> 3m Tail Length Protection

[itigeezer]

Hi,

I'm doing a quote for re-wire in a dwelling sitting behind and above a shop front. Both shop and dwelling have their own meter and CU, but at present they are both located in the shop front. Current wiring is pre my birth date!!

I've advised that it would be more practicle for the tenant to have their CU located in their dwelling around 8-10m away from the meter.

Am I right in thinking this run becomes a submain and will need protection between Head fuse and CU? The only reg I can find close is 434.2.1 (ii)?

Is it a case of 100a Fused Isolator after the DNO fuse and before either a 25mm 3 core swa, or 25mm split concentric cable to the CU? The cable will be ran through the shop front, up high.

I can't confirm the earthing system at present as the shop was closed when I went to look at the job (hence my advice).

Are there any considerations I need to factor in depending on the earthing system (i.e. if it's a TT) and do I need to discriminate between the 100a Head fuse and my isolator?

Also be interested to hear which cable you think it will be easier to make off and get into a domestic CU, I'm thinking SWA will be a right stinker!

Thanks

 

[Technician]

The ESQCR states that the length of the tails

should be as short as reasonably practicable.

At over 3 metres you should have the DNO

involved at this stage before you go much further.

After speaking to him, then start looking at the

arrangements for this supply.

 

[NozSpark]

TBH it doesn't have to be SWA or split con,, you could run it using tails and G/Y in trunking if you like,, assuming fused protection at source of course (not DNO fuse)

 

[vad25]

I've used that : *************************/high-current-mcbs-63-amp-to-125-amp/high-current-mcbs-double-pole/cat_187.html

Metal enclosure and SWA 3core 25sqmm, because SWA cheaper than meter tails.

 

[OnOff]

TBH it doesn't have to be SWA or split con,, you could run it using tails and G/Y in trunking if you like,, assuming fused protection at source of course (not DNO fuse)

Eventually I want to put a new CU in my place - currently it's high up against the ceiling of an open porch. Plan is to re-site this inside, in the hall. Total run is circa 4.5m. I have a DP REC isolator (Wylex 100A) after the meter which I've recently fitted and between me and EDF all the tails are now 25mm sq. TT system BTW. I was thinking of 50x50 galv trunking with long tails within. At 4.5m should I be thinking of a switch fuse? Thanks.

 

[itigeezer]

TBH it doesn't have to be SWA or split con,, you could run it using tails and G/Y in trunking if you like,, assuming fused protection at source of course (not DNO fuse)

For a shorter run I think this would be the gold standard, for this I think a little too expensive.

Metal enclosure and SWA 3core 25sqmm, because SWA cheaper than meter tails.

metal enclosure? do you mean conduit for the swa run, or before going into the CU?

 

[NozSpark]

Eventually I want to put a new CU in my place - currently it's high up against the ceiling of an open porch. Plan is to re-site this inside, in the hall. Total run is circa 4.5m. I have a DP REC isolator (Wylex 100A) after the meter which I've recently fitted and between me and EDF all the tails are now 25mm sq. TT system BTW. I was thinking of 50x50 galv trunking with long tails within. At 4.5m should I be thinking of a switch fuse? Thanks.

OnOff, this would have been better in it's own thread,,, but you have two problems as I see it.

TT installations tend to* require RCD protection for all circuits, you are allowed short tails into an insulated enclosure without but 4.5m isn't short by any means.

TT installations tend to* require insulated enclosures where you have non RCD tals entering so galv trunking would not be a good option

Tend to* - whilst we "tend to" do these things for compliance with the regs there are certain conditions or ways of not doing them whilst maintaining safety and remaining compliant with the regs

---------- Post Auto-Merged at 19:39 ---------- Previous post was made at 19:38 ----------

For a shorter run I think this would be the gold standard, for this I think a little too expensive.metal enclosure? do you mean conduit for the swa run, or before going into the CU?

I did say "could" and "if you like"

 

[vad25]

For a shorter run I think this would be the gold standard, for this I think a little too expensive.metal enclosure? do you mean conduit for the swa run, or before going into the CU?

I mean metal enclosure for double pole MCB, my link for this doesn't work

 

[OnOff]

OnOff, this would have been better in it's own thread,,, but you have two problems as I see it.TT installations tend to* require RCD protection for all circuits, you are allowed short tails into an insulated enclosure without but 4.5m isn't short by any means.

TT installations tend to* require insulated enclosures where you have non RCD tals entering so galv trunking would not be a good option

Tend to* - whilst we "tend to" do these things for compliance with the regs there are certain conditions or ways of not doing them whilst maintaining safety and remaining compliant with the regs

---------- Post Auto-Merged at 19:39 ---------- Previous post was made at 19:38 ----------

I did say "could" and "if you like"

Apologies, thought it quite similar to the OP's thread so didn't want to bother people having to post the same answers twice. The future plan is to obviously fit an insulated / Class 2 CU (existing one is metal clad). The galv trunking thought was mainly for protection against fauna as it will need to run vertically up from the porch, above the ground floor ceiling horizontally for 3m then vertically down into the hall. Wondering if a 100mA TD RCD would be an option instead of the switch fuse?

 

[itigeezer]

OnOff, this would have been better in it's own thread,,, but you have two problems as I see it.TT installations tend to* require RCD protection for all circuits, you are allowed short tails into an insulated enclosure without but 4.5m isn't short by any means.

TT installations tend to* require insulated enclosures where you have non RCD tals entering so galv trunking would not be a good option

Tend to* - whilst we "tend to" do these things for compliance with the regs there are certain conditions or ways of not doing them whilst maintaining safety and remaining compliant with the regs

---------- Post Auto-Merged at 19:39 ---------- Previous post was made at 19:38 ----------

I did say "could" and "if you like"

Cheers Noz, you did indeed!

In relation to OnOff's post, if/when I inspect my quote's earthing arrangement it ended up a TT system, what would be the easiest, safest and cost effective way of installing the sub main as I described above, in your opinion?

Cheers

 

[NozSpark]

Apologies, thought it quite similar to the OP's thread so didn't want to bother people having to post the same answers twice. The future plan is to obviously fit an insulated / Class 2 CU (existing one is metal clad). The galv trunking thought was mainly for protection against fauna as it will need to run vertically up from the porch, above the ground floor ceiling horizontally for 3m then vertically down into the hall. Wondering if a 100mA TD RCD would be an option instead of the switch fuse?

As well as!

It will need RCD protection and fused protection

---------- Post Auto-Merged at 20:09 ---------- Previous post was made at 20:03 ----------

Cheers Noz, you did indeed! In relation to OnOff's post, if/when I inspect my quote's earthing arrangement it ended up a TT system, what would be the easiest, safest and cost effective way of installing the sub main as I described above, in your opinion?

Cheers

Maybe tails into an insulated CU with a 100A 100mA 'S' type RCD and a 63A C type MCB then a galv adaptable box butted up to it with SWA glanded in?

 

[itigeezer]

As well as!It will need RCD protection and fused protection

---------- Post Auto-Merged at 20:09 ---------- Previous post was made at 20:03 ----------

Maybe tails into an insulated CU with a 100A 100mA 'S' type RCD and a 63A C type MCB then a galv adaptable box butted up to it with SWA glanded in?

Just to check I'm following ya......The SWA then carrying on into the dwelling's CU? Also, with what you descride above for TT, do I still need a 100a Fused Isolator before hand??

cheers Noz

 

[NozSpark]

Just to check I'm following ya......The SWA then carrying on into the dwelling's CU? yes Also, with what you descride above for TT, do I still need a Fuse Isolator?? well, a RCD can also isolate and a MCB provides overload protectioncheers Noz

Mine in red

 

[NozSpark]

Or a combined MCCB/RCCB

You mean a DP RCBO?

Do they do a 100mA 'S' type??

 

[itigeezer]

Or a combined MCCB/RCCB

You mean a DP RCBO? Do they do a 100mA 'S' type??

Ah..I think that could of been the link that Vad25 tried to post up. Not sure if it's S type though?

Just want say a big thanks to all, ecspecially Nozz, for helping an aprhensive junior with a limited support network. Realy puts value on the forum/s when time served distinguished members offer spot on non-judemental advice!

Thanks again!

 

[NozSpark]

Ah..I think that could of been the link that Vad25 tried to post up. Not sure if it's S type though? Just want say a big thanks to all, ecspecially Nozz, for helping an aprhensive junior with a limited support network. Realy puts value on the forum/s when time served distinguished members offer spot on non-judemental advice!

Thanks again!

If you really appreciate our help a scoob would be nice,,, sherifs badge type icon at the bottom left of posts, or if you just like a post then you could click on "like"

 

[itigeezer]

If you really appreciate our help a scoob would be nice,,, sherifs badge type icon at the bottom left of posts, or if you just like a post then you could click on "like"

Yeah I was looking for a give thanks button and I all I found was the like, consider yourself Sccobed!!