derating cables

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tom1

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i am extending a ring in a stud wall built for sound proofing, insulation on one side cable on plaster bord. derates cable to 21 amps, am i righting thinking its ok cus off 2 ring cables = 42 amps

 
and in this case in THEORY could one tight arse do a ring in 1.5 te

 
Guiness Drinkfour lookers no takers. busy on here tonight

 
got 1 socket on the wall i need 3 mate

 
yer, dose the insulation make that much odds

 
Well according to OSG pg 44 its permissible (with a max cable run) with 2.5 method 102.

 
could drop 6mm from the socket on floor above and 6mm from socket thats already in the room

 
could drop 6mm from the socket on floor above and 6mm from socket thats already in the room
Not sure what you are saying here. I think you are saying running in 6mm instead of 2.5. I guess you would really need to upgrade the whole ring (thats why I a not keen on rings). Have you got an BRB/OSG there?

 
got osg, thinking 6mm cus of the insulation droping the current capacity

 
this is were it confuses me, if the temp goes up or near insulation it derates the cable, so increase the csa. also i have been told not to mix and match cabe size and also been told its ok if cable is bigger. thats off 3 diff sparks

 
44 is voltage drop in mine. pg 52 methode 102 2.5 t +e drops to 21 amps. thats why i thought it would be ok as the ring has 2 cables

 
So you dont have table 7.1 on page 44? It lists max cable length for different overcurrent devices and cable sizes.

 
Tom. Please can you stop the constant re-posting. It is totally un-necessary, and just annoys peeps. Thanks

To answer the question, extending in 2.5 is fine. If it really annoys you, add the socket as a spur from the ring, and wire in 4.00mm if it makes you happier. But 2.5 is not an issue, subject to the constraints of a ring cct as given in the BRB.

HTH

KME

 
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