continuous load

anesthes

When I was in school back in the early 90s, the continuous load allowed for a circuit per NEC was 80% duty cycle.

I've always gone by the 80% rule since, although I can't remember if it was a rule (shall) or under workmanship (should).

I've got a situation where I have two devices, both pulling 8.3 amps @ 240v and I'd love to put them on one circuit (20A double pole, 12awg), but that would put me at 83%. The total circuit length is under 75 feet.

I briefly flipped through the NEC and couldn't find it, and thought I'd ask if someone off hand recalls ?

-- Joe

TarheelTerp

do those loads normally cycle simultaneously?

Julius793

What kind of load?

__________________
Electricity will kill you if you give it a chance

Speedy Petey

Not everything is a continuous load. Many people flat out put an 80% limit on a circuit, which is wasteful sometimes.

__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

bobelectric

Continuous duty is over 3 hrs. Not 80%

anesthes

Hi Guys,

I usually size my circuits this way (80%).

In this case, it's two electric heaters with fans. Mfg. specs say 8.3 amps each. Doesn't specify if that is peak or rms.

Most likely, both units would be on at the same time. Unsure of start up surge, have not even ordered them yet.

http://www.marleymep.com/en/multimed...-11046-001.pdf

-- Joe

anesthes

Eh? We were taught 80%.

Looks like this changed a number of years ago:

http://forums.mikeholt.com/showthread.php?t=135362

Hrmm..

So it's 80% of the CB, not the circuit. If the breaker is 125% (will have to look at the specs) the cont. load is actually 20amps, but obviously if it's 100% it's 16 amps.


-- Joe

bobelectric

Come on, kids.Art.100,definitions... Continous loads.

AllanJ

deleted

__________________
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.

Stubbie

Fixed electric space heating is considered a continuous load. The branch circuit conductors and ocpd are sized at 125% of the total of the continuous loads plus any non continuous loads.

__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie

anesthes

Right. There is no question of that. It's a continuous load.


Right but CB's are rated for 125% overload, correct?

-- Joe

gregzoll

Overkill. Unless it is a pump motor, fresh air or exhaust motor that is running 24/7, you don't need to. Running your bathroom exhaust should not be on 24/7, nor is it designed for continuous use. Now of course, when determining total load, yes there is a limit that you should place on a circuit, which is clearly stated and already figured in the NEC for you.

__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: Now listen, Cadet. I've got a job for you. See this button?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: Don't touch it! It's the History Eraser button, you fool!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: So what'll happen?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: That's just it. We don't know. Maybe something bad, maybe something good. I guess we'll never know, 'cause you're going to guard it. You won't touch it, will you?

gregzoll

Pick one of the manufacturers and check out what their info states. Mine state that they are rated for up to a 10kva interrupt limit, so what does that tell you.

__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: Now listen, Cadet. I've got a job for you. See this button?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: Don't touch it! It's the History Eraser button, you fool!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: So what'll happen?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
: That's just it. We don't know. Maybe something bad, maybe something good. I guess we'll never know, 'cause you're going to guard it. You won't touch it, will you?

Speedy Petey

What are you talking about???

__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

Furd

General purpose circuit breakers should not be continuously subjected to more than 80% of their rated ampacity. There ARE some circuit breakers that are rated for continuous loads at rated ampacity.