Sylvia Else said:
On 19/06/2011 1:20 PM, William Sommerwerck wrote:
I think it's perfectly normal for appliances to switch only one pole
of the power supply, that pole being the live one. Same with power
points and light switches. I don't think I've seen an appliance with
a double power power switch.
I have have. I've owned two of the classic GE/B&D toaster ovens, and they
switched both sides of the line when you opened the door. This is a good
safety precaution. My current B&D toaster oven does not remove the power
when the door is opened.
With respect to this particular oven, something "live" was NOT being
switched. How do you explain the spark, otherwise? The 208V or 240V are
(presumably) taken from across two phases (or whatever you want to call
them -- we needn't rehash that argument), one of which is not switched. The
oven's "metalwork" is grounded/"neutraled" so that a short from the
heating-element circuit to the metal will trip the breaker -- which it did.
What's not normal, and dangerous, is for the neutral wire to be the
one switched. Either the oven is miswired internally, is miswired to
the mains supply, or the mains supply is miswired. Whichever it is
needs to be fixed.
If I understand multi-phase wiring, the 240V is taken from across two
phases. Connecting or disconnecting the neutral would have no effect on that
voltage.
In single-phase systems, it would, of course, be foolish to switch just the
neutral. This would leave the hot "hot", and open the possibility of
electrocution from hot to ground, such as a plumbing fixture.
Yet again, an example of how a simple question becomes a tsimmes.