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  1. #1
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    Exhaust Hood Motor Issue

    The other day, I was changing a light bulb in an exhaust hood and noticed no air was moving through the hood. So, I went on the roof and, sure enough, the exhaust fan motor wasn't running.

    This is a 3/4HP, 1725RMP, 208-230/460V, 1.25SF, 2.65A-2.66A/1.33A, 5/8" shaft, belt drive, no thermal protection motor wired for 460V. In the drop ceiling above the exhaust hood is a G. E. motor starter. When I checked the overload heaters, all three were open. So, thinking the motor was having starting issues, I inspected the motor and noticed nothing visually unusual with the motor, though I didn't take it out and open it up. I did isolate the motor leads and checked to see if it was grounded, but my meter showed no grounds on any of the three leads. I OHMed the windings and the resistance between the three windings was the same, 3.64OHMS.

    Before I condemn the motor or burn up three new overload heaters, is there anything else I should be looking at more closely? By the way, the breaker was not tripped.
    With your chrome heart shining in the sun, long may you run.

  2. #2
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    It actually opened your heaters? You cant reset them ?

  3. #3
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    Sep 2011
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    California
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    12

    Hmm

    What about the sheave and belt conditions?

  4. #4
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    Quote Originally Posted by commtech77 View Post
    It actually opened your heaters? You cant reset them ?
    Yes. No. They're one-time heaters. This is them.

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    This is the starter.

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    Quote Originally Posted by avlu View Post
    What about the sheave and belt conditions?
    All good. Rotor spins freely.
    Last edited by SandShark; 05-04-2012 at 08:35 PM. Reason: Added photo
    With your chrome heart shining in the sun, long may you run.

  5. #5
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    You know, after I posted, I got to thinking that something has to be wrong with the starter and overload relay. I'm thinking if there was an overload condition, the overload relay should have tripped rather than frying the overload heaters. I didn't spend much time with the starter, so I'll have to go back and spend more time with it. All I had was a flashlight and it was kind of dark up above the ceiling. That doesn't necessarily mean there's nothing wrong with the motor, but the overload relay should have tripped.
    With your chrome heart shining in the sun, long may you run.

  6. #6
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    Quote Originally Posted by SandShark View Post
    You know, after I posted, I got to thinking that something has to be wrong with the starter and overload relay. I'm thinking if there was an overload condition, the overload relay should have tripped rather than frying the overload heaters. I didn't spend much time with the starter, so I'll have to go back and spend more time with it. All I had was a flashlight and it was kind of dark up above the ceiling.

    Ive had heaters open before but not all three.

    One time heaters with a reset ? I don't think there is such a thing as a one time overload heater. Why have a reset then ?

    Chances are you tripped the starter and it needs to be reset. Check the rating for the installed heaters

  7. #7
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    Quote Originally Posted by commtech77 View Post
    Ive had heaters open before but not all three.

    One time heaters with a reset ? I don't think there is such a thing as a one time overload heater. Why have a reset then ?

    Chances are you tripped the starter and it needs to be reset. Check the rating for the installed heaters
    The motor is rated at 1.33A. The heaters are rated at 1.63A. The overload relay can be field adjusted to + or - 10%. The overload heaters were open when I checked, so I pulled them. When I pulled them, the bimetal coiled wire came out in pieces. That's what I meant when I said they were "one-time". Once they burn up, that's it.

    Here they are:

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    With your chrome heart shining in the sun, long may you run.

  8. #8
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    Quote Originally Posted by SandShark View Post
    The motor is rated at 1.33A. The heaters are rated at 1.63A. The overload relay can be field adjusted to + or - 10%. The overload heaters were open when I checked, so I pulled them. When I pulled them, the bimetal coiled wire came out in pieces. That's what I meant when I said they were "one-time". Once they burn up, that's it.

    Here they are:

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    One time heater......gotch ya.


    Those are the right sized overloads. If you' ve checked every thing electrical plus starter contact condition and determined there are no shorts grab 3 more heaters plus some spares ( they're not that expensive ) and try to run the motor and monitor amp draw.

  9. #9
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    I didn't have any spares. I called the local electrical supplier and he can get them the next day after I order them. The thing is, at $17 each, I don't want to take a chance and burn up $51 in overload heaters. Before I install any new heaters, I'm going to investigate the starter and overload relay a little more closely. I'll post back when/if I find out anything. Thanks for the help.
    With your chrome heart shining in the sun, long may you run.

  10. #10
    Join Date
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    Location
    SE Texas
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    Update

    Well, I found some cheaper heater overloads for $3.00 each, so I ordered 9 of them just in case. I took apart the starter, looked at the coil and the contacts. Nothing was out of the ordinary. I installed 3 new heaters and supplied power to the starter. Immediately, all 3 heater overloads burnt up in an instance. The overload relay tripped, too.

    I forgot to mention, but at the ventilator on the roof, there is a 3-pole single-throw toggle switch. When I installed the 3 new heaters, the switch on the roof was in the off position and I had made sure beforehand and checked that the switch was open on all three legs. So, I pulled the switch and examined it. What I found was, believe it or not, I had a direct short between the three line side terminals on the switch where the line voltage wires and the load (motor) wires are connected. I really don't know how the terminals were shorted because there was no physical connection between the terminals, but I could see that arcing had taken place across all three terminals because I could see they were physically damaged. I took the switch apart and examined the contacts, but there was no physical damage to the internals of the switch. What's weird is someone had taken the trouble to wrap electrical tape around each terminal, so that led me to believe there must have been a short issue in the past.

    I pulled the switch and isolated all wires at the ventilator on the roof. I installed 3 new heater overloads, supplied power to the starter and none of the overloads burnt up. So, it was the switch all along. I've got a new switch and will install it tomorrow if it doesn't rain.
    With your chrome heart shining in the sun, long may you run.

  11. #11
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    Quote Originally Posted by SandShark View Post
    Well, I found some cheaper heater overloads for $3.00 each, so I ordered 9 of them just in case. I took apart the starter, looked at the coil and the contacts. Nothing was out of the ordinary. I installed 3 new heaters and supplied power to the starter. Immediately, all 3 heater overloads burnt up in an instance. The overload relay tripped, too.

    I forgot to mention, but at the ventilator on the roof, there is a 3-pole single-throw toggle switch. When I installed the 3 new heaters, the switch on the roof was in the off position and I had made sure beforehand and checked that the switch was open on all three legs. So, I pulled the switch and examined it. What I found was, believe it or not, I had a direct short between the three line side terminals on the switch where the line voltage wires and the load (motor) wires are connected. I really don't know how the terminals were shorted because there was no physical connection between the terminals, but I could see that arcing had taken place across all three terminals because I could see they were physically damaged. I took the switch apart and examined the contacts, but there was no physical damage to the internals of the switch. What's weird is someone had taken the trouble to wrap electrical tape around each terminal, so that led me to believe there must have been a short issue in the past.

    I pulled the switch and isolated all wires at the ventilator on the roof. I installed 3 new heater overloads, supplied power to the starter and none of the overloads burnt up. So, it was the switch all along. I've got a new switch and will install it tomorrow if it doesn't rain.
    Giod luck. Sounds like you nailed it.

  12. #12
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    Location
    SE Texas
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    New switch installed. Running like a champ!
    With your chrome heart shining in the sun, long may you run.

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