TT or not TT. Need clarification

[Stix]

As per title; having a pre fab shed in back garden installed on a concrete base that will have a dp membame. No reinforcing mesh. 15 metres from house. Looking at spurring off socket on back wall to an rcd spur. Runn8ng down outer wall in conduit to a weatherproof box. Then using 4mm swa to shed. Shed will have no gas/water but will have a metal door and galv pearling beams for roof. Only used for mowers;strimmer and a chest freezer. One led light to be fitted also. Am qualified c a g 236 pts 1 an 2 but out the game for 10 yrs. Is TT needed? Was looking at fitting a garden shed tyoe cu with 6a and 16a mcbs. Sockets woukd be rcd type for protection

 

[Pete999]

As per title; having a pre fab shed in back garden installed on a concrete base that will have a dp membame. No reinforcing mesh. 15 metres from house. Looking at spurring off socket on back wall to an rcd spur. Runn8ng down outer wall in conduit to a weatherproof box. Then using 4mm swa to shed. Shed will have no gas/water but will have a metal door and galv pearling beams for roof. Only used for mowers;strimmer and a chest freezer. One led light to be fitted also. Am qualified c a g 236 pts 1 an 2 but out the game for 10 yrs. Is TT needed? Was looking at fitting a garden shed tyoe cu with 6a and 16a mcbs. Sockets woukd be rcd type for protection

file:///C:/Users/Pete/Desktop/Resources/Garage-Shed%20Supplies(1).pdf

 

[Octopus]

If you are spurring off a ring at 13A what is the point of the CU in the out building

 

[Midwest]

file:///C:/Users/Pete/Desktop/Resources/Garage-Shed%20Supplies(1).pdf

That hasn't appeared as it should Pete, i.e. I can't download it so dare say OP can't?

 

[Pete999]

That hasn't appeared as it should Pete, i.e. I can't download it so dare say OP can't?

OK thanks for the feedback

 

[Stix]

If you are spurring off a ring at 13A what is the point of the CU in the out building

Was worried that if a fault developed would take all power out, thinking about having a small undercounted sized freezer in there too.....

 

[Stix]

OK thanks for the feedback

Soooooo; should I drop an earth rod to CU and TT and does galvanised beams need bonding?Then use rcbo rather than mcb's?

 

[Wilko]

Hi - What earthing system does the house have?

 

[Stix]

House has PME earthing, am not sure as to wether roof beams made of Galv would be classed as extraneous. However the door is made of steel, so thinking is it worth TT ing

 

[Wilko]

Do you have test gear to check the rod?

 

[Pete999]

House has PME earthing, am not sure as to wether roof beams made of Galv would be classed as extraneous. However the door is made of steel, so thinking is it worth TT ing

Have you tested the Beams and door to see if they are Extraneous?

 

[bigspark17]

Being as the is no extraneous parts (including the shed) no need to TT. Why not switch fuse spur in house to double socket in shed to switch fuse spur (with 3amp fuse) for the light?
Sounds good, and good to see your thinking it through & planning rather than just lashing it in as you go.

 

[telectrix]

if you're coming off an existing RFC that's RCD protected, it's pointless fitting another RCD in shed. can you come from a non-RCD way in the CU instead?

 

[Stix]

Being as the is no extraneous parts (including the shed) no need to TT. Why not switch fuse spur in house to double socket in shed to switch fuse spur (with 3amp fuse) for the light?
Sounds good, and good to see your thinking it through & planning rather than just lashing it in as you go.

Would the steel door not count as been extraneous ?

 

[Richard Burns]

If there are steel uprights driven into the ground to support he door then it may be extraneous and you would have to test it. However if the door frame is just bolted to the wall then it is very likely to be non extraneous.

 

[Stix]

if you're coming off an existing RFC that's RCD protected, it's pointless fitting another RCD in shed. can you come from a non-RCD way in the CU instead?

not really as it's a lot further and a hell of a lot of upheaval to my home. That's the reason why I'm going down the spur route. May go with big sparks 17 id a. Was I maybe overthinking things? Am in no way going to o load circuit as only constant supply would be small freezer, and that's only if we decide to get one!

 

[Pete999]

As per title; having a pre fab shed in back garden installed on a concrete base that will have a dp membame. No reinforcing mesh. 15 metres from house. Looking at spurring off socket on back wall to an rcd spur. Runn8ng down outer wall in conduit to a weatherproof box. Then using 4mm swa to shed. Shed will have no gas/water but will have a metal door and galv pearling beams for roof. Only used for mowers;strimmer and a chest freezer. One led light to be fitted also. Am qualified c a g 236 pts 1 an 2 but out the game for 10 yrs. Is TT needed? Was looking at fitting a garden shed tyoe cu with 6a and 16a mcbs. Sockets woukd be rcd type for protection

Not really a very good idea to spur from a 32A RFC wired in 2,5mm2 cable, connecting it to a larger csa cable running it 15 Meters and slapping a Garage CU on the end of it, that wouldn't be classed as a Single spur, as you will be adding a CU and a lighting and socket circuit to the mix, far better to run a dedicated supply from the CU in the house, I know its been done before, but it's not compliant, therefore may, render your house insurance invalid.

 

[Pete999]

As per title; having a pre fab shed in back garden installed on a concrete base that will have a dp membame. No reinforcing mesh. 15 metres from house. Looking at spurring off socket on back wall to an rcd spur. Runn8ng down outer wall in conduit to a weatherproof box. Then using 4mm swa to shed. Shed will have no gas/water but will have a metal door and galv pearling beams for roof. Only used for mowers;strimmer and a chest freezer. One led light to be fitted also. Am qualified c a g 236 pts 1 an 2 but out the game for 10 yrs. Is TT needed? Was looking at fitting a garden shed tyoe cu with 6a and 16a mcbs. Sockets woukd be rcd type for protection

Being as the is no extraneous parts (including the shed) no need to TT. Why not switch fuse spur in house to double socket in shed to switch fuse spur (with 3amp fuse) for the light?
Sounds good, and good to see your thinking it through & planning rather than just lashing it in as you go.

Not a very good idea to spur off a 32A RFC wired in 2,5mm2 cable, connecting it to a larger csa cable running it 15 Meters and slapping a Garage CU on the end of it, that wouldn't be classed as a Single spur, as you will be adding a CU and a lighting and socket circuit to the mix, far better to run a dedicated supply from the CU in the house, I know its been done before, but it's not compliant, therefore may, render your house insurance invalid.

 

[Pete999]

What is it with all these double posts Admin? can you delete one please?

 

[Dave OCD]

Not a very good idea to spur off a 32A RFC wired in 2,5mm2 cable, connecting it to a larger csa cable running it 15 Meters and slapping a Garage CU on the end of it, that wouldn't be classed as a Single spur, as you will be adding a CU and a lighting and socket circuit to the mix, far better to run a dedicated supply from the CU in the house, I know its been done before, but it's not compliant, therefore may, render your house insurance invalid.

But I'm sure he intends connecting it all through a 13a FCU at the house end Pete which makes it fully compliant. As suggested though he could then go straight to the socket/s in the shed and use a SFCU with 3a fuse for the light so no need for a CU.

 

[Pete999]

But I'm sure he intends connecting it all through a 13a FCU at the house end Pete which makes it fully compliant. As suggested though he could then go straight to the socket/s in the shed and use a SFCU with 3a fuse for the light so no need for a CU.

That's yoursuggestion Dave, which is a valid one, personally I don't think the OP will take your advice, one thing I don't agree with is the change of cable size, seems illogical to me, as your suggestion states to use a 13Amp spur at the house end, so why use the larger cable it's unnecessary, and goes to prove that although the OP claims to be qualified, in reality he needs to brush up on his decision making. There I've, said what I think, I'll say no more, as I think I will just be going around in circles.

 

[Dave OCD]

Ah but nothing wrong with a bigger cable to minimise volt drop/reduce Zs and 'futureproof' Pete. And if I had a suitable length of 4 or even 6mm SWA 'in stock' when a similar job came up it would surely be put to good use.

 

[Pete999]

Ah but nothing wrong with a bigger cable to minimise volt drop/reduce Zs and 'futureproof' Pete. And if I had a suitable length of 4 or even 6mm SWA 'in stock' when a similar job came up it would surely be put to good use.

Could be that, but I'm not sure, I'm not an optimist Mate, trust your reasoning though.

 

[Toneyz]

Is the existing ring final circuit rcd/rcbo protected if so what is the point of an RCD in the shed or an rcd spur?As you say you cant take the cable back to the consumer unit feeding the shed from a 13A switched fused spur and fusing down to 3A for the light seems ok but preference would be to be on own circuit.Pete can't see the problem with using a larger SWA.

 

[Nigel]

Have you tested the Beams and door to see if they are Extraneous?

No need. They absolutely won’t be.

 

[Nigel]

Judging by what you have said I would just extend the PME earthing arrangement.

No extraneous metallic parts so no need to TT as I see it.

 

[MDJ]

Do you have test gear to check the rod?

What Rod?

 

[bigspark17]

Would the steel door not count as been extraneous ?

Not if its just sitting on concrete pad

 

[Wilko]

What Rod?

Not sure, Stuart?

 

[pirate]

Someone had to say it..
TT, or not TT...that is the question...
My old gaffer once went all Shakesperean on me on the building site, pointing at a JCB and saying "Is this a digger I see before me?"
(Going back to my San Miguel now...)