downsizing wire size to a light fixture

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LarryFine said:
A short-circuit fault is a short-duration event, so there's little time for insulation damage.
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Well, if that's acceptable, then why not allow us to pull #18's from a switch to a single fixture as long it's rated for the load of said individual fixture? I'm just saying the mismatch of manufacturer fixture wire size and typical lighting branch circuit wire size has always kinda bugged me.

I guess the upside to larger branch circuit wiring is room for expansion.
 
Could someone please give an example of how and why they would go from 12 to 18. I have never done this before. Would it be cost\time effective. Thanks
 
Jerramundi said:
Question #1) If the #18's are large enough to open the OCPD during a fault, that is to say, large enough to briefly handle an amount of current that exceeds the rating of the OCPD, why are they not considered large enough to handle the branch circuit current from say the switch to a single fixture? Obviously it's different if that branch circuit section is ahead of multiple loads.
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You say "obviously it's different...". Why is that so obvious? I mean, fault current is fault current, OCPD rating is OCPD rating: whether that's developed by a single fixture or 100 doesn't change anything. I think this an excellent question, and to put a point on it: the question isn't about manufactured fixtures at all. Those are all good. This is about using it in the field...

I know per code there's nothing wrong with a 15A receptacle on a 20A circuit, I'm just saying it bothers my OCD. My mind just conjures up the image of someone plugging in extensions to the point of pulling say 18A and burning up the receptacle.

I think the same of pulling a #14 switch leg from a switch fed by a 20A branch circuit and 20A OCPD. I know I'll catch flak for this, but if the OCPD is 20A, I typically pull #12's all the way to the fixture.

And before you ask, yes.. tap conductors bug me, lol.
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Interesting: I thought technically one did have to stay in 12 AWG for 20A circuit, etc. You are suggesting playing a lot looser with switch legs, for example. I didn't know you could do that I don't think. Although I'm exhausted right now and may not know what I know...
 
CodeQuandary said:
You say "obviously it's different...". Why is that so obvious? I mean, fault current is fault current, OCPD rating is OCPD rating: whether that's developed by a single fixture or 100 doesn't change anything.
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"Obviously different" in terms of sizing the branch circuit for the load under normal operating conditions, not referring to fault current. For example, the portion of the branch circuit feeding multiple luminaires in various rooms (e.g. a single lighting circuit for the entire first floor) is "obviously" going to have a larger load on it than say the portion of the same circuit that goes from a single switch to a single luminaire.

And yes, there is a common debate about whether or not the circuit has to be #12 all the way through. The argument I've heard refers to phrasing such as "the load to be served." It's an old argument that's been rehashed many, many times.

An example being, say you feed a bathroom with a dedicated 20A #12AWG circuit, fulfilling the requirements for the receptacle... do you need to run a #12 to the center light from the switch? I've heard many reputable people argue NO, and reference the phrase "load to be served." Essentially stating that you could feed the bathroom w/ the required dedicated 20A #12 circuit and run #14 from the individual switches.

I like to keep it consistent. I run #12's the entire length and even put 20A switches in when there is a 20A OCPD. There are some who would mock me for doing so and call it "excessive"... and as far as I can tell, they aren't definitively wrong. The only code reference I can think of that would refute their argument is that which says the OCPD determines the circuit rating.
 
CodeQuandary said:
I think this an excellent question, and to put a point on it: the question isn't about manufactured fixtures at all. Those are all good. This is about using it in the field...
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Well, my question is about the manufactured fixtures. I see no reason why #18 would be allowable for the internal wiring of a fixture but not allowable for say, the portion of the branch circuit from the switch to the individual fixture.... UNLESS, as stated in my previous response, that portion of the branch circuit handles multiple loads, then "it's obviously different."

I'm not out there installing #18's. I'm just saying it's always kinda bugged me that the internal wiring of the fixture was allowed to be smaller than that of the portion of the branch circuit feeding said individual fixture. It just seems inconsistent.
 
Personally, I don't think ANY component in a circuit should EVER dip below that of the OCPD rating, not even internal fixture wiring... unless, for example, after crossing a ballast/driver with a built in OCPD that protects the smaller, secondary conductors...

...but I'm not an engineer. I know a lot about the physics of electricity, code requirements, installation methods, et. all, but I'm not yet a "Master Electrician." I give myself the rating of a Sophomore Journeyman as I just recently crossed the 10 year mark, although I haven't yet taken any sort of Journeyman exam. I'm also FAR from graduating from MIT w/ a Masters in Electrical Engineering, lol. I have some humility, lol.
 
Jerramundi said:
Personally, I don't think ANY component in a circuit should EVER dip below that of the OCPD rating, not even internal fixture wiring... unless, for example, after crossing a ballast/driver with a built in OCPD that protects the smaller, secondary conductors...

...but I'm not an engineer. I know a lot about the physics of electricity, code requirements, installation methods, et. all, but I'm not yet a "Master Electrician." I give myself the rating of a Sophomore Journeyman as I just recently crossed the 10 year mark, although I haven't yet taken any sort of Journeyman exam. I'm also FAR from graduating from MIT w/ a Masters in Electrical Engineering, lol. I have some humility, lol.
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I think the thing you are not considering is there are multiple other ways to protect conductors besides an OCPD at the source:. Length limitation, physical protection, controlling the load more stringently, consideration of the likelihood of a fault or overload.....
 
LarryFine said:
No, it's not Kosher to downsize a switch leg.
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I believe it's actually fairly common, no? Perhaps not to downsize below #14, but to say, for example, feed multiple rooms with a #12 lighting branch circuit and feed the lights themselves (from switch to luminaire) w/ #14's. I feel like this is common practice, but I could be mistaken.
 
electrofelon said:
I think the thing you are not considering is there are multiple other ways to protect conductors besides an OCPD at the source:. Length limitation, physical protection, controlling the load more stringently, consideration of the likelihood of a fault or overload.....
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I'm aware. I just suffer from OCPD (Obsessive Compulsive Protection Disorder) :p
 
electrofelon said:
I have never seen that as a common thing.
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I'm certain it is. I've seen the argument on this forum before several times and the argument made in favor of down-sizing the switch leg utilized the phrasing "load to be served."

Few people, in the example I gave, would pull the #12's all the way to the luminaire itself knowing said individual luminaire only pulls a load of about an amp or two.

I know because I distinctly remember that decided to do it against the conventional wisdom just to be excessively safe.

Unless this is some Mandela Effect craziness, I'm certain of it.
 
Jerramundi said:
I'm certain it is. I've seen the argument on this forum before several times and the argument made in favor of down-sizing the switch leg utilized the phrasing "load to be served."

Few people, in the example I gave, would pull the #12's all the way to the luminaire itself knowing said individual luminaire only pulls a load of about an amp or two.

I know because I distinctly remember that decided to do it against the conventional wisdom just to be excessively safe.

Unless this is some Mandela Effect craziness, I'm certain of it.
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No that is not a thing. It is a clear code violation. There is no debate. Maybe they debate that on the DIY forums but not here.
 
electrofelon said:
No that is not a thing. It is a clear code violation. There is no debate. Maybe they debate that on the DIY forums but not here.
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I disagree... and to substantiate my disagreement, here is an example:

Switch leg wire size

. . . and not for connecting fixtures to other fixtures. Agreed, I was merely pointing out that the smaller conductors feeding some fixtures are not required to be an integral part of the fixture.
forums.mikeholt.com
An oldie from 2007, but it's there... and I'm certain there are more if I cared to take the time to dig deeper and refine my search terms. I remember very distinctly reading several forum threads about this topic in the past and it being hotly contested.

I remember because at the time I was engaged in a debate with another contractor who was mocking me for pulling the #12's from the bathroom switch box to the exhaust fan and center light claiming I was being excessive and wasting money.
 
Jerramundi said:
I disagree... and to substantiate my disagreement, here is an example:

Switch leg wire size

. . . and not for connecting fixtures to other fixtures. Agreed, I was merely pointing out that the smaller conductors feeding some fixtures are not required to be an integral part of the fixture.
forums.mikeholt.com
An oldie from 2007, but it's there... and I'm certain there are more if I cared to take the time to dig deeper and refine my search terms. I remember very distinctly reading several forum threads about this topic in the past and it being hotly contested.

I remember because at the time I was engaged in a debate with another contractor who was mocking me for pulling the #12's from the bathroom switch box to the exhaust fan and center light claiming I was being excessive and wasting money.
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Yes there are those fixture tap rules. I thought you were referring to more general "tap a #14 off a #12 circuit for the lighting" like in paragraph 3 post 27.
 
electrofelon said:
Yes there are those fixture tap rules. I thought you were referring to more general "tap a #14 off a #12 circuit for the lighting" like in paragraph 3 post 27.
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Not just tap conductors. See post #29.

Not only that. I know guys I've worked for in the past have done it and while some of them were complete dicks, none of them were hacks or DIYers.
And I know, as referenced in the link provided, I've seen this issue debated on this forum before.

I'm not trying to bash you. I'm just defending what I know was, at least at one point, a reality... and that is that this issue was never a cut and dry code violation, but rather common practice and a hotly contested debate within the electrical community.

I actually agree with you that if starting with a 20A OCPD, the circuit should be #12 or larger, barring a few exceptions such as tap conductors, all the way to the individual luminaire.
 
So I called my local electrical suppliers (2), and they had absolutely no idea what I was talking about when I said fixture wire. I realize 402 lists about 30 kinds of wire that may be or is listed as fixture wire: does anyone know what are the more common types? i.e. XF, or TFF, or whatever? Or, alternatively, anything you have used. Does ordinary lamp cord work? I've never seen a wire-type description of lamp cord, though now that I look I see it is commonly SPT-1 or SPT-2, neither of which are listed as fixture wire.
 
CodeQuandary said:
So I called my local electrical suppliers (2), and they had absolutely no idea what I was talking about when I said fixture wire. I realize 402 lists about 30 kinds of wire that may be or is listed as fixture wire: does anyone know what are the more common types? i.e. XF, or TFF, or whatever? Or, alternatively, anything you have used. Does ordinary lamp cord work? I've never seen a wire-type description of lamp cord, though now that I look I see it is commonly SPT-1 or SPT-2, neither of which are listed as fixture wire.
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Southwire's website has some good tools for this. Here is the spec sheet they provide for TFFN, which also states that MTW or AWM may be used as fixture wire.

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