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Automatic transfer switch: an ATS that moves the loads you care about from utility to generator
An automatic transfer switch is the equipment that moves the building from utility to generator. Size, transition type, and which loads sit downstream of it are the job. An ATS that is too small, or that feeds the wrong can, is a completed install that still fails the outage.
The building side as a whole
Feeders, the load list, and utility coordination with the set are commercial generator electrical.
A defined optional subset
Loads that should stay on, and are not the legal set, are critical-load distribution.
Legally required emergency
Egress and fire that cannot share a can with optional standby are emergency-power distribution.
The transition type and pole count decide whether the switch fits the building
An ATS is not one product. Open, closed, and delayed transition behave differently at the moment of transfer, and whether the neutral switches is a grounding decision — not a preference.
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Open, closed, or delayed
Open transition drops the load briefly; closed transition rides through but needs utility coordination; delayed transition protects motor loads. The building and its equipment pick one.
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Three-pole or four-pole
Whether the neutral switches depends on where the system is bonded. Get it wrong and you have objectionable current or a missing ground reference — a safety finding, not a detail.
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Service or distribution
A service-entrance-rated ATS carries the main disconnect; a distribution ATS sits downstream. Which one fits changes the gear and the labeling.
When an automatic transfer switch isn’t the right job
The switch that transfers is this job. The building generator connection, or a designed subset of circuits, are not.
The generator, the feeders, and the load list are the job
That is commercial generator electrical.
Only a defined subset has to stay on
That is critical-load distribution.
Automatic transfer switch questions
Can we size it to a round number?
No. The ATS is sized to the service and the generator, and to what actually sits downstream. A round number that feeds the wrong can still fails the outage.
The set is not here yet.
The switch still has to match it. The building side as a package is commercial generator electrical.
Is this a residential interlock?
No. A commercial ATS is listed transfer equipment. An interlock is a house device. This job is the switch that moves the building from utility to generator.
Some loads are legally required.
Those cannot share a can with optional standby without saying so. That split is emergency-power distribution.
What does an automatic transfer switch do?
It senses utility loss and connects the generator or UPS source without someone having to pull a handle.
Can you manually operate an automatic transfer switch?
Most listed ATS units have a manual operator for testing and for a failed motor.
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