Electricians can you help?

[87bob]

Here is my situation. I have a pole barn 40x48. I want to run several circuits from one side to another in conduit. To keep running conduit to a minimum a one inch conduit will be run through the attic Here is the circuits and their purposes, they are:

1) A traveler for a 3 way (for lights).
2) Feed for the lights from the circuit above. 6-8 foot two bulb fluorescent fixtures.
3) Two 20 amp circuits for wall outlets.
4) A feed circuit for loft lights. 4-8 foot two bulb fluorescent fixtures.
5) A feed circuit for a security light on the end of the building.

All circuits will be 12 gauge unless otherwise needed. My question is do I need to run a neutral for each of these circuits? If all the neutrals can be combined what gauge neutral do I need to run? Your help and suggestions will be appreciated.

 

[Innovate1]

As long as you are running conduit I would upsize it or run two to make future work easier. Not sure if combining all those neutrals is allowed but it seems like keeping them separate would be easy enough. You could make the 2 wall outlet circuits a multiwire circuit with 2 hots and 1 neutral. The others look to be small loads so could be combined to 1 or two circuits minimizing the neutrals. You didn't mention anything about where switches would be located.

 

[87bob]

Figuratively speaking Switches for the 3 way would be a each end of the building. The remaining switches would be on the feed end of the conduit. Thank you for your response!

 

[alfredeneuman]

As long as you are running conduit I would upsize it or run two to make future work easier.

Upsizing the conduit to run more 12s is not as good an idea as running multiple conduits.
Because of derating for the number of current carrying conductors, any more than 9 in 1 conduit would cause the breakers to be 15A instead of 20A.

 

[87bob]

According to what I have been able to find on the internet that 1" conduit should be able to handle up to 25 AWG conductors I only plan to at most have 15 and it will more likely be nine. Any reason not to be able to run those amounts (9 or 15)? Thanks in advance.

 

[exranger06]

Even though you can physically fit 25 conductors, you need to reduce the ampacity of the wires. In other words, a 12 AWG wire can normally handle 20 amps of current. But when you have more than three "current carrying conductors" in the same conduit, a 12 AWG wire may not necessarily be capable of carrying 20 amps. It might only be able to handle 15 amps, or less. This is "derating" a conductor. Note that not ALL of the conductors in the conduit will necessarily be "current carrying conductors." I'll explain more about that below.

According to Table 310.16, 12 AWG THHN has an ampacity of 30 amps (you use the 90 degree column when derating). When you have 4-6 current carrying conductors (CCC) in the same conduit, you derate them to 80% capacity (table 310.15(C)(1)). 7-9 CCCs gets derated to 70%, and 10-20 CCCs gets derated to 50%.

So, if you're going to have over 10 CCCs in the same conduit, your 12 AWG wires can only handle 15 amps, and you'll need to hook them up to 15 amp breakers. If you want to use 20 amp breakers, you'll need to either run more than one conduit, or upsize the wire to 10 AWG. If you upsize the wire, you'll need to do your conduit fill calculation again to make sure all of the wires will fit in the conduit.

Also, if the wires will be subject to temperatures over 86 degrees F, you need to derate them even more. (Table 310.15(B)(1)). Since this will be running through an attic, I'm assuming the ambient temp will be over 86* in the summer. Figure out the maximum ambient temperature the wires will be subjected to, and find the appropriate adjustment factor in the table. Take your derated ampacity and multiply that by the adjustment factor to derate them further.

Now, about the current carrying conductors: Ground wires are not CCCs, so don't count them when derating (if you're running a ground wire. Running a ground isn't really necessary in EMT conduit)
When you have 2 travelers for a 3-way switch in a conduit, both travelers count as one CCC, since only one of them will be carrying current at any given time.
When you have a multi-wire branch circuit (MWBC), the neutral wire doesn't count as a current carrying conductor, since it's only carrying the unbalanced portion of current between the hot legs, (Ditto for a 240V circuit that also has a neutral wire).
Otherwise, neutral wires always count as a current carrying conductor.

Regarding your question about sharing neutrals: The ONLY time 2 circuits can share a neutral is if you run a MWBC. This circuit must use a 2-pole breaker, or 2 single pole breakers that are handle-tied together. You cannot run a larger size neutral and connect several different circuits to it.

 

[87bob]

Thank you all the conflicting information makes sense. I have nine current carrying AWG wires. In central Indiana I would imagine we could see temps i the attic of 120. I'm going to look up the tables you mentioned. Update : If I take 30 amps as my starting point because of 9 conductors derate it to a factor of 70%I come up with 21. Then multiply it by a factor of .58 I'm down to an amp rating of 12.18. What the heck?

 

[u2slow]

Update : If I take 30 amps as my starting point because of 9 conductors derate it to a factor of 70%I come up with 21. Then multiply it by a factor of .58 I'm down to an amp rating of 12.18. What the heck?

alfredeneuman touched on it - it's the penalty for running many wires in a single conduit.

You may want to check on the wireless switch options for doing the 3-ways. A basic 120V circuit with several lights and long travelers may struggle with voltage-drop.

Big spaces (i.e. long runs) tend to be better served with MWBCs. By balancing them, you get the 'reach' of a 240V circuit.

 

[frankush]

Switch box on opposing walls for 3 ways. 1" TW piped between boxes across attic. NOT adding anything in between. 1 MWBC for outlets. 1 MWBC for lights. 2 travelers for 3 ways. 8#12 THHN total. Additional pipes feed the lights and outlets. Panel feed is also separate. One thing to remember. Differentiate your neutrals. Pick one for lighting and keep it separate from the power when you wire things up. Voltage drop should not be an issue.

 

[87bob]

I am scrapping the single one inch conduit in favor of each circuit having its own 1/2 conduit. I hate the way it will look to have conduit snaking all over the walls. I knew I would have some for the wall outlets and would have preferred to have just that exposed. Oh well the Electrical Gods shall be not tested �� !

 

[Aceman]

Subpanels are very inexpensive.

It's far simpler in general to run one 1" or 1.25" and feed a sub(s), than it is to run multiple smaller conduits across a building by the time you traverse the length of the building and account for the ups/downs.

It also helps with voltage drop as well.

 

[brewchief]

Thank you all the conflicting information makes sense. I have nine current carrying AWG wires. In central Indiana I would imagine we could see temps i the attic of 120. I'm going to look up the tables you mentioned. Update : If I take 30 amps as my starting point because of 9 conductors derate it to a factor of 70%I come up with 21. Then multiply it by a factor of .58 I'm down to an amp rating of 12.18. What the heck?

I think your in the wrong column with your factor of .58

Two 3/4" conduits running across the ceiling instead of going up in the attic would solve everything I think.

Sent from my SM-G965U using Tapatalk

 

[exranger06]

Thank you all the conflicting information makes sense. I have nine current carrying AWG wires. In central Indiana I would imagine we could see temps i the attic of 120. I'm going to look up the tables you mentioned. Update : If I take 30 amps as my starting point because of 9 conductors derate it to a factor of 70%I come up with 21. Then multiply it by a factor of .58 I'm down to an amp rating of 12.18. What the heck?

You're using the wrong column in the table. THHN wire has a temperature rating of 90* C, so you use the 90* column. That gives you an adjustment factor of 0.82, not 0.58. That gives you an adjusted ampacity of 17.22 A. You'd still need 15A breakers with 12 AWG wire. If you upsize the wire to 10 AWG, you'll have an adjusted ampacity of 22.96, and you could use 20 A breakers. You just have to redo the conduit fill calculation and make sure you can fit that many #10 wires in it. (For that, you count ALL conductors, not just the current carrying ones).

 

[exranger06]

According to the Southwire conduit fill calculator, you can fit 16 #10 THHN wires in a 1" EMT conduit, so you can proceed with your original plan of running a single 1" conduit.

 

[ddawg16]

Having a similar situation with 3-way's.....in retrospect, smart switches would be a much better option.

Nothing like crawling into bed, looking out the window and realizing I forgot to turn off a light in the garage.

Is there a reason you want to run conduit?

Romex is fine as long as it's protected from damage. If it's up in the attic, it's considered protected.

But conduit does have advantages...I prefer using THHN/THWN over solid wire.

And....any reason you can't use PVC conduit? Easier to cut....you don't have to debur the ends. I know you can use EMT as the ground....but I'm not a fan of depending on the EMT as the earth ground...I prefer that green wire.