8.5Kw Shower questions

[NickHewitt]

hi there, I'm new to these forums (although I've read more than a few posts while planning my modest project)

here's what I know;
the shower needs a local isolating switch - this is provided by a 45A cord-pull switch.
the shower requires a dedicated 30mA RCD - got
the shower requires 6mmSq TW+E - read the instruction booklet for the wrong shower initially and bought 2.5, then when it flipped the 16A breaker I had another look and felt like a right pillock, but I've caught it and I'll upgrade it to 6mm before it gets used.
the shower requires a dedicated 40A breaker - it's on a 32A for the moment since there's a 'spare' one in the consumer unit, and I've yet to look into the compatibility for Crabtree Loadstar - and they're easy enough changed in any event (assuming due care and attention are used).

my questions are:
should I use a tail as well/instead of the bus bar so as not to excessively load the bar?
and assuming compatibility of the RCD and is there anything to stop me putting it in the consumer unit provided it's still in-line with the shower only?

thanks in advance.

 

[Taylortwocities]

40A may be OK providing the installation method of the circuit and its EFLI check out when you do you cable calculations

shower requires a dedicated 30mA RCD

Does your Loadstar not already have an RCD?


Re your questions

should I use a tail as well/instead of the bus bar so as not to excessively load the bar?

No, you will not overload the busbar

and assuming compatibility of the RCD and is there anything to stop me putting it in the consumer unit provided it's still in-line with the shower only?

The RCD you probably have bought is not designed to go inside the consumer unit. It is meant to be outside. why dont you throw it away and install an RCBO.

 

[NickHewitt]

sorry, should have explained;
I bought this
http://www.diy.com/departments/wylex-63a-sp-30ma-shower-protection-unit-rcd/177830_BQ.prd
which it turns out is CU type RCD in a plastic box with a rail at the back. ~ hence the question of skipping the necessity of messy wiring between a switch the RDC and back through the wall.
there are two separate RCD's in the CU already, one to cover sockets, cooker (not fitted) and immersion heater (also not fitted) and the other covers the lights and combi-boiler.

I was erring on the side of caution and providing it a dedicated RCD.

 

[ericmark]

hi there, I'm new to these forums (although I've read more than a few posts while planning my modest project)

here's what I know;
the shower needs a local isolating switch - this is provided by a 45A cord-pull switch.

No only motors must have local isolators, it's a good idea but not required.

the shower requires a dedicated 30mA RCD - got

Also any cable buried less than 50mm so has to be at consumer unit otherwise it could double as the local isolator.

the shower requires 6mmSq TW+E - read the instruction booklet for the wrong shower initially and bought 2.5, then when it flipped the 16A breaker I had another look and felt like a right pillock, but I've caught it and I'll upgrade it to 6mm before it gets used.
the shower requires a dedicated 40A breaker - it's on a 32A for the moment since there's a 'spare' one in the consumer unit, and I've yet to look into the compatibility for Crabtree Loadstar - and they're easy enough changed in any event (assuming due care and attention are used).

The Crabtree Loadstar is a series of distribution units so hard to give an answer. It also depends on your skill.

my questions are:
should I use a tail as well/instead of the bus bar so as not to excessively load the bar?
and assuming compatibility of the RCD and is there anything to stop me putting it in the consumer unit provided it's still in-line with the shower only?

thanks in advance.

As already said direct onto bus bar is the method used. 6mm² cable has a range of current carrying capacities according to type of insulation and installation method. Reference Method C* (Clipped direct) with thermoplastic insulated it may be rated at 47A but most people bury the cable Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) is more the normal method and then only 34A.

There is more to wiring a shower than simply connecting a cable. It will need inspecting and testing and this is why new circuits require registering with the LABC. If following the rules DIY is an expensive option.

 

[ericmark]

Not sure I would fit that unit when by the 1st Jan 2016 it will not comply see here if already fitted with a RCD no point using a second one.

 

[EFLImpudence]

but most people bury the cable

Most people?

Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) is more the normal method and then only 34A.

Whilst that is true, the solution is not necessarily to install larger cable but to not install it like that.

An 8.5kW @ 240V shower is 33.94A @ 230V plus there is also the time consideration - so...

 

[Taylortwocities]

sorry, should have explained;
I bought this
http://www.diy.com/departments/wylex-63a-sp-30ma-shower-protection-unit-rcd/177830_BQ.prd
which it turns out is CU type RCD in a plastic box with a rail at the back. ~ hence the question of skipping the necessity of messy wiring between a switch the RDC and back through the wall.
there are two separate RCD's in the CU already, one to cover sockets, cooker (not fitted) and immersion heater (also not fitted) and the other covers the lights and combi-boiler.

I was erring on the side of caution and providing it a dedicated RCD.

Firstly, there is NO point in having a second RCD on a circuit that is already RCD protected
Secondly, any device that you put into the Loadstar consumer unit needs to be a Crabtree device that has been type-tested for use in a Loadstar board
Thirdly you do not install an RCD like that inside a consumer unit to protect a single circuit. It is designed to protect a single circuit and toi be mounted externally to the consumer unit.

So take it back to B&Q and get a refund. Buy some Christmas Lights, maybe. Or subsidise the local authority fee….see below!

Next thing. This is a new circuit, yes? So you must firstly raise a building notice with the local authority, and pay their fee. They will want to see and inspect your handiwork.
See http://www.diynot.com/wiki/Electrics%3Apart_p%3ADIY-Electrical-Work-and-the-Law for details

From the sound of it, you need an appropriate MCB in your consumer unit. (NOTE: LOADSTAR approved) to connect to your new circuit. As I said above, you need to do the cable calcs to determine what size that might need to be.

A photo of your consumer unit may help.

 

[NickHewitt]

I should stress that the circuit for the shower was already in place but for reasons best known to the council - who renovated the electrics a few years back while I was renting - they'd used ~1.5-2.5mm wire and spliced it into one of the plug sockets. (yes, really.) and as such you'll understand my reluctance to involve them, also does anyone know the score for a property in Scotland, since the regulations cited in your link only apply to England and Wales.

 

[ban-all-sheds]

Balance your electrical current with this 63A shower protection unit residual current device (RCD).

¿Que?

 

[NickHewitt]

Balance your electrical current with this 63A shower protection unit residual current device (RCD).

¿Que?

I know right, there was me thinking they were to detect an imbalance...

 

[JohnW2]

Firstly, there is NO point in having a second RCD on a circuit that is already RCD protected.

FWIW, I would not personally go quite as far as putting that "NO" in capital letters. The available information on in-service reliability of RCDs is woefully inadequate, but I am sure you will have come across at least some in service which were not functioning satisfactorily (if that weren't the case, why would you bother to test them?). That being the case, the cautious amongst us might see some merit in 'belt and braces'.

Kind Regards, John

 

[NickHewitt]

Firstly, there is NO point in having a second RCD on a circuit that is already RCD protected.

FWIW, I would not personally go quite as far as putting that "NO" in capital letters. The available information on in-service reliability of RCDs is woefully inadequate, but I am sure you will have come across at least some in service which were not functioning satisfactorily (if that weren't the case, why would you bother to test them?). That being the case, the cautious amongst us might see some merit in 'belt and braces'.

Kind Regards, John

this was my thought on the matter, purists might call it excessive, I'm calling it built-in redundancy

 

[JohnW2]

this was my thought on the matter, purists might call it excessive, I'm calling it built-in redundancy

As I said, that is a valid view - but I have to say that very few people seem to do it 'deliberately' - two RCDs on a circuit is not that uncommon, but it is usually as the result of 'ignorance', rather than a deliberately 'cautious' practice.

Kind Regards, John

 

[ban-all-sheds]

I hope we are not seeing any influences of superstitions about electric showers....

 

[JohnW2]

I hope we are not seeing any influences of superstitions about electric showers....

Possibly, but I don't think that alters the fact that, when an RCD is either required or deemed desirable (for whatever reason, 'valid' or not), that some of the more risk-averse amongst us will perceive merit in redundancy.

Kind Regards, John