by ericmark »
Tue Sep 09, 2008 1:05 am
If we look at 314.1 to 314.4 in 17th Edition and 314-01-01 to 314-01-04 in 16th Edition there is very little change. “(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit” would maybe prevent the lighting being for being bunched with power on same RCD but splitting upper and lower floors is hardly going to help only the use of emergency lighting could really help or side to side lighting split and the latter would require quite a lot of rearranging in most cases.
”(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation” this would may be mean spitting the power into a number of circuits and of course keeping it away from any lighting circuits.
The rest with exception of EMC is the same. My house built 1980 has a single lighting circuit I have fitted two emergency lights one at top of stairs and one in garage but this is unusual for the estate and I am sure most are as original with a single lighting circuit. Where the fuse is replaced with a MCB then consideration should be made as to using type C or D to avoid nuisance tripping. This would depend on the earth loop impedance reading of course.
I have heard say many times how floors should have independent supplies but unable to find anything in either old or new regulations to say this must happen. Desirable as it may be. Maybe it is a building regulation but I have not found it and I have attributed it to Chinese whispers.
Although I have seen great lengths gone to in order to split the neutrals between the upper and lower floors where stairs lighting has used both neutral supplies on both Line supplies due to the pour wiring of the two way lighting personally I don’t see it is really worth the effort.
After all a caravan if wired with two 30ma RCD in series which breaks both the discrimination rules 314.1 and 531.2.9 and I think some common sense must prevail.
In the same way as if we followed 522.6.5 and 522.6.6 we can’t bury the wires feeding door bells, computer LAN, and telephone. As neither earthing or RCD’s can be used to protect these cables.
One would have to be rather pedantic to insist these are wired surface.
If anyone can quote the regulation I will be interested of course. But in the same way as lack of earths in lighting circuits are dealt with using a risk assessment and if the owner with now budge you can use class II fitting I would say the same goes for when major wiring is required to split the floors and even though it may not be 100% correct one does need to bend.
Having said that since type C or D RBCO or MCB are to be considered and earth loop impedance will require measuring to ensure they can be safely fitted and only some makes do C and D RBCO’s and there could be compatibility issues it is not a DIY job. And all departures would need entering on the installation certificate this may mean authorisation from overseeing bodies would be required either LABC or self cert system and one would hope the governing body would not be pedantic but one does come across the “jobs worth” from time to time.
Eric
