Hello,  Just thought I would point out something about the use of GFI
devices (in Australia we call them "RCD" -- Residual Current Devices)
when installed in the switchboard.  The leakage current of all devices on
the circuit add up.  So if one device leaks say 10 mA (our RCD's are
usually 30 mA) it won't trip but if you have a few leaky devices it could
easily add up to go over the 30 mA and then trip out.  It may happen that
the last thing plugged in might have the least amount of leakage but it
causes the trip.

Old motors, transformers, and most heating elements often leak a bit, and
this may include other things on the circuit apart from pianos.  It is
good practice to put an RCD on each power circuit only and not one on the
whole house.  A power outlet RCD just for your piano is fine unless you
already have one in the switchboard, but you could run a dedicated
circuit to the piano.  A megger is not a luxury; it is essential for
testing the insulation resistance (thus earth leakage) and a multimeter
just cannot do it properly.

As for DC relays in instruments, if you buy a proper DC relay rated at the
correct voltage, or better still well above it, you will find it is
constructed just like what Craig Brougher described.  It is better to
look at industrial quality relays.  I have not used Solid state relays in
pianos but I use them in industrial machines and they prove to be very
reliable, even in the worst of environments.

Peter Coggins

 [ But even high-quality DC relays will fail unless they are specifically
 [ designed to handle the tremendous energy released (the spark) when the
 [ inductive circuit is opened.  The relay _must_ be rated to withstand
 [ the repetitive 0.3 joules (watt-seconds) energy of the Violano
 [ tremolo coil (or the motor, etc.).  -- Robbie