On 23/10/2014 08:31, harryagain wrote:
"John Rumm" wrote in message
o.uk...
On 22/10/2014 11:29, wrote:
On Wednesday, October 22, 2014 9:54:30 AM UTC+1, Rod Speed wrote:
"Uncle Peter" wrote in message
news
A lot of things might use 4 times the rated load for a bit.

**** all do in fact.

Quite; motors, filament lights, halogen lighting, transformers,
diode/cap input PSUs such as computers, wallwarts etc, none of these
things exist.

Indeed, and if the motor is an induction type, then you can have anything
from 5 to 9 times its nominal current drawn at startup.

Just as well your bog standard type B MCB is designed to permit inrush
current of 5 x nominal.

No, twice is more like.

They are normally specced such that the magnetic response will kick in
at at no less than 3x nominal, and up to 5x nominal.

Hence why the 5x value is the one to use for the adiabatic calculation
when assessing cable survivability under fault conditions.

See the table on the right of the graph:

http://wiki.diyfaq.org.uk/images/d/d...e-MCBTypeB.png

Also see MK explanation in their spec sheet:

http://www.tlc-direct.co.uk/Technica...Sentry/MCB.pdf

--
Cheers,

John.

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