More calculations

[Jacobssi]

This is a fictional example.

A kitchen ring has a design current of 26a
Protection of bs60898 32a
Cable will run through 0.5mm of insulation and be installed as ref. 102 in stud wall with cable touching wall.
Therefore current carrying capacity= 32x0.88=28a
Go to selection of cable osg table 6f and the best cable to use is 6mm. I know it should be 2.5mm bubut where am I going wrong to get a bigger reading?
Also the factor 1.45 for circuit breakers do I X this or divide?
Go to

 

[securespark]

Multiply.

You do mean 0.5m of insulation, don't you?

 

[Spark123]

0.5mm or 0.5m?

Use the breaker size when calculating the loading for socket circuits - it's easier.
The regs require each leg of a RFC to be capable of carrying 20A (433.1.5).
Method 102 from table 4D5 gives the rating of 2.5mm as 21A.
Method C gives the rating of 2.5mm as 27A, apply a correction of 0.88 (table 52.2) for thermal insulation to give 23.76A so is still suitable.
You don't need to bother with the fusing factor 1.45 for a circuit breaker albeit is a different matter if the protective device is a BS3036 fuse.

 

[Jacobssi]

0.5mm.

Thanks for that. Couldn't work out which way round.

Regs say operating current of protective device cnt be 1.45 x greater than current carrying of cable. Yet I cnt achieve this,so what do I do?

 

[Spark123]

Have a read of appx 4 part 5 on page 256 of the regs - for an MCB (fusing factor of 1.45) you do not need to use the correction Cc before selecting a cable from the tables in appx 4 (unless the cable is buried etc).

The tables in appx 4 for current carrying capacities of cables are based on an overcurrent protective device having a fusing factor of 1.45, if this is different as in the case of a BS3036 fuse then you need to correct.

 

[ban-all-sheds]

0.5mm.

1) That mount of insulation will be pointless.

2) That amount of insulation can be ignored when working out cable capacity.

Regs say operating current of protective device cnt be 1.45 x greater than current carrying of cable.

No they don't.

They say that the protective device must be either 30A or 32A fuse or MCB or RCBO and that the Iz of the cable as installed must be at least 20A.