What size breaker?

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kg18

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Whats the maximum size breaker you can put on 6-3 nmb? My co worker and I were arguing about this and i lost my code book so I cant look it up. Is it 50 amp or 60 amp? Thanks
 
Re: What size breaker?

How are you going to win a code fight without a codebook? It's like bringing a gun to a knife fight. :D

60 amps.

60? column of 310.16 as tweaked by 240.4(B).
60? per 334.80.

[ January 24, 2006, 12:36 AM: Message edited by: georgestolz ]
 
Re: What size breaker?

Yep, 60 in most cases.

Except maybe some HVAC units and firepumps.

For instance if an HVAC unit had a Min. Cir. Amp of 55 and a Maximum Overcurrent size of 70, you could put a 70 on it.
 
Re: What size breaker?

dave, just curious...when is the last time you saw a firepump wired with NMB? :D
 
Re: What size breaker?

Originally posted by georgestolz:
It's like bringing a gun to a knife fight.
Click to expand...
I guarantee a win if I bring a gun to a knife fight.

A better analogy would be "It's like bringing the Colts to a playoff game".

But we won't go there..........
 
Re: What size breaker?

Never! :D

I was just trying to think of exceptions. I never saw an HVAC unit marked 55-70 either!
But motors, pumps, welders, HVAC units etc... should be considered when answering a vague question like this.

I have seen sprinkler systems in homes... but now that I think of it I never looked to see if it had a pump or if it was (pressure) fed from public utility.

Is there such a thing as a sprinkler system without a pump?
 
Re: What size breaker?

Originally posted by davedottcom:
Is there such a thing as a sprinkler system without a pump?
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Sure there is. The pump is designed in when city pressure can't meet flow requirements for the structure. Most small commercial installs don't have fire pumps. Most large warehouse "boxes" do.
 
Re: What size breaker?

Originally posted by bdarnell:
The pump is designed in when city pressure can't meet flow requirements for the structure.
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That makes sense.

I guess it would have to be one heck of a pump to require a #6 though! :eek:
Let's just forget I ever mentioned it!
 
Re: What size breaker?

Originally posted by georgestolz:

60? column of 310.16 as tweaked by 240.4(B).
60? per 334.80.
Click to expand...
Goerge, I don't have my code book in front of me but what does 240.4 (B) say to allow one to use any ampacity other than the 60 degree column allows?

[ January 25, 2006, 03:27 PM: Message edited by: m73214 ]
 
Re: What size breaker?

Originally posted by m73214:
Originally posted by georgestolz:

60? column of 310.16 as tweaked by 240.4(B).
60? per 334.80.
Click to expand...
Goerge, I don't have my code book in front of me but what does 240.4 (B) say to allow one to use any ampacity other than the 60 degree column allows?
Click to expand...
Tom, you still use the 60 degree column, and you will see #6 NM is rated at 55amps, but you can use a 60 amp breaker since they don't make a 55 amp breaker. If it complies with 240.4(B)1,2&3 it is fine.

(B) Devices Rated 800 Amperes or Less The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.

240.6 Standard Ampere Ratings
(A) Fuses and Fixed-Trip Circuit Breakers The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60 , 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes.

A VERY common mistake people make is thinking they need #6 SE wire for HVAC units that require a 60 amp breaker. If the Minimum circuit ampacity is 55 or under the 60 amp breaker on #6 NM is fine.

;)
Dave
 
Re: What size breaker?

The circuit is for a electric furnace with a 60 amp breaker. I believe I have won the bet. He wanted to run 4/3 but I said no way 6/3 is what we are pulling.
 
Re: What size breaker?

before you make the final bet here did you any chance you check the electric furance rating in how many KW ?? and distance that what i always count there too.


p.s.
240.6 Standard Ampere Ratings
(A) Fuses and Fixed-Trip Circuit Breakers The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60 , 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes.
Click to expand...
let me add this other standard breaker / fuse size is 601 amperes also


Merci, Marc
 
Re: What size breaker?

Marc, At one time I knew why (the 601 amp), but now don't recall...does anyone know why 601 is listed as a standard size?
 
Re: What size breaker?

Originally posted by kg18:
The circuit is for a electric furnace with a 60 amp breaker. I believe I have won the bet. He wanted to run 4/3 but I said no way 6/3 is what we are pulling.
Click to expand...
As long as the Minimum Circuit Ampacity is 55 or less , you are correct.
:)
 
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