9.5 kw shower on 6mm ?

[jonthesparks]

just been to a job , saw that the shower 9.5 kw is on 6mm t&e the cable goes in the wall and under floor boards ,No insulation, to the board (A cable run of no more than 10 m) . I said downgrade the shower to 8.5 max. Is it really necessary ? never quite sure , its borderline to me .

 

[randym68]

lol i know trev but from what ive seen some electrician have been serious and you know some read this and are not as experienced/DIYers on here may miss read that lol... but i have looked and I've never found anything yet saying in regs that you cant do it...i just know its bad practice....anyone knows the actual regulation love to have it...just to tell this electrician i know he's wrong lol

 

[telectrix]

well getting 4 4mm cables into pull switch might cause a bit of swearing

 

[trev]

Just give em a haircut Tel
The sad thing is I've seen it done

 

[Engineer54]

randym68.... does anyone else wonder why they don't do 8mm , seems most would find it useful in domestic. especially showers and ovens/hobs.

8mm cables and wires are freely available all over South East Asia, this probably has more to do with European standard cable/wiring sizes than anything else!!

Absolutely nothing wrong with single point parallel wiring either. So long as the parallel wiring rules are adhered too, along with the connections at both ends being correctly made, i can't see what possible exception you can have with such an arrangement!!

If you opt for 2 X 4mm, (let's say clipped direct) that would give you a CCC of 72A!! lol!! 2 X 2.5mm would give you 54A!! Perhaps now you can start to see the advantages of parallel supplies and feeders. And that's before you start looking at VD and Zs value improvements....

 

[telectrix]

interesting point. 2 x 2.5mm has a greater csa than a single 6mm by 10A. i can only surmise that this is because the 2.5mm can dissipate heat more efficiently. therefore, for most showers, it would be feasible to use a 2.5mm parallel arrangement, rather than going up to 10mm ( ccc 64A ).

 

[Guitarist]

interesting point. 2 x 2.5mm has a greater csa than a single 6mm by 10A. i can only surmise that this is because the 2.5mm can dissipate heat more efficiently. therefore, for most showers, it would be feasible to use a 2.5mm parallel arrangement, rather than going up to 10mm ( ccc 64A ).

As Eng pointed out...

So long as the parallel wiring rules are adhered too, along with the connections at both ends being correctly made....
​

A fair few "electricians" have a job terminating one cable correctly, let alone two in parallel....

 

[somersetsparks]

I like the good engineers point, Its something we use regularily on the industrial side (may have something to do with the fact that 2 x175mm 4 cores are a bit easier to manoevre then a b*stard 400!)
On a side note many 6mm T+E shower installations on a 32A MCB or 30A fuse now do not comply as method 101 only rates the cable at 27A (over 4" of insulation in loft).

 

[nickblake]

cant belive there is 216 replies on this thread opps its now 217

 

[steveberry11]

also lets all remember we all use a nominal 230V to calculate Ampere, in reality most supplies are 240-249 V , which is 39.5A to 38.5 A, as Richard Burns says clamp it on start up when amps is highest, i have had 20 meters 2.5mm at 27A and no change in temperature, so 6mm will take at least 60A, make sure if cable goes in loft no insulation can be put over cable, and put a note in the consumer unit that must remain 40A cover your self. also do a Zs at the shower itself , i have had exactly same thing on a 5m run, so in theory passes but the Zs failed, so that means it had to be upgraded to 10mm.

does anyone else wonder why they don't do 8mm , seems most would find it useful in domestic. especially showers and ovens/hobs.

Is this for real

very worrying

 

[Guitarist]

Is this for real

very worrying

Are you saying that it's a bad idea to suggest to DIY'ers that "6mm will take at least 60A"?

 

[Engineer54]

I like the good engineers point, Its something we use regularily on the industrial side (may have something to do with the fact that 2 x175mm 4 cores are a bit easier to manoevre then a b*stard 400!)
On a side note many 6mm T+E shower installations on a 32A MCB or 30A fuse now do not comply as method 101 only rates the cable at 27A (over 4" of insulation in loft).

I'd be using 2 X 150mm cables in place of a single 400mm cable!! The easier install is just another benefit of using a parallel supply. As a cables CSA get's bigger, it is able to carry less current mm for mm in real terms. A parallel supply is not limited to just two cables either, ...you would probably have a pink fit and die in it if i tell you how many single core parallel i've used in main distribution supply runs!! lol!!

I'm sure you meant to say 185mm rather than the stated 175mm above?? lol!!

 

[randym68]

guitarist your right that wasn't my intention to suggest you should wire a 60A load through 6mm, i was trying to say and badly obviously, the safety factors mean 60A would be carried by 6mm and not over heat (depending on installation), however the REgs and engineer sense mean you should stick to 40A ish depending on installation method etc etc etc. as long as the MCB is 40A then should be fine, in the example at beguining, unless you get nuisance tripping.

as we electricians who have qualified in 2391 2382 know you have to calculate it out, and my Metrel meter is very kind and tells me if Zs complies with MCB rating, and I find in periodics ( now DEICR) its the Zs that fails more than current carrying capacity. especially if the Ze is up at .21-.30 ohms...

intresting point just to go of subject (i can here the groans) Connect engineer (dno = YEDL) says they disconnect at .31 ohms Ze, irrespective (i did mention TT but thats what he was told) !!!

 

[platty1005]

Ib = 41.3 A then In 45A so use a B45 mcb then It from Table 4D5 6mm Ref C = 47A So

Regs state Ib less than or = to In and In less than or = to It

Conclusion 6mm Ref C = 47A use a B45 Breaker and 9.5Kw shower at nominal current 41.3A everything OK

 

[telectrix]

that's fine, platty, until the insulation muppets arrive and reduce your ccc to 27A.

 

[somersetsparks]

I'd be using 2 X 150mm cables in place of a single 400mm cable!! The easier install is just another benefit of using a parallel supply. As a cables CSA get's bigger, it is able to carry less current mm for mm in real terms. A parallel supply is not limited to just two cables either, ...you would probably have a pink fit and die in it if i tell you how many single core parallel i've used in main distribution supply runs!! lol!!

I'm sure you meant to say 185mm rather than the stated 175mm above?? lol!!

The most I seen engineer is a meagre 3 630awa's per phase, and I thought that was a lot lol!