Few domestic quickies please

[MTI]

Hi all, please can anyone clear up the following:

domestic install:

existing CU in very tight kitchen cupboard and full to brim. Tncs supply on other side of wall in external meter cupboard (newish build)

1) new sub is needed to very large shed/office in garden area.
am i permited to run my sub through external semi recessed cabinet?

2) 16th split load CU is full and in cupboard which is only just wide enough to house it. No chance of getting to tails to split with blocks as they back entry from meter cupboard on other side of wall (external cabinet) If CU is full and fairly heavily loaded and cannot access tails in house, how and where would you connect new swa sub?
obviously new RCD main switch to feed sub - would you use dp rcd or switch fuse isolator?
taking into account its to feed a shed.

3) not sure where to read up on this but i have seen blocks on the tails before in external cupboards. This layout however has straight uncut tails from cut out to CU in house. I doubt im permited to put my isolator in external cabinet with blocks on tails?

4) what about smoke detectors in very large shed/office? its new install and obviously a self contained building which is open plan. Would you put them in? im thinking yes as new install and plus will contain tons of pc's and electricals etc. Go on, tell me they need to be linked to the house too haha! sorry!

dont mean to sound daft guys but any help is appreciated as im working in the dark here until i get my books back tomorrow.

cheers in advance

client wants a price today

 

[Des 56]

am i permited to run my sub through external semi recessed cabinet?

The cabinet is exclusively for use for the suppliers equipment only
Permission should be sought for any consumers equipment to be sited there
Thats the politically correct statement out of the way, so

If it was me,so this is not advise,I would have no hesitation whatsoever mounting equipment in that enclosure,without seeking any kind of permission
If permission was sought,then the answer you will get would probably be "no you cant"
The likeleyhood of any comebacks now or in the future are almost zero

I would split the tails in the external cabinet,fit an isolator mounted in a 2 outgoing way enclosure for one means of isolation ,mcb for household and rccbo for shed/office/garden for overload and fault protection



what about smoke detectors in very large shed/office

A smoke alarm in the shed/office, yes,if they want them interlinked,use radio bases



will contain tons of pc's and electricals
You may have to be carefull of functional earth currents then
With the sub main protected by the 30 m/amp rcbo,it may be better to TT the shed/office so that eough circuits for these computors can be fitted,seperate rcbos possibly to negate tripping problems

so
The RCBO at the house end protecting the sub main(do not connect earth at shed)
The TT in the shed/office will localise tripping (install rod)
The rcbos in the shed reduce tripping due to functional earths

 

[MTI]

am i permited to run my sub through external semi recessed cabinet?

The cabinet is exclusively for use for the suppliers equipment only
Permission should be sought for any consumers equipment to be sited there
Thats the politically correct statement out of the way, so

If it was me,so this is not advise,I would have no hesitation whatsoever mounting equipment in that enclosure,without seeking any kind of permission
If permission was sought,then the answer you will get would probably be "no you cant"
The likeleyhood of any comebacks now or in the future are almost zero

I would split the tails in the external cabinet,fit an isolator mounted in a 2 outgoing way enclosure for one means of isolation ,mcb for household and rccbo for shed/office/garden for overload and fault protection





what about smoke detectors in very large shed/office

A smoke alarm in the shed/office, yes,if they want them interlinked,use radio bases



will contain tons of pc's and electricals
You may have to be carefull of functional earth currents then
With the sub main protected by the 30 m/amp rcbo,it may be better to TT the shed/office so that eough circuits for these computors can be fitted,seperate rcbos possibly to negate tripping problems

so
The RCBO at the house end protecting the sub main(do not connect earth at shed)
The TT in the shed/office will localise tripping (install rod)
The rcbos in the shed reduce tripping due to functional earths

I have a spare double pole RCD incomer in enclosure like often used on showers. could i not use this?

split meter tails into blocks, add my new tails to feed RCD and couple up existing CU tails?

so we are saying blocks are still permitted in cabinet then? supplier has left no switch and installer has put tails straight into meter. they are 25mm with 16 earth and existing CU is half RCD.

TT shed? ok i have read about this but if im splitting and picking up feed as it comes out of meter?
supply is a newish (ten years) TNCS and shed is pure wood construction with no other services.

A few local sparks have said they dont agree with TT in my case so not sure where to turn.
i see where you are coming from with the spike to keep tripping local. does anyone else agree?

spike is no extra real expense but whats the going rate on rcbo's? £25 ish? not used them in years so unsure. if i can keep the tripping local, then all is well really.

was hoping to use a new 6 way board i have already with RCD incomer. if it takes out the RCD incomer in shed then that would not be a problem really as far as customer concerned at this stage. if nuisance later, rcbo's can be added. meter cupboard is local to shed and would take out RCD in board first any how or am i taking the wrong route

also, if you are saying to fit an isolator etc in cupboard, what size breaker are you aying to use for the house and are we not then putting 'other' equipment in the cupboard which is as you said 'not allowed'?

thanks

will 25mm tails be required into my new RCD if straight from meter tail blocks too?

 

[Des 56]

Sorry I didn't notice you stated swa supply to shed(so will amend my post)

If using swa then no need for rcd at origin
I would forget the rcd that you have because you also need overload protection
You will need to terminate that swa into something,so a metal clad switch fuse could be used which will also provide overload protection additional to the suppliers cut out and satisfy the need for isolation
Feed the swa with whatever size tails that the load requires and a main earth The switch fuse providing downstreem overload protection if less than 25mm

Now that there is no rcd at origin,then discrimination would not be needed with the shed and that origin,so an rcd in the shed using the TNC-S supply would be fine
TT in a remote building where the supply is TNC-S can be a much better alternative to exporting that TNC-S and providing discrimination, especially where there are services in that building and a main bond required
Your 6 way board with 30m/amp rcd up front would be ok if it hangs on in there with lots of IT equipment

 

[MTI]

Sorry I didn't notice you stated swa supply to shed(so will amend my post)

If using swa then no need for rcd at origin
I would forget the rcd that you have because you also need overload protection
You will need to terminate that swa into something,so a metal clad switch fuse could be used which will also provide overload protection additional to the suppliers cut out and satisfy the need for isolation
Feed the swa with whatever size tails that the load requires and a main earth The switch fuse providing downstreem overload protection if less than 25mm

Now that there is no rcd at origin,then discrimination would not be needed with the shed and that origin,so an rcd in the shed using the TNC-S supply would be fine
TT in a remote building where the supply is TNC-S can be a much better alternative to exporting that TNC-S and providing discrimination, especially where there are services in that building and a main bond required
Your 6 way board with 30m/amp rcd up front would be ok if it hangs on in there with lots of IT equipment

thanks!

so to clear things up:

1) m/c double pole isolator at mains cupboard to feed swa only? house tails straight into blocks?

2) original 25mm tails to house CU to be cut and blocked?

3) new 25mm tails from blocks to meter

4) new tails from blocks in 6 or 10 mm???? 10 to be safe? does this not contradict the 25mm at mains for etc BS7671

5) 6mm swa to feed RCD board within shed

6) size of main switch to feed 6mm? what do you reckon? not got books on me so if nobody pipes up, ill check in morning. 15-18m buried in soil

thanks for clearing this up Des