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#137532 - 07/14/03 04:21 AM Bad shower wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I had a call yesterday from someone I've done work for in the past. Could I come quick, as the main RCD had tripped and wouldn't reset?

When I arrived, he explained that he'd turned off all the MCBs and the main still wouldn't hold. My first thought was a faulty RCD, and knowing that I didn't have an appropriate spare in stock I started wondering where to find one in this rural area at 4 p.m. on a Sunday.

Anyway, when I got the cover off the panel and checked it out I found a dead short on the neutral bus to ground (TT system, and with our double-pole mains open the neutral should be isolated anyway). Luck must have been with me as I started lifting neutrals off the bus to find the faulty circuit, as it was the first one I tried, which fed the shower (9kW instantaneous type).

Went into the bathroom and decided to look at the ceiling-mounted isolation switch first. The short disappeared as I pulled the switch from its box (I'd left my continuity beeper across N-G at the panel).

Inside the switch box I found the insulation on a neutral wire melted away along one side, and it had obviously contacted the bare earth next to it.

Why had it melted? Well, the feeder into the switch was the correct size cable, but when this guy had installed his own bathroom he'd run 2.5 sq. mm cable from the switch to the shower itself!

Our European and Antipodean members will already be shaking their heads in disbelief, but for our American members that's over 37A on a cable just slightly larger than #14! [Linked Image]


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#137533 - 07/14/03 06:56 AM Re: Bad shower wiring  
David UK  Offline
Member
Joined: Oct 2002
Posts: 134
Inverness, Scotland
A typical bodged diy installation Paul!
I think all of our UK members have similar experiences regarding electric shower installations.
I've seen the entire shower circuit wired in 2.5mm T&E, all the way from the board.
Looks like your RCD saved the day before a fire started.
I constantly see 45A pull cord switches failing, when you remove the switch you find burnt 6 or 10mm conductors. I don't know if the installing electricians are not tightening the terminals correctly, or if it's the switch design, all pull cord switches seem more prone to fail than wall switches.

I have a personal dislike of the British instant electric shower, flow rates are pathetic in winter, not to mention the water & electricity in the shower area aspect. If we had more unvented hot water systems like other developed countries, they might fall out of favour.


#137534 - 07/14/03 01:54 PM Re: Bad shower wiring  
Belgian  Offline
Member
Joined: Oct 2002
Posts: 177
antwerp
Here we never have instant electrical showers for the simple reason that any appliances above 12V is not allowed in the bath area.

[Linked Image]


#137535 - 07/14/03 03:41 PM Re: Bad shower wiring  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
A tankless heater doesn't need to be placed next to the shower. Just like an ordinary water heater with tank it can be placed in the basement or wherever is suitable. In practice, it is natural to put it in the bathroom.

I know there are shower heads with integrated heater, but those are not popular in the developed world.

High power tankless water heaters, like 20 kW, will give you a good flow rate, but there are some difficulties associated with them. [Linked Image]

[This message has been edited by C-H (edited 07-14-2003).]


#137536 - 07/14/03 04:18 PM Re: Bad shower wiring  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
The page in your message reads:
Volume 1 "Waterverwarmer voor vaste opstelling" which I take to mean
Zone 1 "Fixed mounted waterheater" ?

That would include a tankless waterheater, would it not?

Another thing:

Volume 2, "Contactdoos met geïntegreerde differentieelschakelaar (gevoeligheid 10 mA)"
which I take to mean
Zone 2, "Socket with integrated RCD (sensitivity 10 mA)". I can't find any requirement for RCD protection in zone 3?

I looked up the Swedish requirements to check for differences. You're allowed to have IP 67 SELV devices in zone 0, lights and other IP 44 (230/400V) equipment in zone 1, but you can't have sockets in zone 2.

These rules all seem a bit random to me. If smething is safe in Belgium, it must logically be safe in Sweden, and vice versa.


#137537 - 07/15/03 05:36 AM Re: Bad shower wiring  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Paul,
I would agree with David on this one, that RCD has paid for itself!. [Linked Image]
And yes, I AM shaking my head in disbelief. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin

#137538 - 07/15/03 07:36 AM Re: Bad shower wiring  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Too many people here don't realize just how much power these instant showers draw. The cheapest versions are now selling at around £50, and I've had people buy one of these without realizing how much they're going to have to spend on the wiring (and plumbing, although they're more likely to tackle that themselves). A common misconception is that you can just tap the power off the nearest convenient part of the ring.

In many places around here there just isn't any spare capacity in the existing panel -- Add the cost of replacing the entire consumer unit or adding another panel and your bid is firmly rejected: "£200?! But the shower itself only cost £50!"

I have to agree with David over the water systems commonly used here. Pressurized hot water systems have become more common in recent years, but the majority of homes still use the primitive open systems. I've never particularly liked the idea of having 240V to ground inside the shower cubicle with just a plastic case around it for protection either.

Quote
High power tankless water heaters, like 20 kW, will give you a good flow rate, but there are some difficulties associated with them.

Better start wiring British homes for 3 phase! [Linked Image]

Oh, and I'll probably need to go up to 4mm cable, right?! [Linked Image] [Linked Image]


#137539 - 07/15/03 07:50 AM Re: Bad shower wiring  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
Electric showers are common (since the 80s) here in Ireland too following the UK trend. Where possible they're not fed from the non-pressurised head tank system. This isn't always possible in older areas of cities where water pressure would be relatively low but in most places it's quite ok to connect it directly to a mains water supply, aslong as it's not simply branched off the same narrow guage pipe feeding the kitchen sink, dishwasher and washing machine as it risks over-heating and scalding!

So overall, they do provide a decent pressure. It's also quite common to have a pumped electric shower feeding from the head tank in the attic in older houses to ensure a decent pressure.

Technically, under the regulations it's illegal to install a shower yourself here. Same with a cooker, however, DIY stores (mainly UK ones) do sell them to anyone who wants one and I have come across really strange installations.

Interestingly UK DIY chains here also often sell BT type phone sockets (?!?), BS546 outlets (no longer legal here), fuse wire (no idea where you would even put it as rewirable fuses are pretty much unheard of)

The legal requirment here is for a specifically rated individual RCD for the shower unit, isloation switch either on the ceiling, or more commonly flush on the wall outside the bathroom door. If more than one electric shower's used they must also be interlocked to prevent them operating simultaniously depending on the rating of the supply to the premisis.

DIY shower installs often blow the main 63amp fuse on the consumer unit when someone decides to run two of them and the oven, grill, 4 hobs simultaniously (something the designer never thought of in 1960!)


I've seen all sorts of dodgy DIY or cowboy jobs (usually cowboy)... e.g. in an old house the shower was simply connected via surface mounted cable (in badly fitted conduit) from the distribution board up along the stairwell and through the bathroom wall. They'd only installed an extra diazed fuse on the board for it and hadn't bothered adding an RCD. It would be normal practice on an old board like if it had DIN rails to simply snap in an RCD or add on on on an extra board along side.

The system in the house had been installed way back in the 1940/50s and had never been designed to cope with electric cooking or large scale heaters.

(cooking would have been gas, heating was gas fired too.. would have been a solid fuel range originally!)

6 X 16 amp socket circuits
4 X 10 amp lighting circuits

He removed the main fuse unit and replaced it with a 63amp one!! The result was the cables running from the meter to the board got quite warm when the shower was running along with a few heavy appliences like the washing machine, dishwasher and lighting.

The ESB actually disconnected the supply to the house when they arrived when the customer reported a strange smell near the meter (burning insulation!)

[This message has been edited by djk (edited 07-15-2003).]


#137540 - 07/15/03 03:19 PM Re: Bad shower wiring  
Belgian  Offline
Member
Joined: Oct 2002
Posts: 177
antwerp
C-H,

YES, yo're right! I overlooked that part which says that a fixed mounted water heater is allowed in zone 1. I want to add that I have NEVER seen a waterheater in zone 1 in Belgium. I must add that ALL appliances including lights have to be on a 30mA RCD in a bathroom - even in zone 3 (which is between 0.6m and 2.4m from the bath). This is written here:

[Linked Image]

[Linked Image]

In practice we always see to it that the earth resistance is under the 30 Ohm.

P.S. These exerts are not directly from the code book which is called the AREI (It stands for Algemeen Reglementeering van Electrische Installaties). They are from a pamphlet which is published by the biggest controle organism in Belgium (AIB-Vincotte). The reason why I took it from there is because it's written in a much simpler way (The other guys had enough problem as it is understanding Dutch [Linked Image] ).

[This message has been edited by Belgian (edited 07-15-2003).]



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