Help with upgrading shower

[Papabob]

Hi Forum, "Help" I am still trying to obtain help for the following question "I would be grateful for some advice. I intend to change my 7kw shower for a 7.5 Shower. The reason I am not going any bigger is that I don't want to change the 6mm Twin and Earth cable. The cable is less that 10 metres long and travels through a plastic trunking and under floorboards on its own. The shower is protected by it's own 30a MCB in it's own consumer unit placed next to the main consumer unit. The main consumer unit is an old WYLEC, but I have replaced the wired fuses with plugin MCB's. Do I need to change the shower's consumer unit with a RCD? The one I have seen is a 63A 30mA RCD with a 50A MCB. Is this too big? Can I use a 40A 30mA RCD, or can I use a shower consumer unit as per screwfix 69659-90. I have enclosed some pictures.

Consumer Unit

• Papabob
• 7 Sep 2008
• 3

The Lot

Consumer Unit 2

• Papabob
• 7 Sep 2008
• 2

Consumer Unit 3

• Papabob
• 7 Sep 2008
• 2

Consumer Unit 4

• Papabob
• 7 Sep 2008
• 3

Consumer Unit 5

• Papabob
• 7 Sep 2008
• 3

Thanks,
Papabob

 

[Cremeegg]

Read the Wiki on Part P as this is notifiable work.

Pointless changing from 7kW to 7.5kW - you wont notice the difference and you're just being lazy.

Get a new CU that will take a decent shower 9.5kW at least preferably 10.5kW and run in some new cable - need a biit more information before we can quote cable sizes required but if you dont know how to work them out you shouldnt be thinking of doing the job.

 

[Papabob]

Thank you Cremegg,
It's not a case of being lazy, my current 7kw shower drips (worn washer?) and I just want to replace it. It has been a brilliant shower for me and hot enough. Seeing I am happy with it, it don't make sense to renew the wiring when there is no need. I just wanted to add a RCD, as this makes sense to have added protection. As for calculating the size of the necessary cable, I can use the basic formula, Wattage divided by Voltage but I don't know the specialist formula that you probably use. Which brings me to a query I have. Lets say you use your specialist formula and come up with 10mm twin & earth. A fortnight after you complete the job, the customer has a grant to provide extra loft insulation which buries your cable, wouldn't this change the calculation you have made.
Anyway thanks for taking the time to reply.
Bob

 

[davy_owen_88]

Hi Bob, sorry for not replying to your other thread a few days back, I was very busy and assumed that someone else would have answered your questions.

Now that we can see your installation its just clarified what I had in my head. Before you can do anything you will need to contact your DNO and get them to fit an isolator between your meter and your consumer unit - this will allow you or an electrician to carry out the work you need to do safely.

The single way CU for your shower needs to be replaced with a 30mA RCD and 32A MCB. You can't use a 50A or 40A MCB to protect 6mm² cable as it runs in trunking it is only rated at a maximum of 38A.

This work is notifiable and the work needs to be tested to ensure that the protective devices will operate as they should.

Regarding your comment about insulation, well this would indeed change the current carrying capacity of the cable, reducing it by up to half which is why insulation isntallers should be required to inform the householders of the effect it will have on the cables and give them time to get the cables moved/replaced to reduce the chance of dangerous consequences.

 

[Cremeegg]

Glad you are happy with a 7kW one - I was only offering advice that there are far more powerful ones on the market that are a huge improvement on the older less powerful showers especially in the winter when the incoming mains water is far colder.

Obviously Gordon Brown has thought about giving all sparks work with all this new insulation that will be on offer. Or perhaps he's keen to keep the fire crews busy. Most people have no idea how much a few inches of insulation affects the current carrying capacity of a cable.

 

[Papabob]

Thanks Davy and Cremegg, your comments are really appreciated. One other question, if I want to have my primary consumer unit upgraded and have a new shower CU fitted, would the DNO fit 2 isolator switchs between the meter and the 2 CU's?
Thanks Bob

 

[ban-all-sheds]

No - the isolator is fitted before the tails are split, not after.

If you're having 2 CUs you should have an isolator irrespective of the safety issues of making it safe to work, as you should have a single point of isolation for the whole installation.

 

[milliamp]

If you are considering a consumer unit upgrade, why not make provision for the shower in the new unit? The secondary C/U could then be removed.
Should you opt for an isolator the DNO would remove the sub board tails when they fit the switch.

 

[ban-all-sheds]

1) He wouldn't (properly) have the 2nd board before they fit the isolator.

2) The tails to it would not be theirs to remove.

3) You're right about having one CU though - I wasn't paying attention.

if I want to have my primary consumer unit upgraded and have a new shower CU fitted

That's not the way to do it - a secondary CU for the shower is what you do if your existing one can't take it - if you're upgrading it then the shower circuit will come from it - no need for a separate shower CU.

 

[WillB77]

A bit OT but glad I chanced upon this thread.

I'm currently doing up my attic room which includes insulating it. All the current wiring sits on top of old insulation. I have put new insulation on top of alot of this. Currently the room is not being used but before I go any further what safeguards should i take before going any further? should i put all of the wiring in conduit and then re-lay the insulation on top of that?

As an aside a 'company' came round to look at the attic about 2 years ago to do a grant-aid insulation jobby and didn't mention anything about the wiring

 

[davy_owen_88]

What are the cables supplying? If they are only lighting circuits and are wired in 1.5mm² even when derated by half, their current carrying capacity will still be sufficient for a 6A MCB - still though, you should try to keep them out of insulation unless absolutely necessary, and it's never absolutely necessary

If you have cables that feed a shower/immersion heater or socket circuits you will definately need to think about moving the cables so that they are not going to be covered by insulation - just putting them in conduit will not help.

 

[WillB77]

Cheers Davy. Its all lighting and mostly to energy saving bulbs. The cables had been laying on top of insulation for years before I bought the house.

 

[gman76]

If you are quite happy with the shower you have, try here:

http://www.shower-spares.co.uk/

I have found them very good in the past.

 

[Papabob]

Thanks everyone for your comments and advice. I have now decided to have a new CU fitted and upgrade the shower to probably 9.5kw. I will have this done by a professional! For my own satisfaction, would you please advise me on what CU I should have. If it is a split load CU please advise what circuits should be on the RCD side. Also can you tell me what DNO stands for, is it my electric supplier? When I ring my DNO to request an isolator should I also ask then to upgrade their main fuse to 100A from the existing 60A. Besides the shower I have a Washing Machine, Tumble Dryer, Dishwasher, Microwave, 4 televisions and usual household gadgets. My Oven and Hob are Gas. I thank you all again for this brilliant forum. Thanks,
Bob

 

[davy_owen_88]

If you are having the work done by a professional then leave it to them to source the materials as they will often have a preferred manufacturer and they can often get things cheaper than you can. They will also often offer an extended warranty.

As of the 17th edition all concealed cables that are not mechanically protected require RCD protection so its likely that all the circuits will end up RCD protected, some via RCBO's and others by a separate RCD - but your electrician will design this based on your situation.

DNO stands for Distribution Network Operator and they own the network that supplies your area. You can find out who your DNO is by checking here

They may be able to upgrade the service fuse but this will depend on the supply cable, either way you probably won't need more than a 60A fuse because the time/current characteristics allow for a minor overload for quite some time.