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

M

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

mikejd said:
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
Click to expand...
Nobody went into it because its such a stupid dangerous thing to do, get a sparks in.
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Figured as much. You need a physics nerd website my son. One where your theories can be appreciated and discussed out with the confines of the regulations and common sense which shackle us mere mortal sparks
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Also further to ''amlu's'' post #39 There are very strict requirements for ''Parallel'' supply wiring, among others, one very important requirement, being that Both cables must be of exactly the same length and follow the same route. I doubt very much if this will be the case in your situation from what you have told us.

And no you're thoughts on a dual supply from 2 separate OCPD is not perfectly feasible from a theory perspective. Until you know the theory behind the design of a circuit, it's advisable you don't make speculative claims that can't be substantiated!! ....So Again, DONT DO IT!!!
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

I knew if i waited long enough,retribution for my unacceptable 1979 excuse for not returning my physics homework,would be forthcoming...take that teacher...on a lighter note,just because a method is a possibility,does not mean there are not other reasons why it should not be attempted. These reasons are sometimes practical,and sometimes dictated by regulation,now and again it is both. Imagine if someone posted on a serious driving forum,if it was possible to drive around all day long,and just use the handbrake to stop the vehicle. You could,with care,do this,but is this sensible? Now off you go...DON'T RUN IN THE CORRIDOR!:goofy:
 
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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.
 
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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
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

mikejd said:
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
Click to expand...

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

mikejd said:
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
Click to expand...

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

darkwood said:
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.
Click to expand...

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

spark 68 said:
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 ?
Click to expand...

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

spark 68 said:
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
Click to expand...

Yes, I'm off to my pit as well to read another couple of chapters of BS 7671 - it's a great cure for insomnia.
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Im just bringing a few rarely used commercial/industrial practices into the domestic realm... although in practice i wouldn't apply them to domestic but its just to show after all the slating the OP can do in theory what he wanted with just a slight change on his OCPD .... but it comes back to the physical part of getting 2 x 6mm cables into a pull/wall switch although their are ways again around this too .... i probably only wouldn't do it because the next Electrician to test the installation wouldn't have a clue and would likely condemn it just on the principle that he can't understand why its been done that way.
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

darkwood said:
Im just bringing a few rarely used commercial/industrial practices into the domestic realm... although in practice i wouldn't apply them to domestic but its just to show after all the slating the OP can do in theory what he wanted with just a slight change on his OCPD .... but it comes back to the physical part of getting 2 x 6mm cables into a pull/wall switch although their are ways again around this too .... i probably only wouldn't do it because the next Electrician to test the installation wouldn't have a clue and would likely condemn it just on the principle that he can't understand why its been done that way.
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You be careful using them newfangled ideas on here some don't like it ; )

Thinking about the ops problem ( the electrical one) why not 2 of 6mm T and E into suitable enclosure with din rail mounted bolted terminals. Lug ends onto terminals. The cables are in place already as previously stated. Then use 10mm T and E with bolted lugs to extend circuit. You have then got 10mm to go to the isolator and 2 of 6mm cables in parallel protected by a single 40A MCB. Simple.
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Christ just rewire it correctly and be done with all this inane jabberwocky
 
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Re: can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW sh

Soz guys was bored and had a few beers last night i always like rocking the boat and seeing how many will scan the regs to find a flaw in my thinking lol....

I spend most of my time finding solutions that others can't find with machinery etc so thinking outside the box is one of my strong points....and in doing so ive had to utilise the clauses that many never need to use.
 
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can two 6mm csa cables each with 30A mcb in joined at 50A dps to supply 9.5kW shower
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