30 amp breaker protecting #12

[brother]

Well, Ive seen it again. Where someone had done a remodle and they rerouted some circuits and they had put some #12 on a 30 amp breaker!! there were some outlets out of power and I traced it back to a panel, (that was mislabled) and the 30 amp had tripped!! thank goodness that the #12 never over heated. How often do you run into this??

 

[Jim W in Tampa]

Well, Ive seen it again. Where someone had done a remodle and they rerouted some circuits and they had put some #12 on a 30 amp breaker!! there were some outlets out of power and I traced it back to a panel, (that was mislabled) and the 30 amp had tripped!! thank goodness that the #12 never over heated. How often do you run into this??

usually after the fire.

 

[Mule]

We just did a service and panel upgrade on a older home and found the same thing going to a package HVAC unit. So we put a 20 brk on it and told the owner we could not re-install a 30 on it. Told him to call us if it trips and we'll replace it with #10.....Bet it trips !!

BTW...isnt #12 actually good for 25amps without the astrics????

 

[Rewire]

We just did a service and panel upgrade on a older home and found the same thing going to a package HVAC unit. So we put a 20 brk on it and told the owner we could not re-install a 30 on it. Told him to call us if it trips and we'll replace it with #10.....Bet it trips !!

BTW...isnt #12 actually good for 25amps without the astrics????

Are you an electrician?

 

[stickboy1375]

We just did a service and panel upgrade on a older home and found the same thing going to a package HVAC unit. So we put a 20 brk on it and told the owner we could not re-install a 30 on it. Told him to call us if it trips and we'll replace it with #10.....Bet it trips !!

BTW...isnt #12 actually good for 25amps without the astrics????

Your situation was probably legal....

 

[electricman2]

We just did a service and panel upgrade on a older home and found the same thing going to a package HVAC unit. So we put a 20 brk on it and told the owner we could not re-install a 30 on it. Told him to call us if it trips and we'll replace it with #10.....Bet it trips !!

BTW...isnt #12 actually good for 25amps without the astrics????

It's possible that it was a code compliant installation. Depending on the nameplate data, No. 12 conductors with a 30A OCPD may have been fine.

 

[peter d]

Your situation was probably legal....

Yeah, you should see the look on some guys faces when they hear you can sometimes put #12 on a 40 or 50 amp breaker.

 

[stickboy1375]

I like using #14 myself...

 

[peter d]

I like using #14 myself...

No joke, some of the really small A.C. condensors only require an MCA of 15 on a 15 or 20 amp breaker.

 

[Mule]

It's possible that it was a code compliant installation. Depending on the nameplate data, No. 12 conductors with a 30A OCPD may have been fine.

Didnt read the nameplate on the unit.....We installed a rain tight HOM panel nex to the meter base that was around 20ft from the HVAC unit....No service disconect or other protection on the unit itself..

 

[stickboy1375]

No joke, some of the really small A.C. condensors only require an MCA of 15 on a 15 or 20 amp breaker.

Yep... I think its funny when people size the wire to the MAX. OCP... WHY do people do this?

 

[Rewire]

#12 THHN is rated for 30 amps in certain applications like A/C if you use NMC you must use the 60C table which would limit you to 25 amps

 

[Mule]

Yep... I think its funny when people size the wire to the MAX. OCP... WHY do people do this?

Guilty......OK...Im stubborn, as you all know..but humble...:smile:v.I've never dug into this in the code book. But on the surface, I dont see how you could install a larger breaker on a branch circuit than normally allowed, reguardles of the HVAC units contribution to the situation.....????

 

[stickboy1375]

#12 THHN is rated for 30 amps in certain applications like A/C if you use NMC you must use the 60C table which would limit you to 25 amps

I could still use a 40 amp breaker if the unit calls for it.

 

[stickboy1375]

Guilty......OK...Im stubborn, as you all know..but humble...:smile:v.I've never dug into this in the code book. But on the surface, I dont see how you could install a larger breaker on a branch circuit than normally allowed, reguardles of the HVAC units contribution to the situation.....????

Because the breaker is not providing the OCP, only ground-fault and short circuit protection.

 

[peter d]

Guilty......OK...Im stubborn, as you all know..but humble...:smile:v.I've never dug into this in the code book. But on the surface, I dont see how you could install a larger breaker on a branch circuit than normally allowed, reguardles of the HVAC units contribution to the situation.....????

Because the breaker only protects the wire from short circuits and ground faults. A SC or GF will be in the range of 1000's of amps and will trip any breaker assuming correct settings and coordination (not an issue for residential.)

The unit itself is protected by thermal overloads in the motors.

 

[Mule]

Duh, I was always taught that the branch circuit protective device protects branch circuit conductors only....

 

[Rewire]

I could still use a 40 amp breaker if the unit calls for it.

if you look close at the MCA and max CB you will find the MCA will be 80% of the max breaker size.

 

[stickboy1375]

if you look close at the MCA and max CB you will find the MCA will be 80% of the max breaker size.

Here is an easy picture to follow...

 

[Jim W in Tampa]

Guilty......OK...Im stubborn, as you all know..but humble...:smile:v.I've never dug into this in the code book. But on the surface, I dont see how you could install a larger breaker on a branch circuit than normally allowed, reguardles of the HVAC units contribution to the situation.....????

and when or if they call you back will you charge them to put back what was legal ?