what size should I run

[green2012]

Im trying to figure out how long of a run I can have before having to upsize my wire. I wont know the run length before the job starts and I want to be sure I bring the right wire and pipe size with me. Here is what I got..

240v 30amp dryer and a dedicated 120v 10amp washer. Im using THHN copper wire and this will be run in pipe. The weird thing that making me second guess my results is that at 90 feet both circuits require 10AWG wire. I dont think its over 90 feet but can anyone tell me the wire size at 70feet, 80, 90, and 100? ( both circuits)

Also I know the ampacity drops when I run more then 3 wires in a pipe to 80 percent of their rating. This doesnt need to be factored into voltage drop correct?

 

[kingpb]

Very good tool to know this on the fly - is download the Southwire Cable VD app.

You are correct, the derate for ampacity has nothing to do with VD, other than as you upsize your wire (if needed) it will lower VD which is good.

Don't forget that you can start with the ampacity in the 90 deg C column, and as long as the derated value is less than or equal to the 75 deg C column your good to go. Once you have that size, double check for VD. 90 ft is not a long way, and typically (tongue in cheek) it's not a worry until you get closer to 200ft. But always good to check.

 

[infinity]

I dont think its over 90 feet but can anyone tell me the wire size at 70feet, 80, 90, and 100? ( both circuits)

70', 80', 90' or 100', 30 amp #10 THHN, 20 amp #12 THHN.

 

[lielec11]

Very good tool to know this on the fly - is download the Southwire Cable VD app.

You are correct, the derate for ampacity has nothing to do with VD, other than as you upsize your wire (if needed) it will lower VD which is good.

Don't forget that you can start with the ampacity in the 90 deg C column, and as long as the derated value is less than or equal to the 75 deg C column your good to go. Once you have that size, double check for VD. 90 ft is not a long way, and typically (tongue in cheek) it's not a worry until you get closer to 200ft. But always good to check.[/QUOTE

For voltage drop as a rule of thumb I typically allow myself a distance up to the phase-phase voltage before worrying (i.e. 480ft for 480V, 208ft for 208V).

Anyway, regarding your question...

You'll need 2#10,#12G for the 240V 30A dryer, and 2#12,#12G for the 120V 10A washer. Based on the distance and 3% voltage drop, you will be fine with these values. When you factor in derating based on 4 current carrying conductors, you still should be fine. I'm assuming you're using 90 deg C. 3/4" conduit would be fine, although you may be able to get away with 1/2"conduit if you do the calculations.

 

[kwired]

Im trying to figure out how long of a run I can have before having to upsize my wire. I wont know the run length before the job starts and I want to be sure I bring the right wire and pipe size with me. Here is what I got..

240v 30amp dryer and a dedicated 120v 10amp washer. Im using THHN copper wire and this will be run in pipe. The weird thing that making me second guess my results is that at 90 feet both circuits require 10AWG wire. I dont think its over 90 feet but can anyone tell me the wire size at 70feet, 80, 90, and 100? ( both circuits)

Also I know the ampacity drops when I run more then 3 wires in a pipe to 80 percent of their rating. This doesnt need to be factored into voltage drop correct?

Actual voltage drop will depend on actual load. You mention 30 amp dryer - it is likely a 30 amp circuit with an actual load somewhere between 22-25 amps would be my guess. (5500 watts seems to be fairly popular heater size on those) You did mention 10 amps for the washer - which is probably a good average for most washers, unless it maybe has water heating then it could be higher.

Next you have to know how much VD you are going to consider acceptable. NEC only suggests 3 and 5 percent figures in an informational note, it does not require any voltage drop considerations.

Be aware that voltage drop will be higher percentage more easily on the 120 volt circuit then it is on the 240 volt circuit - every amp at 120 will be twice the drop percentage wise as it is at 240- which is likely why you came up with same size conductor so far with whatever you have figured.

 

[green2012]

my voltage drop app tells me that at 100 feet a 10 amp load requires 10AWG. Forgot to mention that this is chicago and cant go past 3% drop. is it 5% drop for national code? I know in chicago cant go past 3 % drop on any branch circuit.

 

[infinity]

There is no voltage drop compensation required by the NEC for these loads.

 

[kwired]

my voltage drop app tells me that at 100 feet a 10 amp load requires 10AWG.

At what voltage? That can make a big difference. You had both a 120 and a 240 volt load in the OP.

I guess the 10 amp load was the 120 volt load. I come up with 10 AWG as well for 3% max drop @ 10A 120V.

For the dryer, if you use 30 amps as the load, you are just slightly over on a 10AWG if you want 3% drop according to my calculations. But so close I wouldn't worry about it myself. But if your dryer actually draws about 24 amps you are just fine with 10 AWG and 3% drop.

 

[don_resqcapt19]

my voltage drop app tells me that at 100 feet a 10 amp load requires 10AWG. Forgot to mention that this is chicago and cant go past 3% drop. is it 5% drop for national code? I know in chicago cant go past 3 % drop on any branch circuit.

I get a 3% drop for 100' of #10 copper at 30amps and 240 volts, or at 15 amps and 120 volts, with the online calculator that I use,

 

[qcroanoke]

You'll need 2#10,#12G for the 240V 30A dryer, and 2#12,#12G for the 120V 10A washer. Based on the distance and 3% voltage drop, you will be fine with these values. When you factor in derating based on 4 current carrying conductors, you still should be fine. I'm assuming you're using 90 deg C. 3/4" conduit would be fine, although you may be able to get away with 1/2"conduit if you do the calculations.

The dryer will require a #10 ground per table 250.122. Or use the conduit as the equipment ground.

 

[kwired]

You'll need 2#10,#12G for the 240V 30A dryer, and 2#12,#12G for the 120V 10A washer. Based on the distance and 3% voltage drop, you will be fine with these values. When you factor in derating based on 4 current carrying conductors, you still should be fine. I'm assuming you're using 90 deg C. 3/4" conduit would be fine, although you may be able to get away with 1/2"conduit if you do the calculations.

The dryer will require a #10 ground per table 250.122. Or use the conduit as the equipment ground.

If it is all in one raceway you only need one EGC sized for the largest overcurrent device protecting conductors in that raceway - 30 amps = 10 AWG. I hope your first 12 was just a typo. Metallic raceway could be used for the EGC.

 

[lielec11]

You'll need 2#10,#12G for the 240V 30A dryer, and 2#12,#12G for the 120V 10A washer. Based on the distance and 3% voltage drop, you will be fine with these values. When you factor in derating based on 4 current carrying conductors, you still should be fine. I'm assuming you're using 90 deg C. 3/4" conduit would be fine, although you may be able to get away with 1/2"conduit if you do the calculations.

The dryer will require a #10 ground per table 250.122. Or use the conduit as the equipment ground.

You are correct I missed that, thank you.

 

[lielec11]

If it is all in one raceway you only need one EGC sized for the largest overcurrent device protecting conductors in that raceway - 30 amps = 10 AWG. I hope your first 12 was just a typo. Metallic raceway could be used for the EGC.

This is as per 2250.122(C). My question is, what do you do at the loads, splice the EGC and extend the ground to each load? I guess I am not used to this because we typically specify one EGC per circuit regardless.

 

[John120/240]

This is as per 2250.122(C). My question is, what do you do at the loads, splice the EGC and extend the ground to each load? I guess I am not used to this because we typically specify one EGC per circuit regardless.

Yes at the first J-box splice a pig tail for that device's EGC, repeat as needed. One EGC conductor per circuit is acceptable but redundant. For metallic conduit systems many electricians will use the conduit as their EGC. The thing about using conduit as your EGC is, Do you have faith that all of your EMT set screw connections are tight ?

If it makes you sleep better pull one EGC sized to your largest OCPD & splice pig tails as needed.

 

[lielec11]

The thing about using conduit as your EGC is, Do you have faith that all of your EMT set screw connections are tight ?
.

One of the reasons why I always spec compression fittings and do not allow set screw type.

 

[Pharon]

One of the reasons why I always spec compression fittings and do not allow set screw type.

Or you could just always make sure to run a separate EGC and not use conduit as a ground path - which I think is kinda hack, to be honest.

 

[don_resqcapt19]

One of the reasons why I always spec compression fittings and do not allow set screw type.

It has always been, and still is, my opinion, that a set screw EMT coupling or connector is a better grounding connection than the grounding connection made by a compression coupling or connector. I have found many more loose or broken compression type couplings and connectors than I have set screw ones.

 

[qcroanoke]

It has always been, and still is, my opinion, that a set screw EMT coupling or connector is a better grounding connection than the grounding connection made by a compression coupling or connector. I have found many more loose or broken compression type couplings and connectors than I have set screw ones.

I agree. But it is really hard to tell a customer that specifying compression fittings or higher ups in my company that it gets you nothing if the mechanic doesn't tighten the fitting...... And we pull a ground also.

 

[roger]

It has always been, and still is, my opinion, that a set screw EMT coupling or connector is a better grounding connection than the grounding connection made by a compression coupling or connector. I have found many more loose or broken compression type couplings and connectors than I have set screw ones.

And I second that. One reason is, it is much easier to get a screw driver into tight areas than it is to get a couple pairs of adjustable pliers into tight areas. I did a group of OR's once where the engineer speced set screw fittings for that reason alone.

Roger

 

[lielec11]

And I second that. One reason is, it is much easier to get a screw driver into tight areas than it is to get a couple pairs of adjustable pliers into tight areas. I did a group of OR's once where the engineer speced set screw fittings for that reason alone.

Roger

This thread has shined some light on this subject for me and I appreciate everyone's input. I wonder why my firm is so dead set on specifying only compression fittings and never set screw?