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#45686 - 12/05/04 01:50 PM Max Load?  
NJ Wireman  Offline
Member
Joined: Aug 2004
Posts: 186
New Jersey (South Jersey)
OK im tired of hearing ten thousand differant answers on this question from people i work with.

SO let me here it from you guys!!!

What is the maximum amps on a 15 amp cir.

What is the maximum amps on a 20 amp cir.

And this one is best what do you count amp wise per device for an outlet?


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#45687 - 12/05/04 02:00 PM Re: Max Load?  
Electric Eagle  Offline
Member
Joined: Apr 2002
Posts: 914
Alpharetta, GA
It really depends on the brand. [Linked Image] I've seen 20 amp breakers with a constant load of 30 amps that never will trip.

No really, 80% of the breaker rating for constant load. So 12 and 16 amps for the 15 and 20 amp breakers.

As a general rule we count 1 amp per device unless we know different.


#45688 - 12/05/04 02:02 PM Re: Max Load?  
Sandro  Offline
Member
Joined: Dec 2001
Posts: 444
Stoney Creek, ON, Canada
I do 80% for continuous loads. Therefore, I do 12amp load on 15A circuit and 16amp load on 20amp circuit. Perhaps unnecessary, but to err on cautious side, I do this calculation for noncontinuous loads as well. Never had a problem.

The Cdn Electrical code allows 12 receptacles per 15amp circuit. To me that works out to 1 amp per device. I think this is fair and reasonable.


#45689 - 12/05/04 02:16 PM Re: Max Load?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Here is the info right from UL I sniped out a bunch of other info and left in only the info you asked for.

From the 2004 UL White Book
Quote
CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT BREAKER ENCLOSURES (DIVQ)

USE

This category covers circuit breakers and circuit breaker enclosures designed to provide service-entrance, feeder or branch circuit protection in accordance with ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC).

<SNIP>

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.


We can also look at the NEC in a few places here is one them.

Quote
210.20 Overcurrent Protection.
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.


The short answer is you can load a breaker to it's rating for up to 2 hours and 59 minutes at a time. If the load will last longer than 3 hours you can only load the breaker to 80% of it's rating.


Feel free to ask more detailed questions.

Oh the outlets, in commercial you have to count them at 180 VA in residential there is no limit.

All of this is based on the NEC you may have local amendments.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#45690 - 12/05/04 04:51 PM Re: Max Load?  
NJ Wireman  Offline
Member
Joined: Aug 2004
Posts: 186
New Jersey (South Jersey)
This would be for commercial work. so to be simple 180va? how many amps per device 1 1.5 etc ? Iwire thanks for the research!!!!


#45691 - 12/06/04 06:41 PM Re: Max Load?  
NJ Wireman  Offline
Member
Joined: Aug 2004
Posts: 186
New Jersey (South Jersey)
Knocking this back to the top again i know theres more of you out there with your thoughts.


#45692 - 12/06/04 07:04 PM Re: Max Load?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Sorry NJ I forgot to get back to you.

Quote
220.3 Computation of Branch Circuit Loads.
Branch-circuit loads shall be computed as shown in 220.3(A) through (C).

(B) Other Loads — All Occupancies. In all occupancies, the minimum load for each outlet for general-use receptacles and outlets not used for general illumination shall not be less than that computed in 220.3(B)(1) through (11), the loads shown being based on nominal branch-circuit voltages.

Exception: The loads of outlets serving switchboards and switching frames in telephone exchanges shall be waived from the computations.

(9) Receptacle Outlets. Except as covered in 220.3(B)(10), receptacle outlets shall be computed at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke. A single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles shall be computed at not less than 90 volt-amperes per receptacle.
This provision shall not be applicable to the receptacle outlets specified in 210.11(C)(1) and (2).


Short version 180 VA per single or duplex receptacle. The last sentence "This provision shall not be applicable to the receptacle outlets specified in 210.11(C)(1) and (2)." removes this requirement from applying to dwelling units.

180 VA @ 120 volts = 1.5 amps per outlet.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#45693 - 12/06/04 07:32 PM Re: Max Load?  
NJ Wireman  Offline
Member
Joined: Aug 2004
Posts: 186
New Jersey (South Jersey)
IWIRE,
Thanks alot, well using that which by the way is how i also see it. THis would mean that acording to code you could install 8 duplex recp. on a 15 amp circuit and 10.66 or (10) on a 20 amp circuit.

THis is really leaning onto the safe side as when I use to work new construction our rule of thumb was 10 items on a circuit no matter the case lighting or recpt's

I guess it never bit us back but with todays lighting it easilly could. I think that i will lean with the 8/10 rule from this point on.


#45694 - 12/06/04 07:53 PM Re: Max Load?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
No problem NJ and I should mention that Roger D straighted me out on this 180 VA issue not to long ago. [Linked Image]

I think you started with 16 and 12 amps for 20 and 15 amp circuits respectively.

You do not have to count receptacles as continuous loads.

That being the case 13 outlets on a 20 amp circuit and 10 outlets on a 15 amp circuit would be NEC compliant.

However code compliance and good design are not always the same thing and some judgment must be applied.

The projects I work on are designed by engineers and it is common for them to only put 3 to 5 outlets on a 20 amp circuit.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#45695 - 12/06/04 08:04 PM Re: Max Load?  
Electric Ian  Offline
Member
Joined: Feb 2004
Posts: 133
MA, USA
quote
-------------------------
THis would mean that acording to code you could install 8 duplex recp. on a 15 amp circuit and 10.66 or (10) on a 20 amp circuit.
----------------------------

I'm thinking that, based on the code info Bob provided, you would be allowed up to 10 receptacles on a 15 Amp circuit and 13 on a 20 Amp circuit as general use receptacles do not fall into the category of continuous load. Bob?


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