Why would an appliance have a "max breaker size"

[JackOfDiamonds]

My mini split has the following specs:

Rated Current: 6.1 Amps
Minimum circuit ampacity: 16 Amps
Maximum circuit breaker: 25 Amps

Based on this, I should be good to run a 20A circuit and 12-guage wire, but I don't quite understand why there is a "maximum circuit breaker". Based on my industrial indoctrination, there is no such thing as a maximum circuit breaker for an appliance, because the circuit breaker is only intended to protect the installed wiring, not the appliance.

I know one day I will kick myself for not running 10ga, but 10ga wire is going to cost $300 and 12ga will be less than half that. Since actually continuous amps is only 6 Amps...

 

[PCustoms]

Because they don't want more then "X" available to the unit I believe.

For example (not you, just generic), it's great that the old unit was fed with #6, but this new more efficient unit needs a breaker at 25A max on that #6 wire

Post a pic of the nameplate, on the unit.

 

[Wrench97]

I've always heard it was to protect the internal wiring of the device.

 

[Bert_]

Are you allowed to put your kitchen toaster on a 50A circuit?

 

[PCustoms]

Are you allowed to put your kitchen toaster on a 50A circuit?

Probably not, but I can put my cellphone charger on a 20A. Proportionally pretty close to your example...

 

[mm08822]

Maximum circuit breaker size, better known as maximum overcurrent protection (moc) is the sum of all loads in the equipment plus an additional 75% (typically) of the largest motor. It provides headroom for motor startup to prevent cb trips.

Basically, it's a motor circuit with special overcurrent protection rules.

 

[JohnX14]

Agree, post the nameplate. The nameplate accounts for all the calcs.

 

[dcg9381]

Are you allowed to put your kitchen toaster on a 50A circuit?

The right toaster, perhaps...

 

[Snapped-off]

The right toaster, perhaps...

She barely pulls over 20 amps at 240v.

 

[Bert_]

Probably not, but I can put my cellphone charger on a 20A. Proportionally pretty close to your example...

Not really, they are both designed for a 20A circuit

 

[micromind]

Since the unit is internally protected against overloads, it need to be externally protected against short-circuits and ground faults. This is done by the branch circuit breaker.

It needs to be large enough to handle any magnetizing and starting currents of the motors but small enough to actually trip on a short or ground fault with a long wire from the panel to the unit.

The wire is protected by the internal overload so it can be smaller than the rating of the breaker.

 

[fitter30]

Manufacturers use different codes NSCIS. And I'm sure there is more.
Industries in the Electrical Equipment, Appliance, and Component Manufacturing subsector manufacture products that generate, distribute and use electrical power. Electric Lighting Equipment Manufacturing establishments produce electric lamp bulbs, lighting fixtures, and parts. Household Appliance Manufacturing establishments make both small and major electrical appliances and parts. Electrical Equipment Manufacturing establishments make goods, such as electric motors, generators, transformers, and switchgear apparatus. Other Electrical Equipment and Component Manufacturing establishments make devices for storing electrical power (e.g., batteries), for transmitting electricity (e.g., insulated wire), and wiring devices (e.g., electrical outlets, fuse boxes, and light switches).

 

[danski0224]

I don't quite understand why there is a "maximum circuit breaker".

Memory is probably off a bit, but I believe it has something to do with the locked rotor amps rating of the compressor.

The wiring has to carry that current safely and requires a correctly sized break.

 

[JackOfDiamonds]

Memory is probably off a bit, but I believe it has something to do with the locked rotor amps rating of the compressor.

The wiring has to carry that current safely and requires a correctly sized break.

But why would there be a maximum breaker?

The circuit breaker is matched to the load and wire size. So a minimum breaker size makes sense to handle the load. If the breaker isn't big enough, it will trip.

But assuming the wire gauge is appropriate, why would there be a maximum breaker for the appliance? If the breaker is "too big", then I just don't see how that could be a problem. As others have pointed out, you can always use a smaller load (including obviously zero load).

 

[danski0224]

But why would there be a maximum breaker?

No idea, just going on info that I vaguely remember being told.

 

[lolaetype]

I don't quite understand why there is a "maximum circuit breaker".

As I understand it you want the breaker to be able to trip based on the amp draw of the appliance and the gauge of the wiring. If the breaker is too "large" it may not trip or take its sweet time doing so, potentially causing a fire or other damage.

This came up when I had the electrician I normally use run a new 240V run from the breaker box to the glass cooktop when we remodeled the kitchen. The cooktop was on an island and I wanted a 120V receptacle on the island and asked the electrician if he could power it off of one leg of the 240V circuit. He explained about the breaker sizing.

 

[Wrench97]

But why would there be a maximum breaker?

The circuit breaker is matched to the load and wire size. So a minimum breaker size makes sense to handle the load. If the breaker isn't big enough, it will trip.

But assuming the wire gauge is appropriate, why would there be a maximum breaker for the appliance? If the breaker is "too big", then I just don't see how that could be a problem. As others have pointed out, you can always use a smaller load (including obviously zero load).

Internal wire size matters too, the manufacturer is telling you the max breaker the internal wiring and contactor can handle without going up in flames if their is a short or compressor lock up.

 

[brewchief]

But why would there be a maximum breaker?

The circuit breaker is matched to the load and wire size. So a minimum breaker size makes sense to handle the load. If the breaker isn't big enough, it will trip.

But assuming the wire gauge is appropriate, why would there be a maximum breaker for the appliance? If the breaker is "too big", then I just don't see how that could be a problem. As others have pointed out, you can always use a smaller load (including obviously zero load).

There many cases where the wire size needed is considerably less then what the unit may draw on start up. The larger breaker is to prevent nuisance trips.
Since the hvac unit has internal overload protection the breaker is basically just protecting the wire in a short circuit case.

In your case you can use #12 nm-b and a 25 amp breaker and be fully compliant with the NEC. I've seen units with a 28 amp minimum circuit ampacity that call for a 50 amp breaker, in that case #10 nm-b and a 50 amp breaker would be perfectly fine.