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.