"Sylvia Else" wrote in message
...
On 24/06/2011 8:53 AM, wrote:
On Thu, 23 Jun 2011 12:27:06 +1000, Sylvia Else
wrote:

On 21/06/2011 12:11 PM, Jeffrey Angus wrote:
On 6/20/2011 7:16 PM, William Sommerwerck wrote:
Remember, it ONLY takes ONE switch to OPEN a series circuit.
That is ALL that is required to control whether or not the
element gets hot or cools off.

You were not paying attention! Any heating device that uses both
"phases"
requres TWO switches to open it.


Oh, and by the way, since you brought it up, the bit about
both of the 240 volt sources being "hot with respect to
neutral". The heating elements are connected ACROSS the 240
VAC source, NOT split with each half going from the two
sources to neutral. (That would require a double contact to
turn each PAIR of heating elements on and off.)

I'm not sure what you're talking about. First, there is no "240V"
source in
my condo. There are multiple 120V sources from which you can get
higher
voltages by spanning them. (I assume each voltage is referenced to
some
"neutral" point.) In my preceding apartment, I took advantage of this
to
build a break-out box -- all to code, I have several electrician
friends who
advised me -- to provide individual lines for my class A power amps.

As someone else kindly pointed out, this oven has one side of its
elements
hard-wired to AC. Bad, bad, bad, bad idea.

Damn you are ****ing dense William.

The heating element from one hot lead to the other hot lead.
At NO time is there a connection to Neutral. Hence it ONLY
requires a SINGLE pole switch to open a SERIES circuit.

I see no inconsistency. A correctly functioning heating element can be
turned off, in the sense of no longer heating, by means of a single pole
switch.

But what about a non-correctly functioning heating element? One, for
example, that's shorted to its grounded covering somewhere along its
length. This could result in part of the element overheating, and an
owner noticing this would likely respond by turning the appliance off at
its switch. In the case of a heating element that spans two 110 v lines
in opposite phase, turning it off by a single pole switch won't have the
desired effect. Better hope that an earth leakage detector is fitted in
the supply lines, and works.

Sylvia.
I had exactly this happen over a decade ago. The center resistance
element started arcing to the outer sheath. This action was clearly
visible. When turning off the oven didn't help, I did what any
intelligent person should do - I turned off the circuit breaker.


I'm not so convinced that people who aren't used to fiddling with the
breaker box would immediately think of that in the heat (?) of the moment.
IMHO the switch on an appliance should disconnect the power, at least if
the appliance and supply are correctly wired. If the appliance uses live
and neutral, then a single pole switch is sufficient, but if it uses two
live wires, it should have a double pole switch.

Leaving aside the fault that occurs while an appliance is in use, if parts
of the appliance are live when the appliance is turned off, then it can
still go up in flames if a fault develops within. This was not such an
infrequenty occurence in the UK when TVs weren't earthed and had
unpolarised power cords which could result in the chassis (!) being live,
even when the TV was turned off.

Sylvia.

In all the years that I was directly involved with with TV sets in the UK,
working for one of the big four rental companies, I can only ever remember
one TV "going up in flames". It most certainly was not a common or frequent
occurrence. Further, I don't think I can recall any commonly sold make or
model, which ever employed an earth connection to the chassis. As for power
cords not being polarised, it depends exactly what you mean by that. In the
very early days, there were some sets that used a two pin plug-in power lead
which could be reversed. Likewise, there were two pin power sockets which
again could have the plugs for them reversed. However, by the time TV was
firmly established in the UK as an 'in every home' item, these sets were
long gone, and fixed power leads with colour-polarised wires, were the norm.
When we went over to the 13 A three pin wall socket convention, then as long
as the plug had been wired correctly, a 'live chassis' TV could never
actually have its chassis connected to the 'live' side of the incoming line
power. As to the chassis being live " even when the TV was turned off ", the
vast majority of sets that I saw employed a two pole power switch, ganged to
the volume control, so when they were switched off, both the line and the
neutral wires were disconnected from the TV.

On the cooker isolation issue, here in the UK, electric cookers are
typically connected via a permanently wired power cord that goes to a custom
outlet plate specifically designed and sold for the purpose. It is usual for
that outlet plate to be well down the wall behind the cooker, but connected
inside the wall to a further 'panel' mounted above counter height. On this
panel is either a large red switch on its own, or a large red switch, and a
three pin conventional power outlet. This is the double pole isolation
switch for the cooker, and is in addition to the fuse and breaker covering
this (independent) circuit, back at the fuse board.

http://www.pvrdirect.co.uk/productin...tref=SMJW45CUC

Arfa