one thing to add about the 12 ga-14ga chat that no one seems to have brought up. the various size wires have always been rated for certain amp ratings based on how much heat the wire insulation will take without deteriorating. the 15 and 20 amp ratings for 14 and 12 wire are based on the old type tw wire, the first with plastic insulation. tw wire was used in romex cable, in conduit, in bx armor. in 1987 tw wire was phased out, replaced with thhn wire for the same uses. thhn has plastic insulation with a clear nylon jacket. if you look thru the tables in the back of the nec code book, you’ll find the amperage of wire is tied not only to wire size, but to the insulation and whether it’s in conduit, cable or free air. when the change was made, 14ga thhn in cable could safely carry 25 amps, 12 ga even more; they left the circuit ratings for those two sizes unchanged, but changed the ratings for the larger sizes. everybody was used to that rule, and they didn’t want some dope replacing his 15 amp breakers with 20’s on the older wire in millions of houses. once i did see a house where someone had put a 100 amp main on an older service entrance cable that shouldn’t have had more than 80 amps. i use 12ga when voltage drop might be a problem, but because ease of use, box fill rules and more than adequate capacity, i use 14 ga wire wherever i can. there are separate rules limiting how many outlets can go on 15 amp (10) and 20amp(12) circuits anyway.
getting off my soapbox now.
ol’ buzzard
Replies
RE: "there are separate rules limiting how many outlets can go on 15 amp (10) and 20amp(12) circuits anyway. "
Actually this is a common misconception. There are no numeric limits, adequacy for the loads present is a different requirement, on how many receptacles can be on any one circuit. You can win a few bets on this point. Many experienced electricians don't understand this point. No harm generally but still not true.
There are rules, in the NEC, for calculating the theoretical load on a circuit per receptacle used for calculating the minimum service size and neutral size. There are also requirements for the designed minimum number of circuits in a building for calculating the minimum service but nothing setting the maximum number of receptacles on a circuit.
The 10 and 12 per circuit, 15 and 20A respectively, are just general rules of thumb passed down by generations of electricians. These are guidelines of reasonableness and part of the electrical culture. Most trades have similar rules of thumb, a reference to the diameter of the stick you were allowed to beat your wife with. These are not in the code.
re - Most trades have similar rules of thumb, a reference to the diameter of the stick you were allowed to beat your wife with.
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Huh ??
Anyway, I dealt with an inspector for an electrical upgrade and he helped me out tremendously by suggesting certain details are left to the best judgement of the person performing the work on any given situation.
I was getting bogged down and worrying about every minute detail that I thought would need to fit the code to a T.
If he felt someone was serious about doing it right or over doing things, he would help tone down the scope to a more sensible level so a serious DIY fool such as myself wouldn't go overboard.
(But he had very little tolerance for shoddy workmanship or outright code violations and was well known for being strict with contractors.)
This has helped me in subsequent electrical projects, all involving full inspections that passed with no incident.
Nothing to do with electricity the "Rule of thumb" reference.
I had always been told that the reference was to a rule allowing beating of your wife with a stick. Provided the stick was no thicker than a thumb. We were human folk back then.
More recently I read that this origin is incorrect. Seems the good money is tha the term has its origin in some long lost event/s that elude modern research.
You can't really go wrong in most cases with your numeric limit. In most cases it is as good a number as any. That these numeric limits are not code and why they are not is probably too involved for most people, and not a few electricians.