cable size on a shower Ask questions and find answers to many subjects relating to electrics and electrical work

[stanley]

hi all

how many people have seen 16 mm cable used on a shower, most people suggest that 10mm is suitable for any shower that is above 8kw, with 6mm for those below .
however the regs state differently !!!
i have a 10500 to fit the regs state 16mm with a 50mA rcbo....bloody ell

diverserty is a strange thing when a 10500 cooker due to diversity can go on 6mm.
there is too many strange areas.

does any one have any suggestions on what they have done... regs or not

[adem]

PLEASE BE AWARE THAT INSTALLING A NEW SHOWER CIRCUIT NEEDS CERTIFICATION UNDER PART P OF THE BUILDING REGULATIONS. FAILURE TO COMPLY CAN LEAD TO PROSECUTION AND RENDER YOUR HOUSE INSURANCE INVALID: DIYDOCTOR

may i ask where in bs7671 does it state a that a 16mm cable is needed for a 10.5 kw shower i woul d use following to caculate cable size
1. Determine the value of I B = Design Current.

IB = P
V

2. Select IN = Nominal current setting of the protective device (fuse, breaker etc.).

3. Calculate IZ = _______IN________
Ca x Ct x Cg x Ci

Ca – Factor for ambient temperature (4C1 + 4C2 p 219)
Ct = Operating temperature of conductor (Bs 3036 x 0.725)
Cg = Factor for grouping (4B1 – 4B3 p217)
Ci = Factor for thermal insulation


4. After calculating Iz select a cable from 4D1A – 4LB4 p220

5. Calculate volt drop (max. permissible vd = 4%, 9.2 for 230V)

Vd = L x Ib x mV/A/m
1000

L = Length of run
Ib = Design Current
mV/A/m = 4D1A – 4L4B

6. Establish tabulated maximum permissible value of ZS from tables 41B1, 41B2, 41C, 41D – p46

7. Calculate ZS

ZS = Ze + (R1 + R2 x L x t)

R1 + R2 = On site guide 9A P158
L = Length of run
T = On site 9B, 9C p159

8. Calculate the maximum earth fault current.

If = Uo
Zs

If = Fault current
Uo = Nominal voltage
Zs = Actual Zs value

9. Check disconnection time of protective device ( Appendix 3 p194-201)

10. Calculate minimum size of cpc.
_____
S = √ I2 t S = Minimum size of cpc
K I2 = Max. earth fault current
T = Disconnection time
K = Factor for resistivity and temperature (54B – 54E p115)
hope this helps :D

[andyman]

PLEASE BE AWARE THAT INSTALLING A NEW SHOWER CIRCUIT NEEDS CERTIFICATION UNDER PART P OF THE BUILDING REGULATIONS. FAILURE TO COMPLY CAN LEAD TO PROSECUTION AND RENDER YOUR HOUSE INSURANCE INVALID: DIYDOCTOR


hi mate.its just so i am doing my 16th eddition now,the ampage used by your 10500 shower is aprox. 45.7A(hense the 50A breaker). the cable you can use to carry the Amps (if clipped direct to the wall on its own and not running threw insulation in your loft) would be 10mm as it can carry 65A at 70 degrees c.you also need to know the length of the cable run to calculate the voltage drop over the entire circuit.you need to find out the Ze from your electric supplier and calculate the correct type of breaker for overcurrent protection.then if you have not had enough yet you must provide suplimentary bonding(eart it to your lighting circuit as well as the shower circuit. hope this helps anything else just pm me and i will try to help

[stanley]

hi
yes i agree but i would assume method 3 would be more likly unless it was really obvious it was all clipped direct.
it is close with the amps page 222 table 4d2a 10500 divided with 230 v gives us 45.6A, bloody close.....i initialy got the figures from this site as it shows on their table 10500kw on 16mm.

i have gone with a rcbo 50 amp with 10mm with supplementary bonding.

[adem]

16th has been in since 1992 or bs7671 as we call it the trade c&g2400 sparky :P

[Gaz]

to be on the safe side use 10mm but put it thru a 40A breaker in the consumer unit, the shower will only pull high amps when set to scolding hot and in my experience this never happens. Then your well covered for correction factors etc.

[thedoctor]

PLEASE BE AWARE THAT INSTALLING A NEW SHOWER CIRCUIT NEEDS CERTIFICATION UNDER PART P OF THE BUILDING REGULATIONS. FAILURE TO COMPLY CAN LEAD TO PROSECUTION AND RENDER YOUR HOUSE INSURANCE INVALID: DIYDOCTOR

[thedoctor]

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