Pme again with workshop help please

[Duane B]

Hi Guys I no this is appears to come up over and over again as I can see from looking through past threads,

I'm going to go for my scam assessment  this year, and have a little project I can do at home to apply. Now then let's start.

At home we have pme system and an extension with a 16mm 3 core submain feeding a small 5 way c/u in it already. Off this I have placed a 10mm xlpe 3 core going up the garden which is off a 32A rcbo, the 5 way board is actually all rcbo. The xlpe swa only goes about 20m run from this C/U

The 10mm 3 core xlpe swa at present is switched off and terminated safe in a rotary isolator, And has been for 12 month's  just sat there on an old shed unused.  The shed is gonna be knocked down but the cable will have to stay because I'm not digging it up or extending it from where it is now. 

So was thinking of placing a waterproof non metallic enclosure in the garden against our neighbours fence on my side, fixing the isolator to the side of it, then come from that with only phase & neutral only to a front end timed delayed rcd unit inside the enclosure then into a new amendment 3 type garage C/U as we're still classed as domestic, the bristish general ones are a nice little job alloy powder coated sealed for £30.00 with 63A main rcd switch 30Ma and a choice of 3 spare ways to play with. 

The supply will eventually feed a new shed at the top of the garden only a light and one socket via swa run from the new setup possible another 20m run, Then bbq area lights and some sockets another swa run of about 8m  this will be in after the scam assessment  though  just wanna get the critical bit right first ready. 

OK my issue, I have fluke 1654 but no spike kit. Do I just put 3 rods in equally spaced patio area by bbq area, middle garden by enclosure, top of garden join them up together take back to C/U met, juice it up carry out ze "Ra"and if well well below 200 ohms were good, obvious  if there are any metalwork these will be bonded back to the new met setup.

Like i say wanna do this for scam assessment so gotta be top notch plus safe as got my family to think off running around the garden plus neighbours etc. Be my first TT install. And a good learning curve with my new flookie wookie 

Cheers guys

 

[Evans Electric]

So you will joint a cable , and extend it to a workshop .   Don't fit an isolator out there or a delayed RCD  just joint it through to the shed .

It sounds so complicated to me .   Its just a sub-main to a shed , fit a board with a 30mA  RCD main switch in the shed  and thats it . 

Flookie wookie  ??

 

[Duane B]

So you will joint a cable , and extend it to a workshop .   Don't fit an isolator out there or a delayed RCD  just joint it through to the shed .

It sounds so complicated to me .   Its just a sub-main to a shed , fit a board with a 30mA  RCD main switch in the shed  and thats it . 

Flookie wookie  ??

Flookie wookie, lol fluke 1654b tested meter.

No,  no jointing of cables,  can't extend pme to outbuildings I'll never pass my assessment for part P,  surely,   I've got an existing pme that's been extended but not exported to a house extension with a 5 way fuse board, from this I have an armoured going into the garden "exported" outside, this is what want to TT not extend it, 

Didn't think my write up was that complicated, 

 

[apprentice87]

Hello!!

"OK my issue, I have fluke 1654 but no spike kit. Do I just put 3 rods in equally spaced patio area by bbq area, middle garden by enclosure, top of garden join them up together take back to C/U met, juice it up carry out ze "Ra"and if well well below 200 ohms were good, obvious  if there are any metalwork these will be bonded back to the new met setup"

No issue there..

So you have not got the spike kit.. Oh, well, just do Zs in the usual way [only this time i suppose it will be "Ze" as the shed or whatever is a separate installation.

You will get the usal flood of "you cannot do zs" comments, Yes you can, and the regs STATE YOU CAN..

We all know that Ra would be better, but the regs are perfectly clear, that if not possible, do Zs in the usual way...

john..

 

[Sidewinder]

Kind of John, it would be Ze at the point of measurement if you were TT'ing the shed.

 

[NozSpark]

I'm afraid that I would be jointing and extending the current cable into the shed and then dropping the earth there just before the CU.

As for an earth rod,,,, I'd use a 5/8" extendable one and test it using the 25A loop test on my meter (method 2) as my Megger 1502 can't do a rod test

 

[apprentice87]

That is what i mean't !!

I assumed TNS or TNCS at the house end makeing sure that Zs is low enough for the OCPD that protects the cable. Insulate the cable CPC at the shed end, treat it as a separate installation, TT it, and just check the Zs at the cable end [shed end] only now, as the shed is a separate install, it would be Ze for the shed install!!!

john..

 

[Evans Electric]

Flookie wookie, lol fluke 1654b tested meter.

No,  no jointing of cables,  can't extend pme to outbuildings I'll never pass my assessment for part P,  surely,   I've got an existing pme that's been extended but not exported to a house extension with a 5 way fuse board, from this I have an armoured going into the garden "exported" outside, this is what want to TT not extend it, 

Didn't think my write up was that complicated, 

I'm thinking how I would do it .   The job seems complicated not the  write up . 

You will probably find that assessor won't have heard of "Exporting " PME .

You need a DP isolator in the extension as RCBOs are only SP ..... forget boxes , time delays & isolators in garden, just joint the cable through to the new shed & put a board on the end  with an RCD main switch .   

Have you found the  " Do not Export PME earths" section in  BS7671 yet ?

 

[steptoe]

Exporting PME is totally different to exporting TNCS

2nd, having an upfront RCBO, why,? it's a SWA,,,

3rd, you can't test a TT using a Ze/Zs/Zdb,  you will get a reading, it just won't be a true reading of the state or condition of the earth your rod is giving you, it will be a reading involving every other bit of metal in the ground though. 

 

[steptoe]

Btw, exporting PME is nothing to do with BS7671, it's about getting permission from the DNO to allow it. :|

 

[kerching]

If you have the 1654B then just buy the Spike Kit here, Phone Megger Mark and get a forum discount.

http://isswww.co.uk/fluke-es165x-earth-spike-test-kit

Mine cane from Mm with a free spike kit ( never realised he had been jailed :innocent )

never used it ...yet

 

[Evans Electric]

Anyone explain the difference between a socket on the outside wall of a house , backed by an RCD and a sub-main to a wooden shed with an RCD socket in it ?  :C

 

[Essex1]

Anyone explain the difference between a socket on the outside wall of a house , backed by an RCD and a sub-main to a wooden shed with an RCD socket in it ?  :C

Nothing. 

 

[Evans Electric]

Thank you Mr Essex , so  what is with all the TT ,ing  I respectfully ask?

 

[apprentice87]

Nothing. TT is a rubbish system if you ask me. If people want to trust their lives to an RCD, the most unreliable piece of junk the world has ever seen, then go right ahead.. BUT, the OP was worried about his assessment, and so does not want to get into anything that might be seen as "controversial" by the assessor...

john..

 

[Duane B]

All I was gonna do is feed the new consumer unit in the garden, as the swa is already there not long enough to reach end of garden, so new consumer unit fitted fed off the swa, minus it's earth,

Front end timed delay main switch before entering consumer unit,  but it's the earth rods do we go with one or multiples joined, what about overlapping pd zones, 

I understand people saying complicated but it will be great skill learning for me. 

Cheers guys enjoying the reading on this thread

 

[NozSpark]

Personally I wouldn't run a mains voltage cable in a garden without an earth.

and like I said earlier,, a single rod that can be lenghtened if necessary

 

[Duane B]

Personally I wouldn't run a mains voltage cable in a garden without an earth.

and like I said earlier,, a single rod that can be lenghtened if necessary

Well the mains voltage feed xlpe swa 10mm 3 core would have an earth off the pme upto the point where it terminates to the Consumer in the garden so in theory the feed will be protected upto where the TT starts but that's it, then we start TT phase & neutral yep 1 x rod extendable or as long as I can get it in the better

 

[apprentice87]

Why would you want a TD RCD at the shed CU??? That will Definitley NOT comply.

You "might" want a TD one at the supply end of the Cable to the shed for discrimination purposes, but once you get to the shed, it HAS to be an ordinary one,

One rod will be plenty as long as you can get Ze for the shed install low enough..

Hi Noz, I think the OP meant doing away with the cable TNCS earth at the extreme end where it meets the shed CU and then TT. Not just running a cable from the house with no CPC, as that would be both stupid and would not comply either...

john..

 

[Duane B]

Why would you want a TD RCD at the shed CU??? That will Definitley NOT comply.

You "might" want a TD one at the supply end of the Cable to the shed for discrimination purposes, but once you get to the shed, it HAS to be an ordinary one,

One rod will be plenty as long as you can get Ze for the shed install low enough..

john..

Was just thinking about a TT & how's it's fed and at the start of its life as it enters the house you have a timed delay unit fitted before the c/u not up the poll in the street, am I thinking wrongly here sorry if I am,