Andy,

Apols for delay - have been away for the weekend...

See inline comments..

Many thanks for your VERY helpful feedback...

I think I will be going with 16mm T&E + additional
CPC - 10mm ? Through a separate 45A or perhaps 60A
Fused switch.

BTW - If, after doing the house diversity calcs, it comes
out greater than 100A, what is the likly response
from the supplier?

Many thanks,
Roy

"Andy Wade" wrote in message
...
RzB wrote:

OK - Should be OK now.... !!!

Yep. My comments on your calcs a

1. Current rating: You've used It = Ib/(Ca*Ci). Since overload
protection is required here this should be In/(Ca*Ci) - i.e. based on the
device rating, not the design current.

Yes - daft typo... formula sasy In then I use Ib... D'oh...

Moreover in your case the Ca factor (for loft temperature) and Ci factor
don't apply simultaneously (the cable thro' the wall won't be at 40 deg.
and the cable in the loft will be well-supported away from thermal
insulation).

My understanding was to use both - really don't understand the
rationalle behind this. However I think the calcs come out OK
with 16mm^2 whatever factors are used!

With Ib = 41.3 A and your intention of using the Wylex 108, we can select
the 45 A BS 1361 fuse, hence It = 45 A / 0.81 = 56 A (10 mm^2 still OK).
Or with a 60 A fuse we get It = 74 A (16 mm^2 required).

Yes - OK.

2. Shock protection: your calcs will be on the conservative side because
you've assumed 70 deg. conductor temperature (the 1.2 factor). In fact
the greatest part of the cable's length will be running well under its
rated current, so the loop resistance to be added to Ze is correspondingly
less.

Yes - understand...


3. CPC thermal compliance and disconnection time, with 6 mm^2 CPC and 50 A
Type C MCB: fault current at 479 A[*] is less than 10*In, therefore 5
seconds disconnection time is not necessarily achieved. Design is
non-compliant, go no further (or retry with larger CPC).

Yes - no need to do adiabatic calc if the 5sec time is not met on
the time const graph table.

For the Type B yes, it's OK to use 0.1 s (compliant), ideally use
manufacturer's published I^2*t data, which can be more favourable.


Yes - I understand.

[*] The fault current will fall as the cable heats up, so you have to err
on the pessimistic side here when anything is marginal.

Yes - I understand.

Design based on the use of measured values of Ze is discouraged, since
this value is outside your control. In principle the DNO could alter
their network, resulting in a higher value.

Yes - good point...


Incidentally, are there any metal service pipes or other
extraneous-conductive-parts entering the workshop? If so, you may need
local bonding to the earth bar in your dis-board - see Regulation
413-02-13 (a challenging read).

Not at the moment but there will be. Thanks for the reminder
re bonding.


--
Andy