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.
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 Im inclined to believe your pump may be on its way out its something easy to check.
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.
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
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.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
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.
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.
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.