Re: Wiring suggestions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Matthew Smith <matt-at-kbc-dot-net.au> 

Eric

If you are desiging your control panel, may I suggest that you try to get 
your hands on a contactor?

A contactor is really just a big relay, but with auxilliary contacts that 
can be wired so that the system can fail safe.  I have found that those 
available surplus/second hand are generally three phase.  As long as the 
coil is still 110V (assuming that this is what you are on), this just means 
that you get a spare power contact.

Further explanation:  Power to the contactor coil passes through one of the 
normally open sets of contacts.  A momentary push button (normally open) or 
even better, a momentary key-operated switch (normally open), sits in 
parallel with these contacts and is used to energise the system.  Power 
then flows through the main contacts to your Variac, etc.

Interruption to the power supply (breaker tripping, etc) will leave the 
system safe.  A stop button (kill switch) in the form of a normally closed, 
momentary operation push button in SERIES with the contactor coil allows 
instant-kill of the system.  You can have any number of series-connected 
stop buttons so that you can kill the system from wherever you 
are.  (Without having to dodge around a live coil that is going into 
meltdown ;-)

Starting up with a key-operated switch on a string around your neck means 
that nobody can walk in and turn it on whilst you're moving your primary tap...

This is a fairly standard way of adding a lot of safety to a system without 
excessive cost.

Hope this helps.

Cheers

M

-- 
Matthew Smith
Kadina Business Consultancy
South Australia
http://www.kbc-dot-net.au