9.5 kw shower on 6mm ?

[Des 56]

Hello, I’m the member of parliament for East Dulwich. I can drone on for hours and hours about nothing in particular, in fact after a couple of houre I’ve usually forgotten what I started talking about. BUT I still keep droning on and on and on……… Er what, where was I, oh yes I remember…. Damn I can’t find my notes about what I was talking about……. Zzzzzzzzzzz

That has gotta be from my favourite of all time comedy Monty Pythons Flying Circus ?

 

[Guitarist]

Its been suggested in this thread, that if the shower is over 8KW they just go ahead and install a 10mm cable.( or even for a 9.5KW shower)I put it to you that its much "Greener" to install an 8.5KW shower on a 6mm cable.The company I worked for, only installed 8.5KW showers in Housing association properties.There must have been enough flow, as we never had any complaints.I think its much Greener for water usage and energy usage and in lower cost of materials(6mm cable instead of 10mm), to install a 8.5KW shower.( Besides its mighty difficult to terminate the 10mm in the isolator). + Austerity and all that??I think anything above 8.5KW should be banned or maybe taxed? on the grounds that it contributes towards Global Warming!!!!

Just installed a 7.5 Kw in my own bathroom on a 6mm cable. Flow is a little slow on a cold morning, but it doesn't use much water

 

[sedgy34]

i thought wet string would comply.

what about the bonding

 

[SPARTYKUS]

what about the bonding

Nah, that shower is exempt.

Its double insulated, honest

 

[Moses]

Just installed a 7.5 Kw in my own bathroom on a 6mm cable. Flow is a little slow on a cold morning, but it doesn't use much water

I'm sure you could have got away with a 4mm cable and a 32A CB.
Your 6mm cable is well over rated!!!!!

 

[Guitarist]

I'm sure you could have got away with a 4mm cable and a 32A CB.
Your 6mm cable is well over rated!!!!!

Don't tell the DIY'ers that mate. They will think you are serious and not factor in all the derating factors.

 

[mojowaky]

If you did go ahead with the 6mm instead of 10mm, then I would recommend you use a 100ma or 300ma RCD to protect against fire risks of the cable breaking down, as you get fire/thermal protection on cabling with a 300ma RCD. I doubt the shower will ever be on max temp for long enough to draw the full 9.5kw anyways (real life example of diversity), 6mm is likely to be enough.

 

[PigletJohn]

Oops, I see Geoffsd has already covered it on page 7.

That'll teach me not to click on links in emails without checking.:dunce2:

 

[Darkwood]

If you did go ahead with the 6mm instead of 10mm, then I would recommend you use a 100ma or 300ma RCD to protect against fire risks of the cable breaking down, as you get fire/thermal protection on cabling with a 300ma RCD. I doubt the shower will ever be on max temp for long enough to draw the full 9.5kw anyways (real life example of diversity), 6mm is likely to be enough.

Not sure where your coming from with this post but the shower will already be required to have 30mA rcd protection, the standard shower is a instantaneous heater and temp' is regulated by adjusting flow rate so if shower is on its drawing 9.5Kw irrespective of the duration you have it on for.

 

[Guest55]

Future note to new forum users :

Please let this thread die , at 8 pages long there is little of use to add that hasnt been argued to death.
;-)

 

[Dave 85]

Convince them they have to upgarde the cable or downgrade the shower or the house will burn down. Quote them a fortune. Then tell them they need a rewire...else the house will burn down. Quote them a fortune.

Robbing people blind is fine as long as you convince yourself its for their own safety......

 

[trev]

That's going to look great on open forum isn't it
People have enough trouble trusting tradesmen without nonsense like that being in public view

 

[Dave 85]

I feel that if you tell them and put it in writing then your covered - the owner said no to bigger cable and they knew if they where going to have it insulated then the cable needs upgrading. Its on their back then if the place burns down - you have noted that no insulation in place and action to be taken and they ignored your advice!

Have you ever tried running 40 amps down a 6mm T&E and then dropping a sheet of fiber glass on it? (or getting a mouse to) Does the cable catch fire when you do this?

Why dont you make them sign an advisory form stating that if someone puts a petrol bomb through their letter box and the house burns down, that you offered to weld shut their letter box but they refused. Just to cover yer back like....

 

[nickblake]

Convince them they have to upgarde the cable or downgrade the shower or the house will burn down. Quote them a fortune. Then tell them they need a rewire...else the house will burn down. Quote them a fortune.

Robbing people blind is fine as long as you convince yourself its for their own safety......

Jesus you'll end up on rouge traders with an answer like that , not really acceptable

 

[trev]

My point exactly Nick

 

[Dave 85]

That's going to look great on open forum isn't it
People have enough trouble trusting tradesmen without nonsense like that being in public view

Come on Trev, you know I'm only messing about. Just annoys me people advising clients to fix things that arn't broken.

 

[trev]

Dave you may well be messing about but put yourself in a potential customer's position. A lot of people are nervous enough about tradesmen ripping them off and we get plenty coming on here looking for advice.

 

[trev]

I agree that there's an over reaction to fixing things that aint broken but you can't tell people's inflection from what they type mate.

 

[Guest123]

Lets not get silly now chaps, remember, potential customers could also be reading this thread........:wink5:

 

[telectrix]

agreed . after all, we're electricians, not plumbers.

 

[somersetsparks]

Just to add my tuppence worth,
I have seen many, many 8kw and above showers wired in 2.5mm flex from the isolator to the actual shower unit in my time testing, none of which showed any signs of damage, poor terminals and terminations cause many more,
I think in an ideal world there should be a 'domestic shower diversity' added to the regs, it irritates be to give a code 6mm supplying showers in houses, in fact I often give it a code 3 rather then 2 if there is no heat damage.

 

[Guest55]

Just to add my tuppence worth,
I have seen many, many 8kw and above showers wired in 2.5mm flex from the isolator to the actual shower unit in my time testing, none of which showed any signs of damage, poor terminals and terminations cause many more,
I think in an ideal world there should be a 'domestic shower diversity' added to the regs, it irritates be to give a code 6mm supplying showers in houses, in fact I often give it a code 3 rather then 2 if there is no heat damage.

Dont understand why you would code it at all ?
On what grounds ? for what rating of shower is 6mm unacceptable ?

 

[sedgy34]

Thread closed!!!!!!

 

[somersetsparks]

Thread closed!!!!!!

Nearly fooled me!
Biff55, I meant when they are on 40MCB's with referencve method 101 or A (or the dreaded 103... arhh!)

 

[Paul P]

Agree with robd , as a fixed load , 9.5kw @ 230v pulls 41.3A
i wouldnt replace cable for an extra 1A for a few mins.

As a shower is a fixed restance i think you will find it rated at 9.5kw @ 240v so only 39.58A

At 230v it would be a 8.7KW shower so only 37.9A

 

[steveberry11]

If you design your circuits correctly you must be aware that.
As a 9.5KW shower draws 41.3A you are unable to use a 40A MCB You need to use the next size up. This would be a 45A
it is correct that the tabulated current carrying capacity of a 6mm T&E cable is 46A this is the value prior to any correction factors being taken to account. I would suggest that the there are multiple cables exiting the DB at the same place so the grouping factor will reduce the cable rating below 41.3A without taking into account any other factors.
It is not acceptable to assume that no harm will be caused to the cable as the shower will only be on for a short while or the loading is only 1A over the 40A MCB rating.
When the electrical installation certificate is issued you are sating that the installation complys with BS 7671 and is a legal document in the event of future problems.
I would suggest if this size shower is to be installed a 10mm cable minimum cable should be used. Pay now or pay later.

 

[Djlelectrical]

Just make sure the MCB is sufficiant for the cable, Either that or upgrade to 10mm cable

 

[sedgy34]

If you design your circuits correctly you must be aware that.
As a 9.5KW shower draws 41.3A you are unable to use a 40A MCB You need to use the next size up. This would be a 45A
it is correct that the tabulated current carrying capacity of a 6mm T&E cable is 46A this is the value prior to any correction factors being taken to account. I would suggest that the there are multiple cables exiting the DB at the same place so the grouping factor will reduce the cable rating below 41.3A without taking into account any other factors.
It is not acceptable to assume that no harm will be caused to the cable as the shower will only be on for a short while or the loading is only 1A over the 40A MCB rating.
When the electrical installation certificate is issued you are sating that the installation complys with BS 7671 and is a legal document in the event of future problems.
I would suggest if this size shower is to be installed a 10mm cable minimum cable should be used. Pay now or pay later.

Welcome steve
what scam do you work for

 

[steveberry11]

How do you know the calculated cable capacity and suitable MCB rating without calculations, you also need to take into account loop values prior to changing MCB's

 

[Old School1]

Good Stuff

 

[Guest55]

If you design your circuits correctly you must be aware that.
As a 9.5KW shower draws 41.3A you are unable to use a 40A MCB You need to use the next size up. This would be a 45A
it is correct that the tabulated current carrying capacity of a 6mm T&E cable is 46A this is the value prior to any correction factors being taken to account. I would suggest that the there are multiple cables exiting the DB at the same place so the grouping factor will reduce the cable rating below 41.3A without taking into account any other factors.
It is not acceptable to assume that no harm will be caused to the cable as the shower will only be on for a short while or the loading is only 1A over the 40A MCB rating.
When the electrical installation certificate is issued you are sating that the installation complys with BS 7671 and is a legal document in the event of future problems.
I would suggest if this size shower is to be installed a 10mm cable minimum cable should be used. Pay now or pay later.

Youre correct of course but your example is out of context to the original post.
The issue that was debated at the start is regarding utilizing an existing cable so as to reduce cost / inconvienience to the customer in having a bigger cable installed.
Its a judgement call that each person will assess differently , but in my experience a 9.5kw shower will run off 6mm with absolutley no problems for years , regardless of any calcs you want to throw at it.

 

[gaulty]

Youre correct of course but your example is out of context to the original post.
The issue that was debated at the start is regarding utilizing an existing cable so as to reduce cost / inconvienience to the customer in having a bigger cable installed.
Its a judgement call that each person will assess differently , but in my experience a 9.5kw shower will run off 6mm with absolutley no problems for years , regardless of any calcs you want to throw at it.

His example is not out of context. He's just shown the calculation showing that 6mm is not big enough! The MCB is not even big enough to take the load of the shower regardless what a clamp meter shows.

Don't take this the wrong way but "in my experience" will not stand up in court. Also how would u fill out the test sheet - "comments on installation- 'I know the calculations state a 40amp mcb is not suitable for a 9.5kw shower along with using 6mm t+e but in my experience it SHOULD be fine'

That's rediculas THERE IS NO GREY AREA

40A mcb + 6mm cable is unsuitable for 9.5kw shower according to the 17th edition IEE wiring regulations regardless of personal opinion, that is fact, law, gospel.

You have two options down size the shower to suit the circuit or upgrade the circuit to suit the shower.

 

[sparc]

Just done new CU installations on a property with three showers - two 9.5 one 8.5. They're all on 4mm on 32A breakers. Asked owner about trips but never appears to have happened. Feed water temperature to the shower is a key factor in power drawn - which is why clamping a shower in summer doesn't tell you anything. I think in the case of this property the cold feeds to all three showers travel through a lot of internal plumbing, so water never really that cold.

 

[nickblake]

One of the biggest problems is what happens after youve installed your shower you do all the calculations select the correct cable then along comes the home improvement energy saving bods and sticks 300mm of insulation right over the top of it , when you look at the de rating factors of cable then for showers we should be installing them in 16mm just in case they are covered in insulation in the future

 

[steveberry11]

Quite right when replacing a shower the electrician should make a judgment on the existing installation. If the cable is not big enough to feed the new load the customer should be informed, what is required to comply with BS7671. It is not a case of it will do or I have never had a problem before I have known these showers run on a 4mm cable with no problems. It is your responsibility to comply with the green book.
It is not acceptable to pass the responsibility to the customer by asking them to sign a piece of paper to cover you. The buck stops with you. As they are hiring you as a skilled and informed person.
The loading of a shower is not dependent upon the water temperature. The only effect this will have if any is the is the amount of time the element is heating this will have a negligible effect.

 

[mickys86]

Future note to new forum users :

Please let this thread die , at 8 pages long there is little of use to add that hasnt been argued to death.
;-)

Maybe you should've aimed this post at the regular posters??

 

[sparc]

One of the biggest problems is what happens after youve installed your shower you do all the calculations select the correct cable then along comes the home improvement energy saving bods and sticks 300mm of insulation right over the top of it , when you look at the de rating factors of cable then for showers we should be installing them in 16mm just in case they are covered in insulation in the future

That makes sense, Nick, but where do you draw the line? If you have to future-proof your installation you'd need to make worse case scenarios assumptions for all your circuit derating calcs - not just for showers.

 

[Guest55]

His example is not out of context. He's just shown the calculation showing that 6mm is not big enough! The MCB is not even big enough to take the load of the shower regardless what a clamp meter shows.

The mcb is to protect the cable not the load , which it does.

Don't take this the wrong way but "in my experience" will not stand up in court. Also how would u fill out the test sheet - "comments on installation- 'I know the calculations state a 40amp mcb is not suitable for a 9.5kw shower along with using 6mm t+e but in my experience it SHOULD be fine'

Court ? Who's going to court ? Has anyone ever ended up in court from connecting a 9.5kw shower to a 6mm cable ?
Stop being a drama queen.

That's rediculas THERE IS NO GREY AREA

Ridiculous even ?

40A mcb + 6mm cable is unsuitable for 9.5kw shower according to the 17th edition IEE wiring regulations regardless of personal opinion, that is fact, law, gospel.

Bs7671 isnt law , that is fact.

You have two options down size the shower to suit the circuit or upgrade the circuit to suit the shower.

I was trying to keep the debate polite and reasonable before all the pedantic know-alls all jumped in.
Get your facts straight next time.

 

[steveberry11]

Correct BS7671 is not law. However the Electricity at work regulations are and it refures to BS7671 as a standard so in a court anybody being prosecuted will have to prove compliance. This applies to any electrical work undertaken not just showers. The MCB is to protect the cable just as the rating factors are used to down rate the current carrying capacitys of the cable. I fail to see how good electrical theory can be classed as pedantic.

 

[sedgy34]

I was trying to keep the debate polite and reasonable before all the pedantic know-alls all jumped in.
Get your facts straight next time.

so now the boxing gloves are out!!!

 

[wade88]

Oooo brilliant i've just sat down for my lunch i definitely think ill be staying to watch this little firework display unfold. How exciting, yet ANOTHER feeble display of bickery.

I would have thought it was a fairly straight forward answer however? Stick with what the regs recommend - and you can do no wrong. Is that not the basis on which we as electricians design and guide our circuits around to adhere to safe and proper practice? Or have i missed something where personal opinion counts for more than the governing body by which we all follow. But i don't know.... that's just my opinion. Am i allowed to say that or do i have to note that as a departure :stuart:

 

[Guitarist]

I am still amazed at how many people think that British electric showers are a variable load. 8.5kw is 8.5kw, regardless of anything (except variations in supply voltage ofc). If you select the "economy mode", which tbh nobody ever does, then it will be a lower fixed load, but still fixed....

 

[Sherwoods]

The cable size must be suitable for the load, no matter what overcurrent protection is provided. No reference method has been mentioned, but if it is "A" then 6mm is rated at 32A, method 100 rated at 34A, and 101 would be only 27A.
A 9.5 kW shower would draw 41.3A.
I have seen a few cases where the shower isolator is starting to disintegrate due to the high load and a situation where the contact resistance continues to increase. This, along with the inadequate cable current capacity is a fire risk. The conclusion must be that the shower in the quoted case must be rewired or the shower replaced with the correct rating.
The overcurrent protection should match the load but not exceed the cable current rating.

 

[Guitarist]

Just to add my tuppence worth,
I have seen many, many 8kw and above showers wired in 2.5mm flex from the isolator to the actual shower unit in my time testing, none of which showed any signs of damage, poor terminals and terminations cause many more,
I think in an ideal world there should be a 'domestic shower diversity' added to the regs, it irritates be to give a code 6mm supplying showers in houses, in fact I often give it a code 3 rather then 2 if there is no heat damage.

I hope you are not condoning 8kw showers being fed with 2.5mm cable.

 

[sedgy34]

i cant be bothered to read through them 10 pages but has anyone thought what the manufacturer wants to keep the warranty in place normally correct fuse rating to the bs7671 and an rcd in place "just my 2penny worth"

 

[Guitarist]

i cant be bothered to read through them 10 pages but has anyone thought what the manufacturer wants to keep the warranty in place normally correct fuse rating to the bs7671 and an rcd in place "just my 2penny worth"

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.

 

[telectrix]

when we look at it, so a 6mm cable is installed method C. it is perfect for the situation at time of installation. OK, so in the future a muppet might cover it in itchy snot, thus derating it's CCC. but, in the future rats/mice may infest the loft, so do we install SWA or cable in steel conduit? client may, in the future, get a plumber to install a 15kW shower, do we allow for that?

 

[Engineer54]

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

 

[telectrix]

exactly.

 

[Dave 85]

Youre correct of course but your example is out of context to the original post.
The issue that was debated at the start is regarding utilizing an existing cable so as to reduce cost / inconvienience to the customer in having a bigger cable installed.
Its a judgement call that each person will assess differently , but in my experience a 9.5kw shower will run off 6mm with absolutley no problems for years , regardless of any calcs you want to throw at it.

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