Wylex Type B plug in MCBs

[ruf]

Hi - Apologies if this has been asked recently. I've tried a search but couldn't find anything.

We have a Wylex 8 position board fitted with the plug in mcbs. We're about to get the bathroom renewed and as part of this put a higher rating electric shower in. The mcb fitted is a 40A but it appears that the 45A version is no longer sold. The new shower we want to get fitted is a 9.7Kw.

The plumber is coming tomorrow but don't as yet have an electrician scheduled.

Would appreciate some advice so I am better informed before electrician turns up to quote for the rest of the job.

I'm guessing that there are no other makes available that will simply plug into board - a friend mentioned GE?

What's the best/most cost-effective solution so that we can use the shower we want?

 

[RF Lighting]

What colour is your fuse box? (no I'm not kidding)

What is the rating of the fuse box? It should say on a label below the main switch.

What size is the cable which currently supplies the shower?

Is there currently an RCD protecting the circuit for your current shower?

Do you want the best, or the cost effective soloution? They are two very different things.

 

[sparkybird]

If you try to fit a higher rated mcb in the board you would be over loading it. In addition your new shower will need to be RCD protected, so unless you have an RCD before your fuse board (ie covering the whole install) then this needs to be fitted too.

The best solution (as I'm sure your electrician will tell you) is probably to get a mini rcd protected board fitted just for your shower. Note that if you don't have RCD protection for the lighting as well, supplementary bonding (all metal parts in the bathroom, connected to lighting and shower circuits) will also need to be done, so make sure your plumber leaves the pipes under the bath exposed!

Hope this helps

SB

Ah, RF you beat me to it and spotted that the cable might need to be upgraded too!

 

[JACKC]

Showers need to have rcd protection, your fuseboard will not reach current standards. 1 way round it is to henley block ( a double pole connector block )main incomers from fuseboard and fit a shower rcd unit. You will need 10mm cable for this size shower. None of this is very cheap and the job is notifiable under Part P. Chances are your bonding will need upgrading and possibly your meter tails to cope with the demand.

 

[industryspark]

9700 watt at 230 volts is just over 42A, at 240 volts its 40A. Either way your 40A mcb will 'hold' for the amount of time you take a shower.

You should probably upgrade to 45A though so as not to be running the circuit at overload, however dont upgrade without first checking cable calculations, loop impedance, ect.

Also is the shower rcd protected? this is important.

not sure the wylex fuseways in the board you describe were ever designed to take more than 30A, some i understand werent, depends on the particular model you have.

can you post a picture of your consumer unit/fuseboard?

 

[ruf]

Wow - thanks for the very quick replies.

I had suspected that an mini RCD board unit would be required. The existing board is white and rated at 100A and the cable is 10mm.

At present to be quite honest it's the most cost-effective solution I want. (The existing set up was tested and is not due a routine retest until 2011)

 

[industryspark]

does the existing shower circuit have rcd protection? it sounds unlikelly from what you describe. Its crucial that the shower has rcd protection, dont let money come into it, get the job done properlly and by a registered spark.

if anything happens when you or your family are showering i wouldnt fancy your chances with no rcd.

 

[GaryMo]

9700 watt at 230 volts is just over 42A, at 240 volts its 40A. Either way your 40A mcb will 'hold' for the amount of time you take a shower.

It depends on the rating of the shower as it's a fixed resistive load. If it's 9.7kW @ 230v then it'll draw more current running at a measured 240v.

I=P/V
9700/230 = 42.17A

Resistance of the heater in the shower

R=V/I
230/42.17 = 5.45ohms

Using a measured 240v supply

I = V/R
240/5.45 = 44.04A

 

[davelx]

Yes, but a 40A type B will take up to 50A almost indefinitely (>10000 sec.) without tripping.

http://www.tlc-direct.co.uk/Figures/3.18b.gif

 

[Spark123]

It maybe will, but imo running a circuit above its ocpd rating is bad desing practice. It also doesn't comply with BS7671:2008 reg 433.1.1 (i)

 

[GaryMo]

As per Spark123's reply, the rating of a protective device should not be less than the design current of a circuit. That's one of the most basic principles of electrical installation of which all first year apprentices should be aware of.

 

[ruf]

Shower rating is 9.8 kW 240 V AC 9.0 kW 230 V AC.

Spoke to electrician used by my plumber. His replies left me feeling uneasy but he is coming out but reckoned the MCB would be OK and didn't need an RCD!

Once he's been I'll get another guy out who is highly recommended by a friend

 

[GaryMo]

I would personally tell him not to bother.

 

[RF Lighting]

he is coming out but reckoned the MCB would be OK and didn't need an RCD!

Ask him to look up Regulation 701.411.3.3 in his copy of BS7671:2008

Section 701 - Locations containing a bath or a shower

701.411.3.3 : Additional protection shall be provided for all circuits of the location [locations containing a bath or a shower], by the use of one or more RCDs having the characteristics specified in Regulation 415.1.1. [an operating current not exceeding 30mA]

 

[securespark]

I think he's rougher than your moniker....