TN-C-S / Pyro / Outbuilding Upgrade

[SW1970]

Hi, bit of a job with scope creep going on. "Oooo it's so good we've found a nice electrician we can get all these things done that we've wanted for years". Client wants new outside lights on garage but existing isolation and circuit protection supplying garage is falling apart so that needs sorting too. Circuit to garage is on buried 2 core pyro of unknown depth and routing. Existing old Wylex isolator and fuse in meter cupboard is rusting and existing old Wylex isolator and fuses for lights and sockets has no RCD (sockets are used for outdoor equip). So these items need replacing and upgrading. Primary concern is earthing, installation is TN-C-S. Earthing to MET is ok. Have a look at this sketch (red is new equipment replacing old, blue is existing and propose to retain):



First time I've worked with pyro. Not sure which rating as existing terminations aren't marked so assuming worst case from Lenny's sticky it's 8.2mm2 equivalent. Any thoughts or guidance on this one? Many thanks as usual!

 

[Mr Mike]

Our industry is all about thinking, first, second and third.

 

[SW1970]

And having a lot of respect for those with knowledge and experience (for example many who have contributed to this thread). You have my respect guys. If there was a handy beer pump nearby it'd be a round on me.

 

[SPARTYKUS]

Ive got an old bit of pyro at home, when I get back off my jolLies i'll conduct an experiment with it in various envirOnments/positions, and my carbonsteel tempered drop forged annealed spade! Just to see if I was perhaps over confident with my claims ...

 

[ayjay]

if its buried deep enough a spade won,t hit it, i used to lay it in a trench, then put soil over it then heptape then the rest of the soil
theres always loads of soil left over isn,t there? cant understand that----

 

[Engineer54]

if its buried deep enough a spade won,t hit it, i used to lay it in a trench, then put soil over it then heptape then the rest of the soil
theres always loads of soil left over isn,t there? cant understand that----

Point 1 ....The correct method of direct buried cables, involves the provision of cable bricks/tiles to protect the cable(s) This is often ommited by many electricians, who only provide warning tape (if your lucky) !!!


Point 2 ....That's because the soil was in a compacted state when you dug it up, so it actually needs compacting back again after your finished. Either that or the soil will gradually sink, and you'll be left looking at a snaking depression, showing exactly where your cable has been laid.

 

[Engineer54]

Your having a laugh mate !!!

Where did you go to clown skool ?

What reg states after laying your cable in a trench, backfill with bricks and tiles ??!! FFS !!!!

I always thought it was SAND followed by a yellow tape....

Never mind perhaps i went to the worong clown skool

Go figure !!!

Yes indeed the cable should be laid on sand as well as being surrounded by sand. How often that is the case in reality, is another matter!!

If you have absolutely no idea what cable bricks/cable tiles are, or the make-up of a correctly organised back-fill of a cable trench, then you shouldn't really be making any comments on what you Don't know!! Most direct buried cables in domestic settings do not comply with any standard, your lucky these days if the installer sifts the back-fill of any stones or debris. Far better to duct any buried domestic cable runs, at least you'll be giving the cable a decent chance of protection and longevity!!

 

[fascally 07]

Rule number 1 Never blow in the pot to clean the dust out always give the pot a tap with your pliers to clean it for the compound

 

[SPARTYKUS]

Ive got an old bit of pyro at home, when I get back off my jolLies i'll conduct an experiment with it in various envirOnments/positions, and my carbonsteel tempered drop forged annealed spade! Just to see if I was perhaps over confident with my claims ...

Hello. just got round to it, not sure really if it proves anything but at a loose end today and found the old bit of pyro (plastic covered) so gave it a good smack with the spade. Straight through :61:

HOWEVER - that was on a concrete floor. Not so likely I think in he ground. No where near as tough as Armoured though. But as was said if buried correctly with all the other stuff, spade'd never get near it.

 

[Risteard]

Can't see the problem with buried MIMS. The sheath is earthed and so will cause rapid disconnection. You could put a spade through SWA if you wanted too.

 

[Knobhead]

I had a look at your location and decided to keep schum!

 

[SPARTYKUS]

Can't see the problem with buried MIMS. The sheath is earthed and so will cause rapid disconnection. You could put a spade through SWA if you wanted too.

True, but only after going at it hammer and tong for a few minutes!

Pyro is adequate I would say, SWA better.

(I have gone through SWA too, but I mistook it as a tree root - it took some doing!!)

 

[Risteard]

I had a look at your location and decided to keep schum!

Presume that's directed at me but must admit I'm completely lost!