With regards to your article Ringing the changes (EMC, April, ), I would like to say that I totally agree, as I dropped the ring circuit three years ago for all the reasons the author stated.

There is one point, though, that I'd like to bring up. You mention a 32 A radial circuit on 4 mm2 cable, which we used to use but since the derating of cables there are only a few jobs now that I could get away with it on.

Now, on refurbishment jobs they are fibreglassing floors and dry-lining walls with insulation. I use 25 A radials, which ensure I am within the regulations, taking other issues into account, of course.

The only reason I am writing this letter is because I was in a wholesalers the other day where an electrician, who I know is not regulated, had a copy of the magazine. He had read your article and had taken it as gospel. When I tried to correct him, he said: "If it's in this magazine, it is good enough for me."

P Knowles RJ Engineering, Folkestone

The author replies: I totally agree with Mr Knowles. Where cables are enclosed in thermal insulation, installation methods six or 15 of the Wiring Regulations apply and cables are derated to the values given in Table 4D5A of BS 7671. A 25 A circuit-breaker would then be the maximum that can be used. This will become more appropriate in the future when Part L starts to bite.

Roger Lovegrove

Source

Electrical and Mechanical Contractor