According to the TLC web site 2 core 2.5mm SWA is rated at 36 amps, and 3
core 2.5mm is rated at 31 amps. If I am using 3 core with the third core as
a cpc (connected to the wire armour ) can I reasonably use a 32 amp breaker
to feed it? The cable is buried.
(It is 30 meters long, fed off a 30mA rcd board, and feeds four 13a sockets
in the control cabinet for my front gate, with very minimal load (a wireless
hub, three cat5 cameras and the gate itself which is only 3 amps peak.
However it would be very convenient to use another socket on this circuit
for the occasional power tool, concrete mixer, 9" angle grinder etc to save
running extension leads, and I know my 9" grinder will trip a 20 amp breaker
on start up)
On Tuesday 14 May 2013 17:37 Andrew Mawson wrote in uk.d-i-y:
I think for 30m you are going to get done by voltage drop requirements - I
suspect 6mm2 will be nearer the mark.
Also, be careful as XLPE cable is often quoted as "X-amps" on the assumption
of running at 90C. Most accessories it terminates in will only be rated for
70C - unless you are using metal boxes with appropriately rated connectors.
I assume you will have RCD protection at the supply end?
Would you like me to look up the numbers properly (or someone else might
have them in their head)?
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/
http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage
Well rest assured that it's not getting 6mm - it's getting 2.5mm as it's in
the ground and has been for a year! Now I'm about to commission the gate
it's the fusing I was asking about NOT the cable. Standing load of the
electronic bits is less than an amp. Normal 'peak' load is something like 3
amps which happens when the gate opens - maybe 6 to 10 times a day for 25
seconds, then once every blue moon I >MAY< plug an angle grinder in which
>MAY<trip the 20 amp mcb I was planning to fit, so I was (and still am)
considering fitting a 32 amp breaker. My question was entirely based on the
current rating of three core (3 phase) swa in a single phase application.
(Don't you just love threads that go off at tangents !!!!!!!!)
But it is not 3 phase is it? (rhetorical)
So Tim was right that you can ignore the 3rd core and treat it as 2 core.
Your CCC is 33A if the cable is buried.
If it was me I would try using a C type 20A MCB and see how things go.
He did say 32A MCB - I think the 20A bit was just an aside that the AG
Indeed. And this is also one of those circumstances where one could
argue that the overload protection is enforced by the nature of the load
(i.e. they are not general purpose sockets, but designed to feed very
specific bits of kit), so all the head end MCB needs do is provide
adequate fault protection.
According to the book, 90degree C SWA cable is rated at 36A when in free
air or on perforated cable tray, clipped direct it is 33A.
Buried is not listed in the table but the 70 degree SWA is rated at 1A
buried than it is clipped direct, so it seems logical that your cable should
be OK at 1A higher (34A).
Must be a Makita! Mine does that on a 20 amp ELCB. I rather wondered if
the build up of dust on the windings was causing 30mA of leakage?
Can you not use a 25 amp breaker or go to *C* rating?
BTW the trencher has reached my budget plus transport and is still a
long way off the last 10 seconds:-)
Must be lots of people planning GSHPs!
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