203 V supply to pool pump motor

[retirede]

The motor is not three-phase


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Very good...I stand corrected.

 

[kwired]

Reminds me of what a wise maintenance electrician once said
"Its always an electrical problem", meaning its never an electrical problem ...ie OL trip because the sewer pump is ragged up.

Any call for OL trips usually means you will be investigating mechanical issues. You may not be the one that fixes the problem but until you can prove the problem is mechanical - the tripping OL is an electrical problem to the owner/operator.

They often will think you need higher setting when you first say it is drawing too much.

 

[electricman2]

When I was doing electrical maintenance for the WWTP I used to work for our maintenance supervisor would come to me and ask why OL's were tripping at a lift station. My standard reply was "have you checked to see if the pump is clogged?"

 

[Jraef]

Back when I was an apprentice in the 70s and underwent training on motor starters and maintenance, I was given what was called a "Horse Chart", depicting motors as "dumb horses" that will work themselves to death if allowed to. The idea was that it was our (electrician's) responsibility to be the Teamsters of the horses and not let them kill themselves in the performance of their duty. On that chart, they showed the effects of increasing the heater element size, with the horse getting sicker and sicker with each increase. As I recall, the rule of thumb was that for every size above what the motor nameplate FLA said, you cut the motor life by a factor of 3. So if a motor was designed to last 30 years under optimum conditions, bumping up the OL heater selection by one size cut that to 10 years, one more size; 3years, 3 sizes too big, under 1 year for a brand new motor.

I've never seen that chart again, but the closest I have found is a widely used axiom that says that for every 10deg. C above rated temperature that a motor operates, you cut the motor life in half.

 

[Jraef]

Hey, found it!

 

[electricman2]

I was once told by an experienced guy who had rewound and rebuilt hundreds of motors that the biggest enemy of any motor was heat. Keep them cool and they will last forever.

 

[winnie]

Essentially true for motors, though a bit of bearing maintenance as also goes a long way.

For my big work project we must drive motors for short times in huge overload. Each motor has multiple RTD sensors and strict temperature limits during operation. If we drove the motors at full power for even 2 minutes we would be burning away the insulation, but they get operated for 20 seconds at a time with sufficient cool down, so the overload is no problem.

Jon

 

[kwired]

I was once told by an experienced guy who had rewound and rebuilt hundreds of motors that the biggest enemy of any motor was heat. Keep them cool and they will last forever.

Some "air over" designed motors are built about same as a lower horsepower non air over rated motor, they just take advantage of the air flow to keep it cool enough to work in their intended applications.

 

[kwired]

Back when I was an apprentice in the 70s and underwent training on motor starters and maintenance, I was given what was called a "Horse Chart", depicting motors as "dumb horses" that will work themselves to death if allowed to. The idea was that it was our (electrician's) responsibility to be the Teamsters of the horses and not let them kill themselves in the performance of their duty. On that chart, they showed the effects of increasing the heater element size, with the horse getting sicker and sicker with each increase. As I recall, the rule of thumb was that for every size above what the motor nameplate FLA said, you cut the motor life by a factor of 3. So if a motor was designed to last 30 years under optimum conditions, bumping up the OL heater selection by one size cut that to 10 years, one more size; 3years, 3 sizes too big, under 1 year for a brand new motor.

I've never seen that chart again, but the closest I have found is a widely used axiom that says that for every 10deg. C above rated temperature that a motor operates, you cut the motor life in half.

That 30 years to 10 years is kind of dependent on duty and or abuse of the motor as well. Something that runs 24/7/365 is not going to last as long as something that runs 10 hours a day 5 days a week but is otherwise driving the same kind of load, or the same kind of load but one application the operator pushes it hard all the time and the other application they don't.

 

[StarCat]

It is likely there is nothing wrong except that the pump does not have enough head on it and it is operating outside of its design curve. See it all the time on commercial pools. It just needs to have a throttling valve on the discharge of the pump to get the flow in line with the pump curve. You just throttle the flow back until the amperage is in line with the motor data plate. If then you do not have enough system flow the you have a design issue and the pump is to small.

This is absolutely a correct way to get a centrifugal pump to stay on line when it is overloaded. I would have to wonder exactly how it is piped, as typically you go into the filter, and then the heater after the pump discharge. There are a lot of untold problems with pump systems due to incorrect piping and or incorrect pump for the application.

 

[Mystic Pools]

It is likely there is nothing wrong except that the pump does not have enough head on it and it is operating outside of its design curve. See it all the time on commercial pools. It just needs to have a throttling valve on the discharge of the pump to get the flow in line with the pump curve. You just throttle the flow back until the amperage is in line with the motor data plate. If then you do not have enough system flow the you have a design issue and the pump is to small.

I had a similar situation about 25 years ago at one of my commercial accounts.

The original 7.5 HP, 3 phase motor died out. The cast iron housing on the pump itself was badly corroded so I elected to replace the entire pump rather than the motor. It was a bank of (3) 36" commercial sand filters.
After about 2 days, the motor fried. Turns out it was drawing too many amps. I throttled back the discharge butterfly valve, all 4" PC pipe, and the amp draw was resolved. But, the flow was cut and now the turnover rate requirement was cut as per NJ code.

I spoke with the sales/tech rep at the time and the solution was to swap the impeller from the new 7.5 HP pump, to a 5 HP impeller. The part was sent free of charge. It solved both problems of the required flow rate and the amp draw.

Throttling back the discharge might work for your situation provided the flow rate is within the guidelines of the state and the local health department. Sometimes the pool's wall fittings can be restricted with a smaller "eyeball" opening.
A flow meter is needed on the discharge after the filters. They create some restriction and the true reading will be at that point.