David Nebenzahl wrote:
On 2/26/2009 11:06 AM Hobbyist spake thus:

When I switch my kettle off at the electric socket, a brief flash of
green light is visible behind the socket. Is this normal, or could it
be dangerous? Supposedly it's ok if the kettle plug is earthed?


Flashes of light accompanying switching something on or off are *never*
OK. Indicates arcing contacts, which can only get worse with time.

So, I'm using one of these Intermatic timers ahead of my home Bunn
coffee maker to remove power from it during the night. That saves us a
little electricity by not keep the water at brewing temperature all the
time.

http://www.intermatic.com/images/misc/TN111C.pdf

The Bunn is rated as drawing 900 watts and the timer is rated to switch
1750 watts resistive, almost twice as much as the resistive heaters in
the Bunn consume.

If I turn the timer dial by hand, when it switches power off I can see a
small spark through the opening the overide control knob protrudes through.

Yet, you say such flashes are *never* OK.

I don't agree. Have you ever closely watched the contacts of a relay
controlling a few hundred watts of load? When the contacts open there is
almost always a small visible spark.

I agree with you that arcing contacts will only get worse with time, but
sometimes there's no easy way to eliminate that arcing, and that "time"
can often be measured in years. That's why we had to change out the
distributor points in our cars when they got blown away by the sparks
occuring every time they switched.

But, that was before they started using solid state switching for that
job, wasn't it?

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Not sure where or what kind of switch you have; "switch my kettle off at
the electric socket" is a bit ambiguous. But it's time to replace that
switch if it sparks. "Earthing" (aka grounding) won't help you here.