Cabling for 8.5kw shower

[zemphis]

Hi, just wondering if anyone can help.

We are considering a new downstairs installation of a 8.5kw electric shower. There is also a shower in the upstairs bathroom. Below are a couple of pics ive taken of the fusebox.

The big cable in the middle (10mm?) which is attached to the first 30A fuse is for the upstairs shower. I think the one next to it is for a cooker but is not in use. Would it be possible to instead use that fuse for the downstairs shower? Of course i will probably need to recable it.

The fusebox is a Memera with a max load of 80A (i can check the model if required).

Couple of other questions:
-Would 10mm cable with a 30A fuse be ok for a 8.5kw shower?
-The fusebox is in the pantry. Would it be safe to take the cable upstairs, under the floorboards and then come back out at the rear end of the house through the ceiling (about 12 metres length)?
-Apart from the cable some type of fused bipole switch at the other end of the cable outside the room?
-Anything else i should consider?

thanks for any help given[/img]

 

[RF Lighting]

That cable is a maximum of 6.0mm². It is definatly not 10.0mm²

An 8.5kW shower draws around 35 amps.

Your fusebox can not take a fuse bigger than 30 amps.

Your fusebox has no provision for RCD protecting the shower, which is required.

Also, the supply to your fusebox looks undersized.

I advise that you should maybe look towards getting your fusebox replaced with a modern consumer unit.

You are required to have a local DP isolator as you mentioned.

It is difficult to comment on the cable route, or required size without seeing the job.

 

[Taylortwocities]

Plus any electrical work in a bathroom, installing a new circuit and changing a consumer unit are all notifiable work

See the WIKI //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law

 

[kkynaston]

Your incomming supply definitely looks undersized to start with.
Can you take a pic of your meter and servicehead.
Even with 1 shower on you are possibly going to be nearing the limits that your incomming cable can handle.

Running 2 electric showers on a domestic supply requires some consideration with respect to your supply. Even after a consumer unit upgrade you may need to find a way to 'interlock' the showers so that only 1 can be on at any one time.

Is a power or gravity shower not an option?
In any case, I think you need a spark in to bring your installation up to date

 

[ban-all-sheds]

Also, the supply to your fusebox looks undersized.

As does one or both of the cables in the 2nd 15A fuse...

 

[MarkBarl]

Not strictly in reply to your question, I just wanted to complement you as this is your first post. Clear pictures and detailed description get clear detailed answers. Welcome to the forums.

 

[zemphis]

Thanks for your responses. I am replying in one go to everyone.

That cable is a maximum of 6.0mm². It is definatly not 10.0mm²

An 8.5kW shower draws around 35 amps.
Your fusebox can not take a fuse bigger than 30 amps.
Your fusebox has no provision for RCD protecting the shower, which is required.
Also, the supply to your fusebox looks undersized.
I advise that you should maybe look towards getting your fusebox replaced with a modern consumer unit.
You are required to have a local DP isolator as you mentioned.
It is difficult to comment on the cable route, or required size without seeing the job.

The upstairs shower is also an 8.5kw, so it is running from that 30A fuse shown. Could it be the 30A will take the load because there is nothing else using power at the same time? Except for a washing machine and microwave, which are rarely ever on at the same time as the shower. But if the upstairs 8.5kw shower is running on 6mm cable and a 30A fuse, is that safe or a risk? Even if its been like that for..over 10 years.

Plus any electrical work in a bathroom, installing a new circuit and changing a consumer unit are all notifiable work

See the WIKI //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law[/QUOTE]

I dont think the current installation has ever been notified. Actually i doubt it was cabled by someone qualified. There has never been a problem with the upstairs shower although it was installed many years ago. Would it be too late to notify them now?

Your incomming supply definitely looks undersized to start with.
Can you take a pic of your meter and servicehead.
Even with 1 shower on you are possibly going to be nearing the limits that your incomming cable can handle.

Running 2 electric showers on a domestic supply requires some consideration with respect to your supply. Even after a consumer unit upgrade you may need to find a way to 'interlock' the showers so that only 1 can be on at any one time.

Is a power or gravity shower not an option?
In any case, I think you need a spark in to bring your installation up to date

Yes i agree running two showers simultaneously would probably cause a problem. It's an old fuse box probably from the late 80s or early 90s. I have attached a photo of the meter below. How much would a new consumer unit upgrade cost to supply and fit? A good one with plenty of power.

Also, the supply to your fusebox looks undersized.

As does one or both of the cables in the 2nd 15A fuse...

I think that thin cable goes to a transformer for the doorbell. Someone has just bunged it into that 15A terminal.

Not strictly in reply to your question, I just wanted to complement you as this is your first post. Clear pictures and detailed description get clear detailed answers. Welcome to the forums.

Thanks, i try .

 

[kkynaston]

WOW

You need those tails upgrading now as a bare minimum.

You will need to contact your electric supplier and request an isolator so that you can safely change the tails. Or, just tell them that you need your meter tails upgrading and can they come and reseal the meter while you have a sparky there
You will need to have some meter tails ready for when they come round but your sparky will sort that out.

 

[kkynaston]

Where in the WM are you? I have a DNO mate might do a

 

[ban-all-sheds]

But if the upstairs 8.5kw shower is running on 6mm cable and a 30A fuse, is that safe or a risk? Even if its been like that for..over 10 years.

The fuse is there to protect the cable, and the cable capacity should be related to the fuse size so that overloads will blow the fuse before they damage the cable. (See //www.diynot.com/forums/viewtopic.php?p=81696#81696 ). 6mm²/30A is fine - all that will happen if the load is too great is that the fuse will blow, which could be a nuisance but not unsafe.

I dont think the current installation has ever been notified. Actually i doubt it was cabled by someone qualified. There has never been a problem with the upstairs shower although it was installed many years ago. Would it be too late to notify them now?

It's only been notifiable since January 1st 2005. See //www.diynot.com/wiki/electrics:part_p

How much would a new consumer unit upgrade cost to supply and fit? A good one with plenty of power.

Nobody can say with any accuracy without inspecting your existing installation, but if there are no horrors there then probably mid '00s.

Get at least 3 quotes, ideally at least one from someone personally recommended, and it'll make life a lot simpler if they are registered.

I think that thin cable goes to a transformer for the doorbell. Someone has just bunged it into that 15A terminal.

Doesn't matter what it's for - it's too small for a 15A fuse.

 

[zemphis]

WOW

You need those tails upgrading now as a bare minimum.

You will need to contact your electric supplier and request an isolator so that you can safely change the tails. Or, just tell them that you need your meter tails upgrading and can they come and reseal the meter while you have a sparky there
You will need to have some meter tails ready for when they come round but your sparky will sort that out.

What are the 'tails' - the red and black cables?

6mm²/30A is fine - all that will happen if the load is too great is that the fuse will blow, which could be a nuisance but not unsafe.

So the 8.5kw shower already installed doesnt pull more than 30A, even though it can pull 35A? Thats why the fuse has never blown.

 

[RF Lighting]

WOW

You need those tails upgrading now as a bare minimum.

I almost choked on my drink as I saw the picture

The tails are the wires which connect to your electric meter.

The grey ones on the left look ok, but the red / black ones to your fusebox are definatly NOT.

The good news is you have a nice new cutout, so that is one less thing to upgrade, and it should hopefully have sufficient capacity to allow you to connect your two showers.

 

[securespark]

So the 8.5kw shower already installed doesnt pull more than 30A, even though it can pull 35A? Thats why the fuse has never blown.

There are countless 1000's of shower circuits running bigger loads than the fuse rating.

Fuses and MCB's can withstand a small overload for a long time before popping. The larger the overload, the shorter the time before it breaks the circuit. Eventually, you get to a point where the overcurrent is so great, the breaker trips instantaneously.

So, 10 minutes in an 8,5kW shower on a 30A fuse will be OK. Run the shower for 20 or 30 mins and it may well pop.

 

[RF Lighting]

Even though it is working as it is at the moment, for the reasons detailed by SS, it is still a bad, non compliant installation.

 

[ban-all-sheds]

So the 8.5kw shower already installed doesnt pull more than 30A, even though it can pull 35A? Thats why the fuse has never blown.

The type of "30A" fuse you have will pass 54A indefinitely, and up to 60A for over an hour....