80% rule for branch circuits

[shaw0486]

can you exceed the 80% rule on over current protection for branch circuits when you include 125% for continuous duty

 

[bphgravity]

There isn't an 80% rule, but I understand your question. The answer is yes.

a 20A rated breaker is rated for 20A, as long as that load does not operate for more than 3 hours. Therefore, a 16A load run continuously can be protected by a 20A breaker forever.

 

[stickboy1375]

I'm always curious about phantom codes, and this one is a biggie.

 

[A/A Fuel GTX]

I think it's just a design issue and not a bad practice to only load up a circuit to about 80%.

 

[stickboy1375]

I think it's just a design issue and not a bad practice to only load up a circuit to about 80%.

Why though?

 

[A/A Fuel GTX]

Just so the OCPD and wire are not too close to the edge. Just a personal choice and not knocking anyone that chooses to take her up to the max.

 

[iwire]

Why though?

Because the breakers we use are not designed to be run at 100% for 3 hours or more.

From the UL General Directory (The White Book) to you


CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT BREAKER ENCLOSURES (DIVQ)

Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for three hours or more.

 

[stickboy1375]

Because the breakers we use are not designed to be run at 100% for 3 hours or more.

From the UL General Directory (The White Book) to you


CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT BREAKER ENCLOSURES (DIVQ)

I realize that... but in the residential world continuous loads are far and few.

 

[iwire]

I realize that... but in the residential world continuous loads are far and few.

I agree.:smile:

 

[realolman]

Although Captain Obvious is not exactly sure what's being discussed here, he feels compelled to be of service.

The load is 80% of the breaker.... the breaker is 125% of the load....

1 /.80 = 1.25.... It's the same thing.:smile: