Thoughts on earth bonding on lights please

[stillp]

If, as implied by stillp's way of thinking, an applied voltage could be withstood satisfactorily for 5 minutes but would result in breakdown of the insulation if it continued to be applied for a further 10 minutes, I would be rather surprised - but maybe that's how it is?!

It is.

"PVC Type 6" to BS 7655-4.2

Yes, that's called up by BS6004.
All I can see at the moment is that the tensile strength of Type 6 or Type 10, the other allowable sheath material is about half that of the Types TI 1 and TI4 that are used for the insulation.

It would seem that there is relatively little variation in either dielectric strength and resistivity across the whole range of PVCs - it's really just the mechanical/environmental properties which vary appreciably.

There can be large differences, depending on the additives used.

 

[JohnW2]

Yes, that's called up by BS6004. All I can see at the moment is that the tensile strength of Type 6 or Type 10, the other allowable sheath material is about half that of the Types TI 1 and TI4 that are used for the insulation.

Thanks. That obviously makes sense.

There can be large differences, depending on the additives used.

I obviously have not been able to explore all possible "PVCs" but, as I said, for what it's worth, all of those I've so far found have similar dielectric strengths and resistivities. There may, of course, be some (that I have yet to find) which have additives deliberately added specifically to make them 'conductive', but I find it fairly hard to believe that they would be used (or even 'allowed') as the sheaths of PVC/PVC cables.

Kind Regards, John

 

[stillp]

That obviously makes sense.

Does it? I'd have expected greater mechanical properties for the sheath.

I obviously have not been able to explore all possible "PVCs" but, as I said, for what it's worth, all of those I've so far found have similar dielectric strengths and resistivities.

Where are you finding these different PVCs?
There are other uses of additives, e.g. for greater plasticity, UV resistance, oil resistance...

 

[stillp]

Ironically, given that I've previously entreated you John to study the standards in your local library, mine has dropped its subscription to BSOL (British Standards On Line)!

 

[JohnW2]

Does it? I'd have expected greater mechanical properties for the sheath.

Whoops. To be honest, I misread what you wrote (read it 'back to front') - and would, indeed, expect (some) mechanical properties to be greater for the sheath, particularly things such as resistance to abrasion and damage due to flexing, and things such as you mention (resistance to UV, oils, other environmental factors etc.). As for the one property you actually mentioned (tensile strength), I'm not quite so sure - elasticity and flexibility are presumably desirable properties for a sheath, and it could be that the price one has to pay for them is a lower tensile strength.

In any event, as you are always reminding me, Standards only specify minimum requirements, and it could be that actual cable sheaths appreciably, or maybe even considerably, exceed some of those requirements.

Where are you finding these different PVCs?

All over the place - mainly in the data sheets of primary industrial suppliers of 'raw' PVC materials.

There are other uses of additives, e.g. for greater plasticity, UV resistance, oil resistance...

Sure, and PVCs with all sorts of permutations of such additives have featured in the catalogues and data sheets I looked at.

Kind Regards, John

 

[JohnW2]

Ironically, given that I've previously entreated you John to study the standards in your local library, mine has dropped its subscription to BSOL (British Standards On Line)!

I see! In fact (and I'm not sure that I ever told you this), when I asked I discovered that my nearest 'significant' library never had had such a subscription (at least, not in recent times, if ever) - which would have the effect of considerably increasing my round-trip time/cost!

Kind Regards, John