Shower upgrade, MCB rating?

[lasors]

Hello all,
We're upgrading our shower from an 8.5kW to a 9.8kW (@240v). Consumer unit currently uses a 40A Crabtree MCB (61/B40) and wiring is 10mm with no more than a 6m run, surface clipped.

Crabtree don't make a 45A replacement, which is the rating advised in the shower manual. Will the 40A one currently installed be ok?

Thanks!

 

[lasors]

Having said that, will a type B MK 45A fit as a direct swap or are they incompatible with Starbreaker consumer units?

 

[JohnD]

incompatible.

Also, there are two sorts of Starbreaker MCB, one with a screw at the bottom and one without.

By my calculation 9800W/240v is 40.8A which is near enough.

 

[riveralt]

You should be guided by the manufacturers instructions which will indicate the size of the MCB you should use.
The 9.8kw @240v rating is just for the outside of the box - the instructions will give you a figure around 9kw @230v and a 40Amp MCB rating.
They will also say that the new shower MUST also be additionally protected by an RCD.
Change the MCB and you're are into notification terriority.

 

[lasors]

You should be guided by the manufacturers instructions which will indicate the size of the MCB you should use.
The 9.8kw @240v rating is just for the outside of the box - the instructions will give you a figure around 9kw @230v and a 40Amp MCB rating.
They will also say that the new shower MUST also be additionally protected by an RCD.
Change the MCB and you're are into notification terriority.

It does give figures of 9kw@230v as well, but also says it requires a 45A MCB, which is what confused me.

The shower MCB is part of a group protected by a 30mA RCD.

So even if I wanted to replace the MCB, I can't do it without paying building control to inspect?

 

[JohnD]

you could have it done by an electrician who is a member of a self-certification scheme, which is very likely to work out cheaper and easier.

 

[riveralt]

It does give figures of 9kw@230v as well, but also says it requires a 45A MCB, which is what confused me.
The shower MCB is part of a group protected by a 30mA RCD.
So even if I wanted to replace the MCB, I can't do it without paying building control to inspect?

I take it is a Mira shower then!
They appear to have moved the goal posts recently by moving the 9.8kw shower to 45Amp MCB. Odd since the purpose of the MCB is to protect the cable which in your case is rated at 63 Amps.
You could always ask Mira or whoever the manufacturer is, if it will be okay to fit a 50Amp MCB since you are using 10mm cable and crabree don't make a 45Amp - though again there is the notification issue again.
The alternates are notify and do it yourself.
Employ an electrician, member of a competent persons scheme, who could either fit a 50Amp if allowed or fit a shower CU with its own 45Amp MCB/RCD next to your current cu.

 

[lasors]

It is a Mira shower, yes. An Azora.

I've seen the option of upping it to a 50A discussed elsewhere, so that might be the way to go.

 

[plugwash]

Personally i'd just leave the 40A MCB in place. It's in-spec at 230V and very nearly in-spec at 240V

 

[scousespark]

Personally i'd just leave the 40A MCB in place. It's in-spec at 230V and very nearly in-spec at 240V

No it isn't (for either voltage)

 

[JohnD]

hey scouse

what do you think the current is at 230v then?

 

[sparkwright]

Even worse at 230, surely?

 

[EFLImpudence]

It does give figures of 9kw@230v.

42.5A @ 250V

 

[sparkwright]

Ah yes, 9 kW at 230 v, my mistake.

 

[ban-all-sheds]

Even worse at 230, surely?

How would that work?