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Inactive, Master Electrician
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Experience:  Electrical Contractor
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1. Is 220 vac 3 phase power service in the US rated as 208

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1. Is "220 vac" 3 phase power service in the US rated as 208 vac or 220 vac or are there both (different) services? 2. Is 208 or 220 vac from phase to phase, or from phase to neutral (if provided) and is neutral (4th wire) provided? 3. Without a transformer I assume that 110 vac is not available from 220 3 phase service, unlike residential so called "2 phase" 110/220 service.
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Im curious - is there a specific reason you need this information? Is there a specific application your preparing for? Can you give me more details?

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Customer: replied 8 years ago.
I want the info for my "background" knowledge. I write manuals for a company that manufacturs rainwater reclaim equipment with single or three phase pumps, and the engineers seem to be rather vague with their input to me. Also, some of our customers are starting to specify that they provide their own external pump controlled by our internal pump control relay. since there are our own on-board pumps--at least one- and only a single three phase power input the voltage for their external pump must be the same as our internal pump (a common 3 phase input terminal). I wondered if a 220 vac single phae on-board pump is compatabile with 3-phase external 220 vac pump. That's why I asked about the 220 vac being from phase to phase (which means it is compatabile, or if it is from phase to neutral.
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Three phase systems in the us work like this. "wye" systems are 120/208. Phase to ground 120v and phase to phase 208v. "Delta" systems are 120/240. Delta systems are dangerous for single phase systems because most people dont know about the high leg. So the voltage with this is 120v phase to ground on two of the phases, then 208v from one of the phases to ground. Each line phase to phase will be 240v.

For single phase services you have 120v phase to ground, and 220v phase to phase. But with single phase services you only have 2 hots.

Now three phase motors do not require a neutral. The only kind of motor that will require a neutral is a 120v motor.

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