Jim presented the following explanation :
Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

Maximum running load of each will be around 2.5Kw, or roughly 10amps -
though the initial start up surge could be much higher than this.
Some/many have a soft start, where the motor is allowed to get up to
speed before the compressor comes on load.


So the ideas I came up with to run the both at once would be

1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

Correct!


2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

You need to determine which circuit the garage is actually fed from,
then you could run the 2nd unit from a different circuit.


3. Try and set the compressors to kick in at slightly different pressures.
Presumably it's just at start up that causes problems once going they should
both run together OK ?

With no pressure, both would attempt to start at the same time. Up to
pressure with air being consumed, it would be very difficult to
synchronise both to start at exactly the same point - so basically
start one, then the other after which there would probably not be a
problem providing they are not both on the 16amp MCB.

Method 4 would be to add a larger air receiver, if you could work in
shorter bursts of activity.

Are you sure 20cfm is adequate for sand blasting?

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk