query

[wannabesparky]

what would or wouldnt happen if you put a board on a tn-c-s pme system instead of an incoming mains switch? forgive me for sounding thick but im still learning.

 

[Grae79]

que?

 

[Des 56]

what would happen or wouldnt happen if you put an rcd instead of a mains incoming switch in a board on a tn-c-s pme system?

Well unless you had a fault ie neutral earth on one of the circuits Nothing would happen
At present at least until the 17th in july There has been no need for rcd protection of lighting cookers central heating etc on a tnc-s system because the primary protection the mcb would operate in the required time and no additional protection was required by an rcd, so you would be providing additional protection but would have no discrimination with the circuits One rcd would be protecting the whole of the installation This I consider to be a minor deviation from bs7671 16th ed
The rcd current rating would have to be adequate for the supply fuse though
No danger would be introduced by installing an rcd instead of a main isolator

 

[wayne]

sort this post out please

 

[Had8Lives]

I can't quite get to grips with what you're asking WannaBee sparky. I'm guessing Des has possibly answered it. Do you mean you are removing an old isolator seperate to the old board and then connecting a new board directly to the tails?

 

[wayne]

des seems to be replying in regards to rcds where as wanna be never mentioned one

 

[Cirrus]

Yeah, the post doesn't seem to make sense. One is an earthing system wannabee and the other is a mains switch. Two completely different things fella. You need to explain what you mean.

 

[ian.settle1]

Wannabe

Can you repost question as your first post and the quote of your question on DES56 do not match

 

[Shakey]

Well unless you had a fault ie neutral earth on one of the circuits Nothing would happen
At present at least until the 17th in july There has been no need for rcd protection of lighting cookers central heating etc on a tnc-s system because the primary protection the mcb would operate in the required time and no additional protection was required by an rcd, so you would be providing additional protection but would have no discrimination with the circuits One rcd would be protecting the whole of the installation This I consider to be a minor deviation from bs7671 16th ed
The rcd current rating would have to be adequate for the supply fuse though
No danger would be introduced by installing an rcd instead of a main isolator

Des, regardless of what the guy was originally asking, you have answered about an RCD as a main switch

Minor deviation? No danger?

Firstly the RCD if used as a main switch would have to be an S type time delay.

Going to the 17th, you be contraveing 134.1 on at least 3 counts

And the first one is the responsibility to design your system to minimize inconvenience and danger in the event of a single fault.

And a little old lady tumbling down the stairs after the house is plunged into darkness because the main RCD has isolated the whole CU after a fault on a socket, or the cumulitive effects of leakage currents of electronic equipment, would be classed as danger in my book.

You would also be causing danger because your smoke detectors would also have no mains power, in addition to contravening the requirement that smokes, if on an RCD (and they preferably shouldnt be) must not be on the same RCD as socket outlets