single phase motor @ double nameplate voltage

[BrianMuir]

Hi,

this is funky.

today I was asked to check out a micro waste treatment plant to find out what has let to premature failure of six submersible pumps in the past couple of years.

When I look at the schematic the pumps are clearly shown as connected L-L, i.e. at 230V. Then I looked at one of the removed pumps and the nameplate indicates it is a 115V unit.

Wow, how about that for a smoking gun!

What surprised me is that some of these pumps lasted for a few years before they died. I suppose they are kept cool in the well, and are not running hard.

Somebody is arguing that I must be mistaken because he measured the current to the pump during operation, and it is right on the nameplate rating, but I think under modest load it would be reasonable to expect it to draw about half nameplate rating - and it is showing twice that because the voltage is doubled.

If anyone has any comments or experience that would help me confirm/deny this opinion please post.

failed pump is from ABS, model EF-05W-@, 0.5HP, 115V 60HZ, 13.2A

 

[BILLY101]

Since the history of these pumps is not provided, the first thing to do would be to measure the voltage at or near the pump while running to determine if the proper voltage is being applied. This is something that could have been changed for any number of reasons. My guess is the wire is sized for 240 volts and then later the voltage was changed to 120. 1/2 hp motor (per NEC) at 240 is 4.9 amps. A 1/2 hp motor at 120 is 9.8 amps.
Are the pumps on separate branch circuits?
Are the circuits long runs that can contribute to voltage drop?
The nameplate amperage 13.2 you provided seems high for a 1/2 hp motor. If it is correct then the voltage drop issue is more likely.
The other thing is the cycle rate of the pumps. The starting switch will only last so long.
A different type of starting control could help extend the motor life.

BILLY

 

[Dennis Alwon]

Apparently this motor is dual rated at 120V or 208/230V. These seem to be a walmart pump. Check here for specs.

 

[Jraef]

The issue is, regardless of what you read on the nameplate the pump is capable of being connected to 230V, so now the question is, was it really wired that way? If someone did on fact wire it for 115V and they applied 230V, you are back to having the "smoking gun".

When you apply twice the rated voltage to the windings, they will saturate and overheat the motor, causing premature winding failure. The "work" current, that which is creating torque in the motor, would theoretically drop through the higher impedance of the lower voltage windings, but then because of the extreme saturation the overall current draw will increase again, the net result could very well look like normal current, but most of that will be expressed as heating, not work. Were it not submersed, death would have been rapid.The fact that it was submersible in poop probably extended the life a little. So if in fact the motor was being given twice the rated voltage, they were cooking some of the "stuff" down there all this time, along with the motor insulation.

If on the other hand if it was connected properly, all the things that Billy101 said remain possibilities.

 

[BrianMuir]

thanks for the input.
I went to the site today and it turns out that three of four pumps are running at 115V, and the other at 230V, so the actual implementation does not match the schematic. We do not know for sure what unit is at the other end of that 230V line, and I have asked for it to be pulled and checked.

I realize that the pump can be internally wired for either voltage but out of the factory I would expect the nameplate rating, which says clearly 115V (and not 115/230V) to be correct. I cannot say for certain that they have not been field modified but it seems unlikely.

I agree, it seems unlikely that the pump could last for an extended period of time at 2x voltage.

by the way, no poop. The pump is in grey water, solids pre filtered.