On Thursday, November 8, 2012 10:46:10 AM UTC, John Rumm wrote:
On 08/11/2012 07:52, harry wrote:
On Nov 7, 10:35 pm, John Rumm wrote:
On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:



Not all faults are dead shorts. Transformer overheat/burnout for
example.

For the purposes of this discussion they are (its in the definition of
"fault current")

Welcome to the strange world of Aurthur Brown. The wiring regs use 'fault current' to specifically mean a dead short, but obviously in the real world appliance faults occur that produce current (fault current by definition) that covers the full range from a smallish increase than only overheats a motor to a dead short. Introducing a narrow perspective definition that applies specifically to wiring and using it outside of where it makes good sense is not productive, and insisting it must mean that elsewhere is illogical. In the world of electronics (which many appliances are) fault current does not usually mean a dead short across the mains.


Transformers are unlikely to be able to present any sustained load above
their design maximum for long - the wire size on their primary winding
will typically be *significantly* thinner than that of the supply flex.

Not all equipment has internal fuses.

If it needs overload protection then it is required to have its own
protection.

In practice not all has, particularly old appliances

Remember in most markets, protection via a plug fuse is not
an option.

Old UK appliances were typically designed for only the UK market

3Kw/13a of sustained energy in an electronic device/small electric
motor could start a nice little fire.

Which would be an overload and not a fault. If there is a plausible
overload scenario, then the device in question must include its own
protection.

But in practice a fair few don't. There are still significant numbers of old electrical goods in use spanning the range from pre-95 to 1920s. And not all new goods meet the standards legally required of them.


NT