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!

 

[Deleted member 9648]

They are still both earth though are they not so can we put the toys back in the prams please !!!

Not when I am told I dont know what I'm talking about by someone who doesn't know what he's talking about.

 

[ayjay]

bet noone knows what heatshrink was---it came out about 25 years back but was discontinued it replaced the micc pots , had to use a special attachment on a blowlamp to terminate it
also there were pots that didnt screw on, they had a separate brass wedge instead-- and you had to use a converted set of molegrips to crimp the wedge into the pot
micc is very underrated imo this new stuff is impregnated with silicone so it doesn,t get moisture in the insu, not like the old days, no silicone then-- u had to work fast or the meggar reading would be low
if an old mineral had damp in it you used a blowlamp to drive it out after removing the pot
bloody sparks these days wouldn,t know **** from clay, if they were presented with an micc job

 

[Risteard]

Mineral Insulated Copper Clad, also known as MIMS (Mineral Insulated Metal Sheathed) or Pyro.

 

[malcolmsanford]

]Pyro is not suitable for burying direct[/B] and it is an extraneous conductive part. I'd start from scratch and abandon all the existing.

I have to ask why not

 

[Deleted member 26818]

So you inventing a new reg, buried metalwork is no longer an extraneous conductive part, lol.

Metalwork such as water, gas or oil pipes or steel reinforcing in concrete are extraneous-conductive-parts.
Mettalic cable sheaths, conduit or trunking and metal enclosures are exposed-conductive-parts.

 

[SW1970]

Thanks for all the comments. In this case the pyro is plastic sheathed.

Pyro can be buried direct: FAQs - Fire and Performance Wiring - Tyco Thermal Controls

So, it looks like it's all down to the earthing arrangements of outbuildings in TN-C-S installations (a well covered topic!), and depth/mechanical protection of the existing buried cable.

Wirepuller - I like your idea "As long as there were no obvious issues...no I wouldnt. I would just do a cert to cover work within the garage, as the refurb of the garage install and a few additional points is the object of the exercise."

But if the job includes the garage installation refurb and new RCD protection at the other end of this distribution circuit in the meter cupboard (per my original pic), are we comfortable with constraining the EIC in this way because this pyro cable is a fundamental part of the circuit.

This is a broader point than just this case. I guess the point goes: is it ok to certify an installation that we have added to or altered, if parts (that we haven't installed) don't wholly meet the regs, even though our works have improved overall safety of the installation? I was taught the answer was no, but that was in a different environment where there was usually budget to sort out any issues.

 

[malcolmsanford]

Are you worried about this MICC. If you have tested it, especially the IR and it is in good condition then utilise and certificate it. By testing the circuit you are confirming all the details on your SoTR such as the IR, Zs etc so that is ok.

As for you SoI there is nothing on the form that asks for a depth of a cable in the ground, so what will stop you filling out one for an already existing cable.

 

[ayjay]

bet when its tested its down , it normaly is

 

[SW1970]

Thanks Malcolm! It tests out fine. >500Mohm and R1+R2 is 0.38ohm, so meets disconnection times even for existing BS3036s.

 

[glasgowbiker42]

pyro should only be in the ground if it is in
a duct.

 

[SW1970]

Hi glasgowbiker, this is from the tyco website. You're probably right, but this is an attempt to save a larger job worth about £1,000 that is not going to happen if I can't re-use this pyro. These are lovely clients with a lawn that looks like it's manicured with a pair of scissors on a daily basis. Malcolm's comment is good; I shall declare the pyro situation in comments on existing installation.

Q. Can Pyrotenax cable be buried directly in the ground?
A. Pyrotenax cables are suitable for burying in the ground and are subject to the same procedures as other cables regarding the depth of trench, mechanical protection and identification of routes. We would always recommend plastic covered cable as some soils can contain elements corrosive to copper.

 

[Knobhead]

Q. Can Pyrotenax cable be buried directly in the ground?
A. Pyrotenax cables are suitable for burying in the ground and are subject to the same procedures as other cables regarding the depth of trench, mechanical protection and identification of routes. We would always recommend plastic covered cable as some soils can contain elements corrosive to copper.

Here endeth the lesson :chillpill:

 

[oxocube]

An extraneous conductive part cannot be part of the electrical installation....I am not inventing regs...you will find this information in the definition of an extraneous conductive part in the BRB/BGB if you bother to read it.......(lol)

You are of course absolutely correct and I am a plonker, I apologise for my stupid post.

 

[Deleted member 26818]

You are of course absolutely correct and I am a plonker, I apologise for my stupid post.

I wouldn't say you're a plonker, you just need to take a little more time to think before posting.

 

[Engineer54]

I wouldn't say you're a plonker, you just need to take a little more time to think before posting.

I think were all guilty of that at times ...lol!!