Consumer unit wiring for 10.8kW shower

[Seb101]

Hi all,

I'm putting a new shower in my own place, 10Kw electric unit. Have made the run from the shower-room isolator using 10mm2 cable, now working out the best way to wire it in to the consumer unit. It's a Memera 2000 AD and the layout is a 100A main isolator with 6 6A MCB lighting circuits directly off it, then a 80A RCD protected second section with 3 32A MCB circuits (two socket rings and a cooker). There is one spare MCB slot (in the middle - so could wire in either side).

RCBOs for this unit are quite hard to come by so my first instinct is to put a new 45A MCB off the RCD side of the unit. Doing a few calcs I estimated that worst case, with the shower, oven, washing machine and kettle all going I might be pushing around 88A, so I reasoned that keeping it on the 80A RCD side would be advantageous, in that if the load did become too high, the RCD would trip but not the main breaker so at least the lights would stay on.

Then my brain kicked in and said - hold on, RCDs don't actually act as over-current protection devices do they? So would it actually be more dangerous to 'overload' the RCD like this, than to put the shower on the main section with an RCBO?

Does anyone know of other manufacturers RCBOs that form-fit the Memera 2000 AD?

Cheers.

 

[winston1]

As its a new circuit you can't do it without notifying first. Have you done that?

 

[ban-all-sheds]

Testing, Testing, 1 2 3

 

[OwainDIYer]

worst case, with the shower, oven, washing machine and kettle all going I might be pushing around 88A,

But you probably won't be, at least not for very long.

Kettle is for a few minutes only. Washing machine only takes max power when heating the water at the start of the wash cycle. Oven will cycle on and off on its thermostat.

Unless you have portable space heaters or an immersion heater, the only appliance that really draws current in most homes is a tumble dryer and that's still less than 13 amp.

 

[Spark123]

Hi all,

I'm putting a new shower in my own place, 10Kw electric unit. Have made the run from the shower-room isolator using 10mm2 cable, now working out the best way to wire it in to the consumer unit. It's a Memera 2000 AD and the layout is a 100A main isolator with 6 6A MCB lighting circuits directly off it, then a 80A RCD protected second section with 3 32A MCB circuits (two socket rings and a cooker). There is one spare MCB slot (in the middle - so could wire in either side).

RCBOs for this unit are quite hard to come by so my first instinct is to put a new 45A MCB off the RCD side of the unit. Doing a few calcs I estimated that worst case, with the shower, oven, washing machine and kettle all going I might be pushing around 88A, so I reasoned that keeping it on the 80A RCD side would be advantageous, in that if the load did become too high, the RCD would trip but not the main breaker so at least the lights would stay on.

Then my brain kicked in and said - hold on, RCDs don't actually act as over-current protection devices do they? So would it actually be more dangerous to 'overload' the RCD like this, than to put the shower on the main section with an RCBO?

Does anyone know of other manufacturers RCBOs that form-fit the Memera 2000 AD?

Cheers.

I'm not sure if you can get 45A MCBs for that board, a board is type tested with their own brand MCBs so fitting another brand is a no go.
You'd be better having an electrician have a look to see what it viable, you may get away with a separate consumer unit for the shower.

 

[EFLImpudence]

50A ?

 

[Spark123]

If the old board is rated for it they are available from the memshield 2 range, you'd need to check with mem.

 

[Iggifer]

Time for a £125 RCBO Pod.....

 

[kai]

The best bet is to go for a stand alone purpose-made shower Consumer Unit, they were specifically designed for showers, and should do the job perfectly.

 

[ban-all-sheds]

No - they are just small enclosures with an RCD incomer and MCB, or an RCBO, labelled as "shower units" in an exercise which owes everything to marketing and nothing to design.

 

[Seb101]

Thanks for the input on this. Got an Eaton 50A Class B MCB from the Memsheild 2 range as Spark123 suggested - it's a perfect match, it's actually identical in all respects (even markings) apart from changing the logo from "MEM" to "EATON".

First couple of uses of the shower the new MCB (or could have been the RCD) was emitting an audible buzzing noise, but it wasn't getting hot or anything. I checked the tightness of all the connections but it didn't make a difference. I was going to return MCB as faulty, but all of a sudden it stopped making the noise and it's been fine ever since. I'm confused as to what that could have been?!

 

[RF Lighting]

A pre fire warning by the sounds of it

What were your test results for the circuit?

Have you extended the supplementary bonding in the bathroom to include the shower circuit?

Have you actually clamped the circuit breaker onto the busbar?

 

[Seb101]

I haven't got the results on me at the moment, will supply later.

The shower is connected by plastic piping from the cold supply to the bath (which is earth bonded). The metal water inlet section of the shower is bonded to the shower radial CPC. No additional bonding is required as far as I am aware?

'clamped the circuit breaker to the busbar' - of course yes! Or did you mean the DIN bar?

 

[RF Lighting]

How did you get this work signed off by building control when it doesn't comply with wiring regulations?

//www.diynot.com/wiki/Electrics:supplementary_equipotential_bonding

Are you 100% sure you've clamped the breaker to the busbar? Have you actually checked?

 

[ban-all-sheds]

He ignored this:

As its a new circuit you can't do it without notifying first. Have you done that?

And this:

Testing, Testing, 1 2 3

I doubt he notified.

And given his question here re his fire alarm cable:

If I disconnect the white cables from all three alarms, is there a quick multimeter test I can do to see if the white cables are connected to Earth or not?

I can't see how he can have done proper testing on the shower circuit.

I haven't got the results on me at the moment, will supply later.

Yeah, right.....