Advice on running conduit in long runs

[scutty83]

Just getting ready to start wiring my shop and needing some advice on proper techniques in dealing with long runs and conduit. The shop is 40' x 72' and wanting outlets all the way around the while shop. The breaker panel is located in the front where my main work area will be and most of the electrical draw will take place.

Questions are as folllows:

Is 12awg wire suitable for running 20A outlets on a run over 100 feet?

Ive read that I can stuff up to 9 12 awg runs in 1/2 conduit. Should I run a "home run" leg for a second branch to start further down the line to combat voltage drop?

Should I run a dedicated ground wire or is it acceptable to just ground to the conduit?

 

[u2slow]

You'll have to do the voltage drop math to be sure. You have to further de-rate for more than one 3-wire circuit in a conduit. Others will chime in... I don't know the NEC particulars.

Your panel... is it central? (i.e. equal wall space to serve from either side?) If not, run the first outlet or two with #10, and then switch to #12 for the rest. Another thought is to run a 40-60A sub over to the other side so the #12 runs are shorter.

Depending on your equipment (and rules), one trick that works in my shop is mixing 120v and 240V outlets on the same 3-wire circuit using a 2-pole breaker. All my 240V stuff is happy on 20A also.

 

[wyliesdiesels]

what are you running on these outlets?

100' would be too far for a considerable load.

How about setting a subpanel closer to the outlet locations?

 

[Terry D]

Lets talk about the conduit fill first. Yes you can put 9 # 12 THWN in 1/2 EMT. The problem with that is, now they can not be on 20 amp breakers no more. They would have to be on 15 amp breakers. See once you have more that 3 current carrying conductors in a conduit , you have to start derating the amount of current that you put on that conductor. You can have up to 6 current carrying conductors in that conduit and still have them on 20 amp breakers. 4-6 conductors you derate by 80%. But its not 80% percent of 20 amps, its 80% percent of 25 amps. If you look At 310.16 of the NEC, if you look at the side for copper conductors and look at #12, it shows 25 amps. Don't worry right know about the 3 different temperature columns. Lets look just at the 60 degree column. 60 and 75 is going to be your most common Colum, its a whole different subject with termination ratings. Now that 25 amps does not mean that you can ever put 25 amps on that wire, it is for calculating purposes only. So 80% of 25 is 20 amps. Every wire in that conduit except the green wire for your equipment ground
( and yes you should always run a equipment ground, never just rely on that conduit for a ground) is a current carrying conductor. Sometimes certain neutrals are not counted, but in you case they are. So if you share the neutrals, you could have 4 20 amp circuits with 2 neutrals or if you don't share neutrals you can have 3 20 amp circuits with 3 neutrals. Hope that makes sense. As far as voltage drop, there is a voltage drop calculation, that I would have to look up if you need it. I have always been told, every 100 ft go to the next size wire. But it seems in your size shop, it will not be a problem. But if you are concerned, look up the formula. I believe you want to stay in between 3% to 5% voltage drop, but I could be wrong. Hope this helps

 

[ard]

#12 will go 53 feet at 20 Amps

You can use #12, but with a 15A breaker - good to 69 ft.

You could 'home run' with #8...thats good for over 100ft. Then at the first device, change to #12.


1/2" looks so puny...


Edit: just saw TerryD post. Should be interesting about grounds.

 

[TheEquineFencer]

#12 will go 53 feet at 20 Amps

You can use #12, but with a 15A breaker - good to 69 ft.

You could 'home run' with #8...thats good for over 100ft. Then at the first device, change to #12.


1/2" looks so puny...


Edit: just saw TerryD post. Should be interesting about grounds.

I've never thought about running a circuit like that, but it makes perfect sense.

 

[alfredeneuman]

Lets talk about the conduit fill first. Yes you can put 9 # 12 THWN in 1/2 EMT. The problem with that is, now they can not be on 20 amp breakers no more. They would have to be on 15 amp breakers.

7-9 conductors derate to 70% of the 90 degree rating which is 30 amps= 21 amps so they still can be on a 20 amp breaker

10-20 conductors derate to 50%, which would require 15 amp breakers

 

[Terry D]

7-9 conductors derate to 70% of the 90 degree rating which is 30 amps= 21 amps so they still can be on a 20 amp breaker

10-20 conductors derate to 50%, which would require 15 amp breakers

better make sure those terminations are rated at 90 degrees

Just cant pick the column that's works best for you

 

[wyliesdiesels]

Lets talk about the conduit fill first. Yes you can put 9 # 12 THWN in 1/2 EMT. The problem with that is, now they can not be on 20 amp breakers no more. They would have to be on 15 amp breakers. See once you have more that 3 current carrying conductors in a conduit , you have to start derating the amount of current that you put on that conductor. You can have up to 6 current carrying conductors in that conduit and still have them on 20 amp breakers. 4-6 conductors you derate by 80%. But its not 80% percent of 20 amps, its 80% percent of 25 amps. If you look At 310.16 of the NEC, if you look at the side for copper conductors and look at #12, it shows 25 amps. Don't worry right know about the 3 different temperature columns. Lets look just at the 60 degree column. 60 and 75 is going to be your most common Colum, its a whole different subject with termination ratings. Now that 25 amps does not mean that you can ever put 25 amps on that wire, it is for calculating purposes only. So 80% of 25 is 20 amps. Every wire in that conduit except the green wire for your equipment ground
( and yes you should always run a equipment ground, never just rely on that conduit for a ground) is a current carrying conductor. Sometimes certain neutrals are not counted, but in you case they are. So if you share the neutrals, you could have 4 20 amp circuits with 2 neutrals or if you don't share neutrals you can have 3 20 amp circuits with 3 neutrals. Hope that makes sense. As far as voltage drop, there is a voltage drop calculation, that I would have to look up if you need it. I have always been told, every 100 ft go to the next size wire. But it seems in your size shop, it will not be a problem. But if you are concerned, look up the formula. I believe you want to stay in between 3% to 5% voltage drop, but I could be wrong. Hope this helps

Table 310.16 has been renumbered to 310.15(B)(16)

7-9 conductors derate to 70% of the 90 degree rating which is 30 amps= 21 amps so they still can be on a 20 amp breaker

10-20 conductors derate to 50%, which would require 15 amp breakers

better make sure those terminations are rated at 90 degrees

Just cant pick the column that's works best for you

incorrect.

Derating is done with the 90* column regardless of the termination rating. The final result will not be the 90* rating.

 

[Terry D]

Table 310.16 has been renumbered to 310.15(B)(16)





incorrect.

Derating is done with the 90* column regardless of the termination rating. The final result will not be the 90* rating.

Sorry, St. Louis county is still in the 2008 Code cycle, it is still table 310.16

And yes the temperature rating of the circuit breaker has everything to do with it, if the breaker is not rated at 90 degree C, then you cannot use that column.


This may be helpful, its a old article, but still applies.

https://iaeimagazine.org/magazine/2000/03/16/wire-temperature-ratings-and-terminations/

 

[Terry D]

you may also want to read this. We are still in the 2008 code. So this is the code article from that book.

110.14(C) 1a

 

[Terry D]

Around here, this is the way we are taught in the code classes. Up to 6 current carrying # 12 conductor's can be on 20 amp breakers. Any more than that, run bigger wire or down size the breaker. It would fail a inspection if caught, I know this from experience.
It seems like we do things different than some other parts of the country, I understand that. This is why I don't post that much in the electrical threads.

 

[Innovate1]

Bigger conduit will make pulling a lot easier even if the fill might be allowed. Cost of going up a size in small sizes is not that much.

 

[Innovate1]

Sorry, St. Louis county is still in the 2008 Code cycle, it is still table 310.16

And yes the temperature rating of the circuit breaker has everything to do with it, if the breaker is not rated at 90 degree C, then you cannot use that column.


This may be helpful, its a old article, but still applies.

https://iaeimagazine.org/magazine/2000/03/16/wire-temperature-ratings-and-terminations/

The article you link has a section about 2/3 of the way down titled "What about higher-rated conductors and derating factors?" There they go through an example that seems very similar to the one here of using the 90C factors for derating due to conduit fill for 90C wire but the wire also meets the current requirements for 75C for the terminations. That seems to be the difference of opinion here and I note the article is from 2000. I don't have a lot of experience with this so am I thinking of this correctly?

 

[Terry D]

The article you link has a section about 2/3 of the way down titled "What about higher-rated conductors and derating factors?" There they go through an example that seems very similar to the one here of using the 90C factors for derating due to conduit fill for 90C wire but the wire also meets the current requirements for 75C for the terminations. That seems to be the difference of opinion here and I note the article is from 2000. I don't have a lot of experience with this so am I thinking of this correctly?

I will be honest, I don't know that code book from one end to the other. But that's what they teach you is not to memorize it. Its how to get in that book and find what your looking for. And I haven't had a full blown 5 month code class in a while, but every 3 years, I have to take a code change class to keep my license active. And this class is just on the code changes. As far as temperature deratings on a circuit. And this is something I don't have to figure out everyday, but you have to go with the weakest link. whether its the breaker, device or conductor. So to my understanding, if you have a lower rating on the breaker or device, than the conductor, then you must use that rating.

 

[Terry D]

Another article

https://www.ecmweb.com/nec/conducto...rminal-temperature-ratings#close-olyticsmodal

 

[Higgins]

If it were me, I think I would
o put a small sub panel half way down the space. That way, you only have to walk half the distance should you need to flip a breaker. and you would be able to use #12 for everything.
o I'd also use 3/4" conduit for everything in the garage. It's the KISS principle, and would allow you to do almost anything in the way of changes down the road.
o As for piping, EMT vs PVC thats your call!

 

[dcg9381]

Agree with Higgins. Sub-panel to a more central location and distribute. Use no smaller than 3/4" conduit.

 

[alfredeneuman]

110.14(C) 1a

2008 NEC 110.14(C) 1a (3) Conductors with higher temperature ratings if the
equipment is listed and identified for use with such conductors.

 

[mm08822]

I will be honest, I don't know that code book from one end to the other. But that's what they teach you is not to memorize it. Its how to get in that book and find what your looking for. And I haven't had a full blown 5 month code class in a while, but every 3 years, I have to take a code change class to keep my license active. And this class is just on the code changes. As far as temperature deratings on a circuit. And this is something I don't have to figure out everyday, but you have to go with the weakest link. whether its the breaker, device or conductor. So to my understanding, if you have a lower rating on the breaker or device, than the conductor, then you must use that rating.

Another article

https://www.ecmweb.com/nec/conducto...rminal-temperature-ratings#close-olyticsmodal

You are confusing wire ampacity used for derating purposes with permitted actual load/ocp of the conductor. In both the 2008 NEC and the ECM article you linked to, each one explains the provision of 90C ampacity usage (albeit poorly).
I underlined the applicable text in the below pic.



NEC 240.4 (D) (4) limits the ampacity of the ocp to 20A for #12 Cu. That agrees with the 75C CU conductor ampacity and termination rating.

 

[brewchief]

Here's a piece from Mike Holt that gives some info when you have more conductors and have to derate( there is also some info on derating for high ambient temp).

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[sparky 1971]

The building is only 2800 sq ft. Don't bother with a sub panel. Use at least 3/4 conduit for everything leaving the panel. Plan out the conduit runs to keep everything as short as possible. Use #10 wire for at least the first half of anything over 100 feet. If a run somehow gets closer to 200" you may want to consider #8 instead. Try to keep high current tools such as chop saws and table saws close to the panel. Use EMT because PVC looks like ****. Make sure all the connections are tight and don't pull a ground. Use grounding tails off the box to the device. If you are going to be by yourself, don't put too many wires in a pipe. It gets to be a heck of a mess trying to feed through boxes without cutting and splicing back together. You can use whatever wire you want, but I prefer stranded when by myself because it's easier to drag through with a fish tape, but it does turn into a tangled mess much easier than solid.

 

[PRH44]

Derate from the 90c Column always when using 90C conductors!Then check your termination’s temperature ratings. Almost always..... more often than not .... pretty much every time your terminations will be 75 C. Check your calculations against the 75 degree column. As long as you are equal to or above that rating you are are good. So (9) #12 THHN copper conductors in a conduit will be good for 20 amps. With all this said there is the ambient temperature in which the conductors will be subjected to, that could result in further ampacity derating. By the way I would never put (9)’#12 THHN in a 1/2” conduit.

 

[scutty83]

Bigger conduit will make pulling a lot easier even if the fill might be allowed. Cost of going up a size in small sizes is not that much.

I already have all the 1/2 stuff. I really don't need 9 conductors any way, was just stating it looks like that is the limit.

 

[scutty83]

You'll have to do the voltage drop math to be sure. You have to further de-rate for more than one 3-wire circuit in a conduit. Others will chime in... I don't know the NEC particulars.

Your panel... is it central? (i.e. equal wall space to serve from either side?) If not, run the first outlet or two with #10, and then switch to #12 for the rest. Another thought is to run a 40-60A sub over to the other side so the #12 runs are shorter.


Unfortunatley the panel is not centrally located. It is in the corner.

 

[scutty83]

I think I got you guys thinking I was gonna actually run 9 wires in a 1/2 conduit, that is definitely not my intention. The panel is located in one front corner of the shop where all the heavy loads i.e. welder, air compressor will run off their own circuits not in the 1/2 conduit run.

This is the what I'm thinking planning to do on one long wall and the back wall, the other long wall will have its own conduit run coming from the other direction:

*(1) 12 awg dedicated ground

*(1) 12 awg leg on the first 70' (long wall) which is 12 outlets

*"home run" a #8 or #10 reducing to 12 awg at the first outlet after the home run to the next set of 8 outlets, (about 40') on the back wall which will be rarely used (all heavy work goes on near the front of the shop where the panel is)

*(2) 12 awg neutral legs, one for the first circuit and the next for the home run circuit.

*(2) 20a breakers

So according to my calculations, that is (4) total 12 awg wires and (1) 8 or 10 awg wire.

 

[mm08822]

#10's for hot and neutral will handle 20a for 100' with 3.5% voltage drop. 20a is worst case. #8's are overkill.

 

[brewchief]

Remember if you upsize the wires for voltage drop you have to also upsize the ground wire.
NEC 250.122(B)

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[BD1]

Money well spent by adding sub panels. I have main and a sub for house and ano panel for garage .
You're only gonna do this once and definitely a plus.
You could even stub out a few extra pipes for future into a box and cover.


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[Dagny]

If you have known large loads run larger wire. Otherwise everyone is making this harder then it needs to be . It's 40 by 70 most things that get plugged in won't draw 20 amps.

 

[sparky 1971]

I think I got you guys thinking I was gonna actually run 9 wires in a 1/2 conduit, that is definitely not my intention. The panel is located in one front corner of the shop where all the heavy loads i.e. welder, air compressor will run off their own circuits not in the 1/2 conduit run.

This is the what I'm thinking planning to do on one long wall and the back wall, the other long wall will have its own conduit run coming from the other direction:

*(1) 12 awg dedicated ground

*(1) 12 awg leg on the first 70' (long wall) which is 12 outlets

*"home run" a #8 or #10 reducing to 12 awg at the first outlet after the home run to the next set of 8 outlets, (about 40') on the back wall which will be rarely used (all heavy work goes on near the front of the shop where the panel is)

*(2) 12 awg neutral legs, one for the first circuit and the next for the home run circuit.

*(2) 20a breakers

So according to my calculations, that is (4) total 12 awg wires and (1) 8 or 10 awg wire.

If you use #10 because of voltage drop on the long run, the neutral has to be #10 also. If you use emt, I wouldn't bother pulling a ground wire. Just make sure all of the fittings are tight. That will give you two #10 and two #12 in the 1/2 conduit.

I know you already have 1/2" stuff, but I think you should consider using 3/4" for things in the future. Install a pull string along with the wires and leave it in. That way, in five years when you get a new piece of heavy duty equipment that goes on the wall you "will never use as of now", all you have to do is tie a couple wires to the string and pull them through. There have been many times I used the ground wire someone else put in to pull the new circuit(s) through an existing pipe.

 

[ard]

I Install a pull string along with the wires and leave it in. That way, in five years when you get a new piece of heavy duty equipment that goes on the wall you "will never use as of now", all you have to do is tie a couple wires to the string and pull them through. There have been many times I used the ground wire someone else put in to pull the new circuit(s) through an existing pipe.

And there are few things in life that will make you feel like the smartest guy you know.....






(edit. while a pull rope is cool, I have found that unless there is a TON of room, I wind up pulling all the wires out, adding what I need, then pulling it back. Pulling two new wires next and within bundle can be fraught... but yeah, I always upsize conduits)

 

[sparky 1971]

And there are few things in life that will make you feel like the smartest guy you know.....






(edit. while a pull rope is cool, I have found that unless there is a TON of room, I wind up pulling all the wires out, adding what I need, then pulling it back. Pulling two new wires next and within bundle can be fraught... but yeah, I always upsize conduits)

Yep. It appears that there will be two #10's and two #12's in the pipe along with a ground if he chooses to. If he up sizes to a 3/4, there will be plenty of room.

This wouldn't be a rope, just a string. I have seen the Ideal string at Menards and Home Depot in a small container . This would be a perfect place for that. I have it in the 5 gallon bucket size. Don't know the length, but it's a bunch.

 

[Milton Shaw]

Run a 100 amp for a sub panel to the other end of the shop. You say now all the heavy work is at the front end, you might change your mind in 5 years and move a welder or some heavy equipment to the other end and wish you had prepared for it. My wife just went into glass fusing this past year and had to have 3 heavy circuits for kilns that years ago didn't even think about. This required a sub panel 50 feet from the original panel. Even if you don't think you will do this at least run the conduit and hang a box as it easier to do before you fill the shop and hang stuff on the wall. Ask me how I know.

 

[OneOfEm]

I'm in the same boat as the OP (44x50 with panel in one corner), but I have been planning on a subpanel in the opposite corner from the beginning.

However, this discussion has got me questioning something else. Since the "main" shop panel is a subpanel and the ground and neutral aren't bonded, should a subpanel off of it have bonded or non-bonded ground and neutral?

I would guess non-bonded, but don't want to guess.

 

[vrinner]

So it sounds like I did mine all wrong. My building is 60X40. My panel is on one corner of the 60' wall. I ran 12/2 from the panel, down 60' then along the 40' section with a bunch of outlets in between.

Sound like I should redo at least the 60' section to 10/2.

 

[u2slow]

So it sounds like I did mine all wrong. My building is 60X40. My panel is on one corner of the 60' wall. I ran 12/2 from the panel, down 60' then along the 40' section with a bunch of outlets in between.

Sound like I should redo at least the 60' section to 10/2.

Meh. How often do draw the full 20A? The breaker will only hold 16A continuous. Two bigger power tools (12-15A) at the same time will trip it anyway.

If it I was loading up the circuit hard, I'd probably run a fresh #10/3 to the far end. Use the 20A breakers from the other circuits and put the existing #12 stuff on 15A breakers.

 

[scutty83]

If you use #10 because of voltage drop on the long run, the neutral has to be #10 also. If you use emt, I wouldn't bother pulling a ground wire. Just make sure all of the fittings are tight. That will give you two #10 and two #12 in the 1/2 conduit.

I know you already have 1/2" stuff, but I think you should consider using 3/4" for things in the future. Install a pull string along with the wires and leave it in. That way, in five years when you get a new piece of heavy duty equipment that goes on the wall you "will never use as of now", all you have to do is tie a couple wires to the string and pull them through. There have been many times I used the ground wire someone else put in to pull the new circuit(s) through an existing pipe.

Great point on the larger neutral and larger conduit. And yes I wish badly that the previous owner had upsized the conduit, but one 70' run was already place when I took ownership and they have left TONS of new 1/2 pipe and fittings to finish the job.