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Thread: Phase Converters - 120/240V Single Phase to 120/208V 3 Phase

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    Phase Converters - 120/240V Single Phase to 120/208V 3 Phase

    The client already placed the order for 3xRTU which are 120/208V 3 Phase and already at the site
    I just heard from the utility company, that they will not be able to provide 3 Phase service to the location anymore.
    If the max fuse size is 50 AMP for the RTU based on the spec sheet, will a PL-20 Phase Converter work?
    Are the converter reliable for RTU loads?
    Will they also work the same way for some kitchen equipment such as a dishwasher and oven which are 3 Phase as well?

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    Quote Originally Posted by BatmanisWatching1987 View Post
    The client already placed the order for 3xRTU which are 120/208V 3 Phase and already at the site
    I just heard from the utility company, that they will not be able to provide 3 Phase service to the location anymore.
    If the max fuse size is 50 AMP for the RTU based on the spec sheet, will a PL-20 Phase Converter work?
    Are the converter reliable for RTU loads?
    Will they also work the same way for some kitchen equipment such as a dishwasher and oven which are 3 Phase as well?

    You will get 240V, 3 phase from the phase converter, not 208V, 3 phase.

    I don't see why a phase converter wouldn't work for RTU loads.

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    Phase Converter Applications

    Quote Originally Posted by david luchini View Post
    You will get 240V, 3 phase from the phase converter, not 208V, 3 phase.

    I don't see why a phase converter wouldn't work for RTU loads.
    What I have experienced is Electronics and other " Subsystems " can act badly depending on where the Phase Converter "Phase " lands. My experience is strictly with rotary units, but the SS units look very capable and possibly better for this application. I would without fail consult the Engineering Department at the HVAC equipment MFG.
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    Usually, the only component inside the RTU that requires 3-phase is the compressor. It may be cheaper (and less equipment to go wrong later) to replace the compressors with the equivalent single-phase components (with run capacitor).

    That said, if on an order has been placed, why can't the correct machines just be ordered instead? Even a "restocking fee" should be the cheapest and easiest way to go.

    I'm an HVAC guy, but not a phase converter guy. AC machines start and stop throughout the day, and are usually also left on for maintaining temperature even when building is not occupied. Would the phase converters be running continuously, or will there be more controls to bring them online every time the AC needs to run?

    I can't see a phase converter at each RTU being the way to do this job.

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    They really should look into returning and replacing them. There is a significant efficient loss in running the phase converter that will cost them a lot in energy over the long run, more than any restocking fees. The 3 phase is not well balanced either, so it will also shorten the lifespan on the 3 phase motors. Phase converters are fine for things like machine tools that do batch runs and don’t run continuously on demand like HVAC.
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    Keep in mind, too, that the derived phase from a rotary converter is basically the same thing as the high leg on a high-leg service, while the other two lines are fed through, so shouldn't be used for any load that expects a neutral reference.

    I'm not sure about SS converters, but I imagine they're equivalent to VFD's without the variable-frequency feature.
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    Quote Originally Posted by BatmanisWatching1987 View Post
    I just heard from the utility company, that they will not be able to provide 3 Phase service to the location anymore.
    ...
    Will they also work the same way for some kitchen equipment such as a dishwasher and oven which are 3 Phase as well?
    Sounds like a bigger problem than just the RTUs. Did the PoCo say they could provide 3-phase then change their mind? If you had 3-phase and now don't, I'd be asking some pointed questions about why. Changing from a 3-phase install to a single-phase one is not trivial (i.e. do you already have 3-phase panels?).

    An oven is probably configurable for single phase, but most things with motors probably aren't. A couple of phase converters is one thing, but installing for more than a few pieces seems like asking for trouble. As suggested, you might be able to change motors/compressors for the single-phase equivalent, but that'll cost, too.

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    Agree

    Quote Originally Posted by MAC702 View Post
    Usually, the only component inside the RTU that requires 3-phase is the compressor. It may be cheaper (and less equipment to go wrong later) to replace the compressors with the equivalent single-phase components (with run capacitor).

    That said, if on an order has been placed, why can't the correct machines just be ordered instead? Even a "restocking fee" should be the cheapest and easiest way to go.

    I'm an HVAC guy, but not a phase converter guy. AC machines start and stop throughout the day, and are usually also left on for maintaining temperature even when building is not occupied. Would the phase converters be running continuously, or will there be more controls to bring them online every time the AC needs to run?

    I can't see a phase converter at each RTU being the way to do this job.
    Being an HVAC guy as well. I agree with this position. Also changing to single phase compressors in a brand new RTU is quite a piece of work, and can get more intricate than expected. Compressor RLA would be different. Nameplates would be incorrect, etc.
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