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robgraham robgraham is offline
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Default Single phase induction motor starting problem

On May 17, 2:52*pm, robgraham wrote:
The wood working club has a bobbin sander made by Jet and bought from
Axminster some 3 years ago. *Recently it has been tripping the C32
RCBO on the ring it is on as it starts up. *This is random. *Many
times it will work OK, but on the umpteenth time there's an initial
spin of the motor and then the system trips - and of course if there's
another machine running on the same ring, then the trips occur more
frequently. *You can then go for another series of starts before it
trips again.

In order to eliminate the RCBO I wheeled the sander along to two other
circuits, both on 32A MCB's (forgot to see if they were B or C but
probably C in a machine environment), and both these circuits tripped
similarly after a number of starts.

So it is the sander. *I took it apart this morning thinking that it
might be the oscillating mechanism needing maintenance, but that seems
fine with plenty of grease and no dust.

So what's the collective's prognosis? *The motor is single phase with
an input power of 650W. *Is it possible that the capacitor is on its
way out - the hoped for option I suppose as that is cheap to replace ?

An interesting side effect of this ring circuit being on an RCBO is
that I didn't know to begin with if this was an overload trip or a
leakage trip - one down side of the RCD and MCB being combined.

Rob


Further guidance now sought - I've got the capacitor off, but am
puzzled by its working voltage of 125vac (capacitance of 200mfd). I
can get one off Ebay that I think will fit the case, but wonder if I
would be better to get a 250vac one and arrange a new fitting.

Comments please - and many thanks so far.

Rob