voltage drop and ground sizing question

[Coyote556]

So I ran a bunch of outlets with 12ga stranded thhn and 12ga ground in 1/2" emt. All on 20a breakers. Now I am worried the runs are too long for the voltage drop. I think they are around 120-165 feet.

1) do you think I should rerun with 10ga?
2). Can I leave the 12ga ground wire for the circuits or does it need to be 10ga also?

I don't want to damage any of my tools with excessive voltage drop.

Thanks

 

[Friartuck]

Using on on-line calculator:
http://www.calculator.net/voltage-d...ce=165&distanceunit=feet&amperes=20&x=49&y=12

The worst case of 165 feet and full 20 amp load using 12AWG leaves an end voltage of 109 VAC, or 8.7% drop in voltage. NEC threshold for low voltage condition is 5 percent drop, which makes your installation unacceptable. Lighter loads and shorter distances yield more favorable percentages, you're right at the threshold.
1) Even if it is rerun with 10 AWG the numbers are just over the NEC limit at 5.5%,
2) Can't comment on whether the ground must be the same size as the hot and neutral.

Changing over to 10AWG at the greatest distance and highest 20 Amp load is slightly over the 5% threshold, so I'll revise my answer to change to 10 AWG. Would consider solid vs stranded.
Agree with unsinkable that separate ground conductor is easier and more effective than relying on EMT.

 

[Coyote556]

It is just one large bldg (48x75) and the runs were right from the 200a main panel. I think I just failed to pick the right size wire. So you think less than 10% drop is OK?

 

[unsinkable]

Maximum allowable voltage drop on branch ckts is 5%.
YES, you need to increase wire size.
YES the ground should be the same size.
As of now it is still legal to use emt as ground, this means you must ensure adequate continuity, no rust, tight connections. Also you need to remove all the little cardboard screwsholders from every device yoke or run pigtails to bond screw in box...Just easier and less PITA to run a grounding conductor.
Compressor motors and brushed motors (drills) really object to undervoltage, and will prematurely give up the ghost.

 

[Norcal]

Maximum allowable voltage drop on branch ckts is 5%.
YES, you need to increase wire size.
YES the ground should be the same size.
As of now it is still legal to use emt as ground, this means you must ensure adequate continuity, no rust, tight connections. Also you need to remove all the little cardboard screwsholders from every device yoke or run pigtails to bond screw in box...Just easier and less PITA to run a grounding conductor.
Compressor motors and brushed motors (drills) really object to undervoltage, and will prematurely give up the ghost.

No you don't, the receptacles need to be self grounding in order to avoid a pigtail & the screw retainer does not need to be removed.

If a grounding conductor is used rather then using a metallic conduit for grounding, then if the ungrounded conductor (hot) is increased in size the grounding conductor must also be increased in size per 250.122(B).

 

[sberry]

How much load are you putting on these circuits? Very rarely is a general branch loaded to 20A, a high power tool other than a comp or welder runs about 13A. Running 4 1/2 grinders, drill motors, trouble light or modest battery charger and it wont notice any difference.

 

[CoopVA]

Are you wrapping this all the way around the building? Split it into two circuits and wrap one around one way, and the other around the other way. That way you cut the length in half and can stick with 12 wire...


Sent from my iPad using Tapatalk

 

[Friartuck]

I still think a subpanel on the other side of the building will 1) reduce these lengths in half, 2) can stay with 12 AWG wire, and 3) provide 220 if you need it later. sberry comment on loads is also true.

 

[sberry]

I have worried about this endlessly till I was near sick when I was a little younger and now I know why the old timers said, relax, a 1/2 pipe is fine for air and so is 100 ft for the 12,, they knew what the real applied load was and for how long.
The same for the endless babble over hi flow fittings. They help a pinch with a 1/2 air gun wide open in a truck shop, on a 1/4 or 3/8 air ratchet not noticeable or pointless and millions of the normal ones have been used by millions of mechanics for millions of hours over decades.

 

[unsinkable]

Sorry, I mistakenly wrote 5% VD for branch ckts, it's actually 3%.
I'm not a code nazi by any stretch, but I do live down the road from from the NFPA, and most local inspectors tend to be very rigid. They do require us to remove any non metallic screw keepers when using the yoke for continuity, assuming no grd conductor.
As others have posted, there are other ways to reduce the resistance (VD) but if you're limited to the paths you've already run, I would still up to #10's.
The cost of one burned up beer fridge (not that !) or motor, you'll wish you did.

 

[sberry]

I agree with motor starts, not so much worry with common tools but fridges maybe. I ran 10 in my storage for this reason. Didn't want an extra panel although it might have been as easy but its 160 ft also and I had the wire and used it on a couple recept circuits, did some welding with a Maxstar from it and never had any reason to feel I wasn't next to the panel.

 

[justsam]

Remember this "excessive" voltage drop is only going to be at the end of your run. The drop will be less and less as you get closer to the breaker, so if you are concerned about things like a refrigerator, put it closer to the breaker.

If these outlets are only going to serve things such as power tool battery chargers, task lights, etc. I would not be too concerned.

I am sure the pro's will correct me but I believe the NEC recommends 5% as a way to provide "efficiency of operation", not as a mandatory rule.

Also remember, as has been stated it has to do with total voltage drop, including all branch and feeders when it comes to maintaining proper voltage for equipment. If your line voltage is already on the high side, say 125, it is less of a problem than if your line voltage is 115.

As the end of the day, whomever has jurisdiction rules based on their interpretations of mandates versus recommendations.

 

[Coyote556]

Instead of pulling wire back out, what if I just put those circuits on 15 amp breakers and ran new circuits with the 10 gauge on 20s? it would probably be more outlets than I need but wouldnt 15 amp breakers on 12 gauge wire with those distance runs be fine for the voltage drop?

 

[23 CHIEF]

....

 

[sberry]

15A breaker wont help with drop, it will still be the same.

 

[Charles (in GA)]

15A breaker wont help with drop, it will still be the same.

It will, indirectly, as it limits the total amperage on the circuit. You get the voltage drop at heavy loads, cut the load by 25% and you will not see as great a voltage drop.

Its still too high however, at 7.17% over 165 ft, 12 gauge, 15 amps.

Charles