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Discussion Starter · #1 · (Edited)
I'm wiring my shop with 3/4 emt and #10 wire. So my plan was to run a multi wire branched circuit from a double pole breaker. 2 hots and a nuetral.

I have half the shop done and have wired several junction boxes with 2ea 110v outlets. The left outlets off one leg and right outlets off the other leg with a shared nuetral. So basically 2 separate circuits in each box.

I intend on installing a few 220v outlets off the same circuit. The problem is that the 110 outlets are of course only rated at 20a so I can't run a 30a breaker to take full advantage of the #10 wire. Therefor I installed a 20a breaker. This will probably be fine for most tools but if I get a power hungry tool in the future, I may just run another set of #10's and a 30a breaker for dedicated 220.

It's a one man shop so there won't be multiple things run at once. My questions are: do I need to derate the dedicated 220 circuit from 30a to 25a if I run it in the same conduit as my branched circuit?

There would be 4 hot conductors and a single shared nuetral for the branched circuit.

And do you see any other issues I have missed? All outlets are individually grounded to the boxes and emt is continuous to the sub panel.

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Discussion Starter · #3 · (Edited)
Maybe I worded the question wrong...

I wasn't asking how much harder #10 was to work with or how much more it would cost. I already have that circuit run and it wasn't difficult at all nor out of my budget.

My question was about derating. The 4 hots and a nuetral would be 2 hots and a neutral for the branched circuit and another 2 hots for the dedicated 220v circuit on a 30a (or 25a if it needs to be derated) breaker. All in my original post.

Edit: I'm all for constructive criticism as I don't claim to be an electrician. But I would prefer some info that would actually help me too. I'm not going to go pull the #10 out of the conduit, respool, and return it. I got enough that I could use it for all the wiring in the shop whether it's 110 or 220 circuits.

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Maybe I worded the question wrong...

I wasn't asking how much harder #10 was to work with or how much more it would cost. I already have that circuit run and it wasn't difficult at all nor out of my budget.

My question was about derating. The 4 hots and a nuetral would be 2 hots and a neutral for the branched circuit and another 2 hots for the dedicated 220v circuit on a 30a (or 25a if it needs to be derated) breaker. All in my original post.

Edit: I'm all for constructive criticism as I don't claim to be an electrician. But I would prefer some info that would actually help me too. I'm not going to go pull the #10 out of the conduit, respool, and return it. I got enough that I could use it for all the wiring in the shop whether it's 110 or 220 circuits.

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You have no idea what you are doing and it is very obvious from your questions and terminology. Then you get snarky with someone that tries to help. A good way to make friends and influence people. Not!
 

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I'm not an electrician. I see no mention of a ground wire. You should have 4 wires in each box unless the EMT is bonded as ground.

For the new circuit I believe you need a separate neutral.

You may have a total of 11 # 10 wires in a 3/4" inch conduit. Source: http://www.alanwire.com/tech/conduit.html
 
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Discussion Starter · #6 ·
You have no idea what you are doing and it is very obvious from your questions and terminology. Then you get snarky with someone that tries to help. A good way to make friends and influence people. Not!
Because you were being unhelpful. I wouldn't have been snarky if you actually gave a helpful response to my question.

I just get a little annoyed at reading forums where people give no actual answers and only try to nit pick something that the original poster did which essentially makes no difference in the end product. I never understand that. If all someone is going to do is put someone down for something when they are asking for help, why even post a response? It's a DIY forum. Obviously I have no idea what I'm doing because of the teminology to use? Wow.

Reference the grounding, the outlets are individually grounded to the boxes and the conduit is bonded to the grounded sub panel. That's why I didn't run a ground wire.
The second circuit would only be 220v so you don't use a neutral.
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Unless you plan on pulling more THHN/THWN. You are still going to end up with only one MWBC.

It does not magically turn into two MWBC circuits.

Also you cannot use that 120 MWBC for a 240.

#10 is hard to work with, when doing outlets. There are some GFCI outlets that will accept #10. They are hard to find at most Big Box stores.

If you want to bend the rules. That is your choice. If you are required to pull a permit and have an inspection, the AHJ will not be happy.
 

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Discussion Starter · #9 ·
Unless you plan on pulling more THHN/THWN. You are still going to end up with only one MWBC.

It does not magically turn into two MWBC circuits.

Also you cannot use that 120 MWBC for a 240.

#10 is hard to work with, when doing outlets. There are some GFCI outlets that will accept #10. They are hard to find at most Big Box stores.

If you want to bend the rules. That is your choice. If you are required to pull a permit and have an inspection, the AHJ will not be happy.
I probably made it sound confusing (made sense in my head). I was talking about pulling another 2 wires for 220 on a separate circuit. That's how I got the 4 hots.

I've never used stranded #12 but the stranded #10 hasn't been much harder to deal with than solid #12 Romex.

As far as not being able to use 220v on a branched 110v circuit, is there something in the NEC that says that? I've been reading otherwise. Thank you guys.

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I do believe that you are confusing yourself.

You can have as many branch circuits as you want. In order to figure out the derating if you even need to, is to pull up the table in the NEC.

I can do it off of the top of my head without looking, because I have done it more times then I care to count.

Suggest you buy a copy of the NEC, or go down to the public library and rent a copy. Even your local building codes office has copies that you can look for the table for what you need.

The little Black Book that Ace Hardware even has the derating table in it.

I bet if you did a search for the derating table, first hit will be ecmweb.
 

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Also you cannot have four hots. A 120 will have a Hot, Neutral, Ground. A 3-wire 240 will have only 2 hots and a Neutral. A 4-wire 120/240 will have two hots, a neutral, ground.

You also need to attach a ground to the outlet ground and connect to the back of the box where the ground screw hole is.
 

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Discussion Starter · #14 · (Edited)
Also you cannot have four hots. A 120 will have a Hot, Neutral, Ground. A 3-wire 240 will have only 2 hots and a Neutral. A 4-wire 120/240 will have two hots, a neutral, ground. I know some people don't like to do that but I believe it's acceptable by NEC (in could be wrong of course).

You also need to attach a ground to the outlet ground and connect to the back of the box where the ground screw hole is.
Right, let's assume I'm using the emt as a ground so there is no grounding wire run through the conduit, all outlets are grounded to the j boxes and the conduit is grounded to the panel.

I have a 3 wire 220v circuit. Red and black hots and a white nuetral. You get 110 between either hot and the nuetral and 220v between the two hots. Isn't that what a MWBC is?

If I ran another red and black from a separate breaker, those would both be hot and have 220v between them just like the other 2. That would mean I would now have 4 hot wires and a nuetral on 2 separate circuits.

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Discussion Starter · #15 ·
Also where are you coming up with the #12 stranded? No one has even stated anything about you using that.

#10 is a bear to work with, when dealing with outlets. It is a lot stiffer then #12.
You mentioned that #10 was harder to work with so I assumed you were meaning i should be using #12. The 10 is thhn stranded so I also assumed the 12 would be the same thhn stranded if that's what I was to use.

I was comparing my experience of using solid 12 compared to stranded 10. I just didn't find the 10 very hard to work with.

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Discussion Starter · #16 ·
It makes complete sense to me. 2 hots for the current 120 volt circuits and 2 hots for new 240 volt circuit. I don't think derating kicks in until you get to 9 current carrying conductors.
Thank you! I kept rereading my posts and it made sense to me but I realize sometimes things read differently to different people.

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Thank you! I kept rereading my posts and it made sense to me but I realize sometimes things read differently to different people.

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Nothing reads different with different people. You are misinterpreting what you post and what we have clarified.

It is very easy as I had stated in my post. A 4-wire 240 vAC outlet is still a 240 vAC outlet.

A MWBC (Multi-Wire Branch Circuit) is still a MWBC. When you want to save on running an extra ground and Neutral from the Breaker box for a set of say six 120 vAC outlets. You are sharing the Neutral and the Ground between the two Hots (Does not matter if both are Red or both are Black) that are on opposite legs in the breaker panel.

Get yourself a copy of the NEC and also pick up a copy of "Black & Decker The Complete Guide to Wiring, 5th Edition: Current with 2011-2013 Electrical Codes". It has everything in it for you to be able to understand what we have tried to explain to you. The pictures show what we have explained on wiring a MWBC and a 120/240 4-wire and a 240 vAC 3-wire branch circuits.
 
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