new shower installation

[Spark123]

Providing the 6mm flat twin and earth cable is installed clipped direct, away from thermal insulation, away from other cables and in an ambient temperature not exceeding 30deg C is the cable rated at 47A. Take into consideration volt drop (OK for about 36m @ 35A) and the cable length not being too long for efli for the Ze (which is where Securesparks 19m limit comes from?).
If the above is compliant, hopefully you have an EIC from when the CU was installed, and as you say you are swopping the shower for one of the same rating as the original then you can swop the shower as a direct replacement without notification to LABC.

 

[sootys68]

ALWAYS ALLOW FOR MAXIMUM DIVERSITY

GOLDEN RULE

BELOW 32 6MM L DO

ABOVE AND BEYOND THEN 6 MM BE GONE.

BS 7671 CLEARLY STATE ALWAYS ALLOW FOR MAXIMUM DIVERSITY .
___________________________
lynda, moderator

please see forum rule 6

 

[Spark123]

PLEASE TURN OFF CAPS LOCK, IT IS CONSIDERED SHOUTING.

Why can't you use 6mm on a circuit over 32A? It is rated 47A max. Maximum demand or diversity?

 

[fattony]

Its a hard one, I think I read the current mcb is 45A, thats over rated for a 6mm, I dont have the figures in front of me but from memory 6mm can carry 38A depending on ambiant temp etc, personally I wouldn't be happy about installing a 40A breaker on a 6mm.

I'd be tempted to install a 32A MCB, correct me if Im wrong but the shower is only pulling maximum current when the temperature is set to the hottest? so it will only trip if you crank the heat up to the max?

Tricky one

 

[Spark123]

4D5A gives a flat 6mm twin+earth as 47A clipped direct, this is before correction.

 

[TopTrumper]

fattony,
our mate 123 is determined he is not ever ever ever going to use a 32mcb on a 6mm for a 8.5 shower

 

[Mikeyboy]

Once again , I thank you all for your very swift replies . Anyway I have decided to install my new shower . If I have any problems , I will let you know . Thanks again , for all of your input , Mike .

 

[Pensdown]

Its a hard one, I think I read the current mcb is 45A, thats over rated for a 6mm, I dont have the figures in front of me but from memory 6mm can carry 38A depending on ambiant temp etc, personally I wouldn't be happy about installing a 40A breaker on a 6mm.

I'd be tempted to install a 32A MCB, correct me if Im wrong but the shower is only pulling maximum current when the temperature is set to the hottest? so it will only trip if you crank the heat up to the max?

Tricky one

I can't understand why you see this a tricky problem. The purpose of the MCB is to protect the cable not the shower so if the cable including rating factors will carry 40+amps then why would you want to fit a 32amp breaker which may result in the shower tripping at full power?

 

[Spark123]

fattony,
our mate 123 is determined he is not ever ever ever going to use a 32mcb on a 6mm for a 8.5 shower

Eh? here we go around in circles again. The OP has a 45A MCB and providing the 6mm cable is installed correctly so the correction factors do not de-rate the cable below this then it is perfectly OK to have a 6mm cable on a 45A MCB.
What you say doesn't comply with the basic requirements for circuit design, i.e. the MCB is under-rated isn't it?

What size breaker do you think we should use for a 35A load?

i think we should use a 35 amp breaker, but seen as we generally only have 32 or 40 we have to decide for ourselves, ie, cable run, reference methods, correction factors and everything else that comes with it..

me personally wont put a 40amp breaker on a 6mm cable

Please explain why you do not feel it is OK to put a 40A MCB on a 6mm cable and why you feel it OK to put a 35A load on 6mm cable protected by a 32A MCB?

spark123
i know exactly what you are talking about, but the guy was asking about his " 6mm" cable
Using the design procedure you would have to pick the 40amp breaker but put it onto 10mm cable

[/quote]
Why? Which design procedure are you using? Providing the 6mm cable is installed correctly taking into account the correct correction factors are applied and do not de-rate the cable below 40A then a 40A MCB can be safely used.
As Securespark says, "..if you're gonna do it, do it right, right?"

 

[TopTrumper]

spark123
you have chosen the reference method, as method 1 for the 47amps.
you have chosen the least likely method for a shower cable.

 

[Spark123]

Yes,for the reason method 1 (clipped direct) is more than likely the most used domestic wiring method, why is it the least likely method for a shower?

 

[TopTrumper]

a bit hasty me saying the least likely there, what i meant to say, was it depends on installation (obviously)

 

[securespark]

PS, i forgot to mention before
I calculate my design current for a 6mm shower cable using reference method 4, as it usually ends up in trunking for a shower circuit....

the design current becomes 34 amps

What about the loft? Surely there is the likelihood of coverage on one side by insulation exceeding 500mm?

And why is the design current 34A?

 

[TopTrumper]

ok securespark
let me ask you this, a 9.5kw shower design current is 41 amps, would you run it on your 47amp rated 6mm cable?

 

[RMS]

Think he's going to need allot more infomation than this.
length of run, de-rating factors, reference method, ze etc