adding shower CU

[ianphilip007]

hi

just wanted to check something,
when adding a seperate shower CU (split tails) from a 80amp or even 100amp main supply the tails feeding the shower CU do they have to now be 25mm? or will 16mm be adequate due to the fixed load of the shower

The seperate shower cu (63amp 30ma RCD) is this again due to the CU supplying one fixed load so no need to be rated at the 100 or 80amp supply fuse

many thanks

 

[ianphilip007]

its ok now have it sorted, 11kw shower will only draw 47.8 amps max so the 63amp rcd is fine.

same for tails supplying shower CU max of 47.8amps so 16mm would be fine. got confused with minimum of 25mm for MAIN TAILS for above 60amp main fuse

 

[telectrix]

11kW shower makes a complete mockery of fitting energy saving lamps. how many low energy lamps would it take to recoup the extra, non-essential 3kW in that shower.?

 

[sedgy34]

if you split the mains tails and the incoming fuse is 80amp your new cu for the shower main switch would have to be 80amp rated 16 mm tails are sufficient

 

[Fin170]

11kW shower makes a complete mockery of fitting energy saving lamps. how many low energy lamps would it take to recoup the extra, non-essential 3kW in that shower.?

That 3kw will probably never be used, mostly down to humans having that issue with excessive heat

Anyway, Looking at the manufactures cables inside the average shower I'd say none of them will ever draw anything close to that and manufactures are just playing it safe

 

[telectrix]

in other words. lying.

 

[Guest123]

433.2.2 & 'backfusing' come into mind here.

 

[ianphilip007]

if you split the mains tails and the incoming fuse is 80amp your new cu for the shower main switch would have to be 80amp rated 16 mm tails are sufficient

so why do all of the shower rcd units come with a 63A rcd/mainswitch doesnt make any sense especially as most shower manufactures state there showers must be connected to at least an 80amp mainswitch also

 

[sedgy34]

they do 80amp 30ma

 

[ianphilip007]

do they make a shower cu with a 80a or 100 a rated mainswitch/rcd they all seem to be 63a

 

[Snapester]

The RCD cannot be used as an OPD, the rating of the RCD is what current it is rated to, you will need still need an MCB along side it in the enclosure? Unless of course it is an RCCB.

 

[i=p/u]

could have 63A rcd main switch then 40A mcb?????

 

[Snapester]

Yeah that would do it, also if the main fuse is 60/80amps then 16mm tails would be ok, if 100amp then 25mm tails would really be needed dude to CCC ratings.

 

[Guest123]

433.2.2 & 'backfusing' come into mind here.

:wink_smile:

 

[Snapester]

Hey Lenny, reading that reg doesn't make much sense like so many of them, what is it trying to say? I kind of have an idea what its trying to say but not sure lol cheers

 

[ianphilip007]

so you can feed a (63a/30ma rcd/ 45a MCB shower cu) from a 80amp fused tails?

 

[sedgy34]

Read the question snapester

 

[ianphilip007]

by backfusing Lenny are you saying that the cable feeding the shower CU (if under 3 meters) is protected by the MCB in the shower CU lets say 40amps for a 8.5KW shower.

i agree reg not very clear

 

[D80]

Yip! Stick in 10mm tails if you have them.

Seen on a few sites the fire alarm on the mains panels fed directly off the busbar in 1.5/2.5MM cable. 1000Amp supplies to the panel and the like.

 

[Snapester]

I think what he is saying is if the feed ie 16mm tails are over 3m from the origin then you will need a KMF switch at the origin of supply.
So if your shower CU is in the airing cupboard or something and over 3m from the origin of supply you will need a isolator/KMF switch.

 

[ianphilip007]

yes i agree snapster, if the shower cu is within 3 meters no need for a switchfuse to protect the 16mm tails. the way i see it they would be protected via the mcb/rcd in the new shower cu. if over 3 m the 16mm tails would have to be protected and fused down via a switchfuse at origin before beeing routed to shower cu.

so i think that the 16mm tails can feed the 63a/30ma rcd mainswitch of the shower cu directly from the 80amp/100amp main fuse via henly block.

 

[Guitarist]

As long as your reduced fuse or breaker is within 3M of the supply point, then the cables only need rating at the new fuse/breaker. Hence, if your new shower CU had a 40A MCB installed and that is therefore the maximum current which can flow through that system, then 10mm tails would suffice (or 63a/16mm). As said previously tho, the RCD rating is NOT your circuit protection. You will need an additional MCB or RCBO

 

[ianphilip007]

thankyou guitarist thats what i was thinking, so would you agree that as the shower cu can only draw 40amps the shower CU 63a/30ma rcd switch is adequate ?? no need to replace with a 80a/30ma

 

[Snapester]

The RCD is just a switch it will not operate as an overload device, you will need MCB to proved overload protection.

 

[telectrix]

but a 63A/30mA RCD is fine.