circuit ampacity

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  #1  
Old 01-06-20, 11:37 AM
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circuit ampacity

My question relates to an over current protector and the ampacity of a branch circuit.

The actual run is nm-b 6 AWG. This shows as 55 Amps capacity.
My load is 43 Amps, a heating system, which I will call continuous load.
Using 125%, that equals 54 Amps ampacity required.
I want to use a 50 Amp breaker; I called the manufacturer, and they insist it is good for 50 Amps continuous; the breaker is temperature compensated.

Is this a code compliant setup?
 
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Old 01-06-20, 12:45 PM
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Yes. Because the wire is 55A technically you can use a 60A breaker because it is the next standard size after 50A. Using a lesser 50A breaker is not a code issue.
 
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Old 01-06-20, 01:07 PM
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Pattenp. I agree with using a breaker with a smaller amp rating than the wire but disagree with using a breaker with a larger amp rating than the wire. Who knows what the next standard larger ampacity is? I don't know the code but can't believe it would allow it because it is a fire hazard.
 
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Old 01-06-20, 02:04 PM
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The NEC does allow the next standard size breaker to be used when there is no matching breaker to the wire amp size for circuits supplying equipment. The next standard size is not to be used on branch circuits supplying more than one receptacle for cord and plug loads. See NEC 240.4(B)
 
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Old 01-06-20, 05:13 PM
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I called the manufacturer, and they insist it is good for 50 Amps continuous; the breaker is temperature compensated.
I would question that answer to a higher authority. What kind and type of breaker is it? I would agree the breaker should be good for 50 amps, but continuous duty (3 hours or longer) generally requires the conductor AND breaker not be loaded over 80% of it's rated capacity. I would use a 60 amp breaker. You mentioned this is a heating application, is it a 10 KW furnace?
 
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Old 01-06-20, 07:49 PM
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Yes, a 10kW heat strip with blower. Leviton makes the claim for their breakers.
 
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Old 01-07-20, 06:25 AM
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Does the NEC 240.4(b) require this one outlet be identified as a bump up circuit so it is obvious to any end user (owner, renter. electrician, inspector, etc.) that the requirements of the bump up circuit are maintained? If not, seems like an accident waiting to happen. Any people out there working for AHJ (authority having jurisdiction) that have experience with such a circuit being identified?
 
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Old 01-07-20, 08:08 AM
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I think this is a case where theory meets reality. No breaker manufacturer will make breakers in 5A steps above 30 Amps. The variability becomes extreme when you add the AFCI, GFCI, AFCI/GFCI, EPCI, screw down, with neutral, etc. variants. Stocking would become prohibitive. The industry is moving rapidly to even 240V breakers being ground fault protected.
 
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Old 01-07-20, 07:05 PM
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Variable amperage breaker would probably be a thing in residential if people could be trusted with them. People would just max them all out to avoid breaks.
 
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Old 01-08-20, 09:51 AM
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Talking

It may be possible to make a one time only programming setting for a new breaker. Maybe I should patent that today.
 
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Old 01-08-20, 03:16 PM
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beelzebob

Does the NEC 240.4(b) require this one outlet be identified as a bump up circuit so it is obvious to any end user (owner, renter. electrician, inspector, etc.) that the requirements of the bump up circuit are maintained? If not, seems like an accident waiting to happen. Any people out there working for AHJ (authority having jurisdiction) that have experience with such a circuit being identified?
The same issue can be found with an electric welder circuit. You could have a 50A circuit using #10 or less size wire. There is no NEC requirement that the outlet be labeled as a welder circuit outlet. I believe it is prudent to label the outlet as such when the wire is reduced based on welder duty cycle, but I personally for a residential use suggest using the matching wire amperage capacity to the OCPD.
 
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Old 01-09-20, 07:01 AM
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Pattenp, I agree 100%. As I see it the only time this could happens is when the connecting wire size gets based on the load and not the protection device. Like putting the cart before the horse. I know nothing about welders but I wonder how this limiting duty cycle value, based on the ampacity of the cable attaching the welder outlet to the protection device, is not exceeded from user to user or a change of welding machine using the same outlet.
 
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Old 01-09-20, 04:11 PM
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No breaker manufacturer will make breakers in 5A steps above 30 Amps.
Sure they do, Just a few months ago I bought a 2-pole 35 amp Cutler-Hammer CH series breaker for a 3 1/2 ton condensing unit. They also make a 2-pole 45 amp breaker and 35 and 45 amp single pole breakers.

Check page V1-T1-37 of this catalog.
https://www.eaton.com/content/dam/ea...a08100002e.pdf


The industry is moving rapidly to even 240V breakers being ground fault protected.
I agree. The industry generally is in lockstep with the NEC. I believe the 2020 NEC is even requiring electric range receptacles to be GFCI protected if they are within 6 feet of the kitchen sink. This requirement will mean 10s of thousands of dollars in sales across the country in the new home market. Now I am expecting someone to come out with a GFCI range receptacle.

I do not always agree with everything in the NEC and think they sometimes just go too far.
 
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Old 01-10-20, 02:37 AM
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NEC says the breaker must be rated at 125% of the continuous load...unless the breaker is listed to handle continuous loads (most are not, is my understanding). So in this case, use a 55A breaker, or 60A if a 55A isn't available.
 
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Old 01-10-20, 06:49 AM
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NEC says the breaker must be rated at 125% of the continuous load...unless the breaker is listed to handle continuous loads (most are not, is my understanding).
Here is Leviton published info, verified with a phone call:

SIMPLE - An all plug-on design - no wiring to the circuit breaker (applications up to 60A when using copper wire or 50A when using aluminum wire)
PRECISION - More precise trips based on current, even in extreme temperatures: -40C to 85C, without re-rating
EASY - Color indicators in the handle to easily see operational status at-a-glance.


Like Eaton; they do 5Amp increments up to 50A, then 10A increments.
 
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Old 01-10-20, 09:29 AM
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I am not familiar with the Leviton Panelboards or breakers, haven't seen any yet.
 
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Old 01-10-20, 04:23 PM
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Here is Leviton published info, verified with a phone call:

SIMPLE - An all plug-on design - no wiring to the circuit breaker (applications up to 60A when using copper wire or 50A when using aluminum wire)
PRECISION - More precise trips based on current, even in extreme temperatures: -40C to 85C, without re-rating
EASY - Color indicators in the handle to easily see operational status at-a-glance.
If they don't say, then you have to assume it's the standard 80%-continuous rating.
 
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Old 01-10-20, 05:29 PM
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A circuit breaker should hold to it's rated ampacity.
The 80% thing is an NEC rule for circuit loading not a circuit breaker rating. And it is actually a 125% rule for certain loads not 80%.
 
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Old 01-10-20, 06:57 PM
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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 contin‐
uous and noncontinuous loads, the rating of the overcurrent
device shall not be less than the noncontinuous load plus
125 percent of the continuous load.
Exception: Where the assembly, including the overcurrent devices
protecting the branch circuit(s), is listed for operation at 100 percent of
its rating, the ampere rating of the overcurrent device shall be permitted
to be not less than the sum of the continuous load plus the noncontinu‐
ous load.
When a breaker/panel is listed for 100% continuous operation, it means it can tolerate the heat generated by running continuously close to its trip point.
 
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Old 01-11-20, 06:23 AM
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Who knows what the next standard larger ampacity is?
The standard Ampere ratings of circuit breakers and fuses are listed in Art 240.6 of the NEC.

I am not familiar with the Leviton Panelboards or breakers, haven't seen any yet.
Leviton load centers have recently come on the market and I have seen samples in the supply houses. Their big selling feature is they look pretty. I may consider using one when their breakers are available in every hardware and home center in the US.
 
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Old 01-11-20, 06:32 AM
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Leviton claims UL listing to UL 943 for GFCI and UL 489 for all.
Looking thru 943, I find this:

6.7.1.4 The performance of any ground-fault circuit-interrupter shall not be impaired by any of the
following:


.....

c) Any electrical load within the rating of the interrupter.
d) Any ambient temperature between -35C (-31F) and 66C (151F).


also, this chart (partial), describing a pre-test set-up condition, including an ambient of 150.8 deg F and full rated current for 2 hours:

66.0 2.0C
(150.8
3.6F)
Rated voltage and
current
Establish thermal equilibrium with at least two hours of exposure. Do not
test.



I find this for 489:

Test UL 489 Parameter UL 1077 Parameter
Calibration
100% of rating – hold
135% of rating - trip in one hour (<50A)
200% of rating - trip in 2 min. max. (<30A)

summary: I don't see a basis to cause a derate at rated Amps. In my case in post one, there is over 10% headroom.

ref: https://www.mechprod.com/hubfs/_2017...20Breakers.pdf

and, Burst simulator, surge simulator, ESD simulator, impulse current & voltage generator- Suzhou 3ctest Electronic Co.,Ltd, a professional EMC solutions supplier.

www.leviton.com/en/docs/DIV_26_Leviton_Load_Centers.doc
 

Last edited by telecom guy; 01-11-20 at 06:50 AM.
  #22  
Old 01-11-20, 07:12 AM
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The bottom line is using a smaller breaker is not going to hurt anything. The worst that will happen is the breaker will trip.
 
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Old 01-11-20, 09:19 AM
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I may be coming off trying to be a Lev. sales engineer. That is not the case. But, I do have now two examples of how my new load center/subpanel job is coming along.

My second example is the boathouse subpanel. It is fed with 6 awg from a 60A load center breaker. As part of the boathouse, will be a 50A 240/120V marine twist lock. I intend to feed that one with a 50A GFCI 2P breaker and 6 awg THHN in conduit. I don't want to consider a upsize to 60A, and there is not a 55A available. Further, i don't want the situation where the main panel breaker feeder trips out before the subpanel branch breaker.
fyi, the subpanel is a QO panel. I "might" have considered a leviton sub, but none are avail.
 
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Old 01-11-20, 10:24 AM
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I may consider using one when their breakers are available in every hardware and home center in the US.
I see Leviton loadcenters and breakers are now on the Home Depot website, but I know of no store that actually stocks them......yet. Can't find any distributor within 100 miles that stocks them either.
 
 

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