Voltage drop problem not resolved with bigger cable

[TingleFingers]

Currently working on a job where the client was concerned about the swimming pool heat pump tripping the mcb (the mcb is more than adequate for the job).
The heat pump 4kw and pool pump 1.2kw were drawing 27/28 amps with only 197 volts measured at the pump room. It’s about a 60 meter run.
I replaced the 6mm cable run with 10 mm and the figures are still very much the same - I expected the voltage drop to be much less and therefore the amps to come right down, but no.
Any thoughts??

 

[Deleted member 105166]

Are you sure that the local grid has the power to power the heat pump ?.
It could simply be that the local supply grid is maxed out,
And therefore the power just aint there !

The heat pump referred to is only 4kW

 

[Lucien Nunes]

The main panel voltages are given in post #6. L3, serving the heat pump, is low at 218V, but that is a separate issue to the unaccountable drop in the heat pump circuit.

 

[marconi]

Further thoughts:

It is a swimming pool heat pump so I'd expect long periods of running.

Maybe:

1. Bearings are failing/have failed in compressor or its motor or both.
2. Low lub oil level in compressor.
3. High pressure fault in refrigerant circuit not detected by faulty HP pressure sensor.

All would cause comp motor to work harder and draw more current.

 

[davesparks]

The main panel voltages are given in post #6. L3, serving the heat pump, is low at 218V, but that is a separate issue to the unaccountable drop in the heat pump circuit.

It doesn't seem clear to me whether the OP has measured that incoming voltage with the heat pump running or not.
My thoughts at the moment are that if the incoming voltage is dropping to, or near to, 197V when the heat pump is running then that will be relevant.

 

[marconi]

Re my #18: I forgot to add a fourth:

4. Check that water flow through the condenser ( an heat exchanger) - which transfers the heat of the hot pressurised refrigerant vapour to the circulating pool water - is not restricted or throttled by defective valves or valves not fully open. Also check that the pool pump is running at its correct speed and the pump is not restricted - is there a strainer which needs clearing/replacing? If the volumetric flow of the pool water is lower than it should be, the refrigerant in the condenser will be at a higher temperature than it is designed to be at which means a higher back pressure at the compressor outlet. The compressor will have to work harder - more amps - to pump the refrigerant into the condenser.

 

[Kidsolo]

The online instructions for the heat pump state a 10mm cable

6mm should be fine if the pump is drawing the same power as it is rated at.

 

[Lucien Nunes]

Don't forget starting current which may be 5 times higher on a conventional motor. The manufacturer might specify a maximum cable resistance that allows reliable starting at a certain head pressure at minimum supply volts.