Breaker Sizes

[LarryFine]

I will consider the source. This will be my last comment on this forum.

 

[Grouch1980]

If there were a 5A or 10A breaker, it likely would have the same physical construction as a 15A breaker, with just a different trip calibration. Usually, the DIN rail breakers that would exist in 5A or 10A sizes, are built in sizes up to 30A, and all breakers in any given family, are 90% the same with just the trip mechanism being different.

Understood.

 

[don_resqcapt19]

Except for SABCs, bathroom receptacles, laundry and some other dedicated circuits, you could put the entire rest of the house on one 15A circuit if you wanted.

-Hal

Only if the house was 600 square feet or less. 210.11(B) requires that you install the number of 15 or 20 amp branch circuits based on the general lighting and receptacle load at 3 va per square foot.

 

[hbiss]

Where do you see that? This is from the 2023.

(B) Load Evenly Proportioned Among Branch Circuits. Where
the load is calculated on the basis of volt-amperes per square
meter or per square foot, the wiring system up to and including
the branch-circuit panelboard(s) shall be provided to serve not
less than the calculated load. This load shall be evenly proportioned
among multioutlet branch circuits within the panelboard(s).
Branch-circuit over current devices and circuits shall
be required to be installed only to serve the connected load.

-Hal

 

[don_resqcapt19]

Where do you see that? This is from the 2023.

(B) Load Evenly Proportioned Among Branch Circuits. Where
the load is calculated on the basis of volt-amperes per square
meter or per square foot, the wiring system up to and including
the branch-circuit panelboard(s) shall be provided to serve not
less than the calculated load. This load shall be evenly proportioned
among multioutlet branch circuits within the panelboard(s).
Branch-circuit over current devices and circuits shall
be required to be installed only to serve the connected load.

-Hal

right there

 

[hbiss]

But where does it say I can't have only one? Certainly would be evenly proportioned.

-Hal

 

[infinity]

But where does it say I can't have only one? Certainly would be evenly proportioned.

-Hal

I think what he's saying is that you need one circuit for up to 600 square feet of floor area. If you have more than 600 square feet you'll need more than one circuit.

 

[garbo]

Never made sense why they never made single pole circuit breakers to match size of Edison base screw in fuses. Often came across a red little single pole safety switch that supplied power to fire bells in triplex and small apartment units that had a 3 amp fuse. All the wiring was in type AC cable. My moms old house still has a gravity feed natural gas heater that the 15 amp circuit breaker only feeds a maybe 50 VA 120 to 24 volt transformer that draws less then 0.5 amps and would rather have a 3 amp circuit breaker protecting it.

 

[jim dungar]

My moms old house still has a gravity feed natural gas heater that the 15 amp circuit breaker only feeds a maybe 50 VA 120 to 24 volt transformer that draws less then 0.5 amps and would rather have a 3 amp circuit breaker protecting it.

Primary side OCPD are not intended to protect the transformer, although they might. Their real purpose is to remove a faulted transformer before it causes issues with the premises wiring.
Small transformers, like for furnace and door bells, are usually impedance protected against excessive current on the secondaries.

 

[LarryFine]

Never made sense why they never made single pole circuit breakers to match size of Edison base screw in fuses.

Cooper Bussmann 15 Amp Plug Type Circuit Breaker BP/MB-15 - The Home Depot

The Cooper Bussmann MB Series 15 Amp Mini-Breaker Plug Fuse has an Edison base and is intended for use as a permanent fuse replacement for most Edison-based fuses. The fuse has a built-in time delay that

www.homedepot.com

Cooper Bussmann 20 Amp Plug Type Circuit Breaker BP/MB-20 - The Home Depot

Mini-breaker for permanent fuse replacement. Replaces most Edison base fuses. A press of the button restores current. Built-in time delay prevents nuisance tripping during appliance start-ups.

www.homedepot.com

 

[Fred B]

The device should be designed so that the 15 amp OCPD does protect it.

Load demand and designed withhold can be 2 different things. Newer code is recognizing a 10A load and breaker but still requires no smaller than 14G wiring.

 

[david luchini]

But where does it say I can't have only one? Certainly would be evenly proportioned.

210.11(A)

 

[hbiss]

Ok. I calculated that one 15A circuit is sufficient to supply the general purpose receptacle and lighting loads of a 1200 sq ft house.

(A) Number of Branch Circuits. The minimum number of
branch circuits shall be determined from the total calculated
load and the size or rating of the circuits used. In all installations,
me number of circuits shall be sufficient to supply the
load served. In no case shall the load on any circuit exceed the
maximum specified by 220.1 .

-Hal

 

[david luchini]

Ok. I calculated that one 15A circuit is sufficient to supply the general purpose receptacle and lighting loads of a 1200 sq ft house.

New math?

 

[BarryO]

So given that fact, when someone goes to get their NRTL (UL, ETL, CSA) listing of a DEVICE that is small enough to be used on a 15A branch circuit, the listing of that device has to take into account that the BCPD protecting it will be 15A.

A nit, but the device has to take into account that the BCPD protecting it will be 15A or 20A, since 20A branch circuits may have NEMA 5-15 receptacles on them.

 

[jaggedben]

Ok. I calculated that one 15A circuit is sufficient to supply the general purpose receptacle and lighting loads of a 1200 sq ft house.

(A) Number of Branch Circuits. The minimum number of
branch circuits shall be determined from the total calculated
load and the size or rating of the circuits used. In all installations,
me number of circuits shall be sufficient to supply the
load served. In no case shall the load on any circuit exceed the
maximum specified by 220.1 .

-Hal

Is that a multi-wire branch circuit?

 

[Grouch1980]

So, from what I gathered from this thread, is the following:
1. For small loads, such as a 2.6 amp air handler with a 15 amp breaker, it's not the job of the circuit breaker (or fuses) to protect the load. The breaker or fuses only protect the wiring to the load. The manufacturer has to design their equipment appropriately, so that there's no spontaneous overloads. Or in the case of something like christmas lights, the load can sometimes come with its own internal / secondary protection.
2. For larger loads, say a 50 amp heater, the manufacturer may now rely on the circuit breaker for protection, unless they design their equipment appropriately as I mentioned above.

Do I have it right?

 

[electrofelon]

I think sometimes the serving OCPD is taken into account when designing the equipment, but it nothing you have to worry about. Equipment typically has to meet some listing or product standard, and I am not familiar with those requirements and the testing process, but I imagine the serving OCPD is considered. A few examples are HVAC units that have a max fuse or breaker size. Another is transfer switches where the SCCR will depend on the OCPD. The manufacturer provides a list of different OCPD 's and the resulting allowed SCCR.

 

[jaggedben]

To add electrofelon's last reply, in my experience if it is a hardwired appliance it will almost always say something about the max OCPD in the instructions. If it is a plug-in load then I believe the design and listing process assumes that the receptacle will be properly wired according to the code, and thus certain assumptions are made based on the type of plug used. That is, I agree that as long as instructions are followed you don't need to worry if the OCPD is larger than the load. The OCPD rating always needs to be larger than the expected load anyway to avoid nuisance trips.

Also, one thing to add is that 10 amps is a standard breaker size and the manufacturers do make them. Harder to find (probably buy online or special order if going through a supply house) but they exist.

 

[jaggedben]

I have seen some talk on the forum about the code possibly allowing 10 amp lighting circuits with 16awg in the future, but that hasn't happened yet. With mostly LED bulbs all the lighting in my house wouldn't draw 10 amps.