New wiki article: Terminating MICC / Pyro

Many thanks to Dave P for all the words and hard work... I did the cutting and pasting ;-)
Comments etc as usual:
http://wiki.diyfaq.org.uk/index.php?title=Terminating_MICC_/_Pyro
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Cheers,

John.

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On Mon, 07 Sep 2009 20:08:09 +0100, John Rumm

Some comments from one who has never done this, so apologies if some comments seem jocular or stupid! :-O ...

Omit "only", it makes it sound as if this insulation is in some way inferior.

Usual? what determines if you should use one?

I'm struggling to imagine what the kit components look like; a photo's worth a thous... etc.

Decide how long the tails need to be, then mark and

Do you mean to peel it off in a spiral (helix really), or are you taking the sheath of in 1" cylinders? Why can't you cut the longitudinal slit directly into the end of the cut cable, as opposed to making the circular cut first. Sorry but I did say I've never handled this stuff.
How thick is the outer, so I can have an idea of how hard/easy it is for my siide-cutters to cut it?
What do you do with the insulating powder that (presumably) spills out? Worth stating that its inert, harmless, whatever.

until the outer sheath sits flush ... ?

sounds as if there must be enough free cable to be able to get the end vertical, yes?

I'm visualising vertical conductors now. I don't get the right angles bit.

sounds like a 3-handed operation - what's holding the cable?

Remove the seal first? How? Is there a bit sticking out that you can grip, or does it go in flush.

Ahh, so you are stuffed if there is still no excess compound oozing out?

I can't see what you're getting at here. Seems to me at some point you have to release the grips on the seal and poke it below the pot with 'something'.

Would help to state the length of the pot (hence largeness of the side-cutters).

Yikes, doesn't the seal keep them separated? If not, what is the seal sealing? Or do the two sleeves go inside holes in the seal to complete the sealing?

With what dear Lisa, with what?

Is there any way to check if this has happened? what if it has?
Sorry to inflict my editor mode on you John, but hope it will make it clearer for other newbs like me. As usual its easier to criticise than create!! Nevertheles, I've learnt a lot from your piece, thank you.
Phil
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Glad that's a bit John added...

Likewise. ;-) You can do without the gland - indeed there were backing boxes that clamped onto the pot. Plaster depth. So for use where the fireproof etc qualities were less strict.

I'm working on that.
Fitting the gland is easy. It's similar to to a compression fitting, and simply slides over the sheath. It's the termination (pot and seal) which is more tricky.

Any method which allows you to remove the sheath without damage to the conductors will be fine. The tools for the job remove it in a spiral, so I've stuck to this as it pulls the sheath away from the conductors.

Hmm. Less than 1mm is my guess. But I'll measure it

Yes. That's what the pot screws onto.

No - the compound is just like putty and won't fall out regardless of the angle.

You're just pushing compound into the pot via the largest space in it - ie at right angles to the conductors.

Since you need some force one grip will hold it while you apply the other.

There are stubs sticking out of it that the conductors go through - that the sleeving pushes onto. Your fingers will easily grip them to remove the seal. Before it's crimped, obviously.

Yes. But most will fill it to the top so there will be excess. You can put any squeezed out back with the rest of the compound.

Just that the seal goes slightly below the top of the pot onto a shoulder. You need some 'spare' at the top of the pot to crimp over. And if using parallel grips the top of the pot will stop the seal being forced to the shoulder.

I'll do some pics. It's about 1/2 inch.

There's a slight possibility you could bend the conductors inside the pot when fitting the seal. Giving them a tug makes sure they're straight and can't be touching.

Sane as you'd mark PVC with to identify it - some brown sleeving, etc.

It pretty obvious as the insulation sort of sets rather than being a powder. It takes a long time to penetrate far so the act of terminating usually gets you back to good stuff. It can also be heated with a blowlamp to dry it out. But not if you wish to retain the PVC outer.

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On Tue, 08 Sep 2009 00:56:46 +0100, "Dave Plowman (News)"

ROFL
ok
ok, but I still don't get the bit about cutting circles in it.

I was only suggesting changing 'cable' to 'outer sheath'.

OIC now , but you can't extrude putty, this must be quite a bit less viscous?

In that case omit the 'right angles' bit, its clear enough now you've described it as putty like.

But you implied that both grips grasped the seal. I think you actually mean one to grip the cable and the other the seal?

Got it.

So not stuffed if you do what most do. Better add that.

So as I said, you need 'something' to poke it below the pot.

I'm still not clear what this seal is like. Does it have two holes through it, one for each wire, or is there just one hole for both wires with fresh air between them?

My problem is that you didn't indicate what the sleeve is like (ie material) so I didn't know what will write on it. Oh just a minute, by 'mark one' I took it to mean 'write on it'. Do you mean mark it with sleeving (sleeving on sleeving??) or wrap sticky pvc tape round it etc. Is this just a temporary marking until you complete the installation, or meant to be permanent for future electricians to see?

ok
I just thought of another point: No mention of terminating the wires. Perhaps obvious but it would complete the task of 'terminating the cable'.

Ditto to Dave Noise!! Phil
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For the pot to fit easily you need a perfect end to the sheath. Hence the use of a pipe cutter. The part of sheath between that and the cable end is scrap and has to be removed. It can't just be slipped off as the mineral insulation is tightly packed and holds it in place. The normal way is to peel it off - but you could remove it in very small pieces using the pipe cutter. As they will then slip off. But it is possible to peel it off with side cutters. I had to do this once when I'd forgotten to bring the correct tool. Using the correct tool reduces this to an easy task. But by the link given earlier they now cost about 60 quid.
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On Tue, 08 Sep 2009 09:09:27 +0100, "Dave Plowman (News)"

OK, so say something like ...
Establish the length of bare conductor you need, and mark this distance on the outer, back from the cable end. Cut (nearly/completely?) through the outer at this point using a normal pipe-cutter suitable for ?mm diameter copper pipe. Then using one of the methods below, strip off the outer ensuring that it is finished clean and square so that the pot will fit snuggly on it.
Note that the outer cannot just be slipped off after cutting round it as you can with PVC cable, because the mineral insulation is tightly packed and this holds it in place. The normal way is to peel it off, but you can cut and slip off a short length at a time using a pipe cutter.
Phil
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Dave Plowman (News) wrote:

I was just attempting to highlight that unlike most cables the conductors have no individual insulation. Can you think of a better way of phrasing it?

That was the bit I missed - did not realises you could do it without the gland...
If you do, how do you make the earth connection?

I think "right angle" is perhaps in the wrong plane... you are pushing it into the put all around the conductors by the sounds of it.
BTW, does the putty set, or stay erm, "putty like"?

What is the pot made out of BTW?

An insulation resistance test to the sheath would also probably tell you in short order...

Well its Dave your mostly inflicting it on (apart from the bits where I bolloxed the meaning!)...
I will await some new words and piccies and paste em in.
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John.

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I was thinking of the best way to put it. The compound comes in sticks approximately the width of the pot. You sort of push the edge of the stick down from the top of the pot which slices off a chunk and leaves it inside the pot. This should be done as far away from the conductors as possible into the emptiest part of the pot - hence at right angles or opposite to the conductors. This way, two slices will suffice. You don't need to pack it in carefully as forcing in the seal will do this for you and expel any excess. But it *must* be totally filled with compound.

Doesn't set.
[snip]

Brass
[snip]
It would indeed.

As I said it's what I know the parts by. May not be universal though - like pattress. ;-)

Hopefully I'll do something today. I have found some new glands and terminations. I do have some cable somewhere too.
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On Tue, 08 Sep 2009 09:26:55 +0100, "Dave Plowman (News)"

How about ...
"The compound comes in sticks approximately the width of the pot. If you push the edge of the stick down and across the top edge of the pot this will slice off a chunk and leave it inside the pot. If this is done opposite eaach side of the conductor pair, i.e. into the emptiest part of the pot two slices will suffice. You don't need to pack it in especially carefully as the act of pressing in the seal will compact it and expel any excess. Note that the pot *must* be totally filled with compound so that [no voids are left which will contain moist air]*
*(insert correct explanation, I'm not sure if this is the reason).

So with slight re-wording you could say "Fitting the gland correctly is the tricky bit. The gland comes as a kit of parts - a *BRASS* pot, a seal, sleeving, and potting compound. It is usually supplied in packs of five." and add something like " The potting compound is a non-setting material with a consistency similar to soft putty".

Phil
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On Tue, 08 Sep 2009 03:45:11 +0100, John Rumm

Really the 1st 'Gland' sentence should be in the 'Intro' as its describing the cable itself rather than the gland. Then you could rephrase it something like "The individual conductors in MICC are bare copper separated from each other and the overall sheath by a powdered mineral insulator instead of conventional PVC insulation." Possibly add that the mineral MgO2(?) is an excellent and stable insulator good for temperatures far higher than PVC can withstand.
Phil
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On Mon, 07 Sep 2009 20:08:09 +0100, John Rumm

I had a go at this in 1963 while working for a local electrician during my school holidays. The little I can remember is:
Be very careful when removing excess copper sheath. If you wobble them about too much the copper conductors will work harden at the point where they cease to be supported by the copper sheath and drop off. This can be catastrophic at the end of a long run along a ceiling and down a wall to a consumer unit for instance. If the ends drop off the only way of saving the job would be to move the consumer unit up the wall where it may then be too high for the customer. It happened to us.
Check the insulation with a megger before using a length of MI cable, if it's compromised by damp cut a foot or so off and measure again.
Damp aside the insulation is very robust and MI cable can be hammered flat without short circuiting.
What distinguishes a professional quality job is getting the runs installed straight (it's surprisingly conspicuous if a cable runs off by a few inches along 40 feet of restaurant ceiling) and without kinks which are nearly impossible to get out. To this end measure and mark the wall etc. first, drill and fix the clips in advance, and don't let the working loop of MI cable hang from a clip unsupported.
HTH
Derek
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Indeed - I didn't cover this bit as it's largely common sense for an experienced DIYer. And I'm not suggesting this would be a good first project. ;-)
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On Tue, 08 Sep 2009 08:57:48 +0100, "Dave Plowman (News)"

Seems very good advice to me, especially the dire warning about work hardening. We've all discovered that problem re-working wiring thats crammed into back boxes (haven't we?). I suppose if you do start to see work-hardening on your precious tails you could recover normal flexibility by heating to red heat (can someone verify this!).
Phil
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Derek Geldard wrote:

It's not particularly robust electrically. The insulation can be susceptible to breakdown caused by voltage spikes, particularly in inductive circuits such as discharge lighting. Here's a short thread on the subject in the IET/IET wiring regs forum: http://www.theiet.org/forums/Forum/messageview.cfm?FTVAR_FORUMVIEWTMP=Linear&catid 5&threadid)238
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On Wed, 09 Sep 2009 01:02:31 +0100, Andy Wade

http://www.theiet.org/forums/Forum/messageview.cfm?FTVAR_FORUMVIEWTMP=Linear&catid 5&threadid)238
Sadly the forum moderator munged the vital URL. Here's the actual article by the Pyrotenax manufacturer, in which they point out that IEE Regs (16th Edition) states that the fitting of suppressors across such inductive loads is the (cable) installer's responsibility - http://www.tycothermal.com/uk/english/wiring/literature/PyrotenaxCables_IR402.pdf
The Pyrotenax home page on the manufacturer's site (Tyco Thermal Controls UK Limited) is http://www.tycothermal.com/uk/english/fire_performance_wiring /
Pyrotenax/Tyco themselves sell appropriatel VDR suppressors to be fitted at the cable termination, and the doc gives purchase and fitting details.
Phil
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On Wed, 09 Sep 2009 14:01:55 +0100, Phil Addison

http://www.tycothermal.com/uk/english/wiring/literature/PyrotenaxCables_IR402.pdf
Further browsing of that site reveals some nice exploded illustrations of the gland assembly on page 12 of http://www.tycothermal.com/uk/english/wiring/pdf/CDE-0801_R2.pdf and an 8-step Terminating Procedure on P13.
Also on P13 is a cross-section drawing of an assembled gland/cable. This shows that the spacing of the two bare wires increases as they pass through the gland seal, and the seal itself does NOT guarantee separation of the wires within the gland, so Dave's step of pulling them straight (but splayed out a little) is worth emphasising.
Actually, wouldn't it be better to put that step at the beginning of "Fit the seal" rather than the end, so you can still see if the wires are straight or not in the critical area where the seal will go.
Phil
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You don't need anything other than a straight pull as the seal has quite long tubes on it so they can only go in one direction. See the latest pics. I also mentioned marking the pot with the position of the wires so you don't introduce a twist. Also why I emphasised being careful removing the scrap sheath - even with the correct tool it's possible to twist the conductors together.
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John Rumm coughed up some electrons that declared:

"Fitting the pot"
Not done one, but have read about it... Might be worth adding something like:
"Ensure there are no slivers of copper left. But do not blow the end out with mouth as the moisture in the breath may compromise the insulation. The usual way would be to tap the cable if it's possible to invert the end, or use a can of air or a vacuum cleaner".
Perhaps some review needed, but I think "not blowing" is worth a mention as it's an instinctive thing to do.
Cheers
Tim
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Photographic 'bulb' dust blower?

Phil
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On Tue, 08 Sep 2009 22:07:59 +0100, Phil Addison wrote:

================================================ Bicycle pump - also pretty good for clearing dust from computer internals.
Cic.
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