[ Ref.: Grounding Connectors for Electric Motors

There have been some interesting postings regarding the earthing, or
not, of electric motors in pianos.  Even though I am a purist when it
comes to restoration there are some things that have to be changed when
it comes to safety.  Electrical standards is the most important of
these.

In the engineering profession there are two principles (at least) to
be considered where safety is a consideration.

1. ALARP.  This stands for 'As Low As Reasonably Practicable'.  The
risk of the piano's owner electrocuting himself must be reduced to as
low a level as is reasonably practicable.  It is quite conceivable that
the owner may touch the chassis of the motor and it is also conceivable
that the motor could be harbouring a dormant failure of a winding to
earth, which in itself will not already have caused the motor to blow
a fuse or trip a breaker.  If the rebuilder has left in place an
electrical system which may be authentic, but could have been made
safer, then that rebuilder is responsible for the subsequent events.

The rebuilder may have thought that the owner wouldn't touch the motor,
but that act is possible and shouldn't be second guessed by the
rebuilder.

2. With knowledge comes responsibility.  If a rebuilder knows that he
can make the piano safer by earthing the motor and he chooses not to
do so, even for the sake of authenticity, then he is not acting
responsibly.  If an accident were to happen subsequently due to the
motor having not being earthed then the rebuilder would be held liable
as he has acted in contravention of his knowledge of the safer system.

The rules of electrical restoration are very simple.

Always earth any metal casing around an electrical appliance.

Replace open mercury switches with microswitches and relays.  Usually
one can retain the original switchgear levers and pneumatics.

Replace all original wiring with that to modern standards.  Original
metal wiring trunking can be retained for that authentic appearance,
but make sure it is also earthed if retained.

Plugs and sockets within the piano should always have the 'protected'
female side connected to the supply.  Some original installations were
the other way round so the male pins were always live.  Would any
rebuilder these days be stupid enough to follow that philosophy for the
sake of authenticity?

It just is not worth the risk of leaving an electric instrument
knowingly unsafe.  Eventually, in today's litigious world, someone will
get sued, and anyway we should all act responsibly and professionally
in making the instrument work correctly and be safe.

Best regards from the UK where the Ground is known as the Earth,

Nicholas Simons