Cables in parallel

[johnboy6083]

Ive just read the report , try this: http://www.google.co.uk/url?sa=t&rct=j&q=eca%2F%20era%20report%20on%20conductors&source=web&cd=1&ved=0CEsQFjAA&url=http%3A%2F%2Fwww.wiley.com%2Flegacy%2Fwileychi%2Feca_wiringregulations%2Fsupp%2FAppendix_16.pdf&ei=cqCuT9KFG4LU0QWzhai0CQ&usg=AFQjCNEm0O1r9ZSztXLNacYz8Fyv7PFnEQ

to summarize, the only cables that will not meet disconnection times using armour as CPC are: 120 and 400mm2 2 cores. These are rare cables to install anyway.
If by bad design, you find that your Zs values will not be met, then a CPC at least 1/4 of the pahse conductor can be used.

IMO, if your using very large cables, then they are either to feed DB;s or large machines.

If your feeding a DB in an envbiroment with little or no extraneous metal, then i would probably use an external full size CPC, in order to keep the size of my final circuits down in order to meet Zs values. In an environment where there is lots of extraneous metalwork, then i would probably be happy to use the armour as CPXC, providing the envromental conditions allowed.
If your feeding a large machine opr motor, then fruther manufacturers guidance would be used, and the use of an external CPC would probably be neccesary.
All of the large pumps i install, have external CPC's that are smaller than the phase conductors. But they also have lots of other SWA cables running in paralell. The distibution of fault currents cant be equal, or all of the cables would fry. On one job i fed a 160Kw motor with 150mm scpre, and it had a 25mm2 external CPC. the fuse size was 315A, and it was fed via a VSD.

 

[Silly Sausage]

Personally, I'm in the 'if you're going to run an additional CPC, run one big enough to carry out the function by itself' camp.

I suspect that's what a certain Chinese resident person will probably agree with.

 

[Darkwood]

Its clear with different bodies out there having differing views there wont be any clear resolve to this debate and in that case and until proven without doubt (on the acceptance of earthing to make up the difference of a armour that falls short) ill obviously have to ignore my teachings and go with the method that is known to be adequate; so matching the csa of the phase conductor is the method that takes the crown.

As i said though, its an swa size i dont use and its just for knowledge basis only, it makes the grey matter twitch and adds to my ever increasing understanding of my job even if this is still a debatable grey area.

 

[Engineer54]

I'll have to read this ERA report again. I speed read it last night, and it seems they were changing bits and Bob's to suit their measured values on a 7 metre test rig!! Not sure what they were up too, but a 7 metre test rig isn't going to relate too much, to a circuit measuring in the 10's of metres. According to this report only 2 SWA 2 core cables were found not suitable, where i would have said that all 2 core SWA cables over 95mm wouldn't comply. As i said i'll have to go through this report again...lol!!

I wouldn't agree at all, that the use of 120mm SWA cables are rare. 120mm SWA cables are a very common size on commercial and industrial installations, and commonly used for parallel runs replacing 300mm single cable. Probably less common mind, in 2 core configuration... lol!!

 

[Guest123]

I'll have to read this ERA report again.QUOTE]


I can e-mail you the reports from both camps if you'd like.

 

[Engineer54]

I'll have to read this ERA report again.QUOTE]


I can e-mail you the reports from both camps if you'd like.

That would be very useful Lenny thanks!! Always better to see both sides of the coin so to speak!! lol!!!

I take it you have the/my e-mail address i use with the forum??

 

[Guest123]

I take it you have the/my e-mail address i use with the forum??

I'll PM you.