panel breaker sizing for appliances & machines

[megloff11x]

I poked around the code book but didn't find a complete answer.

How much large can the breaker at the panel be for a machine or an appliance? This is both a home and industrial question. I found a bit on the wiring but not so much on the breakers in the panel.

I've had some replacements of machinery - same ampacity as the old. But when the day comes again, is there a rule or code citation to go by? I recently went to a larger AC unit. It was more efficient and only had a slightly greater amperage rating, but did not exceed the breaker used for the old unit. We had an electrician install it and handle those details. I would have liked to have gone larger but would have incurred a building re-wire & bigger panel.

A non-work example, I once rented a house that had the clothes dryer hook up in the garage. The vent was there and it "shared" a 50A outlet with a welder - plug in which one you were using at the time. The dryer was your typical ~24A unit designed for the usual 30A plug, but the hardware store had the 50A plugs for clothes dryers too...

When shopping for machinery I try to avoid buying something that will result in a $$$ re-wiring, or worse re-wire & new panel as we're usually already maxed out from previous "additions."

I'm looking for guidance in this regard. What % of the breaker/outlet rating can the appliance or machine be before I'll burn my fingers if I have to flip the breaker. And how much smaller can it be before I have a fire hazard with the unit burning up while the protection takes no notice of this puny device?

I would note the progression to home washers & dryers that can handle an Army GP Large tent on the one extreme and the higher efficiency other things that use a fraction of the power of their predecessors on the other.

 

[suemarkp]

The answers vary depending on the equipment. For appliances, see 422.10 and 422.11 (basically minimum size is the nameplate amps, maximum size is 150% of the rated current with round up to next standard breaker permitted). There are also many other limits (50A max for many things, 20A max for things rated 13.3A or less).

For HVAC equipment and motors, minimum wire size is the MCA or nameplate *1.25. Max breaker size can be per the HVAC nameplate (generally about 1.5 - 2X the MCA) or 250% of the motor nameplate.

 

[augie47]

I'm not sure you will find a "general" answer. The overcurrent device serves more than one purpose. One task from 240.4 which requires us to protect conductors at their ampacity which should be our basic rule, however, there are exceptions in 240.4 (A)-(G).
A second task of the OCP device is to protect the equipment and, as suemarkp stated, you are going to have to refer to the applicable Code Article: 430 for motors, 440 for air conditioning and 422 for appliances. As noted in those Articles in in Art 409 for Industrial Control Panels, the Code requires the maximum overcurrent device to be noted by the manufacturer.