Extended meter tails and protection on TT system

Discussion in 'Electricians' Talk' started by Jack2006, Jan 5, 2014.

  1. Jack2006

    Jack2006 New Member

    Existing installation has voltage operated RCD mounted adjacent to meter before terminating into local consumer unit.

    A new plastic enclsure consumer unit with RCD's is to be installed that will be positioned approx 7 meters from meter.

    Looking at 531.4.1 it seemes to suggest that an RCD at origin is required unless class 2 equipment is used?

    In any event I will use an 80A double pole fused isolation to protect the tails and was going to use a plastic enclosed unit with no external metallic parts.

    Question is can I just use the 80A DP fused isolation unit or will I need to add an RCD say 80A/100ma after the isolator? (the consumer unit will have 30ma RCD's fitted to cover the various circuits).
  2. unphased

    unphased Screwfix Select

    If all of your circuits are going to be 30mA RCD protected then all you need is a main switch.
  3. seneca

    seneca Screwfix Select

    You would only need the rcd if the tails were buried <50mm below the surface.
  4. Jack2006

    Jack2006 New Member

    Thanks for advice the tails will be enclosed in plastic mini-trunking on surface so will go for just the 80A isolator.

    Had a look at the Click DB700 80A Fused main switch which seems to be a good price but never used this make tending to go for MK or Wylex usually. Have either of you used this switch? Just remember horrors we used to have when Tamlex hit the market in the late 70's and we had a fair flow of work ripping them out due to welded and melted isolator/fuse contacts.

    Thanks Jack
  5. Lectrician

    Lectrician Screwfix Select

    Many DNOs don't have a max tails length these days, so a main sw at the meter location may not be required.
  6. Lectrician

    Lectrician Screwfix Select

    Umm...

    30mA protection to a whole install? In front of a dual split load?
  7. seneca

    seneca Screwfix Select

    I never mentioned 30m/a Lec!
  8. Jack2006

    Jack2006 New Member

    Old habits I guess but would prefer to fit the fused isolator and not depend upon the supply authority incomer for disconnection.

    Regarding diversity and TT systems, when I fitted out my unit in France a few years ago they had 500ma 125A 3-P RCCB before I had to 'break' down to 300ma and 100ma TP&N RCD's to respective distribution boards. Installs over there were/are done to CENLEC agreement and when I came back here 4 years ago see the same rules being applied. I think a few others on the forum have mentioned the Euro regs and after living and working in France its a bit of a worry if we adopt some of the european standards, especially the sockets that drop to bits!!!
  9. Lectrician

    Lectrician Screwfix Select

    You can't use anything but to provide supplementary protection to buried cables...

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