Voltage drop on residential branch circuits

[kwired]

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.

I believe there is energy codes in a lot of places but not many that put much emphasis on enforcement.

 

[retirede]

I believe there is energy codes in a lot of places but not many that put much emphasis on enforcement.

For sure. Which makes it even more important to mention which code is being discussed.

 

[Fred B]

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

The old NM not NM-B was a 60⁰ conductor as the insulation was not up to the higher temperature. And then there was also the problem with lighting fixtures mostly where 2 things happened, fixtures had no heat insulation or it was removed and the HO would put in a higher wattage bulb than was indicated as a maximum, both led to heating of the wire (not due to load) and insulation becoming very brittle and breaking up.
So, I think, the code rather than say ALL old NM be replaced, it just stays with a lower amp limit for even the newer NM-B.

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.

While it did show a higher ampacity there was an *note that limited the #14 to a 15A overcurrent protection in other than what was allowed in 240.4(E) or (G). In 1999 a reference to 240.3(D) that limited the small conductors #14 to 15A, And in '08 a reference to 240.4(D) was that limited to 15A was added and continues to 2023. This reference also appears to include even THHN, that it would still be limited to 15A, and respectively even #12 and #10 limits it to the lowest amperage rating. Not sure why the code shows to start with a higher rate on these "smaller" conductors even though for a long time they were limiting the overcurrent protection to the lowest or lower value.

 

[nizak]

A 15A branch circuit is being upsized to 12/2 romex for a long run (130'). Can you pull the homerun in 12/2 romex and have jumpers to other receptacles downstream be in 14/2 Romex?
Question is from a Code standpoint to begin with. But also from an electrical theory standpoint.

The voltage dropped is across the whole circuit (someone could potentially pull 12A off that 15A circuit at the last receptacle. Would this cause an issue to say, the 10' jumper from box containing the HR (with 12/2 HR) to next receptacle (14/2 from HR box onward).

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?

General purpose receptacles wired with 12/2. Lighting 14/2.

In residential wiring pretty hard to go wrong with this scenario.

Even seemingly long runs very seldom if ever are problematic.

Most residential guys around here wouldn’t give a second thought to overall circuit length of up to 150-200’+with 14/2 for receptacles.

I use #12 for receptacles and have never knowingly had a complaint in 25+ years.

Just my opinion.

 

[electrofelon]

The old NM not NM-B was a 60⁰ con

So, I think, the code rather than say ALL old NM be replaced, it just stays with a lower amp limit for even the newer NM-B.
.

Which makes no sense. The code covers new installations and new NM is rated 90.

 

[kwired]

So, I think, the code rather than say ALL old NM be replaced, it just stays with a lower amp limit for even the newer NM-B.

I've seen a fair share of even 90C conductor (not just NM-B) that was heat damaged by lighting fixtures. Even basic keyless with 200 or 300 watt incandescent lamp in it will do so in some cases.

 

[Little Bill]

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.

The 180Va per receptacle doesn't apply to dwellings.

 

[Strathead]

The 180Va per receptacle doesn't apply to dwellings.

I didn't say that it does. I also didn't say that it applies to voltage drop calculations. I said that I just use it when there is not valid information and instead of an arbitrary number I use it.

 

[Strathead]

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.

In reality, when I made that statement, I don't even know whether the OP knows that code. I was informing the forum so that our subsequent answers WOULD have that information.

 

[Little Bill]

I didn't say that it does. I also didn't say that it applies to voltage drop calculations. I said that I just use it when there is not valid information and instead of an arbitrary number I use it.

And I didn't say you did say it does. I posted that for anyone that doesn't know.