9.5 kw shower on 6mm ?

[Top Cat]

I'm just wondering how many of these manufactures stated KW ratings are actually achieved in the real world??

I posted a thread about a month ago where i accidentally put a temporary socket on a 6Amp RCBO. A 3Kw kettle was used all day long and it didn't trip. Someone said to put an Amp meter on it, i did and got 9.5 Amps so just shows that elements are not always what they apear to be!

 

[steveberry11]

What an insult to good electricians. A proper electrician will always follow the green book. Why have regs if you second guess them they are there for a reason. To protect you and the customer. In law your only defence is that you carried out your work to the current regulations at the time of installation. As the electricity at work regs state. This will form part of your EIC. I have not yet seen a EIC with a tick box with the wording how were cables sizes worked out GUESSED or CALCULATED perhaps they should it is not only about saving the customer money. Is it not our duty to ourselves and our customers to give them the best job possible and to the current regulations. If we do not do this are we no better than DIYers Perhaps it is a judgment call if you can't calculate cable sizes.

 

[telectrix]

all very well there. perhaps then the manufacturers of showers could then be made to calculate the KW ratings instead of guessing them, as i've yet to see 1 that draws the stated wattage.

 

[sedgy34]

A lot of shower manufacturers state a minimum cable and MCB size. All this has been said so many times before, yet still people are arguing about whether to work from "experience" or adhere to the regs! We know that everything has a safety margin built-in, but that's exactly what it's for, safety.
I think that the phrase "well, the last house didn't burn down", is not going to be much use if it all goes belly-up.

the scams would love this thread saying yep thats why we are here boys

 

[Guitarist]

And here we have the difference between a proper sparky and a regs jockey.

I think you have to be a bit careful with comments like that Dave. There are many times on here when sparkys who know the regs inside-out help the ones who claim to be "experienced".

 

[randym68]

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.

 

[Silly Sausage]

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

A pair of 4 mils in parallel

 

[telectrix]

we used to have the very thing 7/044 , till the foreign metric rubbish took over. 50A and still not warm.

 

[randym68]

oh archy nice thought but i have replaced many a 2x 4mm in parrallel, (and due to poor fitting really) load transfered over to one cable and melt down..... really don't like using paralleled , which i know is really a ring with one point....just seen too many issues, of one cable damaged or not good connection and transfer/share load over.

 

[trev]

He wasn't serious Randy

 

[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!

 

[sedgy34]

wow!! whos gonna last longer this thread or our forum dinosaurs? lol no insults intended the love on here is awesome

 

[steveberry11]

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

Don't forget all those correction factors that need to de applied to the tables you have refured to.

 

[wade88]

i think a lot can be said for a bucket with a few holes punched through hung on a pole huh.

 

[steveberry11]

i think a lot can be said for a bucket with a few holes punched through hung on a pole huh.

Z


What size bucket ( oh no here we go again)

 

[Engineer54]

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

Try 19 X 95mm per phase+N run Trefoil + N on tray for around 150m and more from TX to Main Switchboard, via Stand-by Genny changeover switchboard... There were 6 TX's supplying that building, all with similar numbers of supply parallel feeders...

TX's were mainly 127/220V, (Malcolm will recognise that voltage band instantly!! lol!!) with a couple of 220/380 TX's supplying the bigger equipment...

 

[platty1005]

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

First post says NO INSULATION so i was just answering the original question and stated that 6mm is ok for REf C

If REF method 101 then 16mm cable is just big enough but i would not like to wrestle it into a pull switch !!

 

[telectrix]

i totally agree with you. we design a circuit to comply under existing conditions. if these itchysnot installers don't know any better than to smother cables, then they should get fresh employment selling the big issue.

 

[sedgy34]

i totally agree with you. we design a circuit to comply under existing conditions. if these itchysnot installers don't know any better than to smother cables, then they should get fresh employment selling the big issue.

Tel, the insulation installers is monkey see monkey do they don't know about all the Calcs to do with cables etc they just fill the area with the stuff off the van and move on to the next job.
its us poor guys who have to think of all that derating factors etc

 

[Geordie Spark]

in his towel

Why would he have an MCB in a towel ?

 

[sedgy34]

Why would he have an MCB in a towel ?

you have some posts to catchup on fella

 

[Litttle Shonet]

Just or all the posts about insulation (itchy Snot, I think some of you call them). You can't future proof for every eventuallity. If you did, then you may as well put cabling in from the roof just in case customer wants PV later on.

 

[Guitarist]

Just or all the posts about insulation (itchy Snot, I think some of you call them). You can't future proof for every eventuallity. If you did, then you may as well put cabling in from the roof just in case customer wants PV later on.

Totally agree mate. If the loft has only 4" of insulation tho, it is very likely that at some point in the foreseeable future there will be some addition. I always take my oval conduit 6 inches above existing insulation for just such an eventuality

 

[Geordie Spark]

Totally agree mate. If the loft has only 4" of insulation tho, it is very likely that at some point in the foreseeable future there will be some addition. I always take my oval conduit 6 inches above existing insulation for just such an eventuality

Good thinkin' bonny lad .. are ye a Geordie by any chance?? ....... If yer not, divven't worry ... aahl make ye an honourary one for noo.

 

[stevothespark]

Havnt bothered to read the other pages so this may have been said. 6mm will do for a while, id never put a 6mm cable in for anythin over 8.5kw shower, simply because ive been to far too many homes where a 9.5kw has been on an 6mm and the cable is burnt out/switch etc. Over a period of time, the 6mm will begin to melt, usually from the women who spend an eternity in the shower ! 10mm everytime for showers over 8.5kw every time.

 

[Moses]

Tel, the insulation installers is monkey see monkey do they don't know about all the Calcs to do with cables etc they just fill the area with the stuff off the van and move on to the next job.
its us poor guys who have to think of all that derating factors etc

I think that we must recommend that all new circuits installed in lofts that have no loft insulation, should be installed, at least 300mm above the plasterboard, on the loft wall or along appropriate battens installed for the purpose.

This would circumvent the "monkeys".

 

[Geordie Spark]

I think that we must recommend that all new circuits installed in lofts that have no loft insulation, should be installed, at least 300mm above the plasterboard, on the loft wall or along appropriate battens installed for the purpose.

This would circumvent the "monkeys".

The good folks of Hartlepool knew how to deal with monkeys.

 

[Dan]

I'm just bumping some threads in the Electrical Forum, don't mind me while I do this, you don't have to respond to them. Although if they are still current topics, and you do wish to reply, you're welcome to. Keep the thread on-topic and make sure you stick to the forum rules though.

 

[Gnasher]

Only one answer to this. Carry out the full design process to determine the answer.

Just remember.

9.5 KW = 41A so the protective device must be 45A or 50A depending on CU. take into account the following down rating factors for starters.
Grouping factors
Insulation
Installation method.

6mm has never been big enough for 9.5 KW so can not be classed as does not comply with current regulations.
If it trips regularly there is an issue that must be addressed. The fact that it is only used for a short time is not the correct approach.
This is a C2 fault potentially dangerous.

 

[Megavolt]

6mm on a 32a Mcb all day long

Tin hat on