12AWG to 15A breaker... Allowed?

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hurk27 said:
Voltage drop is a must learn for any person in the electrical field, even though it is an FPN in the NEC and not enforceable,
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I was told that your only allowed something like a 3 percent difference in "acceptable voltage" versus "allowed voltage" or "120V" versus "115" or something to that effect. Thus being enforceable, no?
 
lunalilo said:
I was told that your only allowed something like a 3 percent difference in "acceptable voltage" versus "allowed voltage" or "120V" versus "115" or something to that effect. Thus being enforceable, no?
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Nope see 90.5(C) voltage drop is only an FPN

Good idea to follow and makes for a good designed system, but not enforceable
 
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The other thing to keep in mind with voltage drop is that the goal is to maintain the nominal 120V as much as possible. There are areas with high supply voltages (I've seen as high as 127V/254V where even the farthest endpoint may still be above the nominal voltage with regular sized wiring and supply houses in that area only stock 130V bulbs. Other areas may be at 116V/232V and every bit of help is needed to maintain the already low voltage.
 
jaylectricity said:
So the wire only needs to be #10 until it gets close to the receptacle? Then it doesn't matter any more? That doesn't sound right. Either you need larger wire or you don't.
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Jay, you seem to have had good explanations now, but I'll add another situation.

I deal in electrohydraulics. Our control panels will frequently have a 24VDC 20A power supply for our valves which typically draw 1 to 2 Amp each. Casual observation says #12 wire, right ... ???

Well, the power supply is located 150 feet from the machine. Thus, (+24V and 0V), we have 300 feet of wire. That's roughly 0.5 ohm. 20A, 0.5 ohm ... 10V drop. Start with 24, have 14 at the load ...

What we typically do is run a pair of large conductors (maybe #6) from the panel to the machine, then branch off with individual (typically #16 MTW) short runs to each load. Individual runs of #14 would work ... #16 might, but not well.
 
lunalilo said:
I was watching a rerun Holmes on Homes, and his electrician was redoing a panel and made a big deal out of the fact that the panel was holding all 15A breakers and there were 12AWG romex coming out of it. "Where are these connecting to?" He says afterwards.

1)Is it not allowed for 12AWG romex to connect to a 15A breaker?

2)If not, what would you do if you needed larger gauge wire for voltage drop?
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I saw that episode too. I just laughed. :D
 
Getting back to the original post. Usually when I watch holmes on homes, the biggest problem with the electric is two things, they have #14 wire on a 20A breaker, and the 2nd issue is that they enclose junction boxes with no access to them. Both of those are illegal in the US.
 
hurk27 said:
Voltage drop is a must learn for any person in the electrical field, even though it is an FPN in the NEC and not enforceable
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This is changing for commercial buildings in jurisdictions that have adopted ASHRAE 90.1-2004 or 2007 (Energy Code). In ASHRAE 90.1-2004, Chapter 8 (Power), 8.4 - Mandatory Provisions states,

8.4.1.1 Feeder conductors shall be sized for a maximum voltage drop of 2% at design load.

8.4.1.2 Branch circuit conductors shall be sized for a maximum voltage drop of 3% at design load.

In SC where I live/work, this is an enforceable code, so now voltage drop is code, just not NEC code. It does state, "at design load", meaning a 20A circuit only feeding a 9A is only required to have voltage drop calculations based on 9A, not 16A (20A x 0.8).
 
he's generally pretty good but maybe we all need to look in the mirror. We have grown to accept our code, as so many things in life. But the reality is that I find the NEC insane. On these very forums it becomes difficult to find a consensus about a code question. While each of us believes we know the answer, someone else finds an exception or a story of a different interpretation. Electricians, engineers, and inspectors rarely can agree on a code interpretation--it gets installed per design and spec for a multitude of reasons. 100 electricians=100 different installations and interpretations
 
I watch that show also , and have you noticed that most of the electrical panels shown in the shows have all the branch circuits coming in on both sides of the panel an hardly ever enter from the top of the panel.

Just curious is to why they do that and it looks funky to me.
 
agree on the sideways panel!!! Odd--but I spent 37 years in Chicago where everything is in conduit and now live where almost everything is romex and I learned so many of the myths about conduit. I built my home here and it's all romex---wouldn't have it any other way. Different areas =different methods
 
WinZip said:
I watch that show also , and have you noticed that most of the electrical panels shown in the shows have all the branch circuits coming in on both sides of the panel an hardly ever enter from the top of the panel.

Just curious is to why they do that and it looks funky to me.
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Probably because the top section, where the service/feeder enters, has a separate enclosure. They're protected from contact with the incoming conductors.
 
That's because that "electrician" on that show is a moron. They could have ran #12 to the first junction box then switched to #14. Unless you pull apart the whole circuit you would have no idea what was down down stream. Nothing wrong with using a 15 amp breaker on #12 wire.
 
Lot of existing circuits I run across the exact opposite happens, starts out with #14, somebody makes an add on (should I insert the word hack here?) using a length of #12 romex . Nothing wrong with it at all, but it raises my "Danger Will Robinson" antenna to be on the lookout for other goodies when I come across it.
 
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