9.5Kw Shower on-site guisde? 16mm Twin & cpc?

[ian65]

Hi every one,
I should know better but can’t get my head round this one and lost my notes from College.
On site guide is saying up to a 9.7Kw shower the cable CSA should be 16mm this seems rather high to me and impossible to work with.
I am fitting a 9.5Kw shower and looking at smaller CSA than 16 probe’s 10 but this will be for an assessment for a company and has to be correct can some one give me the formula for CSA, the fuse to be used are 40Amp and the total run is 11Meters from consumer unit to the shower.

Thanks Ian.

 

[JamesBrownLive]

As per Instructions with the shower a 40A fuse is to be used.

Thanks Ian.

As Pushrod has already stated, wouldn't you be better sticking to the regs and using a 45A fuse, rather than following what seems to be the wrong advice in the instructions included with the shower ?

Although the shower manufacturers are probably selling the product as a 9.7Kw unit when in actual fact it is much less
That is probably why they are advocating a 40A protective device. Either that or they are numpties.

 

[JUD]

As Pushrod has already stated, wouldn't you be better sticking to the regs and using a 45A fuse, rather than following what seems to be the wrong advice in the instructions included with the shower ?

Although the shower manufacturers are probably selling the product as a 9.7Kw unit when in actual fact it is much less
That is probably why they are advocating a 40A protective device. Either that or they are numpties.

Some manufacturers still use 240V instead of 230. The shower is probably rated at 9.5Kw at 240V. 9500 ÷ 240 = 39.6A.

 

[UKMeterman]

So what happens when the volts creep up to 253 or 255V?
42A, how will the fuse like that long term with many loading cycles?

 

[malcolmsanford]

To be honest the amount of time the shower will be under load I would imagine that it would cope quite happily with 2 extra amps. Also as the shower runs the load will also go down.

 

[JamesBrownLive]

So what happens when the volts creep up to 253 or 255V?
42A, how will the fuse like that long term with many loading cycles?

Well then the current drawn will actually go down, not up... 9.7Kw / 255v = 38.04A.

 

[Des 56]

James

The shower has a set resistance so the KW rating varies

Use 10 ohms an example
250 devided by 10 = 25 amps
240 " 10 = 24 amps
220 " 10 = 22 amps

Its more the K watt rating that is affected,the current goes up with more voltage

 

[JamesBrownLive]

James

The shower has a set resistance so the KW rating varies

Use 10 ohms an example
250 devided by 10 = 25 amps
240 " 10 = 24 amps
220 " 10 = 22 amps

Its more the K watt rating that is affected,the current goes up with more voltage

Doh, thanks for clearing that up. Obviosuly getting my Power Triangle and Ohm's law mixed up back to the classroom for me.

 

[pushrod]

The only theoretical constant is the resistance. Power, current and voltage are all variables. Increase the voltage and you will increase the current and the power. As already mentioned you can still find powers of appliances being calculated on the old 240v (P = V²/R) which would mean a smaller current was flowing. Also a 40A fuse should hold on 44A for an hour [ for an mcb as a guide, 1.12 x In should not trip within an hour and 1.45 x In should trip within an hour]. Personally though, on an assessment i would not want margins to be so close.

 

[telectrix]

6mm on a 40A more than adequate if clipped direct. never seen a so called 9.5kW shower pull more than 36A.

 

[lost-sole]

I would use 10mm clipped direct above loft insulation, although 6mm would be ok but 10mm is better if they upgrade the shower at a later date, minimum 45amp breaker or although the norm is to use 50amp. I used to work for a council refurb company and that setup was always used. however i have never seen one over draw 40amp breaker unless you ran it scolding hot for ages. One thing that was always over looked when sparks fitted 50amp breakers that the shower iso was only rated at 45amp. Just some points from my experience

 

[ian65]

Many thanks folks,
for all advice given i will now add a 50 Amp Isolator to the list i was thinking of doing that as well as the pull cord.

From the looks of it the shower isn't going to be put in quite yet so i have some time to play with until the full instal is complete. Am looking to get cables in place though ready for the go ahead.

Cheers every one Ian.

 

[ian65]

Just a passing thought,
I condemd the washing machine last week it took out the RCD and PAT tested it and it failed on Insulation and Earth leakage but they know got all new parts in the machine.

Ian.