Mechanical Music Digest  Archives
You Are Not Logged In Login/Get New Account
Please Log In. Accounts are free!
Logged In users are granted additional features including a more current version of the Archives and a simplified process for submitting articles.
Home Archives Calendar Gallery Store Links Info
MMD > Archives > January 2004 > 2004.01.31 > 10Prev  Next


Grounding Connectors for Electric Motors
By Mark Kinsler

> My question to everyone is this:  Do you have the motor rewired
> (and rewire the electrical connections on the piano) to accept
> a three-prong grounded plug from the Holtzer-Cabot Motor, or do
> you leave the wiring the way it is with the original ungrounded
> two wire connection?

This may be a question of authenticity vs. getting sued by the piano's
owner.

The restored instrument is, legally, an electric appliance.  Laws
probably vary, but I believe that if the electrical parts of an antique
are repaired, modern safety standards must be applied.  In the USA,
this would involve a dead-front three-pronged plug whose third prong is
connected through a green wire in the power cord to the frame of the
motor.

I'm sure that everyone here understands the concept: the idea is that
the insulation between motor windings and frame can fail.  This
energizes the motor frame.  If there's a path to ground from the motor
frame through the plugs third prong, the house fuse will blow.  In the
absence of that third wire, a person's body could provide that path.

The exception is for 'double-insulated' appliances, in which the case
or other touchable surfaces are made of non-conductive materials like
approved plastics.

Now, I cannot conceive of a means by which someone could shock himself
on a piano: you'd have to lie on the floor, reach up and touch the
defective motor and a water pipe simultaneously.  (Though now that
I think of it, that's the sort of thing I would have done as a boy.)

But the wood of a piano is probably not an approved insulating
material, so the court could rule that the fatal piano could not be
considered a double-insulated appliance, so the three-prong plug would
have had to have been used.

That's the story as I understand it.  For the USA, the rules are in
the National Electrical Code, which is published by the National Fire
Protection Association.  If I was going to give legal advice, which
I'm not permitted to do because I'm neither a lawyer nor a professional
engineer in the legal sense, I'd suggest that you put the three-prong
plug on the thing and tell the owner of the instrument that your
responsibility for authenticity ends at the electric power input.

Mark Kinsler


(Message sent Sat 31 Jan 2004, 16:19:44 GMT, from time zone GMT-0500.)

Key Words in Subject:  Connectors, Electric, Grounding, Motors

Home    Archives    Calendar    Gallery    Store    Links    Info   


Enter text below to search the MMD Website with Google



CONTACT FORM: Click HERE to write to the editor, or to post a message about Mechanical Musical Instruments to the MMD

Unless otherwise noted, all opinions are those of the individual authors and may not represent those of the editors. Compilation copyright 1995-2024 by Jody Kravitz.

Please read our Republication Policy before copying information from or creating links to this web site.

Click HERE to contact the webmaster regarding problems with the website.

Please support publication of the MMD by donating online

Please Support Publication of the MMD with your Generous Donation

Pay via PayPal

No PayPal account required

                                     
Translate This Page