armoured cable to the shed, advice needed

[MikeThePrinter]

i have a reel of 1.5mm 3 core armoured cable, i want to run it to a shed at the end of my garden, it will only be running a double socket and light switch,

i want to run it from a unit i have in my outhouse which is shown below, this unit is running 2 double sockets and a light, then i have the spare 20A & 40A trips, which would i use to go to the shed?

just incase it makes a difference, the pic below is from the house consumer unit, the tripswitch on the right labelled "garage sockets" runs the outhouse unit

is the above all ok to do and use, i'd rather not go all the way to the house consumer unit with the new shed cable, but can do if required

thanks
for any advice

 

[malcolmsanford]

Does not seem to be the greatest of designs as you have a 20amp MCB from your house CU protecting a 80amp 30mA RCD in the outhouse CU.

What size cable is going from the house to the outhouse CU?

At the moment you have 2 protection devices in the house out. The sockets is 32 amp and the lights are 6amp. Already as it stands you have the very real possibilty of plugung things into those sockets that will bypass the 32amp and trip the 20amp back at the house CU. Obviously you havn't plugged a sufficent load to do this yet but it is possible.

Your 1.5mm^ Armoured cable can give you a total of 22 amp depending on erection methods and length of run, all that will have to be calcualted. Therefore I would use niether of those spare ways in your outhouse CU and fit a 16amp to cover the garage. You may have to go lower if the run is to long.

The major thing really is to get the situation sorted out and designed properly. That is why I asked what size cable is feeding the outhouse CU. If it was big enough you maybe able to upgrade that 20amp protection device in the house CU. If it wasn't then you may want to think about replacing the cable and making it a sub main feeding the outhouse CU direct off the header by use of Henley blocks.

 

[MikeThePrinter]

thanks for the input, i see what you mean, was only a year ago i had someone in to fit the outhouse cu, as the previous install cable went throught the wall, along an outside wall on the drive where cars could scrape it and it was only a grey shower cable!!!, it was also run off the old 4 black fuses, no CU present in the house, so i asked the sparky to update to 17th ed CU in the house, run armoured to the outhouse CU leaving me able to run down to the shed at the end of the garden when the time was right, seemingly this hasnt been done properly as i requested from what you're saying above, i'm not sure what the armoured cable is now going to the outhouse, but it is very thick, i would say at least 3 to 4 times thicker than the 1.5m cable i have to use for the shed,
at present the outhouse sockets (which there are 2 doubles) run an extention lead to the shed, which i use to run lighting off and my drill or angle grinder when doing stuff, also runs a light switch in the outhouse running a double tube light, so i imagine this is where i havent had it tripping out as they dont have much load use from them

to put it in a nutshell, the outhouse will end up having 2 double sockets and lightswitch, sockets probably running a freezer, stereo and odd power tool when doing stuff, the shed will be running a lightswitch, and a double socket, which may run the odd power tool, dimming light set-up for my birds and security light/camera system, not much load in either the shed or outhouse i dont think

if the armoured from the house CU is ok, what trip sizes would be ideal design from house through to shed?

i can quickly put up a pic of my complete house CU, armoured cable and outhouse unit if it helps

thanks

mike

 

[MikeThePrinter]

n.b. the shed is about 60ft from the outhouse

 

[malcolmsanford]

Looks like another wonderful advert for our industry.

Did the guy give you any certification for the the armoured going to the out house. You should have got an Electrical Insualtion Certificate and a certifcate called certificate of inspection and results. The one for results should be like a Excel grid with a set of results on, this should tell you the size of the cable going to that out house CU.

If as you say it is 3 or 4 times thicker it could be 6mm^. if that is the case personally I would remove it from you house CU. The cables from your meter to the house CU is called tails. I would cut them an then connect them into what is called an henley block, which is just a big connector block. Then take one set of tails back into you house CU and another perhaps 16mm^ set into a small enclosure. I would fit another double pole switch and depending how the cable is run fit either a fuse/mcb or RCD.

Once you identify what size the cable, how it is run and the length you can work out the size of that protection device.

All that i'm telling you is quite involved and would nead an electrcian to do it. To work out the calcualtions and design. You also have the added task of if you have a TNC-S system would the DNO let you export the earth to the garage. If your going to have water in either the outhouse or garage you need to think about bonding it. It's not an easy job for most electricians let alone a DIY'er

 

[MikeThePrinter]

yeah defo not a job for me really disappointed though after paying someone to have the options in place not that long ago

live u learn i suppose!

thanks for your help

mike

 

[Deleted member 9648]

You also have the added task of if you have a TNC-S system would the DNO let you export the earth to the garage.

I have to take issue (yet again) with this part of malcomsanfords otherwise excellent reply....it has naff all to do with the DNO and there is nothing in Bs 7671 to prohibit exporting the earth....Why oh why does this keep coming up?

 

[malcolmsanford]

I have to take issue (yet again) with this part of malcomsanfords otherwise excellent reply....it has naff all to do with the DNO and there is nothing in Bs 7671 to prohibit exporting the earth....Why oh why does this keep coming up?

You are quite correct there is nothing in the Regs saying you can't do this. For me I've argued the fact that I can't see a problem with it if all the bonding in the house and houses around are done.

Unfortunately as I said in the OP it's the DNO's Earth and you have to get their permission to export it. As they are worried that if there is a neutral failure in the system anywhere that is not correctly bonded will make an extraneous part live. That's their rules and as it's their earth you have to abide by them.

If you make any out building TT where do you think your Rod will pick up it's earth path, in a local TNC-S system it will be the nearest DNO rod, I've had countless "discussions" with DNO over the years and have yet to win one. if they say no then it's no. So now I would call and expect a no, if I get a yes yippeee bonus time, and that rod I bought for the job will do another job when the DNO say no.

 

[WayneL]

You are quite correct there is nothing in the Regs saying you can't do this. For me I've argued the fact that I can't see a problem with it if all the bonding in the house and houses around are done.

Unfortunately as I said in the OP it's the DNO's Earth and you have to get their permission to export it. As they are worried that if there is a neutral failure in the system anywhere that is not correctly bonded will make an extraneous part live. That's their rules and as it's their earth you have to abide by them.

If you make any out building TT where do you think your Rod will pick up it's earth path, in a local TNC-S system it will be the nearest DNO rod, I've had countless "discussions" with DNO over the years and have yet to win one. if they say no then it's no. So now I would call and expect a no, if I get a yes yippeee bonus time, and that rod I bought for the job will do another job when the DNO say no.

I totally disagree.

What you do on the consumer side of the installation is nothing to do with them.

In discussions I've had with them they are only concerned with the installation complying with our Wiring Regs.

Scottish Power actually told me they would rather you extend the 'Exponential Zone'.

The regs, if it was that important, would say that it wasn't allowed.

Guidance Note 8 gives examples of extending a PME (TN-C-S) system to other buildings.

The IET technical helpline said they have nothing against it.

What do you think the DNO are going to do if you run a bonding/earth conductor to your shed - disconnect you??? They're not allowed to without reasonable cause.

 

[Deleted member 9648]

I have to agree......again why does everyone seem to pick on sheds and garages to bring up the old exporting earth thing?....why doesnt anyone ever come on here and ask "I've got to install some lights up the drive fed from the house,it's a TNCS,should I bang a rod in for those lights or can I export the earth"?......never.

 

[malcolmsanford]

There seems to be confusion here where some think I'm advocating never to export PME. If my posts were read they would see I'm the exact opposite. Providing Regulations 411.3.1.1 and 542.1.8 was achieved, then I personally think that it would be a better situation than TT.

The restrictions on exporting PME outside the equipotential zone (typically regarded as being the exterior walls of the house) used to be in a document called the "PME Regulations", which were a supplement to the Electricity Supply Regulations. With the "wooliness" that came with the ESQCR regulations, a lot of this goodness has disappeared into the various DNO's own technical standards.

The risk is that taking a class 1 appliance into the garden, its metal case is not connected to earth, it is actually connected to the supplier's neutral conductor, which is at or about earth potential under normal circumstances. Incidentally, the original PME regulations also required a plastic insert in the pipework to an outside tap, to prevent that from becoming momentarily live under fault conditions. This is now all lost to us.

The bottom line for me is that if you do not ask the DNO permission to export their earth from the origin of the installation to an outbuilding then your the one responsible. If for any reason an incident occured as your the one signing the EIC it will be you in the dock not the DNO.

Finally in answer to wayne and what can they do if you did it without their permission, this is what they can do

26. - (1) Where a connection to a distributor's network has been made, or is proposed, and the distributor is not satisfied that the consumer's installation or other distributor's network or street electrical fixture which is or would be connected to his network is or would be so constructed, installed, protected and used or arranged for use so as to prevent, so far as is reasonably practicable, danger or interference with his or any other distributor's network, or with the supply to any consumer's installation or street electrical fixture, he may issue a notice in writing to the consumer or other distributor or owner of the street electrical fixture (as the case may be) requiring remedial works to be carried out within such reasonable period as may be specified in the notice. - The Electricity Safety, Quality and Continuity Regulations 2002.

So they can ask you to change it at your cost.

 

[Deleted member 9648]

There seems to be confusion here where some think I'm advocating never to export PME. If my posts were read they would see I'm the exact opposite. Providing Regulations 411.3.1.1 and 542.1.8 was achieved, then I personally think that it would be a better situation than TT.

The restrictions on exporting PME outside the equipotential zone (typically regarded as being the exterior walls of the house) used to be in a document called the "PME Regulations", which were a supplement to the Electricity Supply Regulations. With the "wooliness" that came with the ESQCR regulations, a lot of this goodness has disappeared into the various DNO's own technical standards.

The risk is that taking a class 1 appliance into the garden, its metal case is not connected to earth, it is actually connected to the supplier's neutral conductor, which is at or about earth potential under normal circumstances. Incidentally, the original PME regulations also required a plastic insert in the pipework to an outside tap, to prevent that from becoming momentarily live under fault conditions. This is now all lost to us.

The bottom line for me is that if you do not ask the DNO permission to export their earth from the origin of the installation to an outbuilding then your the one responsible. If for any reason an incident occured as your the one signing the EIC it will be you in the dock not the DNO.

Finally in answer to wayne and what can they do if you did it without their permission, this is what they can do

26. - (1) Where a connection to a distributor's network has been made, or is proposed, and the distributor is not satisfied that the consumer's installation or other distributor's network or street electrical fixture which is or would be connected to his network is or would be so constructed, installed, protected and used or arranged for use so as to prevent, so far as is reasonably practicable, danger or interference with his or any other distributor's network, or with the supply to any consumer's installation or street electrical fixture, he may issue a notice in writing to the consumer or other distributor or owner of the street electrical fixture (as the case may be) requiring remedial works to be carried out within such reasonable period as may be specified in the notice. - The Electricity Safety, Quality and Continuity Regulations 2002.

So they can ask you to change it at your cost.

Yes I remember the old PME regulations document issued by SEEBOARD in my area.....As far as the highlighted part of your post goes though,if an EIC is issued on an install it will (or should) comply with Bs7671 which is all that matters,only if an incident occured and it could be shown that the install did not meet the requrements of 7671 would the installer be in the brown stuff.

 

[malcolmsanford]

Isn't electrickery wonderful lol. The ESQCR-2002 reg 8(4) prohibits the use of a PEN conductor inside an installation, this is re-inforced with reg 543.4.1 unless certain criteria is taken. So in affect your changing that TNC-S at origin to a TN-S supply.

Then you have to ensure that reg 542.1.8 is also enforced. When you complete your EIC for say a garage installation and if you have fitted a new CU you will have to complete on the Schedule of Results location of the Distribution Board and then the Type of supply which will be TN-S

If you have not been granted the DNO permission to export their earth then I would be wary of filling out the EIC and subsequent documents saying you have created a TN-S supply to another installation. Where as if you TT the installation and confirm reg 542.1.8 that is covered as far as the Regs go.

There are so many contentious areas in this industry and one call to the DNO to confirm yes or no is all that it takes. It's about for me making things safe and protecting yourself as well.

 

[WayneL]

The bottom line for me is that if you do not ask the DNO permission to export their earth from the origin of the installation to an outbuilding then your the one responsible. If for any reason an incident occured as your the one signing the EIC it will be you in the dock not the DNO.

You are the one responsible anyway - consumer side of the installation is nothing to do with the DNO.

Finally in answer to wayne and what can they do if you did it without their permission, this is what they can do

So they can ask you to change it at your cost.

Only if it didn't comply with BS7671 - which it would.

So in affect your changing that TNC-S at origin to a TN-S supply.

Ridiculous - It is TN-C-S ......combined on the supply side........seperate on the consumer side - that's what the letters stand for.

TN-S is seperate all the way.

Then you have to ensure that reg 542.1.8 is also enforced. When you complete your EIC for say a garage installation and if you have fitted a new CU you will have to complete on the Schedule of Results location of the Distribution Board and then the Type of supply which will be TN-S

No it won't - it's still TN-C-S.

If you have not been granted the DNO permission to export their earth then I would be wary of filling out the EIC and subsequent documents saying you have created a TN-S supply to another installation.

No you haven't - it is one supply - one installation - one earthing system.

There are so many contentious areas in this industry and one call to the DNO to confirm yes or no is all that it takes. It's about for me making things safe and protecting yourself as well.

Do you confirm all our regulations with the DNO before you do anything?

 

[blackiel]

Does the Exportation rule also apply to sauna/bubble baths at the end of the garden,same length as the shed???

 

[stu_guy]

using a quick rule of thumb on this one you could only have a round 11A on that circuit so would recommend a bigger cable i would personally use minimum 4mm 3 core

i have a reel of 1.5mm 3 core armoured cable, i want to run it to a shed at the end of my garden, it will only be running a double socket and light switch,

n.b. the shed is about 60ft from the outhouse

[h=2]RESULTS[/h]

Phase	Single Phase
Power	2.53kW / 11A
Length	20m
Core Size	1.5mm²
Voltage Drop	6.82volts

Calculate Another​

 

[dan86]

wtf. how do people find these old threads :-\