Pump under 1megohm

[Jako13!]

If a pump is below 1mega ohm should it be condemned? Pumps reading about 0.9meg? Thank you for your replies

 

[Pete999]

If a pump is below 1mega ohm should it be condemned? Pumps reading about 0.9meg? Thank you for your replies

Is it the pump or the pump supply wiring that's giving you this reading?

 

[Jako13!]

Is it the pump or the pump supply wiring that's giving you this reading

The pump itself

 

[Pete999]

The pump itself

If you can't see any obvious damage /problems, send it away for repairs or source a replacement

 

[Jako13!]

If you can't see any obvious damage /problems, send it away for repairs or source a replacement

We’re awaiting replacement my question is should it be condemned until we have the replacement?

 

[telectrix]

it's not going to trip a RCD. only take it out of service if it's not a critical component.whilst awaiting replacement. might be an idea to check for any water ingress to terminals etc.

 

[Jako13!]

it's not going to trip a RCD. only take it out of service if it's not a critical component.whilst awaiting replacement. might be an idea to check for any water ingress to terminals etc.

It’s crucial yeah but no rcd on the circuit fed from BS88 2 16 amp fuses

 

[telectrix]

so leave in service pending further investigation or replacement.

 

[Lucien Nunes]

What size motor? Squirrel cage? Submersible? Outdoors? Cold & damp?

On some motors I would be delighted to get nearly a megohm and would be quite happy to leave in service. Others I would expect better.

 

[Jako13!]

What size motor? Squirrel cage? Submersible? Outdoors? Cold & damp?

On some motors I would be delighted to get nearly a megohm and would be quite happy to leave in service. Others I would expect better.

It’s a 2.2kw submersible pump?

 

[telectrix]

possible that the IP68 rating has started to break down.

 

[Lucien Nunes]

Sounds OK to me for a used pump. There are many variables with a submersible, including the length and type of cable submerged, that make a single insulation resistance reading a rather imprecise indicator of motor condition. What is more important is how that reading varies with time. If you come back in 3 months and find it at 600kΩ, and then at 300kΩ, you can see something is deteriorating. But if it stays around 900kΩ it's probably fine.

There's a good summary here:
YCC Pump insulation test recommendations

I've just read that and the paragraph about cable capacitance charging up is not strictly correct, they are confusing capacitor charging and dielectric absorption. The cable does have capacitance, and the capacitance to earth is increased by the cable being submerged in earthed water. The capacitance does have to charge up when the IR test is first applied but this will typically happen within seconds (the time constant is the product of the dynamic source resistance of the tester's voltage source and the capacitance) What then happens over a longer period of test voltage application is the dielectric absorption effect. This involves a smaller current than the charging current and it is limited by the properties of the insulation. It can influence the resistance indication on the tester so there is value in waiting for the numbers to stop increasing.