17 years ago
I've got a strange problem with a new borehole pump - it trips the RCD on
the circuit whever it's turned on. However, after about 3 attempts in
succession (resetting the RCD each time), it starts OK.
According to the manual, you are able to use and RCD with it, although they
recommend use of a RCD that can sense pulsed DC faults, which it seems
standard RCDs might not. At the moment the pump has a standard RCD, but my
impression is that a pulsed DC type RCD will be even more sensitive.
The pump has a soft-start - to check this I put a clamp meter on the pump -
there is a 2 second delay after switch-on before the motor starts and there
was no initial kick in the current at all - the current rose smoothly up to
8.5A over about 5 seconds and then settled back to 8A.
The circuit is brand new, and the pump is the only thing on it. Next time
I'm there I'll try and check to see if there's anything between active and
earth and neutral and earth, in case there's some threshold current.
I suspect it might be due to the nature of the pump's current draw - as far
as I can tell the pump (Grundfos) uses some kind of frequency converter
drivng a permanent-magnet motor.
Anyone have any experience with this kind of pump?