lighting disconnection times

Reg 411.3.2.2 Max disconnection time for a 230v ac circuit below 32a on a tn system is 0.4 seconds

 

Correct, (on TT system it's 0.2 sec.)

 

Blimey that £300 i paid for my 17th update course last month must of been worth it as i knew the answer.

 

I thought your answer was rather 'word perfect' mbat!

 

Sen in this case maybe 0.04 secs? With the RCD the 0.4 is largely immaterial?

 

on TT it is 0.2, if you have main bonding on services you can use 0.4s

Gary

 

Any circuit subject to a fault on a RCD will disconnect within the tripping time of the RCD surely?..So this makes some values immaterial?..although can see that as long as you are below the requieste times, then I suppose what I say is irrelevant with respect to this.

 

on TT it is 0.2, if you have main bonding on services you can use 0.4s
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I think you've misunderstood something there Gary, where would you have a TT system that didn't have main bonding to services?

 

JP, the 40 m/s is at 5x times the rcd rating.

 

In the regs it says if you have main bonding conductors to incoming services then you can use the TN system 0.4s disconnection times.

page 46 main regs book

 

Thanks Sen.

 

Also JP remember that the rcd will only disconnect on an earth fault, it won't see L-N faults!

 

Thanks Sen..about time I started studying up a bit really..its not the sort of game where guessing at stuff is relevant really. Anyway thanks again Sen, and have a good evening M8.

 

page 46 main regs book
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This is talking about bonding connecting all extraneous conductive parts of the location, eg supplementary bonding, not main bonding. As supplementary bonding isn't always necessary in 17th due to rcd protection etc the max disconnection time is 0.2 seconds.

 

Has anyone here actually tried witnessing such a fault whilst in possession of a Swiss-made stopwatch?

Lucia x