Voltage drop on residential branch circuits

[Little Bill]

If I saw a #12 cable enter a panel and the hot(s) immediately reduced to #14, I would read it as a 15a circuit.

I don't think the OP was reducing back to #14 at the panel. He was talking about reducing at devices in order to better fit the device terminals.

 

[LarryFine]

I don't think the OP was reducing back to #14 at the panel.

You're right. I suggest that be done.

 

[CoolWill]

You can't spend a lot of time worrying what someone MIGHT do in the future. Really, even if someone puts in a 20 amp breaker in the future, it isn't much of a hazard. It isn't likely any specific portion of the circuit will see 20 amps, even if the homerun does. Just run it all in MI cable and rest easy.

 

[electrofelon]

You can't spend a lot of time worrying what someone MIGHT do in the future. Really, even if someone puts in a 20 amp breaker in the future, it isn't much of a hazard. It isn't likely any specific portion of the circuit will see 20 amps, even if the homerun does. Just run it all in MI cable and rest easy.

Right, plus 14 NM is actually rated for 20 amps.

 

[solarken]

A 15A branch circuit is being upsized to 12/2 romex for a long run (130').

Bonus Question - If you do a voltage drop calculation on this (2x12.9x130'x12A = 40240/3.6V(3% VD on 120V circuit) = 11,180cm) (#10 = 10380cm). This leads me to believe, to properly stay below 3% Vd, you should run 8/2 NM to these receptacles. Is this "Correct" and are people doing this?

What am I missing/ not understanding?

10AWG will keep VDrop below 3% for 130ft run at 12A. 8/2 is overkill.

 

[kwired]

I've been wyring for 25 years now, and I don't think I have ever upsized a resi branch circuit for VD.

With LED's being somewhat sensitive to voltage fluctuations it could possibly be worth some consideration in some circumstances. Still won't matter if the fluctuation is occurring before your branch circuit though.

 

[kwired]

I don't think the OP was reducing back to #14 at the panel. He was talking about reducing at devices in order to better fit the device terminals.

Or just making the home run 12 AWG because of it's length and running the rest of the circuit in 14 AWG.

 

[kwired]

Unless some other code comes into play, NEC alone doesn't have any voltage drop requirement here, just the 3 and 5% suggestion mentioned in an informational note. Most things we typically have in dwellings can handle at least 10% variation in voltage from 120 nominal and not have any serious consequences. When voltage fluctuations cause lights to dim a little that can become somewhat annoying but still isn't really hurting the light in most instances. I try to keep lighting on circuits that only supply lighting and that helps with this issue, still won't matter if the voltage dip causing the dimming is on the feeder or service conductors though.

 

[retirede]

With LED's being somewhat sensitive to voltage fluctuations it could possibly be worth some consideration in some circumstances. Still won't matter if the fluctuation is occurring before your branch circuit though.

Not putting lighting and receptacles on the same circuit would seem to be prudent.

 

[Flicker Index]

You can't spend a lot of time worrying what someone MIGHT do in the future. Really, even if someone puts in a 20 amp breaker in the future, it isn't much of a hazard. It isn't likely any specific portion of the circuit will see 20 amps, even if the homerun does. Just run it all in MI cable and rest easy.

A lot of seemingly overzealous things in code is to take such thing into consideration.

 

[CoolWill]

A lot of seemingly overzealous things in code is to take such thing into consideration.

But the code didn't take that into consideration. It says we can upside a wire for voltage drop. But it doesn't say to put a label on it at the breaker warning that there are portions of the circuit that contain smaller conductors. It's over thinkers worrying about unlikely future events outside of their control that ponder such things.

 

[Flicker Index]

But the code didn't take that into consideration. It says we can upside a wire for voltage drop. But it doesn't say to put a label on it at the breaker warning that there are portions of the circuit that contain smaller conductors. It's over thinkers worrying about unlikely future events outside of their control that ponder such things.

I'm saying generally speaking, code takes future implication of present day actions into consideration.

 

[Fred B]

Right, plus 14 NM is actually rated for 20 amps.

Yes and no, while #14 @ 90^o C is 25A and then most only @ 75^o C due to terminations is 20A, NM-B is even though technically a 90^o wire shall only be used @ 60^o C for a Calculated load of not more than 15A.

 

[suemarkp]

In older versions of the NEC (at least through 2008), #14 even at 60C was rated at 20A. Not sure when that changed and if there was evidence that 20A was to high or it was just another notch in the safety margins. 240.4(D) still limited it to 15A though in most cases.

 

[electrofelon]

Yes and no, while #14 @ 90^o C is 25A and then most only @ 75^o C due to terminations is 20A, NM-B is even though technically a 90^o wire shall only be used @ 60^o C for a Calculated load of not more than 15A.

Of course. But my point was if you just go by the ampacity tables that we use for everything else. Yes you would have to ignore the small Conductor rule and the 60 degree requirement - but not sure anybody knows why those rules are in there anyway

 

[Strathead]

From an NEC standpoint, there is no requirement for voltage drop. As long as the conductors are properly protected, it’s fine.

This is correct from an NEC perspective, however the energy codes of the Florida Building Code REQUIRE compliance to a combined voltage drop of 5% on feeders and branch circuits, so it is code in the OP's area.

 

[Strathead]

I highly doubt my receptacle will draw 12A, but at what point am I required to protect against the potential load? (Always right?).

I also live in Florida and my opinion is never. I specify wire size to my guys all the time for voltage drop, unless the receptacle is clearly identified for a specific piece of equipment I use 180va per duplex and will validate this as the value the code uses for general purpose receptacles.

 

[infinity]

This is correct from an NEC perspective, however the energy codes of the Florida Building Code REQUIRE compliance to a combined voltage drop of 5% on feeders and branch circuits, so it is code in the OP's area.

Does this energy code tell you how to calculate the voltage drop on a general purpose branch circuit in a dwelling? If not then the 5% number is meaningless.

 

[retirede]

This is correct from an NEC perspective, however the energy codes of the Florida Building Code REQUIRE compliance to a combined voltage drop of 5% on feeders and branch circuits, so it is code in the OP's area.

To be fair to the rest of us, he simple said “code” and since this is an NEC forum, responses are crafted in reference to the NEC.

It would be a good idea if anyone mentioned a code other than the NEC on here that the spell out what code they are referring to.

 

[kwired]

Of course. But my point was if you just go by the ampacity tables that we use for everything else. Yes you would have to ignore the small Conductor rule and the 60 degree requirement - but not sure anybody knows why those rules are in there anyway

Small conductor rule doesn't apply to 430 and 440 applications as well as a few other applications. Of course 60 C still applies to NM cable. Really confuses some people when they see 12 AWG on a 40 amp breaker and are told it is ok.