1 - 20 of 27 Posts

Joined

·
13,346 Posts

It's more like a guideline!:whistling2:

Joined

·
90 Posts

There are fully rated breakers / panels that are rated for continious use And will be listed for this application.

It is a good practice to load branch circuits to a fraction of their rating.

For example a lighting circuit on a 20a braker should only be loaded to no more than 16a. Or 16a continious load x 125% = 20a.

Joined

·
243 Posts

Some but not all, some even start slightly after the handle rating.

Joined

·
2,969 Posts

I have seen plenty of circuits loaded to 100%.

But they tend to trip for no apparent reason sometimes !

So thats why I tend to use the 80% thing

it's saves on nuisance tripps.

Joined

·
656 Posts

The 3 hour continuous rule is in 210.19. (Everyone calls it the 80% rule, but it's really the 125% rule.) :thumbsup:Interesting. So there isn't a word of this in the nec? And what about an exam?

There is also 210.23 that says for fixed utilization equipment (i.e. dishwasher, etc.) on a circuit that also supplies lighting and receptacles, the equipment can't exceed 50% of the branch circuit rating.

Joined

·
5,563 Posts

What he means by this, in case it confuses you, is that you must size the CONDUCTORS to 125% of the FLC of the equipment, so the inverse of 125% is 80%. In other words since you cannot load the conductors to more than 80% of their rated ampacity anyway (for continuous loads as defined above), there is no point in having the breakers rated beyond that 80% level.The 3 hour continuous rule is in 210.19. (Everyone calls it the 80% rule, but it's really the 125% rule.) :thumbsup:

...

Since breaker loading relates to heat, which then has everything to do with panelboard design, that is how breakers are rated when used in panelboards. If you want to use a "100% rated" breaker and follow the other rules associated with that, you will find that 100% rated breakers cannot be used in panelboards, they can only be used stand-alone.

Not ranking on you, but your method is now done by nearly every contractor/electrician. The true result of AFCIs, residential wiring that is more dangerous then every.It depends on what , in the world of overpaid, underachieving afci breakers, I max + every circuit out to limit how many of those worthless breakers I need to buy. New house im wiring this week gets five.

CMP is a joke.

this is what baked my noodle in school. just multiply 20 X .8 to get your 16 haha. Throwing that 125% in there complicated things in my opinion.For example a lighting circuit on a 20a braker should only be loaded to no more than 16a. Or 16a continious load x 125% = 20a.

Joined

·
656 Posts

It's also important to point out that the whole point of this exercise is to size circuit breakers that will protect the wire from overheating and catching on fire. That's it. Everything else is secondary.

i understand how to do it

It's also important to point out that the whole point of this exercise is to size circuit breakers that will protect the wire from overheating and catching on fire. That's it. Everything else is secondary.

im saying it needlessly complicates it. we're talking 80 percent 80 percent 80 percent and then this 125 comes out of nowhere.

That is not correct. A branch circuit can be loaded to 100% as long as the load is not continuous- ie, on for 3 hours or more. I can have a calculated load of 20 amps on a 20 amp breaker as long as the load is not continuous.Branch circuits at 80 % service breaker at 100 %

Wait, I thought they began around 100 or more often at 125%?

Joined

·
5,261 Posts

Branch circuits at 80 % service breaker at 100 %

That is not correct. A branch circuit can be loaded to 100% as long as the load is not continuous- ie, on for 3 hours or more. I can have a calculated load of 20 amps on a 20 amp breaker as long as the load is not continuous.

Our rule for it reads like this......

.(3) The calculated load in a consumer’s service, feeder, or branch circuit shall be considered a continuous load(b) a total of more than 3 h in any six-hour period if the load exceeds 225 A

unless it can be shown that in normal operation it will not persist for

(a) a total of more than 1 h in any two-hour period if the load does not exceed 225 A; or

Joined

·
4,154 Posts

It is a circuit breaker not an exact device at those percentages, ambient and connections play into it for long time, you are close to the truth at somewhere above 100%Wait, I thought they began around 100 or more often at 125%?

1 - 20 of 27 Posts

Join the discussion

Electrician Talk

A forum community dedicated to professional electricians, contractors, and apprentices for residential and commercial work. Come join the discussion about trade knowledge, tools, certifications, wiring, builds, scales, reviews, accessories, classifieds, and more!

Full Forum Listing
Recommended Communities

Join now to ask and comment!