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MMD > Archives > June 1997 > 1997.06.25 > 05Prev  Next


Electrical Safety
By Jeffrey Borinsky

Bruce Clark asked, "Is your electric piano wired safely?...."

There are several of us in the MMD who are qualified electrical engineers
and I'm sure that my own experiences of vintage equipment are not unique.
I have never worked on an electrical musical instrument, but radios and
TVs, etc., are little different as regards safety.

There are two main electrical hazards: Shock and Fire.  (The latter may
induce the former :>).  Vintage equipment is unlikely to conform to
modern standards of electrical safety, even when it was new.  This is not
usually a major problem since a mixture of minor modifications and a
little engineering common sense will usually give a plausible answer.

    ********** Shock hazards ***********

We are more painfully aware of this in Europe, where the mains voltage is
around 230V.  While 110V _can_ be unpleasant it is more difficult to be
badly hurt.

When Europeans are using an auto-transformer to operate 110V gear from
230V, ensure that the neutral is connected to the common point on the
transformer.  Otherwise the whole equipment will be floating 110V above
ground (= earth, UK ... maybe I should be including a US/UK glossary of
terms before I confuse myself.)

 [ I've moved your subsequent US/UK terms to a new glossary.  -- Robbie

*All* old wiring should be carefully checked, both visually and with an
insulation tester.  In particular the insulation resistance between live
connections and any exposed metal parts should be checked with a high
voltage tester ("Megger"- is this just a UK term?) at 500V for 230V
equipment and 250V for 110V.  If there is any leakage worse than about 50
megohms then track it down.  Motors are bad offenders and leakage down to
1 megohm is normally tolerable here.  If there is *any* doubt then repair
or replace.  If original-style rubber (or whatever) wire is not available
then use modern plastic-insulated wire.  Authenticity takes a poor second
place to safety.  If any wiring is in a hot place (lamp housings, some
motors and solenoids, etc.) then use suitably heat resisting insulation.

Even if the original mains lead  was 2-wire it is worth considering a
3-wire connection and grounding all exposed metalwork.

 [ It will also reduce interference to nearby radio and TV receivers.
 [ Be sure to ground the frame of the motor(s).  -- Robbie

The ultimate and highly recommended protection against shock (and to a
lesser extent against fire too) is a Residual Current Device (RCD,
RCB, ELCB, Earth leakage circuit breaker, Ground fault interrupter).
Please do not treat it as a panacea, but it is very highly recommended.

When you are working inside some equipment (as against merely using it)
remember that the shock hazard can be much greater.  A dry work area,
rubber mats and an RCD are all excellent precautions.  If you are
deliberately working around exposed live parts the old pro's trick is to
keep one hand in your pocket to prevent a potentially lethal shock
between the hands.  I appreciate that this may be impractical.

    ********** Fire hazards ***********

The best precaution is the simplest:

    ** Unplug the equipment when not in use **

Most of the advice for shock hazards will help prevent fire.  The main
additional protection is a fuse or circuit breaker.  Ideally the rating
should be carefully chosen but this is often difficult to do accurately.
The surge currents taken by a motor starting can make correct protection
quite tricky.  The empirical method is to use the lowest rating that does
not blow or trip in normal use.  In the UK we are well served by fused
plugs and fitting a 3 amp or 5 amp fuse here will usually give good
protection.  In the US and other countries the first level of protection
may well be a 20 amp or larger fuse in the house wiring system.

If you fit fuses in the equipment then choose the right type.  Do not use
glass cartridge fuses; they will explode if there is a short circuit.
Use the proper ceramic cartridge fuses rated for mains duty [ and motor
protection ] or the kind of miniature circuit breakers (MCB) that you
might find in the house fuse box.

I hope that the MMD demographics department will never have to record
lapsed membership due to electrocution or house fires.

If anyone has any questions on electrical safety I will be pleased to
help as best I can.  Just email me and cc: it to MMD if it is of wider
interest.

Jeffrey Borinsky
Oxford, UK


 [ Glossary:
 [
 [    --UK--                       --US--
 [
 [ mains voltage                line voltage
 [ (230 VAC 50 Hz)              (120 VAC 60 Hz)
 [ earth                        ground
 [ mains lead                   power cord
 [ Residual Current Device      Ground Fault Interrupter
 [ Megger                       Megger = "Megohm-meter"
 [
 [ (The Megger actually applies 250 or 500 volts and measures
 [ the resulting leakage current.  It's very different from
 [ a simple multi-meter.)
 [
 [ I had the pleasure of meeting Jeffrey and Nina Borinsky on my
 [ tour to England last month.  Jeffrey is a successful, independent
 [ consulting electrical engineer, and regularly works with the
 [ UK and EC regulations concerning modern electrical and electronic
 [ equipment and practice.  And his practical experience repairing
 [ electrical antiques is evident in his article.  Well-done, Sir,
 [ and thank you for your contribution!  :)  -- Robbie


(Message sent Wed 25 Jun 1997, 09:29:11 GMT, from time zone GMT+0100.)

Key Words in Subject:  Electrical, Safety

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