Rotary phase converter and compressor on same circuit?
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    Default Rotary phase converter and compressor on same circuit?

    I'm planning the wiring layout for a rotary phase converter. Is it possible to have an air compressor and phase converter on the same circuit? The 7.5 or 10 HP phase converter will be on the opposite corner of my shop from the main power source. I would like to place the 5 HP compressor somewhere in between?

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    Quote Originally Posted by beeser View Post
    I'm planning the wiring layout for a rotary phase converter. Is it possible to have an air compressor and phase converter on the same circuit? The 7.5 or 10 HP phase converter will be on the opposite corner of my shop from the main power source. I would like to place the 5 HP compressor somewhere in between?
    That depends on loading and your breaker

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    Quote Originally Posted by Strostkovy View Post
    That depends on loading and your breaker
    It makes sense that the breaker would be sized for the combined loads to protect wiring but shouldn't there be consideration given for the load device itself?

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    You are thinking the phase converter draws power? The RPC itself will only draw a tiny amount of power, the machines you connect to it will draw the real power so use them to figure your loads.

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    Quote Originally Posted by Rob F. View Post
    You are thinking the phase converter draws power? The RPC itself will only draw a tiny amount of power, the machines you connect to it will draw the real power so use them to figure your loads.
    I realize the phase converter itself draws little power and the significant loads are from the connected machines.

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    So I am not sure what your question is then? Remember that the labeled amp draw of the 3 phase motor is not the same as amp draw on single phase (single phase is 1/3 more?) So a 10 amp 3 phase motor draws 15 single phase amps. Double check this but I think it is right.

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    Quote Originally Posted by beeser View Post
    I'm planning the wiring layout for a rotary phase converter. Is it possible to have an air compressor and phase converter on the same circuit? The 7.5 or 10 HP phase converter will be on the opposite corner of my shop from the main power source. I would like to place the 5 HP compressor somewhere in between?
    Loads are loads, wherever they sit. Physical location only affects wire routing, length needed, and its Ampacity, de-rated, thereby up-sized "sometimes".

    Your idler is about a 90-95% pass-through once running. Even a Phase-Perfect is only 97% efficient, (per their own manual) so that ain't half bad.

    An idler WILL look like most any other motor when first being spun-up from a cold-start, so there is the usual "starting" inrush. Ordinarily, that is brief enough that a breaker sized for the "running" loads will stand it.

    Simplest way forward is to copy the Amp rating published for store-bought RPC controls for your same idler HP and loads.

    Each of my 10 HP Phase-Perfect wants 55 A @ 230 VAC. The 10 HP RPC - Phase-Craft + Weg, about the same for starting its maximum-rated loads. It is not bothered @ 30A if the loads are dedicated and known to be lighter in advance. My max load on ANY of these is only 7 HP, but it that is about the same on any or all anyway.

    Even so, the electrical CODE is what rules here. It is supposed to be blind to "possible" reduced loads, partly because stuff is taken for granted, special cases forgotten about as loads tend to "grow" over time.

    Wire and breaker sizing isn't about light-load best-case, it is about nameplate-expected case or even "worst case."

    If you can separate an air compressor load, it is nearly always best to do so.


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