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  1. #1
    Join Date
    Sep 2019
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    Iowa
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    Pump motors and starters

    This might be more suited for an electricians forum, except that our in house electrician keeps saying there's no problem.

    I have two redundant water circ pumps used for DI water. 1.5 HP, 208v 3p. They are on a timer that rotates them every 10 hours, for even wear. Intermittently, the overload trips on the starter. It has an over load sized for the motors attached to the contactor.

    Talking with the electrician on site, and with the in house water specialist, they've been going round and round on whether it's a pump issue or an electrical issue, without either of them digging into it... Side note, this kind of bickering between people all working for the same team blows my mind...

    For the trouble side, line side of the contactor reads 211 210 210. Load side reads 189 210 168. After that, there's the overload elements, and then comes the motor. Contacts are super pitted. The other pump reads within a volt line and load side (210 with decimals). Contacts are pitted slightly.

    Typically, I've had trouble 'selling' contactors before a motor fail event. Now that I'm an in house gig, seeing this even before a motor failure is a great learning moment for me, and maybe the electrician, if he wants to stop complaining about the HVAC guys just being belt and filter changers.

    What's a reliable way of testing contactors for wear to change them out before they damage or kill their load? Some of the motors on site are 30 and 50hp, and I would prefer to repair contactors every few years instead of changing those beasts.

  2. #2
    Join Date
    Jan 2013
    Location
    Oregon
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    65
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    You might try reversing the 3 Phase Pump briefly to get an idea if the pump is starting to seize.

    Sent from my SM-G955U using Tapatalk

  3. #3
    Join Date
    Aug 2015
    Location
    Buffalo,NY
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    Have you disconnected the motor to verify that your voltage drop is due to the pump and not a contractor going bad? How to the contacts look on the contractor. While I’m inclined to believe your pump may be on its way out it’s something easy to check.


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  4. #4
    Join Date
    Mar 2008
    Location
    kansas
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    You can manually engage the contactor with the power off and ohmn the contactor separate of the ol. It should have less than 1 ohmn resistance.
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  5. #5
    Join Date
    Aug 2002
    Location
    Southold, NY
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    27,207
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    I prefer 24 hr changeovers.

    Measure voltage across the contacts. L1 - T-1, L2 - T2, L3 - T 3 Zero voltage across.

    Heaters are they set for full load + SF?
    Have you measured the amperage, should be below nameplate.
    Motors duel voltage 208 / 230? Wired for 208!

    Good read on motors:
    Attached Images Attached Images

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  7. #6
    Join Date
    May 2014
    Location
    Bay Area California
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    26,556
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    Key into the highlighted below.


    Quote Originally Posted by Velociraptor View Post
    This might be more suited for an electricians forum, except that our in house electrician keeps saying there's no problem.

    I have two redundant water circ pumps used for DI water. 1.5 HP, 208v 3p. They are on a timer that rotates them every 10 hours, for even wear. Intermittently, the overload trips on the starter. It has an over load sized for the motors attached to the contactor.

    Talking with the electrician on site, and with the in house water specialist, they've been going round and round on whether it's a pump issue or an electrical issue, without either of them digging into it... Side note, this kind of bickering between people all working for the same team blows my mind...

    For the trouble side, line side of the contactor reads 211 210 210. Load side reads 189 210 168. After that, there's the overload elements, and then comes the motor. Contacts are super pitted. The other pump reads within a volt line and load side (210 with decimals). Contacts are pitted slightly.

    Typically, I've had trouble 'selling' contactors before a motor fail event. Now that I'm an in house gig, seeing this even before a motor failure is a great learning moment for me, and maybe the electrician, if he wants to stop complaining about the HVAC guys just being belt and filter changers.

    What's a reliable way of testing contactors for wear to change them out before they damage or kill their load? Some of the motors on site are 30 and 50hp, and I would prefer to repair contactors every few years instead of changing those beasts.
    I do a triple evac with nitro to remove non condensables.

  8. #7
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    First of all, the only way you can read a voltage drop is when there's a load...i e ....when the pump motor is running.

    Secondly, if you have that much of a voltage drop from the line side to the load side when the pump is running, you definitely have to replace those contactors before you go anywhere else with diagnosing anything having to do with this.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  9. #8
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    Diagnosing a contactor based on how its contacts looks is damn near impossible unless you are looking for work.

    but a very easy way to diagnose their condition is to measure across the contacts...lower is better but I generally give a customer a heads up when the voltage drop AT FULL LOAD is 0.1 VAC or higher. I have seen hot thermal images of contactors at 0.25 VAC across the contacts.

    At FULL LOAD is important if you have the ability for the motor to run in a lighter condition.
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

  10. #9
    Join Date
    Mar 2019
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    I used to service contactors regularly as an electrician before i had began my HVAC trade and so ive seen my few share of burnt contactors.

    When diagnosing the condition of a contactor, its always best to do this under load if possible. The contacts across the 3 phase load terminals are by far the number one cause of a failed contactor so naturally this is where you should look.

    When the contactor is under load, set your multimeter to mV and measure the mV drop across each phase contacts. Then measure the current for each phase. The mV drop x Amp reading across the contacts for each phase will give you the wattage dissipated. Obviously the higher the wattage the worse it is and the more heat generated, however this will vary depending on the amount of current flowing, so from experience contactors had usually ended up failing down the line when the mV/Amp % was over 100%.
    For example - Contactor L1 pulls 50 amps, voltage drop across contact is 50 Millivolts. So 50 mV x 50 Amps = 2.5 watts and has a ratio of 100% (50mV/50A x 100)
    Anything over 150% i would replace as a preventative measure. For example 100 mV x 50 = 5 watts and has a ratio of 200% (100/50x100) - Replace!

    This heat is not good and is what causes the pitted surface causing contactors to fail. Now add to that, the constant switching of these contacts and the extra heat generated from the loosening of the electrical connection of the cable to the contact surface of these terminals every time it switches... = More heat and a very high resistive connection will occur overtime.

    A quick way to also check is to use a thermal image camera if you have one. Even easier if you have 2 contactors pulling the same amount of current right next to each other. A quick scan of the thermal camera will let you know if one contactor is worse than the other from the heat discrepancy between the two.

  11. #10
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
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    I agree w/ others. Sure looks like the contacts are bad w/ those voltage drops.

  12. #11
    Join Date
    Jun 2008
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    33
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    Quote Originally Posted by pecmsg View Post
    I prefer 24 hr changeovers.

    Measure voltage across the contacts. L1 - T-1, L2 - T2, L3 - T 3 Zero voltage across.

    Heaters are they set for full load + SF?
    Have you measured the amperage, should be below nameplate.
    Motors duel voltage 208 / 230? Wired for 208!

    Good read on motors:
    Electrician here. Excellent information above. The amount of voltage drop you listed in unacceptable. The contacts within the contactor have high resistance & are getting hot. The heat will be transmitted down to the thermal overloads causing a false trip.

  13. #12
    Join Date
    May 2019
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    Quote Originally Posted by 508gm1 View Post
    Electrician here. Excellent information above. The amount of voltage drop you listed in unacceptable. The contacts within the contactor have high resistance & are getting hot. The heat will be transmitted down to the thermal overloads causing a false trip.
    Agree, that much voltage drop top to bottom of contacts produces a lot of heat.
    The longer it runs the hotter it gets. This takes the temper out of the metals and then the snowball effect happens.
    Eventually will drop a phase and hopefully the OL opens......but by then perhaps 2 of the phases are welded in place and OL's will not help.....motor time.

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