ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades The Pyro thread

Guys, I was trying to explain to John (Renosteinke) in the Chat room last night about the cable we call Pyrotenax.
To give it it's correct technical name, it's called Mineral-Insulated, Metal-Sheathed or Mineral insulated Copper Sheathed.(MIMS or MICS)

It's a type of cable that is under-utilised down in this part of the world these days.
But I'm told it's still used quite a bit in the UK.
Considering it will withstand temperatures up to 250C (482F), this alone makes it ideal for fire protection circuits and the like.
Here is a guy holding a sample of the stuff:



This PDF file(331kb) tells you all you ever wanted to know about MIMS cables, even how to strip, terminate and fix this type of cable:

http://www.aeicables.co.uk/literature/mic.pdf

Believe me this isn't an easy cable to work with, it's rather finicky about being bent too sharply (just think Refrigeration piping) and the insulation inside the sheathing is very suseptible to moisture if the end of the cable is not sealed properly.
Keeping moisture out is important because the wires are bare inside the densely packed powder insulation.
There have been cases of this cable exploding, where a kink has been put in the sheath during installation of the cable and the sheath has cracked and it has gone un-noticed, until one day the cable fails.

{Message edited to re-size picture}

[This message has been edited by Trumpy (edited 05-31-2005).]

Trumpy, while I was doing my training, that's one thing I saw WAY too much of, I can still hear my mentor now.. "Dress that d*** cable, looks like a dog's hind leg, do it neatly, *DON'T yank on the seal like that*... Kids today.."
I always thought it was an odd, yet absolutely excellent concept. Nothing organic in the bare copper version, and excellent earth continuity, I believe the sheath is something like 3x the cross sectional area of the conductors.

Thanks, Trumpy, for the info. It certainly does look like a very good wiring method from an electrical standpoint- if a bit of a bother to work with!

John,
No problems, mate.
Chipmunk,
Oh and you had them comments too?.
I'm glad I worked with Pyro during my time, it's certainly saved some suprises when turning up to Industrial and some Commercial places, only to find the wiring has been run in Pyro.
I realise that it's use is rather limited but I believe it's one skill every Electrician should have under thier belt, especially jointing it.
Even though it's not being used like it was earlier on, there is still a chance you'll come across it sooner or later.
Which brings up another thought, these days with respect to Electrical apprentice training, there seems to be a lack of knowledge from newer Electricians (ie: just registered) in the repair or replacement of older wiring systems, like Steel conduit, wood trunking and of course Pyro.
It seems that the majority of trainees only ever get to work with standard PVC cables and standard fittings and once they go out on thier own, they've never worked on any "legacy" wiring systems, which could use any number of different (and strange) fittings and wiring methods.
There, that's my rant for today!.

Absolutely Trumpy ! I've been called to MIMS cable failures in old Christchurch buildings and I don't even know where to start with terminating that stuff ! MIMS is the most permanent cable type and therefore it will be in service for decades. But very few of us know how to maintain it.

MIMS cable techniques should be included in the Trade Certificate practical curriculum. It could possibly replace other outdated items such as Soldered Lugs and Bargeboard Tie-offs

Trumpy,
i fully agree with you that alot of newly qualified sparkies do not know what to do with some of the older installations installed years ago.

me personally i love Pyro, its on of the best forms of wiring i know, its not the easiest of cables to use but after a bit of practice it can look sooooo good.

in LOndon all the fire ssytems that were fitted during the reign of the GLC (Greater London Coucil) it was a requirement that all Fire Alarm Systems were installed with Pyro.

Also a national brewer that owned a few thousand public houses had ALL circuits wired in pyro, it was because of the low fire hazard that Pyro has.

i have been to installations that are prior to metrication and they are still going strong, (some of the Recepticals and switchgear needs replacing but he cable is good).

Britspark

Gidday Britspark!,
Welcome to the Forum, great to have you along.
Yeah, that's one of the good things about Pyro, it's temperature rating is basically the melting point of copper.
And yes I must agree there aren't many things that look as nice as a whole set of Pyro cables nicely laid into and clipped to a cable ladder.
Kiwi,
The only reason we were trained in it's use here, was because back in the 1950's the Power Board here used to use this cable for Commercial Service Mains (from the intake point to the Switchboard panel) and there are quite a few buildings with this set up still in them around the place here.
Always run as 4 singles, with the sheaths bonded at each end and also at regular intervals along it's length, depending upon the length of the run.

Yes, nicely run pyro cables are a joy to behold. Installing them must be a science in itself. Trumpy, I have even seen pyro mains in old houses here running right up to the old fusebox. Makes opening the door of the fusebox a bit nerve-wracking in case moving the pyro end causes it to fail ! ! Especially if you're like me and don't know the first thing about fixing it. How much can you flex those tails before they fail ? They seem kind of fragile, and I always worry about moving them.

Pyro is also installed to supply fire sprinkler pumps in multi-storey buildings, especially in hotels. I think it's a building code requirement.

Here in the UK, I have known the power company mains to be pyro, generally something akin to 16mm 2 core, although obviously the old imperial equivalents . This mainly seems to happen on blocks of flats (apartments) built for social housing in the 50s. The PoCo main incomer to the building will be 'normal cable', a distribution unit of some kind in the basement or service area, and pyro to the individual main fuses/meter cases. The scary thing for me was to see that they treated the pyro the same as any other cable, just had the sealing pot sat on the end, 2 sleeved conductors to the service fuse block, and a clamp for the earth. I guess it cost them less than a custom [pyro only] box for the mainfuse and neutral link.
Again, these cables seem to be in excellent condition, and were left alone during the remodel, the only part of the electrical system that wasn't totally ripped out.

quote:
---------------------------------
...the only part of the electrical system that wasn't totally ripped out.
-----------------------------------------

By the occupants.

Alan