Worst things about your current workshop!

[Adam]

Ahhh As an electrical and electronics design engineer before deserting to lecture for more dosh,

I believe I can shed some light on this

The problem is not a degredation of the insulation due to contact with the polystyrene

Hope this:
a is not too boring
b is useful

Also as an electrical and electronics design engineer 8) :lol: I will disagree on this occasion!, it is due to contact between the polystyrene and the plastic in the electrical cable. It is due to migration of the molecules in the cable, into the polystyrene - leaving the cable unsafe. Although heat is important - it is the actual contact that causes the problem. I did quite some research into this after hearing it, to decide if I thought it was likely to be a problem.

http://www.feuerstein.ch/BELDEN_Electri ... glisch.pdf

To quote the relevent bit
"Plastics like ABS and polystyrer are chemically attacked by the standard plasticizers used in PVC. For applictions where there is direct contact between cable and ABS or polysyrene, special non-migrating cables containing plasticizers of a high molecular weight should be used. Blah blah blah."

I can assure you, high molecular cabling is not the stuff you get from your local electrical trade counter. So, to be safe, you should ensure there is not direct contact!

Learn something every day eh Tony?

I did hear of a case in London, where a office block/tower had a central conduit running up the centre with all the cables (I mean all, data, fire alarm, mains, etc), the conduit had fire compartments every floor, but despite being told this was bad practice, the fire safety officer insisted fire-resistant expanding foam should be injected into each cavity. After about 2-3 years, the entire beuilding had to be stripped due to corrosion at a cost of over £100K!!

Hope that clears it up.

Adam

 

[Adam]

adam

I also did an experiment and sandwiched a piece of cable between 2 pieces of poly held with an elastic band. In nearly 12 months I can see degradation at all. This is not a scientific test of course only food for thought.

AndyP

Have you tried bending and flexing the cable?

Adam

PS: Good idea for an experiment - should have thought of that myself!

 

[DaveL]

In the first bungalow I bought there was no loft insulation.
At work I had all sorts of stuff delivered in boxes packed with polystyrene crisps/pebbles and it seemed a good idea to bring them home and fill the loft.
In those days I only rode an old BSA and could often be seen with a very large ruck sack on the way home :shock:
In time most of the loft was covered
I had plans drawn for a loft conversion, about 5 years later. The chap who did them took one look at my free insulation and commented that it was not a good idea for it to touch the cables. :!:
On close inspection the pebbles in contact with the cables where now stuck to the PVC. I spent almost as long getting the stuff back out of the loft as I did putting it up there in the first place :twisted:

The cables survived, but given more time breakdown of the PVC would cause problems.

 

[Anonymous]

Asleich said
Also as an electrical and electronics design engineer

Really? small world

Asleich said
"I can assure you, high molecular cabling is not the stuff you get from your local electrical trade counter. So, to be safe, you should ensure there is not direct contact!

Learn something every day eh Tony? "

Gloating or insinuating?

Adam, as you say, I have learnt somethig new. Something interesting. Never came across this before but then I did not usually get involved in many civil engineering installations as my specialism is control system design.

Do you know what physicaly happens to the insulation over time and how long it will take before any damage is done? I take it from your post that the insulation simply becomes brittle as the old rubber insulated cables used to?

The points I raised in my post were intended to help people wiring their shops and are still valid. Whatever cable is used one must take care that it is derated where neccesary to prevent heat build up and excessive volt drop.

Cheers

Tony

 

[Anonymous]

DaveL

Did the poly actually eat into the insulation or were they simply stuck to it?

 

[DaveL]

DaveL

Did the poly actually eat into the insulation or were they simply stuck to it?

It was starting to eat in, after I had removed it all the cables looked a little mottled and that was only after 5 years. Most cables and insulation get put in and not looked at for 10 to 15 years :!:

Just to update the on job front:

I did an apprenticeship as a Telecommunications Technician, many moons ago
Worked in electronic development doing processor controlled telecomm kit. Left for a lecturing job, which turned into a network manager role, from which I was made redundant.
Joined a large international IT services company and now work as a technical consultant. Sounds very grand but means the more tricky stuff gets pushed in my direction, good for keeping the brain going and I still manage to get my hands dirty at work :lol:

 

[dedee]

Tony/Adam

Thanks for the update and articles, very interesting. I think I had read yours or similar posts elsewhere along the same lines so in my own shop I routed all the cables, power and lighting, so none of them even touch the poly, never mind being sandwiched by it.

The very non-scientific test was on a short 3" length of power cable that does not have any current running through it so will never heat up in the manor described.

AndyP

 

[Adam]

Tony said

Gloating or insinuating?

Sorry, I just meant it as a normal comment, literally, you learn something every day. It was meant neither to be gloating or insinuating.

>Adam, as you say, I have learnt somethig new. Something interesting. Never came across this before but then I did not usually get involved in many civil engineering installations as my specialism is control system design.

I'm in wireless systems, so this was news to me to when I first heard it, although I was aware of problems in ships with radar cabling and fire retardent foam - when I was doing Radar and EW design.

>Do you know what physicaly happens to the insulation over time and how long it will take before any damage is done? I take it from your post that the insulation simply becomes brittle as the old rubber insulated cables used to?.

Yes, that's what I believe happens, and of course, when the stuff gets "stuck" onto the cable, your comments on heat apply even more.

>The points I raised in my post were intended to help people wiring their shops and are still valid. Whatever cable is used one must take care that it is derated where neccesary to prevent heat build up and excessive volt drop.

Yes, in fact the risk of overheating is likely more of a risk (I would imagine), in the circumstances, so your advice is very good.

Laters,

Adam

 

[Anonymous]

Aislech wrote
Sorry, I just meant it as a normal comment, literally, you learn something every day. It was meant neither to be gloating or insinuating.

I too must appologise. I had a bad day at work and was in the wrong frame of mind when writing my post and reading yours.

I am tempted to try a little experiment myself now and look for the degradation in the insulation. Especially interested in seeing the migration of the poly into the PVc

Now where did I leave that polystyrene packaging frommy table saw?.