Whats the biggest shower I can fit please?

[scotster]

I have a 45A breaker at the CU and 6mm2 cable running around 18m. The 18m is the total run length to the unit. Obviously there is a DP 45A switch in the circuit.

I have read on one table (http://www.tlc-direct.co.uk/Technical/DataSheets/Sadia/Carousel.pdf ) - page 9 I can use up to a 10.8 Kw

But in I have also read in a DIY Guide that "45A feeds up to 8KW". Maybe they were playing it safe as they did not state a cable length?

Any guidelines please? I would like to fit at least a 9.5KW but of course dont want to risk burning down the house.

 

[scotster]

Cable is not chased into wall at any point but runs through stud walls.... I think that may make a difference.

 

[ColJack]

clipped direct.. 6mm² can take 47A.. ( table 4D5A regs.. )

47 x 230 = 10810W... or 10.8kW..

if it's in insulation at any point along it's route then this needs to be de-rated

that doesn't sound right to me though.. I was told that anything over 9kW should be put on 10mm² cable...

 

[scotster]

Just found this post : http://www.screwfix.com/talk/thread.jspa?threadID=4677&messageID=46161.

Bloomin' 'eck. What a debate....

'Safe' opinion appears to be 10mm for 9.5 but my question is will 6mm take it and be within regs? No one seems to give a reasonably straight answer.

I understand that each case is different but within reasonable tolerances I should be able to say '9.5KW with 6mm and 45 A will be fine'. Or no - regs say 9.5 Kw is 10mm only.

 

[ColJack]

unfortunately the regs is not exactly black and white ( watch that comment start a ruckus... )

it gives you the info and tells you what to do with it, but most people have their own interpretation of it..

and on a strictly legal note..

the regs are not statutory.. you don't have to by law adhere to them..

doing so does however ensure compiance with another statutory document

 

[Softus]

The manufacturer's figure of 10.8kW is likely to be rated at 240V, but you need to verify this. At that voltage the load will draw 45A, but what you're not understanding is that there is a process used to derive the cable gauge, not a handy table that you can just use to look it up.

No one seems to give a reasonably straight answer.

Since PVC sheathed 6mm² T&E cable in conduit in thermal insulation can only [safely] carry 32A, you need to use 10mm² cable. And even this could be bordering on unsafe if you have a section of cable fully enclosed

If the shower is rated at 230V then using 6mm² cable is even less safe.

Is that straight enough?

 

[scotster]

Ta.

Just looked at the shower that I am replacing - 10.5KW .

Will probably safe and put in a weedy 8Kw

 

[Softus]

An 8kW shower (if rated at 240V), when at full power, will draw more than 33A.

Do you know what surrounds your 6mm² cable, over the entire 18m of its length?

 

[John_D]

16th regs part 110-04
The regulations are non-statutory regulations. they may, however , be used in a court of law in evidence to claim compliance with a statutory requirement. The relevant statutory provisions are listed in Appendix 2...

resting against one wall of an insulated space
Appropriate reference method = 15 so look at table 4D5A
according to table 4D5A reference clipped method 47A voltage drop 7.3mV/A/m
but resting in insulated wall 35A

but if it's fully buried in insulation material
referring to table 52A
50mm length insulated derate by 0.89
100mm ... 0.81
200mm ... 0.68
400mm ... 0.55


0.073x18x9500 = 12.483 volt drop
max allowable voltage drop 4% 230x0.04 = 9.2 volts
YOU CANNOT use 18 metres of 6mm cable for 9KW5 as the voltage drop is too high the maximum is 7KW
0.044x18x9500=7.5 volt drop
YOU CAN USE 18 metres of 10mm cable for 9KW5 shower as voltage drop is acceptable and cable rating is 47A in resting against one surface of an insulated space can be up to 11A

pvc cable must not be heated above 70C as the insulation melts, this is the basis of these tables

all defined if you know how to decode regulations
John

 

[ColJack]

see this is what i'm talking about...

at no point does he mention conduit or thermal insulation.. the only info given is that it runs in a partition wall.. at least for part of it..

I took this a reference method 1 clipped direct since there should be plenty of space

and why do we not apply diversity to showers like we do cookers.?

you only use it for 10-30 mins a day so even if it does get a little warm in use then it has plenty of time to cool down.. it's not like it's constantly overloaded for hours at a time...

normally I would recomend 10mm² for anything over 9kW anyway, i'm just curious..

 

[dingbat]

you only use it for 10-30 mins a day.

Unless there are women involved. The daft bird in the top flat where we were working last week took an hour-long shower every morning. (Almost an hour and a half on Tuesday, when she managed to flood the first and ground floor landings!)

 

[John_D]

All partition cavity walls are filled with insulation now as part of L1 building regs so I always assume current standards. To quote a different standard for a lower quality building situation is risking legal liability

 

[ColJack]

0.073x18x9500 = 12.483 volt drop

maths a little rusty today?

7.3mV/A/m is 0.0073V/A/m not 0.073V/A/m

and 9500 is watts not amps..

and the answer you get is actually 12483 volts drop since you already put the mV into V...

0.0073 x 18 x 39.58 ( for 9.5kW@240v) = 5.2V drop...

 

[Softus]

0.073x18x9500 = 12.483 volt drop

max allowable voltage drop 4% 230x0.04 = 9.2 volts

Er, 0.0073V/Am x 18m x 45A = 5.9V - well within 4%.

and why do we not apply diversity to showers like we do cookers.?

A shower, like an IH element, is a fixed single load. A cooker isn't.

you only use it for 10-30 mins a day so even if it does get a little warm in use then it has plenty of time to cool down.. it's not like it's constantly overloaded for hours at a time.

The effects of overheating PVC are cumulative, so it's as unsafe to overheat in small doses over a long period as it is to overheat a lot for a short period.

 

[davy_owen_88]

and why do we not apply diversity to showers like we do cookers.?

Because unlike cookers, showers draw their full load for the entire time they are switched on. Cookers on the other hand cycle on and off so at any one time there may be no elements on, or just 1 etc...

But i agree with some of your points. For normal people showers are used for a relatively short period of time so the negative effects on the insulation will be minimal compared to a circuit that is constantly overloaded.