9.5 kw shower on 6mm ?

[telectrix]

agreed^^^^^. i've known 9kW showers run happily on a 30A 3871, no tripping.

 

[Kenny.]

Disregard, my maths is $h**

 

[Guest55]

Errr have I said something!!!
all I was saying last week is I recommend 10mm on a 40a so no iinconvenience occurs to the user

Apart from the inconvienence to the customer that his 6mm cable will have to be ripped out , replaced with 10mm , and replaster his hallway, and will cost at least £200 , even though in many cases 6mm will do the job.
Very convienent lol.

 

[Moses]

Why do you say that?

 

[Fin170]

6? 10? 9 out of 10 times you'll open it up and it's all in 4mm anyway :shades_smile:

 

[Moses]

I think you are correct.

Just had a look at the BRB, graph for type-B 40A, page 249(haven't got round to getting the BGB)

At around 56A load current, the 40A Breaker will on average trip in 10,000 seconds!!!!

Which is around 2-hours and 47-minutes!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

so at 41.56A, it would probably trip in about two weeks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Even if you had more than one person in that shower, getting up to naughty but nice things,

The breaker would still hold.......................until they had finished...................................

with the shower.

 

[Moses]

Disregard, my maths is $h**

why do you say that?

 

[GLENNSPARK]

has the O/P even bothered to clamp this?....i think thats the first thing to do....arm yoursen with some info see...

 

[Geoffsd]

On the contrary, there is a very important point to be made here and all electricians must understand that while the nominal volts in UK are 230V, the actual volts are anywhere from 255V to 218V as already mentioned on in this thread.

For a 9500W shower for example, the currents are:
at 218V = 35.96A
at 230V = 37.93A
at 240V = 39.58A
at 252V = 41.56A

If you are consistently getting 252V at a property, and you install a 40A breaker for a 9.5Kw shower, then you will be called back to rectify the tripping shower, although you can try to explain to the customer as much as you like that the BRB states......, the nominal voltage is supposed to be ........ etc etc.

Yes, but the point is that the regulations are written allowing for this.
230 is only used as a sop to Europe.

When n.v. was reduced from 240 to 230 all the values we use were also derated ( x230/240 )
so that the results were the same.

If the voltage never went above 240V then we would have higher CCC values which we were allowed to use.


Do you know the csa of 100A fuse wire?

 

[Moses]

Yes, but the point is that the regulations are written allowing for this.
230 is only used as a sop to Europe.

When n.v. was reduced from 240 to 230 all the values we use were also derated ( x230/240 )
so that the results were the same.

If the voltage never went above 240V then we would have higher CCC values which we were allowed to use.


Do you know the csa of 100A fuse wire?

Yeah, the CSA of a 100A fuse is 3.142mm2.

 

[Spazz]

I have a rule where anything over 8KW I install a 10mm cable.

There are some new grants available in Wales recently where they are installing insulation free of charge for people on benefits, they even installing between floors and in stud walls for houses with energy rating of E or below.

I will not risk installing a 6mm cable or keeping a 6mm cable for a 9KW shower when next week they could get this grant and put insulation ontop of the cable changing the max current it will take.

If they insist that they wont allow me to put a 10mm cable in then they sign an advisory form stating that the cable must be upgraded if anything happens around the cable - i.e. insulation in loft or walls.


What ever happens cover your back!

 

[telectrix]

apparently you can train insulation fitters not to put their size nines through the ceiling. it's not such a big step forward to tell them " don't insulate over cables". ssimpless.or am i being naive, thinking that they are a step above monkeys?

 

[Spazz]

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!

 

[Moses]

I have a rule where anything over 8KW I install a 10mm cable.

There are some new grants available in Wales recently where they are installing insulation free of charge for people on benefits, they even installing between floors and in stud walls for houses with energy rating of E or below.

I will not risk installing a 6mm cable or keeping a 6mm cable for a 9KW shower when next week they could get this grant and put insulation ontop of the cable changing the max current it will take.

If they insist that they wont allow me to put a 10mm cable in then they sign an advisory form stating that the cable must be upgraded if anything happens around the cable - i.e. insulation in loft or walls.


What ever happens cover your back!

I quite agree with your line of reasoning.

But as explained earlier in this thread, the 6mm cable should be clipped to the walls in the loft above the insulation height along wooden batons to the point where it has to be dropped down to the isolator Switch.

save on material costs, protect the cable, but increase on labour.

 

[telectrix]

or........ get a proper insulation job done.....insulate between the roof rafters with kingspan..... no itchy poo, loft usable for storage, no frozen water pipes, no derating of cables, no downlights causing fire. no brainer.

 

[Spazz]

Agreed Moses, Im mainly talking about upgrading a shower which is the case 9/10 times and the cables are already inplace, moving the cable could mean extending it - even if your putting it ontop of the batons - but saying that these insulation installers just throw the insulation down and cover everything including cables - they dont check - these ones with the grants aim to do 5 a day to get the max income.

 

[Geoffsd]

Yeah, the CSA of a 100A fuse is 3.142mm2.

So - a 3.142mm² conductor can carry 100A 'for ever'.

Even with the maximum derating of 50% for thermal insulation a 3.142mm² conductor can carry 50A 'for ever'.

 

[Guitarist]

So - a 3.142mm² conductor can carry 100A 'for ever'.

Even with the maximum derating of 50% for thermal insulation a 3.142mm² conductor can carry 50A 'for ever'.

It may get a little hotter than we want tho

 

[Moses]

So - a 3.142mm² conductor can carry 100A 'for ever'.

Even with the maximum derating of 50% for thermal insulation a 3.142mm² conductor can carry 50A 'for ever'.

You are right.

But at 100A the fuse will be glowing in the dark, and that's why the fuse wire comes un-insulated. Any PVC insulation would be cinders, and a fair bit of voltdrop, contributing to the heat dissipation.

Cables have a CSA to allow for heat dissipation due to load current at Watts/Amp/meter so that the temp rise is not detrimental for the insulation.

 

[Geoffsd]

I have a rule where anything over 8KW I install a 10mm cable.

Why do you think it necessary to make up your own rules rather than use the regulations?

A shower stated by the manufacture to be 8.5kW (exaggeration aside) will be at 240V - 35.4A.
With the nominal voltage we use this is 7.8kW - 33.9A.

There are some new grants available in Wales recently where they are installing insulation free of charge for people on benefits, they even installing between floors and in stud walls for houses with energy rating of E or below.

I will not risk installing a 6mm cable or keeping a 6mm cable for a 9KW shower when next week they could get this grant and put insulation ontop of the cable changing the max current it will take.

If the customer agrees that is acceptable.

But ignorant insulation installers are not your responsibility.

I have long wondered about older buildings with the cabling in the wall cavities, then along comes a company to pump the cavity full of recycled paper and wool (even if treated). I'll bet they check.
Whose fault is that - the electrician who installed it in the 60s and 70s?

If they insist that they wont allow me to put a 10mm cable in then they sign an advisory form stating that the cable must be upgraded if anything happens around the cable - i.e. insulation in loft or walls.

Fair enough.

 

[Geoffsd]

It may get a little hotter than we want tho

That's true - but it is just over half the csa of 6mm² which some think cannot live with a 40A shower and mcb.

 

[Philpot]

I carry out small jobs for a charity that has about 5 buildings on the site and are all fed from a Transformer on a pole. The voltage in the day time was 252 ans 253 volts. I contacted Scottish power who put a monitor on the supply for two weeks. The result was that the voltage was found to go over the max during the night. The agreed to re-tap the transformer within 6 months( I think this is a statutory requirement). The voltage is now 242v during the day. There was no charge.
The pint is that high voltages mean, as has been demonstrated, cause higher currents and higher bills. Bit of a cheek really, don't you think. As for voltage stabilising equipment, this can safe considerable amounts of money but it's like PV it's not an instant saving due to the initial cost.
Philpot

 

[Spazz]

I only have it to protect me - If they say no then no it is.

All new shower circuits I do have 10mm as standard.

Its called looking after your customers (not saying you dont)

The average joe upgrades showers with no care to cable size.

I work it on 230v @ 8KW - 35A.

6mm T&E in insulation - 34A
6mm T&E Direct Clip - 47A

Cover your back - if the owner says no then you can only do what they want!
If its direct clip I push for 10mm in case they insulate - if they say no then it stays 6mm with an advice letter.

If they insulated the week after and you have a 9.5KW shower and the place burns down they could say that sparky Joe didn't tell me - you will be infront of the wigs.

Its no harm in advising and giving them an advice letter.

 

[Moses]

All had enough of this then?

 

[telectrix]

yeah. i'm going to use 4mm uninsulated , bare cable,as it will stand the 40 odd amps and there's no insulation to be frazzled. just have to space the conductors with porcelain bits.

 

[Guitarist]

Why do you think it necessary to make up your own rules rather than use the regulations?

I think he is using the regulations. It's the electricians who look at the regs and see what a cable can take "clipped direct", and either don't care, or don't understand other factors which can drastically reduce the CCC of a cable who are the problem here.

 

[GLENNSPARK]

I have a rule where anything over 8KW I install a 10mm cable.

There are some new grants available in Wales recently where they are installing insulation free of charge for people on benefits, they even installing between floors and in stud walls for houses with energy rating of E or below.

I will not risk installing a 6mm cable or keeping a 6mm cable for a 9KW shower when next week they could get this grant and put insulation ontop of the cable changing the max current it will take.

If they insist that they wont allow me to put a 10mm cable in then they sign an advisory form stating that the cable must be upgraded if anything happens around the cable - i.e. insulation in loft or walls.


What ever happens cover your back!

this is all very well...but 10mm cable run method 101=36A....method 102=47A....but its method 103 that could present probs....as its down to 32A....

 

[Darkwood]

At last! Someone else who undestands the shower ratings and the effects of Ohms Law when the voltage is reduced!

Except that I think you made an arithmetic error:

(9500 x 230) / 240 = 9100KW

Ib = 9500/240 = 39.6A
or
Ib = 9100/230 = 39.6A

So, fine on a 40A for non-continuous use (or leave a space on at least one side of the MCB)

Just reading through this thread and saw this and made me chuckle lol.... 9100Kw now thats one hot shower!!!! + the calcs are totally wrong too.
No offense pc electrics i know it just an error but funny with re' of the point of your post.

 

[Spazz]

where did u get that from - the table Im looking at 4.7 - run in insulation or conduit = 43A - direct clip = 63A

Based on 230v - 41A with a 9.5KW shower - fine for insulation and conduit - might be looking at wrong table but dont think so

 

[GLENNSPARK]

4d5...osg (green) p (150)..flat cable..

 

[GLENNSPARK]

look at 523.9 table 52.2 as well in the osg...p 141...

 

[Spazz]

I will look tomoz - I only got the BGB on me.

OSG in van and not going out at this time. Bed time for me instead of going to van

 

[GLENNSPARK]

its a derating factor table for cable in insulation for more than 50, 100, 200, 400 and >500 mm of its length...knocks hell out of CCC does insulation......it really cant be underestimated...

 

[Geoffsd]

At last! Someone else who undestands the shower ratings and the effects of Ohms Law when the voltage is reduced!

Except that I think you made an arithmetic error:

(9500 x 230) / 240 = 9100kW

Ib = 9500/240 = 39.6A
or
Ib = 9100/230 = 39.6A

So, fine on a 40A for non-continuous use (or leave a space on at least one side of the MCB)

I'm sorry but that's not how it works.

The resistance of the element is the only constant.
A 9500W shower @ 240V is as you say 39.6A

To find the 230V wattage it is necessary to find the resistance of the element which is 6.06Ω
At 230V 6.06Ω results in 8724W.

So 8724 / 230 = 37.9A

 

[Geoffsd]

........

 

[Darkwood]

240v	230v
7.5kW	6.9kW
8.5kW	7.8kW
9.0kW	8.2kW
9.5kW	8.7kW
9.8kW	9.0kW
10.8kW	9.9kW

Can i make something clear as many of you (not all i might add) are making errors in calc, if the rating for a shower is based on 240v, you cant just change the voltage and apply ohms law as the element is a fixed resistance so putting less voltage to it will change the showers Kw rating. You need to see what the shower info says as it may be classed as a 9.5kw at 240v (before voltage amendments came into reg's) so using table above this same shower will be 8.7kw if supplied with 230v.
Personally not knowing what the stated voltage is on the 9.5kw shower the O/P has been involved with and whether hes assumed its 230v or actual stated on the shower 230v you can't just magically change the voltage to 240v and apply ohms law, through out this thread ive seen this done by many members.... A little worrying i might add too:13:

 

[Darkwood]

Here's the calcs you need to be doing if converting...a 240v rated shower to 230v

9500/240 = 39.58A
This will mean the element resistance is :-
240v/39.58A = 6.06ohms

To convert this to a 230v supply the element resistance must remain the same thus:-

230v/6.06ohms = 37.95A Which gives a KW rating of:-
230v x 230v /6.060hms = 8.73Kw
alternate method;

230v x 37.95A = 8.73KW

Sorry Geoffd and moses just seen you've already shown this but at least with a few posts now showing it it might sink in - something that i would class as first year basics.

 

[PC Electrics]

Just reading through this thread and saw this and made me chuckle lol.... 9100Kw now thats one hot shower!!!! + the calcs are totally wrong too.
No offense pc electrics i know it just an error but funny with re' of the point of your post.

I'm sorry but that's not how it works.

The resistance of the element is the only constant.
A 9500W shower @ 240V is as you say 39.6A

To find the 230V wattage it is necessary to find the resistance of the element which is 6.06Ω
At 230V 6.06Ω results in 8724W.

So 8724 / 230 = 37.9A

Here's the calcs you need to be doing if converting...a 240v rated shower to 230v

9500/240 = 39.58A
This will mean the element resistance is :-
240v/39.58A = 6.06ohms

To convert this to a 230v supply the element resistance must remain the same thus:-

230v/6.06ohms = 37.95A Which gives a KW rating of:-
230v x 230v /6.060hms = 8.73Kw
alternate method;

230v x 37.95A = 8.73KW

Sorry Geoffd and moses just seen you've already shown this but at least with a few posts now showing it it might sink in - something that i would class as first year basics.

If this meant to be some kind of a "dig", then perhaps you should go back to page 3 and read posts 78 to 84, where I realised and accepted my mistake for all to see and in the spirit of this Forum (or so I thought) put it up for others to learn from.

For those who don't make mistakes, we know one thing for certain - not doing much work!

 

[Darkwood]

PE Electrics....dont take it personel others within the thread had done the same, and if you read a little closer i did say i know you made an error as i have read the whole thread, I mearly said it made me chuckle as it contained 2 big errors when the post was actually written in response as a correction to someone elses calc's. So apologies if it has offended, i make mistakes too and when i do i take em right on the chin and hold my hands up as you did but others were making similar errors and for whatever reason stop posting when moses and geoff threw in the corrections.
I been on here quite a while now as have you and i know who i consider competent and who i believe belong to the neon driver brigade of which i know your well capable and knowledgable about your job again i tried to write it with a tone of humour so as not to offend and the last post was written because no-one else had explained why you had to do the calcs shown so i explained why with respect to the element having to remain at contant resistance regardless of the voltage applied.

 

[SPARTYKUS]

On the contrary, there is a very important point to be made here and all electricians must understand that while the nominal volts in UK are 230V, the actual volts are anywhere from 255V to 218V as already mentioned on in this thread.

For a 9500W shower for example, the currents are:
at 218V = 35.96A
at 230V = 37.93A
at 240V = 39.58A
at 252V = 41.56A

If you are consistently getting 252V at a property, and you install a 40A breaker for a 9.5Kw shower, then you will be called back to rectify the tripping shower, although you can try to explain to the customer as much as you like that the BRB states......, the nominal voltage is supposed to be ........ etc etc.

Hi Moses,

as already mentioned it's very unlikely, I'm sure you are aware of the 1.13 multiplier for a type "B" MCB, it would run all week long (theoretically) around 45 Amps.

 

[Engineer54]

Hi Moses,

as already mentioned it's very unlikely, I'm sure you are aware of the 1.13 multiplier for a type "B" MCB, it would run all week long (theoretically) around 45 Amps.

Wow!! .....140 replies and climbing, to a simple question of, can a 9.5KW shower run on a 6mm cable?? lol!!!

 

[SPARTYKUS]

Wow!! .....140 replies and climbing, to a simple question of, can a 9.5KW shower run on a 6mm cable?? lol!!!

hmmm..... not all by me, and until this post you were the last say!!

 

[Engineer54]

hmmm..... not all by me, and until this post you were the last say!!

Maybe, but i only included your post, as this was pointed out by myself way, way back!! ...lol!! The thread seems to be going round in circles, the question was answered 4 pages ago!!! lol!!!

 

[Moses]

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!!!!

 

[SPARTYKUS]

Maybe, but i only included your post, as this was pointed out by myself way, way back!! ...lol!! The thread seems to be going round in circles, the question was answered 4 pages ago!!! lol!!!

Ahhhh ... sorry not read through ! Didn't realise was covering old ground. Funny thread agreed! :8:

 

[Geoffsd]

Likewise - apologies to PC. I only saw it when requoted.

Sorry - I missed the corrections which followed. There is a lot to read.

 

[telectrix]

how big a cable does this shower need?????

 

[Guest55]

^^^ 10mm , just in case.

 

[telectrix]

i thought wet string would comply.

 

[Knobhead]

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