On this page 3 sections
Motor circuits: sized for start and run — protection that holds through the inrush
Motors are not lighting loads. Inrush, service factor, and the disconnect at the machine decide the circuit. An undersized breaker that trips on start, or an oversized one that will not protect the winding, are both wrong.
A compressor
Air or refrigeration compressors surge on their own terms. That circuit is compressor circuits.
A pump
Sump, booster, well, or process is pump circuits.
A three-phase machine
Rotation and the landing at the unit are three-phase equipment connections.
A motor circuit protects twice — the conductor for a fault, the winding for an overload
A motor branch circuit is not one breaker. The short-circuit device protects the conductors on a fault; the overload protects the winding from running hot. Article 430 sizes them separately, off the nameplate current, not off a general breaker.
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Sized off the nameplate
Conductors are sized to the full-load current with margin; the branch device can be larger to let the motor start. A single breaker doing both jobs does neither well.
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The overload is separate
Thermal or electronic overloads sit at the starter and hold the winding — a breaker sized to let a motor start will not protect it from a slow overload.
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A disconnect in sight
The motor needs a disconnecting means within sight so it can be locked out for service — a code item, not a convenience.
When a motor circuit isn’t the right job
A generic motor feed is this job. A compressor, or the three-phase landing at a machine, are not.
It is a compressor
That is compressor circuits.
The machine is three-phase and the landing is the job
That is three-phase equipment connections.
Motor circuits questions
It trips every time it starts.
That is inrush, not a bad motor by default. We size the circuit and the protection for start and run before anyone swaps a breaker.
It is a shop compressor.
That is compressor circuits. This job is a motor that is not already a compressor or a pump.
The new machine is three-phase.
The circuit still has to hold through start. The landing — rotation and the disconnect at the unit — is three-phase equipment connections.
Can we put it on a lighting breaker until the new circuit is in?
No. A motor on a lighting circuit will nuisance-trip mid-shift, and it does not protect the winding.
Still not sure it is the right job? Call (279) 972-9272 — available 24 hours.
Serving 19 communities across the Sacramento area
Litel Electric serves businesses throughout all 19 communities in our service area — from Davis and Woodland to Roseville, Folsom, and Elk Grove.
Get estimate
Tell us what is happening, or what you are planning. We read the details, tell you what else we need to know, and explain the next step before anything is scheduled.
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You send the problem or the plan, with the address if you have it.
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We reply with what it involves and what has to be seen in person.
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Nothing is scheduled, and nothing is priced, until the equipment has been looked at.
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- CSLB #1115460 · C-10 electrical