Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 01-12-2012, 04:01 PM   #1
011010100110111101100101
 
Join Date: Jan 2011
Posts: 240
Share |
Default

continuous load


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

anesthes is offline   Reply With Quote
Old 01-12-2012, 04:03 PM   #2
MarginallyQualified
 
Join Date: Dec 2011
Location: Winston-Salem NC
Posts: 3,647
Default

continuous load


Quote:
Originally Posted by anesthes View Post
I've got a situation where I have two devices, both pulling 8.3 amps @ 240v
do those loads normally cycle simultaneously?

TarheelTerp is online now   Reply With Quote
Old 01-12-2012, 04:04 PM   #3
Member
 
Julius793's Avatar
 
Join Date: Dec 2011
Location: New york
Posts: 1,053
Default

continuous load


Quote:
Originally Posted by 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
What kind of load?
__________________
Electricity will kill you if you give it a chance
Julius793 is offline   Reply With Quote
Old 01-12-2012, 04:16 PM   #4
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,772
Default

continuous load


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.
Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.
Speedy Petey is online now   Reply With Quote
The Following 2 Users Say Thank You to Speedy Petey For This Useful Post:
gregzoll (01-12-2012), J. V. (01-14-2012)
Old 01-12-2012, 05:56 PM   #5
Member
 
Join Date: Mar 2007
Location: Eighty Four, Pa.15330
Posts: 1,211
Default

continuous load


Continuous duty is over 3 hrs. Not 80%
bobelectric is offline   Reply With Quote
The Following User Says Thank You to bobelectric For This Useful Post:
gregzoll (01-12-2012)
Old 01-12-2012, 05:57 PM   #6
011010100110111101100101
 
Join Date: Jan 2011
Posts: 240
Default

continuous load


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 is offline   Reply With Quote
Old 01-12-2012, 05:58 PM   #7
011010100110111101100101
 
Join Date: Jan 2011
Posts: 240
Default

continuous load


Quote:
Originally Posted by bobelectric View Post
Continuous duty is over 3 hrs. Not 80%
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

Last edited by anesthes; 01-12-2012 at 06:08 PM.
anesthes is offline   Reply With Quote
Old 01-12-2012, 06:10 PM   #8
Member
 
Join Date: Mar 2007
Location: Eighty Four, Pa.15330
Posts: 1,211
Default

continuous load


Come on, kids.Art.100,definitions... Continous loads.
bobelectric is offline   Reply With Quote
Old 01-12-2012, 06:23 PM   #9
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,838
Default

continuous load


deleted
__________________
Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.

Last edited by AllanJ; 01-12-2012 at 06:35 PM.
AllanJ is offline   Reply With Quote
Old 01-12-2012, 06:33 PM   #10
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 4,851
Default

continuous load


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
Stubbie is offline   Reply With Quote
The Following 3 Users Say Thank You to Stubbie For This Useful Post:
Furd (01-12-2012), gregzoll (01-12-2012), Speedy Petey (01-12-2012)
Old 01-12-2012, 06:36 PM   #11
011010100110111101100101
 
Join Date: Jan 2011
Posts: 240
Default

continuous load


Quote:
Originally Posted by Stubbie View Post
Fixed electric space heating is considered a continuous load.
Right. There is no question of that. It's a continuous load.

Quote:
Originally Posted by Stubbie View Post
The branch circuit conductors and ocpd are sized at 125% of the total of the continuous loads plus any non continuous loads.

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

-- Joe
anesthes is offline   Reply With Quote
Old 01-12-2012, 06:40 PM   #12
Retired from the grind
 
gregzoll's Avatar
 
Join Date: Dec 2006
Location: Midwest - Central Illinois
Posts: 13,716
Default

continuous load


Quote:
Originally Posted by anesthes View Post
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
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.
__________________
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: 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 is online now   Reply With Quote
Old 01-12-2012, 06:43 PM   #13
Retired from the grind
 
gregzoll's Avatar
 
Join Date: Dec 2006
Location: Midwest - Central Illinois
Posts: 13,716
Default

continuous load


Quote:
Originally Posted by anesthes View Post
Right but CB's are rated for 125% overload, correct?
-- Joe
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.
__________________
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: 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 is online now   Reply With Quote
Old 01-12-2012, 07:01 PM   #14
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,772
Default

continuous load


Quote:
Originally Posted by anesthes View Post

Right but CB's are rated for 125% overload, correct?
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.
Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.
Speedy Petey is online now   Reply With Quote
The Following User Says Thank You to Speedy Petey For This Useful Post:
gregzoll (01-12-2012)
Old 01-12-2012, 07:14 PM   #15
Newbie
 
Furd's Avatar
 
Join Date: Aug 2007
Location: Near Seattle, WA
Posts: 18
Default

continuous load


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.

Furd is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Beware of Inappropriate Load Calculation Software - Source ACCA.org JJboy HVAC 5 09-06-2011 06:25 PM
Load Calculation Fee - HVAC Contractors Please DIYerIT HVAC 2 07-30-2011 04:39 PM
Want to open up a load bearing wall - I need advice on a header to carry the load graysqwrl Building & Construction 4 07-16-2011 08:16 AM
Help 30 amp Load center for my HID lights and miscellaneous Mont@n@ Electrical 9 03-06-2010 11:49 AM
More Accurate Load Calculation zootjeff HVAC 9 12-14-2009 12:06 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.