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  1. #1
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    Starter Overloads

    We have a new 7.5 ton 480Volt split system (HP) with 15Kw auxiliary heating with a Hand-Off-Auto safety switch (provided by Elec) controlled by t-stat. The indoor unit says it will have an MCA of 25-amps. Blower motor has a a 2.9 FLA. What good are thermal overloads on the Hand-Off-Auto Switch since we have to size them to include the units FLA? Blower motor is not protected?

  2. #2
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    Thermal overloads are used in a starter for individual pieces of equipment, like a blower or a compressor or a pump. I would be very surprised if a 7.5 ton compressor did not have internal overloads. Electric heat does not require a heater\starter. The thermal overloads will be in the individual starter not in the HOA. The blower motor and its starter are the most likely spot for overload heaters.

    It sounds like you need to get an electrician or knowledgeable HVAC person to help you out.

  3. #3
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    Quote Originally Posted by jrr1970 View Post
    We have a new 7.5 ton 480Volt split system (HP) with 15Kw auxiliary heating with a Hand-Off-Auto safety switch (provided by Elec) controlled by t-stat. The indoor unit says it will have an MCA of 25-amps. Blower motor has a a 2.9 FLA. What good are thermal overloads on the Hand-Off-Auto Switch since we have to size them to include the units FLA? Blower motor is not protected?
    It’s wired wrong!

  4. #4
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    Thread Starter
    Quote Originally Posted by wolfdog View Post
    Thermal overloads are used in a starter for individual pieces of equipment, like a blower or a compressor or a pump. I would be very surprised if a 7.5 ton compressor did not have internal overloads. Electric heat does not require a heater\starter. The thermal overloads will be in the individual starter not in the HOA. The blower motor and its starter are the most likely spot for overload heaters.

    It sounds like you need to get an electrician or knowledgeable HVAC person to help you out.
    This is a combo starter which includes HOA and is provided by the electrician next to the indoor unit. The engineer told him since the unit has a motor he had to provide the combo starter. He installed the thermal overloads sized for the indoor unit including aux heat.

  5. #5
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    Quote Originally Posted by jrr1970 View Post
    This is a combo starter which includes HOA and is provided by the electrician next to the indoor unit. The engineer told him since the unit has a motor he had to provide the combo starter. He installed the thermal overloads sized for the indoor unit including aux heat.
    It’s wired wrong!

  6. #6
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    Quote Originally Posted by pecmsg View Post
    It’s wired wrong!
    It's wired wrong.

    A conventional blower motor has an internal overload and does not require a starter.

    Similarly, a motor that does NOT have internal protection DOES require a starter, and it can energize ONLY the motor. No heat packages on the starter. Period.

    Check with the motor manufacturer to see if the motor is internally protected. If it is, ask if they know of any scenario where a motor starter would be used. My bet is that the say, "no."

    Someone above your pay grade.. probably the manufacturer...will be tasked with explaining the error of this to the engineer...who should know better.
    Last edited by timebuilder; 06-17-2019 at 04:42 PM.
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  7. #7
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    Quote Originally Posted by timebuilder View Post
    It's wired wrong.

    A conventional blower motor has an internal overload and does not require a starter.

    Similarly, a motor that doe NOT have internal protection DOES require a starter, and it can energize ONLY the motor. No heat packages on the starter. Period.

    Check with the motor manufacturer to see if the motor is internally protected. If it is, ask if they know of any scenario where a motor starter would be used. My bet is that the say, "no."

    Someone above you pay grade.. probably the manufacturer...will be tasked with explaining the error of this to the engineer...who should know better.
    Gotta love Engineers!

  8. #8
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    3 phase motors generally do not have internal overloads. Reason for starters. Motor tag will state if internally protected. It is wired wrong

  9. #9
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    Quote Originally Posted by hvac69 View Post
    3 phase motors generally do not have internal overloads. Reason for starters. Motor tag will state if internally protected. It is wired wrong
    We don't know the type of motor. We DO know that heat packages would not be wired to a starter.

    3 phase motors can and do have internal protection. Carrier wires their internal protection to open the 24 volt circuit in many rooftop units.

    I just checked a York Predator 3 phase 2 HP blower motor. Thermally protected, Type A, right on the label.

    The newer Sunline units have an external overload for the blowers. Not a great system, either.

    Some Magic Aire units have an ABB starter for the blower.

    So, like the underwear.

    Depends.
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  11. #10
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    Thread Starter
    The 3-phase blower motor has integral overloads. The unit is single-point of connection, so there is not a way to wire-in the aux heat without touching internal wiring. The engineer is set to review his design. Thank you for comments.

  12. #11
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    Please follow up with a resolution post.

    Thanks.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  13. #12
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    Hand - Off - Auto .... I've only seen these heavy duty "contactors" with this knob , usually on lighting

    But im sure it can be used for heat strips too

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