00 PM
If he's running conduit, there is no reason to pull NM-cable and some inspectors will give you grief about running NM in conduit. If conduit is required, he's better off pulling THHN/THWN.

Rob

Pulling NM in conduit can be painful, too.

Steve Roxberg
01-15-2008, 8:09 PM
I'm actually redoing most of the electrical. When I first wired the shop I had less equipment and didn't know where it was going to sit. Now everything is getting hooked into a dust collector with pipe so I'm considering rewiring it.

My thoughts on runnint two circuits would be the ablity to run a saw and vacuum on two different circuits. I had a breaker throw the other day because I plugged the vacuum into the same circuit as the space heater and it popped.

Not worth the hassle if I don't gain anything.

I will buy new wire, what is the is recommended for 20 amp? 12g, white, black and green and then buy a spool of each.

Is the stranded easier to work with?

If you use stranded should you solder the ends to tin them, or just twist it together, I've only use solid copper wire in the past.

Jim Becker
01-15-2008, 8:56 PM
IDo they even make a GFCI that supports 20amp, and is grey?

I can't answer the grey part...but for sure you can buy 20 amp GFCI receptacles. I have them in my shop and on the exterior outlets I installed for the convenience of the contractors who constructed our addition. White and ivory absolutely. Other colors, I don't know...

David G Baker
01-15-2008, 9:57 PM
I think HD has the 20 Amp gray GFCI receptacles.

Rob Russell
01-16-2008, 7:21 AM
I'm actually redoing most of the electrical. When I first wired the shop I had less equipment and didn't know where it was going to sit. Now everything is getting hooked into a dust collector with pipe so I'm considering rewiring it.

My thoughts on runnint two circuits would be the ablity to run a saw and vacuum on two different circuits. I had a breaker throw the other day because I plugged the vacuum into the same circuit as the space heater and it popped.

Not worth the hassle if I don't gain anything.

I will buy new wire, what is the is recommended for 20 amp? 12g, white, black and green and then buy a spool of each.

Is the stranded easier to work with?

If you use stranded should you solder the ends to tin them, or just twist it together, I've only use solid copper wire in the past.

Yep - a spool of black, white and green. No need to tin the ends on stranded - just make sure your devices are rated for stranded. Some residential grade devices are only rated for solid conductors on some terminals.

In terms of easier to work with, stranded is more flexible than solid, the solid seems marginally easier to attach to devices - but that's just me and your preferences may be different. Buy 2 feet of solid and stranded and do 6 test attachments to devices - see which you prefer.

Rob Russell
01-16-2008, 7:22 AM
I think HD has the 20 Amp gray GFCI receptacles.

Different HD's stock different items ... it's certainly worth checking what the local big box stores have.

Jim Becker
01-16-2008, 9:07 AM
Some residential grade devices are only rated for solid conductors on some terminals.

Excellent point, Rob. For the extra few pennies or a buck, the commercial quality products are a better long-term buy, anyway. Personally, I can see no good reason to ever compromise on quality of electrical components in the home and shop. There is no real savings in doing so.

Steve Roxberg
01-16-2008, 9:57 AM
Excellent point, Rob. For the extra few pennies or a buck, the commercial quality products are a better long-term buy, anyway. Personally, I can see no good reason to ever compromise on quality of electrical components in the home and shop. There is no real savings in doing so.

I agree with this statement, I've replaced most of the outlets in the house over the years and have always used the commercial quality outlets, you can tell a difference.

Chris Padilla
01-16-2008, 10:34 AM
Get the BACK-WIRED receptacles (not back-stabbed). I believe the "Commercial" or "Pro" grade of receptacles are back-wired. These are much easier and more secure to wire and will take either stranded or solid up to #10. There is no reason to tin stranded...none at all...just twist it up with your fingers...good enough.

When I did my whole garage in #10--it was all stranded. The reason I did my whole garage in #10 was that I didn't want to buy spools of #10 and #12. As it was, 3 spools of 500' (or whatever a spool holds) of #10 in red, black, and white were just right. I goofed and got my green in #10. The green or bare ground wire can be smaller so I could've gotten away with #12 or perhaps #14.

I put everything in 3/4" flex conduit and used the large 4 11/16" metal boxes. If you see the need in the future to pull wires to make yourself a 240 V/30 A receptacle, you might be glad you put stuff in conduit.

Steve Leverich
01-16-2008, 11:15 AM
Not only is it not necessary to tin wires, it's against code. Solder has a low (typically around 400-450 degree f) melting point so it's possible, in most wiring terminals (and wire nuts) to have wires "get smaller" under a current overload - and loose connections generate even MORE heat. For this reason, code specifically states that you will NOT use solder... Steve

Joe Chritz
01-16-2008, 12:01 PM
Very true that NM isn't required in conduit (or even desirable) but I see the other runs were exposed through the floor trusses for upstairs and run through conduit down the wall. That would require conduit for the exposed areas, although with the correct use of a box running NM in conduit could be avoided.

I like my outlet colors like my equipment. Different everywhere, wish they made them in green and yellow. :D

Joe

ETA: Just to add, at least one of my shop circuits uses a GFCI breaker with no plug. They were on close out and it was cheap. Another option if the 20amp GFCI's are hard to find or to expensive.

David Motherwell
01-17-2008, 10:30 PM
Just a few thoughts:
1) A GFCI Rec. has 4 terminals, 2 labled "Line" and 2 "Load". If you have a series if Recs, the first could be GFCI with the feed from the panel connected to the "Line" side and the feed to the other recs connected to the "Load" side (Actually top and bottom). This will result in the downcircuit Recs being protected by the GFCI Rec. The downside to this is that it is not possile to split a GFCI like a regular Rec by running two hots and removing the tab between the terminals on the hot side.
2) Take your local electrician out for a coffee/beer.

Cheers

Jim Becker
01-18-2008, 10:27 AM
David, one solution might be to start two circuits with GFCI protection in a large quad box. (you need larger boxes to work comfortably with GFCIs anyway) Or use GFCI breakers.

The big concern I have with multi-circuit setups like this is being sure that BOTH circuits are killed at the breaker if you need to work on one of them. I think you are supposed to use a dual breaker in this situation...I certainly would just from a logical standpoint. I'd consult a qualified electrician on that point and agree that buying beverages or lunch is a nice way to get some support. :) I know that the excellent electrician working on our addition has filled in some gaps for me on many things in our conversations.

Chris Padilla
01-18-2008, 10:39 AM
Jim,

In a multi-wire situation (black/red hots), the breakers are required by code to be tied together...known as a "tiebar" so that both can be/must be disconnected at the same time. If one side trips, it'll force the other side to trip as well. If you're working on it, you'll be forced to shut both legs down. All in the name of safety!

I have this setup in my shop: large 4 11/16" boxes, two GFCI receptacles, black/white, and red/white-"red" wiring. As I mentioned earlier, I almost got bit by overlooking the fact that each GFCI circuit needs its own neutral. I was able to pull a second neutral (the white-"red") and thus was "saved". :)

Jim Becker
01-18-2008, 10:50 AM
Thanks for confirming, Chris. Good point on the need for the dedicated neutral, too...I'd do that anyway even without a GFCI. 'Just the way I am about such things.

One point, though...you can't assume "red/black" (the colors)...with THHN, there are so many kewel choices that folks might decide to use. LOL

Chris Padilla
01-18-2008, 11:03 AM
I think Rob told me that some 3-phase wirings have specific colors. Isn't it part of the code to use specific colors...at least for residential? I can't imagine buying a home and digging into the wiring to find blue, orange, and purple wires and going, *WHAT?!* It would be time to dig out the DVM (digital voltmeter) and figure out what the hay is going on. :)

Ken Fitzgerald
01-18-2008, 11:24 AM
In the electronics in hospitals that I work with....3 phase ........has the color codes you mention Chris....

Rob Russell
01-18-2008, 1:05 PM
There are some specific color requirements on 3-phase wiring ... let's just leave that discussion alone though.

The requirement for a 2-pole breaker or handle-tied breakers applies when you have multiple circuits terminating on the same yoke. In other words when you splitwire a duplex receptacle such that the top (or left if the receptacle is mounted horizontally) outlet is on 1 circuit and the bottom/right outlet is on another circuit, the hot conductors feeding the 2 outlets must have a common disconnect. The applicable NEC section is 210.4(B) if you feel like looking it up.

FYI, there is no NEC requirement to have a 2-pole breaker or single breakers with handle-tie just because you have 2 hots going into the same box. If you have a (2) device box like a 4" square with (2) duplex receptacles and each receptacle is on it's own breaker - that's fine according to the NEC. Personally, I've generally wired my circuits such that all circuits in a box are deenergized at once, but that's not always possible. We have some switch boxes with 4 switches and I know some of the switches are on different circuits. For any workshop boxes where there are (2) duplex receptacles, if they are on different circuits I still have a 2-pole breaker. That's going beyond the code, but it means that I don't have to worry about working in a box with 1 circuit dead and 1 circuit hot. For that 4-switch box, it means killing multiple breakers if I want to work in the box.

Rob

Randy Denby
01-18-2008, 3:07 PM
Heres a quick tip...for those using stranded wire under terminals. Stranded wire usually comes either straight or maybe alittle clockwise wound inside the conductor shield/sheath. Ever notice how when tightening the terminal screw, the wire wants to walk out from under the screw? If you twist the exposed wire counterclockwise beforehand, then wrap it around the screw, it will want to pull in and under the screw....saving alot of frustration.

Joe Melton
01-18-2008, 6:34 PM
I'm impressed that so many members know so much about electrickery.
I'm nearing the end of wiring my new shop and have a couple of questions.
I put in three 15-amp breakers and three switches for the overhead lights. The shop is lighted in zones, and I wanted to be able to light only a portion at a time. I have the wiring to the triple-switch box and now need to wire from the box to the panel. My plan is to run two 14-2s, rather than three. Both of the blacks will be hot and one of the whites will be hot (with black tape on it inside the box and panel). The second white will be neutral for all three lights and there will be either one or two grounds. Is it ok to do this as I have explained?
Secondly, I am wondering if it is ok to attach two or three #12s or #14s to a stud with a single staple on the runs.
I hope to get the inspector out next week. That will be a huge relief to get it passed. This wiring took far longer than I anticipated.
TIA,
Joe

Rob Russell
01-18-2008, 9:35 PM
I put in three 15-amp breakers and three switches for the overhead lights. The shop is lighted in zones, and I wanted to be able to light only a portion at a time. I have the wiring to the triple-switch box and now need to wire from the box to the panel. My plan is to run two 14-2s, rather than three. Both of the blacks will be hot and one of the whites will be hot (with black tape on it inside the box and panel). The second white will be neutral for all three lights and there will be either one or two grounds. Is it ok to do this as I have explained?


Joe,

The simple answer is "No".

What you're proposing is to have 3 circuits with 1 common neutral. Unless you're running 120/208 "Y" 3-phase and won't have a lot of harmonics, you can't do this - and I think that's a pretty safe bet for a residential installation.

The neutral conductor carries just as much current as the hot conductor. For standard 120v circuits, you need to have a separate neutral for each circuit. That means you need to run (3) 14-2s. I didn't even get into the rules about all conductors for a circuit being in the same raceway or cable.


Secondly, I am wondering if it is ok to attach two or three #12s or #14s to a stud with a single staple on the runs.

I've done plenty of runs where I stapled (2) NM cables under 1 staple, but (3) don't really fit. When you staple, make sure you don't hammer the staple too hard. You don't want to crimp the wires - just hold the cables in place.


I hope to get the inspector out next week. That will be a huge relief to get it passed. This wiring took far longer than I anticipated.

Good for you (the inspection). My experience when dealing with our inspectors is that they are there to help and protect, not be a pain in the neck.

Rob
Addy protocol: unlicensed, homeowner electrician