17th editions consumer unit

8 Oct 2009
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United Kingdom
Recently fitted 17th edition consumer unit with 2 rcds and insatlled 40 amp shower circuit downstairs of the house - this is fine.There is also a shower upstairs. All is fine except the shower upstairs trips both rcds when the cord of the switch is pulled. It does not trip the mcb. I have replaced the cable from the cu to the pull cord switch and replaced the switch. I have connected a different length of cable to the shower but it keeps trippining both the rcds. Am i correct in saying the shower itself must be at fault ? I am not long qualified, help and advice would be much appreciated
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what you're describing there is a neutral in the wrong bar...
post a picture of the CU with the cover off...
Am I confused - how does it trip "both" RCDs?

Edit .. and if this is the fault finding procedure of someone recently qualified I'm astounded.
live goes out on RCD 1 but doesn't come back... trips RCD 1..
neutral comes back on RCD2, but more comes back than goes out.... RCD 2 trips..
it used to be similar with split load boards, but you didn't have the second RCD to trip..
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There's no such thing as a '17th edition consumer unit'. It's merely a dual RCD consumer unit.
I can install a non RCD protected consumer unit with a standard main switch yet still make the installation comply by adding RCBO's to the circuits which require them.

Also, you say you fitted the consumer unit? Are you an electrician?
You replaced the cable supplying the shower - was this on a whim hoping it would solve your problem?
If not, I assume it failed certain tests? Which tests and what were the results for that circuit?
Why would you think an RCD would be sensitive to the length of a cable?

Do you think you're competent to be carrying out the replacement of a consumer unit including inspection and testing and the installation of a new circuit?
live goes out on RCD 1 but doesn't come back... trips RCD 1..
neutral comes back on RCD2, but more comes back than goes out.... RCD 2 trips..
it used to be similar with split load boards, but you didn't have the second RCD to trip..

Of course, my point was something odd must be wired up incorrectly to trip both. Presumably still wrong after the cable has been replaced...?
I would first look as already said for a neutral in wrong block. But I have had two RCD's for 17 years and on the odd time when one is tripped through genuine fault they other will trip I would guess through spikes produced when first one tripped.

As to 17th Edition consumer units together with digital aerials and DOS yes there labels do not really fit we should call it a Twin RCD consumer unit and a wide band aerial and CLI (Command Line Interface) but for those who do not understand it does make it easy.

Although when my wife complained that the game (Marked DOS 3 and above) would not work on her PC compatible running Windows98se the shop keeper was insistence it was her mistake. She did point out that 98 was higher than 3 and that 98 system did operate the device! Then he started that D stud for Disk at which my wife referred to manufactures book showing it as Device Operating System. (Still had Amiga's then) I could see both sides and the same points can be raised using 17th Edition.

So if the "17th Edition consumer unit" trips due to excessive protective conductor currents produced by equipment in normal operation where there are just too many items leaking a small amount then the consumer unit will not comply with 17th Edition 314.1 (iv) so how can it be called a "17th Edition consumer unit"?

I suppose is should be called a Consumer unit designed to comply with 17th Edition but that is rather a mouthful. And any PC not made by IBM should be called a PC compatible as PC is a registered trade mark of IBM yes and we are all going to do that!!!

Anyway wife says I must get Hover out. Even although it's made by Dyson so I have to go!
Well - when you've done Dysoning (which will go faster if you whizz round on Rollerblades) you can relax in the Jacuzzi with a Thermos of tea, listening to music on your iPod. Is yours in a Portakabin, by the way? And did you Megger the supply cable as part of the testing? I hope you used a Biro to fill out the certificate, and not a Magic Marker, as it's easier to correct mistakes on the former with Tippex. But neither affects how easy it is to repair tears with Sellotape.

Bored trying to think of others - there's a big list here:


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