Paralleling conductors

[overskilled]

Just bouncing something off people here..

Got a job on, customer currently has a single phase 230v 16Amp commando socket he wants changed for a 32A ( Seemingly has a few machines in mind with a larger than 16A draw but below the full 32 that he's considering buying in...hasn't decided which yet tho...)
Its currently supplied via 1.5mm2 6491X singles in plastic conduit (checked the book 4D1A, Ref method B and its good for 17.5Amps) run is sub 10 metres, but a pain in the backside to alter (heavy immovable stuff in the way for starters)
conduit is 20mm, so no way I'm going to pull 4mm2 or 6mm2 singles down there...and because of obstructions..I can't change out the conduit for bigger nor run another piece of conduit..
Socket has to go where its going.

So my only option it seems....pull in another 1.5mm2 line and neutral and parallel them (for some unknown reason the CPC is 2.5mm2 (who knows why...I didn't install it whenever it was done)...which should give me 35Amps so more than enough to cover matters...be a royal pain to pull it in more than likely...but with some extensive blue language...it should be doable. I don't especially like the idea...but I can't see any other way around the problem....

Anyone got anything to add that I've missed here?

 

[Richard Burns]

The paralleling of the cables would be acceptable and should be OK for CCC.
However if you can get two 1.5mm² cables in there why can you not pull in two 4mm² cables to replace the existing 1.5mm²?
There should be more space to do that than pulling cables against each other to pull in another two 1.5mm².

 

[overskilled]

partly - I'm concerned about 4mm "hooking up" on a couple of hidden bends (had an issue with that recently on a diff job, end kept catching on the entry or the exist of the bend, fish tape will work its way through and the 1.5s should pull through given they are thinner than 4s and a lot more flexible too..decent amount of lubricant will help matters too

Ideally I'd have the 20 out and replaced with 25 or better yet SWA...but neither is an option in this case...

 

[Lucien Nunes]

I'd also go for pulling new full size cables in rather than doubling up. If you are having to push a tape round bends past existing cables, there's a chance of damage and the new cables will end up interwoven with the old, making them harder to pull. Consider using fine stranded cable for flexibility, and ferruling at the termination. If you use the old cables as the draw wire and make a gently tapered joint to the new, smoothly taped with tape lapped the right way there's no reason for them to catch. FWIW (and I know it's not a legitimate conduit loading) I once got IIRC 4x 4mm + 6x 1.5mm through 20mm conduit with two 90's and a couple of light sets.

4D1A, Ref method B and its good for 17.5Amps.... ..pull in another 1.5mm2 line and neutral and parallel them...which should give me 35Amps

What about Cg = 0.8? Takes it the other side of 32A...

 

[overskilled]

Fair point on the cg. ...knew I was missing something (looking at calcs and knowing it didn't make sense given 4 is rated at 32 and 2 X 1.5 was coming out at 35...hence posting this...knew there was a flaw in my cunning plan.....lol)

Hmm some rethinking required here methinks. ...

 

[overskilled]

I did actually consider pulling 4 mm2 flex down it and ferruling the ends but didn't seem "right" if you know what I mean. Might end up being the easiest option tbh....

 

[Spoon]

What about Cg = 0.8? Takes it the other side of 32A...

There is not grouping factor for a parallel circuit. 0.8 is for 2 circuits, a paralleled circuit is just 1 circuit.

 

[Hellmooth]

Surely tying 4mm to existing 1.5mm cables and pulling through the conduit is going to be easier than attempting to add another set of 1.5mm through, or am I missing something?

 

[Spoon]

Just out of interest. Also please keep this clean..... What is the best lubrication for pulling cables through? I have seen washing up liquid used. What can you use and what can't you use? (e.g. products that react with the PVC)

 

[Hellmooth]

Yellow 77

Ideal Yellow 77 Wire & Cable Pulling Lubricant 950ml | Electrical Conduit | Screwfix.com

 

[Lucien Nunes]

There is not grouping factor for a parallel circuit. 0.8 is for 2 circuits, a paralleled circuit is just 1 circuit.

By the definition of a circuit as being fed from one OCPD, yes it's one circuit. But for grouping, ten pairs of cables each carrying 1/10 of a 100A circuit, will heat each other up as much as ten 10A circuits. The ten separate circuits would need derating to 4.8A, why would the ten paralleled pairs still be able to carry 10A each?

 

[Spoon]

By the definition of a circuit as being fed from one OCPD, yes it's one circuit. But for grouping, ten pairs of cables each carrying 1/10 of a 100A circuit, will heat each other up as much as ten 10A circuits. The ten separate circuits would need derating to 4.8A, why would the ten paralleled pairs still be able to carry 10A each?

I like you. I has the exact same discussion on this forum with Eng54 about 2 to 3 years ago. The thread went on for a bit, as some may remember.
I was sure I was right in that you had to apply grouping factors. Eng54 and Rockingit said I didn't.
I was wrong.

 

[overskilled]

Any link to that thread?
Sounds interesting

 

[Spoon]

Any link to that thread?
Sounds interesting

You did ask......
http://www.electriciansforums.co.uk...-under-buildings-backed-up-200-amp-fuses.html

 

[ImpededLoop]

You did ask......
http://www.electriciansforums.co.uk...-under-buildings-backed-up-200-amp-fuses.html

That link opens at the last post of the thread that finishes with one of Eng54's trademark "lol"s - which actually made me lol!