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.

 

[shocking_eg]

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.

You only need to earth at one end. But I have always done both ends

Helps keep your ZE low

 

[GLENNSPARK]

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.

yep....you`d get some tryin to tug a length of 10mm G/Y in here n all....
no need....

- - - Updated - - -

You only need to earth at one end. But I have always done both ends

Helps keep your ZE low

25mm CSA ....and your goin on about Zdb....lol....

 

[atm84]

I always thought it was ok to earth one end of armouring till a college lecturer once told me both ends should be earthed in case of difference in potential occurred between the armouring at the unearthed end and the interval cpc.

 

[rmc86uk]

I never understand why people gland into a metal apatable box at the side of a metal CU? Why not just gland straight into the CU? I must be missing something!

 

[shocking_eg]

I never understand why people gland into a metal apatable box at the side of a metal CU? Why not just gland straight into the CU? I must be missing something!

Think there on about a plastic CU

 

[rmc86uk]

No he says this

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.

Also even if it was a plastic CU still no reason not to gland straight into it.

 

[shocking_eg]

No he says this



Also even if it was a plastic CU still no reason not to gland straight into it.

Hmmm I see...

I often use a metal adaptable box if terminating into a plastic CU as most CU's are so flimsy these days and they don't take kindly to a 25mm SWA hanging off the enclosure !

 

[Knobhead]

I always thought it was ok to earth one end of armouring till a college lecturer once told me both ends should be earthed in case of difference in potential occurred between the armouring at the unearthed end and the interval cpc.

Was this in the pub or at collage?

 

[atm84]

Sorry guys yes the fuse board in the garage is plastic.

Tony- what was at the pub or college (or collage as you say, I assume you mean college)

If you mean the part about earthing at one end. Yes I have been informed by many people including an earlier post here that's its acceptable to earth only at one end. Secondly it was a college lecturer that told me it should be earthed at both ends. If you insist on knowing more details just in case I have not convinced you enough yet it was during the 2391-20 design, erection and verification course in Rotheram with Connaught electrical when they were around. Think the lecturer was called Dave and we had ham sandwiches for lunch. No beer was allowed so it certainly wasn't in the pub. Convinced now?

 

[telectrix]

Sorry guys yes the fuse board in the garage is plastic.

Tony- what was at the pub or college (or collage as you say, I assume you mean college)

If you mean the part about earthing at one end. Yes I have been informed by many people including an earlier post here that's its acceptable to earth only at one end. Secondly it was a college lecturer that told me it should be earthed at both ends. If you insist on knowing more details just in case I have not convinced you enough yet it was during the 2391-20 design, erection and verification course in Rotheram with Connaught electrical when they were around. Think the lecturer was called Dave and we had ham sandwiches for lunch. No beer was allowed so it certainly wasn't in the pub. Convinced now?[/QUOTE

the armour of the SWA must be earthed. if it is not used as a cpc, then it only needs earthing at 1 end. if used as a cpc, then both ends need to be earthed. hope that clarifies it.

 

[Knobhead]

My doubts come from “a colleague” and “I’m not doing the job”, the by lines of many a DIYer.

Why aren’t you doing the job?

 

[atm84]

The reason why i am not doing the work Tony is because I'm not Part P registered also I no longer work in installation work, after being on the tools for 10 years. However I still like to have an understanding of the game though.

 

[clematis432]

The reason why i am not doing the work Tony is because I'm not Part P registered also I no longer work in installation work, after being on the tools for 10 years. However I still like to have an understanding of the game though.

Agree with your sentiments ! I am also no longer working but enjoy the forum and the interest of current electrical theory. Most on this forum appreciate this but several diehards on it don,t. Afraid to say not, Tony is one of the worst offenders.

 

[richy3333]

I never understand why people gland into a metal apatable box at the side of a metal CU? Why not just gland straight into the CU? I must be missing something!

ripping off the customer for an extra £100?

 

[micknew]

If he thinks he's missing something he must be a DIYer fishing to see what is required, because no sparks would do that.

 

[DaveyD]

separately metered in the garage.


Then live and neutral into the meter then out of the meter into the new fuse board.

You may have missed this bit of info?

 

[atm84]

What you getting at Davey D? I don't follow?