can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW shower

[mikejd]

Hi I have two 6mm csa cables in the loft each going back to a separate 30A mcb in the CU. One is redundant, the other goes to a broken 8.5kW shower. I want to fit a new 9.5kW shower and would like to join both 6mm cables together at a 50A dpst shower switch, then run a short length of 10mm csa cable from the switch to the shower. Can anyone see a problem with doing this. Both 6mm cables are approx same length (12m), there is a RCD in the CU.
Thanks

 

[scammell man]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

I think you need to spell out your reasons for NOT doing this somewhat better. In power transmission this is normal practice! You ARE allowed to deviate from BS7671 provided the resultant safety is as good as compliance with BS7671 and you state you have deviated. The generic test docs are not compulsory. As I have said on this forum before, dual supply IS allowed. Every installation with solar panels has this as do auto start standby generators etc.
having said all that, I agree with all the statements that it is poor practice etc and certainly would not pass as a standard circuit.

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

The mind boggles

What he said.

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

According to his profile he's a teacher, hope he knows a bloody sight more about that than he does about electrics .

Just wondering if he teaches all these 5WWs.

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

What this forum needs is a filter to automatically chuck all posters like this into the Screwflux Forum

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Fingers crossed he's not a science/Physics teacher!

The old adage goes something like; "Those who can do - Others teach".

 

[Darkwood]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Thinking about that, could always put it down as a ring

Nice try lol.. a ring by its nature has to have more than 1 point otherwise its parallel cabling disregarding the 2 mcb crap.

 

[Silly Sausage]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

The old adage goes something like; "Those who can do - Others teach".

That's similar to "Those that can't, get promoted."

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Thanks to you who have replied genuinely to my question, without feeling the need to result to sarcasm. No I am not a qualified electrician and never claimed to be but I am both a physics graduate and electronics engineer. I never doubted that regs would not allow this to be done, though from an electrical theory perspective it is perfectly feasible, Its a shame very few replies seemed to go beyond 'you cant do it as it breaks the regs' and considered the theoretical reasons why...of which there are few.
Thanks again

The "regs" are in place for a reason and part of that reason is to keep idiots safe from themselves.

You're very welcome to the advice.

Take care, goodnight and may your dog go with you.

 

[Darkwood]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

If the OP used a DP linked device it is plausible although not the norm in domestic ...


So to the regulars ...ill put a revamped version of the OP's question up... 2 x 6mm T&E short run clipped direct to a 10.5KW shower fed from a DP 25 amp mcb - trip interlocked - would it comply?

For arguments sake cable calcs all comply.

 

[shanky887614]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Thanks to you who have replied genuinely to my question, without feeling the need to result to sarcasm. No I am not a qualified electrician and never claimed to be but I am both a physics graduate and electronics engineer. I never doubted that regs would not allow this to be done, though from an electrical theory perspective it is perfectly feasible, Its a shame very few replies seemed to go beyond 'you cant do it as it breaks the regs' and considered the theoretical reasons why...of which there are few.
Thanks again

Its not just that it is against regs.

If someone gets a shock in your house you will get reamed and go away for a long time.

If there is a fire I hope you can salvage some clothed because your insurance wont pay out

 

[spark 68]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

If the OP used a DP linked device it is plausible although not the norm in domestic ...


So to the regulars ...ill put a revamped version of the OP's question up... 2 x 6mm T&E short run clipped direct to a 10.5KW shower fed from a DP 25 amp mcb - trip interlocked - would it comply?

For arguments sake cable calcs all comply.

Not on that setup,as the OCPD would still be effectively SP, If I am following you correctly ? or two OCPD in parallel.

Edit: or did you mean 25A in total ?

Edit ii) Asuming you mean a true DP trip at 25A each, then Ha! I was wrong, reg 434.4 for fault protection only (conductors in parallel), but this comes with caveats that may not be suitable in domestic.

I don't think I have seen linked MCB's used in this way before (ACBs yes).

There are two types of DP MCBs that I am aware of, type one has two trip elements with linked trips and operating switch, used on two phase equipment, the other has a single trip element with the other pole being just a switch disconnector (linked as before), this type usually has one pole (the switch disconnector part) marked N for connection to the Neutral only.

I had to look it up though! it's late lol

 

[Geordie Spark]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

That's similar to "Those that can't, get promoted."

Looks like ye 'n' me went t' diffrent skyules together bonny lad.

 

[Engineer54]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Not on that setup,as the OCPD would still be effectively SP, If I am following you correctly ? or two OCPD in parallel.

Edit: or did you mean 25A in total ?

Not exactly sure what you mean ?

DP means 25A each Still single pole but each live conductors into each pole, so by definition, are still dual circuits even if operation of one pole affects/trips the other...

 

[Silly Sausage]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

So effectively a 50A breaker with a || Line in each pole?

 

[spark 68]

Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Edit ii) Asuming you mean a true DP trip at 25A each, then Ha! I was wrong, reg 434.4 for fault protection only (conductors in parallel), but this comes with caveats that may not be suitable in domestic.

I don't think I have seen linked MCB's used in this way before (ACBs yes).

There are two types of DP MCBs that I am aware of, type one has two trip elements with linked trips and operating switch, used on two phase equipment, the other has a single trip element with the other pole being just a switch disconnector (linked as before), this type usually has one pole (the switch disconnector part) marked N for connection to the Neutral only.

I had to look it up though! it's late lol

Yes I realised after, it is getting late lol, about time I was in bed.

I am sure DW eats the regs for breakfast lol

Reg 433.4 also mentions a single device for overload protection (conductors in parallel ), I suppose it is how you define a single device