Pyro Vs SWA

[sham]

Hello spark's

i am querying on a job i visited at Willowbrook Refferal unit, this is were they send children with special teachings.
The unit is having a new gym room, the electrical work was done by some contractor who i haven't met but did talk to about the work carried out by himself on the phone, all looked fine, gym comprised of it's own consumer unit split board:
2---16A mcb for 2 extractor fan's
3---6A mcb for 3 lighting

R.c.d 30ma

1----40A mcb for 1 shower
2----32A mcb for 2 ring circuits

all o.k so far, till i noticed he took a 16mm SWA cable from an isolater in the secound switch room supplying the consumer unit which had a lower incoming CSA than the SWA he took to the CU in the gym room. the incoming to the isolater was 10mm pyro cable.

Now when i questioned Mr Contractor on this he assured me that a 10mm pyro has a higher power and would comply with the outgoing 16mm SWA cable.

Im still not assured by his answer so im leaving this to all you sparkies to comment on.

all replies appreciated in advance......................................................

 

[Lectrician]

Standard 10mm Pyro is rated at 77amp clipped direct.

XLPE SWA 16mm is rated to 110amp clipped direct.

PVC SWA 16mm is rated to 89amp clipped direct.



Cable sizing doesn't just take into account current rating. It takes account of volt drop, and earth fault loop impedance.

As the new cable is LARGER, there is not alot to worry about - the 10mm Pyro should be protected against overcurrent anyway - probably by a 60amp device.

Why are you looking for problems?? Have you reason to dis-trust this contractor??

 

[sham]

can you point to me were you got these figures for the cable sizing for pyro, swa and xlpe as i was checking in the regs but couldn't find them.

if they are in the regs please tell me the page no' on BS7671....

 

[Spark123]

Appendix 4 contents on p202
Tables:
4D4 for 70 deg C armoured multicore
4E4 for 90 deg C armoured multicore
4J1 or 4J2 for the pyro

 

[kendor]

pyro as it doesn't have plastic insulation like the swa has it can therefore operate to higher temperatures so the current rating tends to be higher than the plastic insulated cables, the contractor was basing his comment on the general rule that you can go down one size if using pyro. This is not always the case though as stated above volt drop needs to be considered with long runs.

 

[ban-all-sheds]

pyro as it doesn't have plastic insulation like the swa has it can therefore operate to higher temperatures

If they can be tolerated in the environment where the cable is.

You won't win many friends if people can touch the sheath when it's running at 70°, let alone 105°......

 

[TraineeSpark]

When you say "special Teaching" do you mean kids with learning disabilities? If so, help the poor little mites as much as you can. Or do you mean like this is a Borstal? If so, let the bastards burn and do us all a favour.