new shower installation

[Mikeyboy]

My old shower , has unfortunately died . Beyond any form of economic repair . I have bought a new 8.5 kw. unit . The original unit was fed by a 6mm. twin and earth supply , via a ceiling mounted pull-switch , at bathroom ceiling level . My query is this , will it be , within current regs , acceptable to simply remove the old unit , and fit the new shower to the the existing wiring ?

 

[Spark123]

I doubt it, 6mm will be about on its limit at 35A depending how it's installed. As it sounds like your new shower is bigger than the old one and requires changes to the circuit to be made it becomes notifiable to LABC under part p of the building regs. Your new shower will likely require a 10mm cable and a 40A fuse, this depends again on how the cable is installed i.e. grouped with other cables, ambient temp, through thermal insulation, length of run.
Replacing the unit for one the same rating as the old one however does not require notification to LABC.

 

[TopTrumper]

spark 123
41amps its rated at, and you put an 8.5 unit on a 32amp fuse...

no need to recable mate, just swap the shower, no higher than an 8.5 though

 

[Adam_151]

and you put an 8.5 unit on a 32amp fuse...

Isn't that in violation of 433-02-01 ?

 

[Spark123]

I got 6mm² rated at 47A before correction factors, but won't go very far before it fails on volt drop. I agree with adam, it is not a very good idea to run a circuit above the capacity of the fuse, although I am aware the fuse blows at iirc 1.45 times its rating within 1hour, but when there is a burning bakelite smell coming from the fuse box.....

 

[securespark]

Yeah, the general ROT is that 6mm2 is good for 8.5kW up to a maximum of 19m, not including any correction factors.

But you should not be using 3036's for a shower because there is a derating factor involved. And, certainly not a 32A device... 40A instead.

 

[TopTrumper]

its run at 35 amps, no way should you put a 40amp breaker on

or use a rewirable, has to be MCB

 

[Spark123]

its run at 35 amps, no way should you put a 40amp breaker on

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

 

[TopTrumper]

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

 

[Spark123]

What size breaker would you use for a circuit with a design current of 35A? I've not seen a readily available 35A breaker, afaik the preferred values are 32A, 40A/45A.

 

[TopTrumper]

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

 

[Spark123]

Design current (Ib) for a resistive load is KW/Volts, nothing to do with the installation method. 8500/240 = 35A approx. Selection of the correct cable (Iz) to use for the protective device (In) needs to incorporate the correction factors and volt drop.

Iz => In => Ib. (=> equal to or greater than)

 

[TopTrumper]

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

 

[Adam_151]

If I had a shower circuit with a 8.5kw shower and cable I calc'ed at 37A (for example) I'd protect it with a 40A breaker ... my understanding is that overcurrent protection need not be provided where the load is fixed and incapable of overloading, and the breaker is just for shorts and earth faults. The only issue with this approach is a diyer or plumber might uprate the shower

 

[Mikeyboy]

Thank you all , for your swift replies to my query . I am not increasing the power consumption of the shower unit , just fitting the same 8.5 kw . with a new model .As I mentioned earlier on , on this thread , basically it is a straight swop . The circuit is protected by a 45 amp mcb . So then , can I safeley carry this out ?