PVC temprature rating

[Gardner]

Obviously code restricts PVC and twin and earth to 70*C max, but out of curiosity what is the designed temperature rating of the insulation? Just wondering.

 

[yellowvanman]

Don't know of a max temperature, but have seen some info on how higher temperatures caused by over current reduce the life span of cables! So whilst they can still work at higher temperatures this reduces their life span.

 

[walsh builders]

I think that the ambient temp is stated as 30*C

 

[Richard Burns]

I am not sure what you mean by the designed temperature rating.
However the 70°C temperature limit for the conductors in a PVC insulated cable is there to prevent the PVC from suffering heat damage.
I believe PVC fails at about 120°C, however in a fault situation the temperature of the conductors in a cable may be expected to be up to 170°C for a short time. The given melting point of ordinary PVC as a plastic is 212°C,however i do not know how the plasticisers, etc. change this.
The external temperature of a cable is about 10-20°C below the core temperature.

 

[Marvo]

I think you've got to refer to the individual cable manufacturers data sheets because depending on the PVC blend and the additives used there can be significant variations in thermal properties of the insulation and sheathing.

 

[Deleted member 26818]

Yep PVC is not created equal.

 

[Gardner]

Ok thanks! I will check out the specs, but its more curiosity than anything.

Looking at North American cables the PVC (called THHN) is rated 90*C, but the code forces it to usually be run at either 60 or 75*C much like the regs force 70*C.

 

[Darkwood]

There is a buffer zone applied but not much, the integrity of the insulation will breakdown if run at over 70c be it from the conductor or the ambient temp' and is subject to the temp' and the time, and as above its subject to manufacturing processes.

Regardless of cable rating it will b derated to the equipment it is connected to so as most is manufactured to 70c then a 90c cable connected to a standard 70c rated switch gear has to be derated to suit.

 

[Gardner]

There is a buffer zone applied but not much, the integrity of the insulation will breakdown if run at over 70c be it from the conductor or the ambient temp' and is subject to the temp' and the time, and as above its subject to manufacturing processes.

Regardless of cable rating it will b derated to the equipment it is connected to so as most is manufactured to 70c then a 90c cable connected to a standard 70c rated switch gear has to be derated to suit.

Ok that makes sense, slipped my mind for a moment there. The terminal temperature also has a final say. So 4D5 also takes into account terminals limited to 70*C?