Installing triton 300Si 9.5kW shower

[Peter boucher]

My previous shower has come to it end of life and i am planning on replacing it with a triton 300Si 9.;5KW shower.

the current circuit is a 6mm2 wire to its own shower consumer unit with a 50amp mcb, the cable is run in uninsulated stone walls through a loft space and under some very draft fllor boards. What i want to know is it going to be ok to reuse the 6mm2 cable and the 50amp fuse seems a little high for what was the previous shower a triton 80si, (not sure if it was 7.5 kw or 9.5kw.

any advice on whether im looking at needing to run a 10mm2 cable would be appreciated as this will not be an easy run, also what sort of cable length will 6mm satisfy thank

Pete

[davelx]

6mm^2 is rated 46A clipped direct, which I think will apply your installation as described, but 50A MCB does not give the required protection - a 45A max MCB is required to protect this cable.

Your load is almost 42A, so you should replace the 50A MCB with a 45A one (if these are available for your brand of CU)). Failing that, a 40A MCB would actually be OK as it will handle 42A indefinitely, and a shower is only used for short periods. Note that no account of voltage drop is taken here as we don't know the length of the cable run. If it is greater than 30m (!) you will need to upgrade to 10mm2 cable.

Don't forget that if the shower manufacturer specifies it, the circuit must be RCD protected. If there is no RCB in the consumer unit, an RCBO would kill two birds with one stone.

[Peter boucher]

Thanks for that, i will check the MCB tonight and also whether the consumer unit has a rcd trip, cable is about 20m in length

[Steve]

Its always preferred nowadays to run 10mm² cable where possible, so if you can, do it.

Then you can keep the 50A MCB and have a 10.8kw shower. Heaven. Especially in summer

[Softus]

Your shower will draw around 40A (if the 9k5W rating is at 240V), so it depends on where and how the 6mm² cable has been run.

For example, PVC sheathed 6mm² T&E cable in conduit in thermal insulation can only [safely] carry 32A, and in that case you'd need to use 10mm² cable.

[davelx]

"the cable is run in uninsulated stone walls through a loft space and under some very draft fllor boards."

[Peter boucher]

Thanks for the advice, i have checked the shower consumer unit and it has a 30ma rcb with 50a mcb , am going to replace the mcb with a 40 A type B mcb as that is all that is availble for this particular unit.

As i have access to the shower cable for at least 60% i will change the cable to 10mm at a later date, when i can persuade her indoors to allow me to ripp up the floor baords for the remaining run, and reinstate the 50amp fuse if thats correct ?. In the meantime anymore holes in the house and i might end up in them

[Adam_151]

No need to use 50A breaker really 9500/240 = 39.6A

The headline rating on showers is nearly always at 240v, there is a lower 230v rating underneath (for 9.5kw it'll be 8.7kw which is 38A ish), but as we have a 240v rating and the supply is normally at 240v it makes sense to calc with 240v


Technically you could probably get away with a 50A breaker on 6mm cable as long as the cable can carry the load of the shower, theres a regulation that says you don't have to provide overload protection where the load isn't capable of overloading(and I'd consider the shower as such*), however if you do this you have to calculate short circuit protection separatly (normally as long as you have protected against overload and the breaker can break the level of fault current at the position its installed, then the regs allow you to consider it protected against short circuit without any further design work) - but of course if you can get away without doing that, then its easier and if you can get a B40 for your board

[Same principle applies to spurs off a ring final circuit, except a rfc with spurs is a 'standard circuit' as defined in the OSG so you can just install it as per the 'recipe' without any design work]

*I suppose in the real world though, a plumber or odd job man might replace the shower with a more powerful unit without any concern for the increased electricial load

[Softus]

Adam_151 wrote:

...a plumber or odd job man might replace the shower with a more powerful unit without any concern for the increased electricial load

A plumber if any repute wouldn't, because he/she would read the MIs, which would lead the way towards reviewing the CCC and the overload protection.