N
NickT
Hi All,
First of all, I'm new here. Second, I would have posted in the DIY forum, but it appears to be the only one I don't have permission to contribute to. Having said that, his isn't a DIY question, but an unqualified one:
Forgive me if this touches on many of the threads that I've read over the hours that I've researched
this, but I'm after a sanity check and a bit of advice please on what an Electrician can and can't do in this case:
We have a 1930's semi that was rewired in twin and earth some time in the past (probably the 80's). It
goes without saying that the main building protection does not meet current standards. I am also about
to renovate a detached garage with a workshop underneath (it's just about two stories) which gets its
power from the house. Let me start by stating that I intend to get the works professionally done, but I
wanted to understand my options and how it should be done properly, so the upshot is:
I want to fit a 17th edition-compatible multi-RCD high integrity consumer unit. Two RCDs will feed the
main house. The earth is TT, so I would like to add a third RCD to the unit rated at 100mA with a time
delay. This will supply a single MCB which in turn will provide the supply to the garage via underground
SWA (4mm/6mm depending on load) with spare core/sheath connected to the (upgraded) main earth rod for the CPC. The garage does not need bonding, but I only want to do this once, so I will either bring back an additional
(suitably rated) earth or add a local earth spike (the garage is about 5m away) to allow for any future
upgrades. The garage will then have another high integrity dual 30mA RCD consumer unit for sockets,
lighting and maybe external sockets, lights etc.
Having looked around for options, something like the BG Electrical consumer units appear to have the
right combinations, and I particularly like the cost-effective time delay RCD. However, three RCDs
doesn't seem to be possible in any CU unless I go for a very large one(e.g. 22 modules). This isn't out of the question, but is quite big for a three-bed semi, particularly where it will be sited in the kitchen (yes, I've followed
lots of those threads on the NET too. Access won't be brilliant.). Given that the third RCD will only supply one
MCB, I don't necessarily need 4 neutral bus bars. The garage MCB ins could be wired directly to the
switched L/N outs on RCD 3. What I was wondering is: do the smaller dual-RCD high integrity consumer
units have enough resources to wire to three RCDs and can I wire directly from an RCD to a MCB to avoid
the need for additional bus bars? Please read 'Professional Electrician' for 'I'. Seriously, I want the place properly certificated.
Thanks in advance.
First of all, I'm new here. Second, I would have posted in the DIY forum, but it appears to be the only one I don't have permission to contribute to. Having said that, his isn't a DIY question, but an unqualified one:
Forgive me if this touches on many of the threads that I've read over the hours that I've researched
this, but I'm after a sanity check and a bit of advice please on what an Electrician can and can't do in this case:
We have a 1930's semi that was rewired in twin and earth some time in the past (probably the 80's). It
goes without saying that the main building protection does not meet current standards. I am also about
to renovate a detached garage with a workshop underneath (it's just about two stories) which gets its
power from the house. Let me start by stating that I intend to get the works professionally done, but I
wanted to understand my options and how it should be done properly, so the upshot is:
I want to fit a 17th edition-compatible multi-RCD high integrity consumer unit. Two RCDs will feed the
main house. The earth is TT, so I would like to add a third RCD to the unit rated at 100mA with a time
delay. This will supply a single MCB which in turn will provide the supply to the garage via underground
SWA (4mm/6mm depending on load) with spare core/sheath connected to the (upgraded) main earth rod for the CPC. The garage does not need bonding, but I only want to do this once, so I will either bring back an additional
(suitably rated) earth or add a local earth spike (the garage is about 5m away) to allow for any future
upgrades. The garage will then have another high integrity dual 30mA RCD consumer unit for sockets,
lighting and maybe external sockets, lights etc.
Having looked around for options, something like the BG Electrical consumer units appear to have the
right combinations, and I particularly like the cost-effective time delay RCD. However, three RCDs
doesn't seem to be possible in any CU unless I go for a very large one(e.g. 22 modules). This isn't out of the question, but is quite big for a three-bed semi, particularly where it will be sited in the kitchen (yes, I've followed
lots of those threads on the NET too. Access won't be brilliant.). Given that the third RCD will only supply one
MCB, I don't necessarily need 4 neutral bus bars. The garage MCB ins could be wired directly to the
switched L/N outs on RCD 3. What I was wondering is: do the smaller dual-RCD high integrity consumer
units have enough resources to wire to three RCDs and can I wire directly from an RCD to a MCB to avoid
the need for additional bus bars? Please read 'Professional Electrician' for 'I'. Seriously, I want the place properly certificated.
Thanks in advance.
