30 amp breaker protecting #12

[Jim W in Tampa]

when wiring it new i would have ran #10 just to be in safe zone if mr ac installs a unit other than planned but if this was 100's of units then i would check first as to what will be installed. Very costly to be wrong

 

[Mule]

You wont when they are brand new units, but over time there could be.

So, I havent been doing wrong, just didnt understand it fully?

So back to my pnl/service upgrade...I just check the nameplate and insure the existing wire is to the min cir amps, and brk is to the max fuse or hacr brk size?

 

[JohnJ0906]

So back to my pnl/service upgrade...I just check the nameplate and insure the existing wire is to the min cir amps, and brk is to the max fuse or hacr brk size?

Yes.

Don't trust the existing breaker - at least 1/2 the time it isn't correct anyway, check the nameplate.

 

[Mule]

when wiring it new i would have ran #10 just to be in safe zone if mr ac installs a unit other than planned but if this was 100's of units then i would check first as to what will be installed. Very costly to be wrong

Im with you, normal installations the cost difference is hardly nothing in the scheme of things....

In my world of upgrading old services, I find old branch circuits "hot rodded" with too large of breakers all the time...not just hvac circuits..

 

[stickboy1375]

So, I havent been doing wrong, just didnt understand it fully?

So back to my pnl/service upgrade...I just check the nameplate and insure the existing wire is to the min cir amps, and brk is to the max fuse or hacr brk size?

Correct....

Manufactures dont just make these numbers up, They are sized by using sections 440.22 (A) or (B), So lets say you had a AC compressor rated at 18 amps. The conductors are sized at 125% of the compressor current rating,

18A x 1.25 = 22.5A 12 AWG rated at 25A at 75 degrees.

To find Branch-Circuit Protection, [440.22(A)] at 175%,

18A x 1.75 = 31.5A, next size down [240.6], 30A device.

 

[brother]

I suppose my thread took a 'life' of its own. Im curious as what did prevent the #12 from overheating, I was just thinking about the time curve of some of these breakers. It just seems like this shouldve been a 'burn out'. However at the momment, I thought I read somewhere that one can put ligting and ONLY lighting on a 30 amp with #12. It excapes my memory right now.

I know there are exceptions for motors, but these were only receptacles.

 

[Jim W in Tampa]

I suppose my thread took a 'life' of its own. Im curious as what did prevent the #12 from overheating, I was just thinking about the time curve of some of these breakers. It just seems like this shouldve been a 'burn out'. However at the momment, I thought I read somewhere that one can put ligting and ONLY lighting on a 30 amp with #12. It excapes my memory right now.

I know there are exceptions for motors, but these were only receptacles.

Yes your tread took a wrong turn, sorry. Other than motors #12 should never been on anything higher than 20 amp breakers. As to what saved the number 12 was the guy upstairs and plain good luck. #12 can handle 30 amps but its at risk. In time if the load was at full 30 it will start doing damage to insulation. Keep in mind breakers are actually doing nothing unless amps go over its rating. If we have no shorts or overloads we do not even need fuses or breakers. When is last time you tripped a breaker in your house ?

 

[brother]

Yes your tread took a wrong turn, sorry. Other than motors #12 should never been on anything higher than 20 amp breakers. As to what saved the number 12 was the guy upstairs and plain good luck. #12 can handle 30 amps but its at risk. In time if the load was at full 30 it will start doing damage to insulation. Keep in mind breakers are actually doing nothing unless amps go over its rating. If we have no shorts or overloads we do not even need fuses or breakers. When is last time you tripped a breaker in your house ?

I really cant remember the last time i tripped a breaker in my house, a gfci yes, a breaker no. Yes i believe it was divine intervention that kept that wire from over heating. What gets me is that this is not that old of work (maybe a few years back) and it was in a hospital!! This just shows the need for inspections.

Ill have to check my old code books, but I recall there being an 'exception' at one time where so long it was just 'ligting' and no other circuits that a #12 coud be on a 30 amp. I always thought that was a BAD idea, and if they deleted it then thats good!!

 

[Cold Fusion]

Ill have to check my old code books, but I recall there being an 'exception' at one time where so long it was just 'ligting' and no other circuits that a #12 coud be on a 30 amp.

I don't remember anything like that back to the 75 edition. I can't figure why there ever would have even been anything like that. Why would it be okay to overload a lighting circuit and not a receptacle circuit?

I'll be interested to know if I'm wrong on this. It would be good to know the panel reasoning on the difference.

cf

 

[Jim W in Tampa]

I don't remember anything like that back to the 75 edition. I can't figure why there ever would have even been anything like that. Why would it be okay to overload a lighting circuit and not a receptacle circuit?

I'll be interested to know if I'm wrong on this. It would be good to know the panel reasoning on the difference.

cf

I know of no exception for lights. Could see a reason to maybe allow if it had restrikes in a parking lot or warehouse but far as i know there are no exceptions in nec.

Inhouse electrician/maintenance men often trash systems with repairs and additions that are far from code compliant. Unless local laws change there is little to stop them. They pull no permits so get no inspections. I have even seen buildouts that you know never got permited from the number of open violations. Seen one that even had open wiring with thhn and splices, receptacles and switches that had no box. They work on the idea that if it works then its ok.

 

[brother]

Not only that, I had found where a someone had not put a duplex receptacle (same yoke) on a 'common' disconnect (basically a tie handle). They couldnt do it cause they had the circuits too far apart (#3 and #40). I tried to tell them but it was just a debate even after I showed the 2005 code (which is what they are under)!! Their claim is that when the 'tab' is broken then its not the same yoke!! give me a break!! it gets frustrating sometimes over little this stuff. Well at least the wire appeared to sized right, so if it overloads it will trip the breaker.