Garage install- incoming configuration

[atm84]

First of all just to let you know i am not doing the work, i have been asked by a colleague for my opinion before a spark goes in and does the work. The garage mentioned below is actually going to be used as accommodation for an elderly relative and will be separately metered in the garage.

Have a 25mm 3 core armoured entering a garage in the corner. The armoured comes from the house straight from some henley blocks and into a switch fuse unit before leaving the house.Now my colleague couldn't tell me but he was unsure if the fuse board in the garage is going to be metal clad or not. (He is buying the parts himself)

I suggested (if the fuse board is metal clad) terminating the armoured into a metal adaptable box inside the garage, using the metal box as a through box. Then live and neutral into the meter then out of the meter into the new fuse board. The earth would just go straight the the adaptable box and into the fuse board. Now question is would it be satisfactory to only earth the armouring at the house end. I always think its best practice to earth at both ends due to possible problems of difference in potential.

Also don't see the point off TTing the garage. Why install a rod and get an earth loop path of 50 ohm when you can use the DNO's earth. Any thoughts?

 

[micknew]

Your electrician is the man who will do it safely, ask him.

 

[atm84]

It's not for me. I used to be an electrician but no longer work in installation hence being a bit rusty.I will not be doing the work but I am still interested and would like to be able to provide my colleague with some feed back.

 

[Octopus]

It's not for me. I used to be an electrician but no longer work in installation hence being a bit rusty.I will not be doing the work but I am still interested and would like to be able to provide my colleague with some feed back.

Thats fair enough. So come back when you have the info from the Sparky! That said I never give enough infor to a customer so they can DIY!

 

[atm84]

They are not DIYing it. Like I said, colleague is having some work done, he has asked me what I think should be done before his sparky comes round. I would like to be able to give him some info. That is all!

 

[telectrix]

the cable is laid. that's about it before sparks comes.

 

[atm84]

The sparky will be laying the cable. I'd like to think the kettle will be on before sparky comes round.

 

[driverman]

Food for thought here. You say that it is going to be occupied. If so no doubt water supply /plumbing will exist. From what I can understand from the 17th regs, any detached building with metal services, metal beams etc must have it's own earthing system ie TT in this case. Any earthing arrangement must be divorced from the house. What do others think?

 

[atm84]

Yes driver that is what I always thought but I have seen numerous posts where electricians do not use a TT system and continue the earthing system incorporated in the house. There is no steel frame.

 

[driverman]

atm84....The fact others use the house earthing system doesn't make it right though re 17th edition. Past practice we all used the house earthing system but not now. There is a reason for this.....I'm not that bright know to know it though lol but it's something to with potential differences within the earth mass around the two buildings. Now that may well open a can of worms!

 

[telectrix]

you can extend the earthing from the main house, but if it's TNC-S, then all extraneous metalwork in the garage/whatever, needs to be bonded back to the house MET, min. 10mm.

 

[atm84]

There are no extraneous parts as far as I am aware, however the sub main cable has a 25mm2 earth conductor and armouring too.

 

[telectrix]

that 25mm 3rd core will serve as cpc and bonding conductor. if the garage is going to be living accom., then surely there will be water supply and maybe gas as well.

 

[atm84]

Yes water but is in plastic pipe hence it is not an extraneous part. There is no gas. Hot water via instantaneous heater, heating via a air source heat pump.

 

[driverman]

Re water......all plastic piping though out the plumbing installation?

 

[Knobhead]

When people start several threads with the words “my colleague” my mind flashes up DIY chancer. But I’m nasty and suspicious like that.

Ask you’re fictitious electrician.

 

[atm84]

Nothing fictitious about this. It is as I say but I guess nothing I say will make you change your mind. Thanks for everyone's help.

 

[atm84]

Driver, yes as far as I am aware it's all plastic pipe however even if there is a piece of copper pipe its not an extraneous part.

 

[shocking_eg]

you have no worry's even if its extraneous, your bonded with your 25mm SWA and outer amouring. the min CSA of the CPC should work out fine when you do the cable calcs.

 

[atm84]

I am less concerned about the earthing arrangement. My initial concerns were with regards to the meter configuration and whether the armouring should be earthed at both ends.