Wylex 17th Edition Consumer Unit

9 Feb 2006
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United Kingdom

Can anyone enlighten me, what is the difference between consumer units to the 17th Edition and those to the 16th.

I ask because I have just been looking at some in a catalogue which says it has Dual RCD and I don't know what the second RCD would be for.

I understand ring mains and wiring circuits in bathrooms are now RCD protected.

Is the second one for bathroom circuits, I assume the rest of the lighting in the house is not though the RCD, so they don't all go off under fault conditions.

Many thanks for any help

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A good 17th CU design will include a direct (non RCD) rail for RCBO's and circuits that might be leaky and hence cause RCD nuisance tripping.

Then it should have 2 x RCD rails, the idea being that you fan service across both to avoid all the eggs in one basket.

A classic (simplified) config would be

Direct- RCBO for smoke detection- so the smoke detectors only trip if they have a problem

RCD1 ground floor ring, 1st floor lights
RCD2 1st floor ring, ground floor lights

hence if RCD 1 pop and kills service to grd ring and 1st lights, RCD 2 will still be active and with service to lights on the grd and ring on the 1st.
In very very simple terms all household circuits must be RCD protected under the 17th edition. The old 16th edition split load boards had a number protected by one RCD - usually the power circuits and then others that weren't. One of the new Regs under the 17th requires you to consider what happens to other circuits if one fails. Protecting the whole lot by one RCD is bad news think of old ladies stairs power trips out and takes lights with it. 17th edition boards have two or more RCD's protecting banks of circuits.

To my mind two RCD's on a board doesnt really meet the 17th edition - but thats a whole new debate.

Far better (and more expensive) to use RCBO's on each circuit then you just lose the circuit thats tripped.
Hi Chris 5 & Cremeegg

Thanks for you comments guys, I’m not sure which way to jump as when the house is done up I shall be hopefully looking for a move.

So just wondering if I could still use the existing CU and have the ground floor ring, electric oven and first floor lights on the RCD and then fit RCBOs for the first floor ring, ground floor lights and smoke alarms as there aren't enough ways to fit a second RCD.

I am right in assuming RCBOs take the same amount of space as an mcb?
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Most RCBO's take up one way widthwise so take the same width as an MCB. Some are two ways wide. However they are all a good 25mm taller so it's a very tight squeeze in several boards and impossible to fit in others. Even where they do fit you need to do a neat job to get all the wires in what space there is left.

Personally I prefer RCBO's in each way - but at at least 5x the cost of MCB's not all my customers agree with me! Would prefer to shuffle potentially "leaky" circuits like cookers fridges freezers onto RCBO's and say leave the lights on the RCD.
I know what you are saying Cremeegg about using RCBOs, they are very good but at a price as you said, and as there is so much other work to be done in the house I think I’ll go for the shuffle option.

The CU is a GET with get GET MCBs, if I don’t mix and match the make of the RCBOs maybe they will fit, unless of course the 17th Edition CUs are made bigger to accommodate the RCBOs.

Guess I could contact the manufacturer and ask them if RCBOs will fit the existing unit, unless you are familiar with the make and have any ideas.
Just a word of caution here.
Single module RCBOs are single pole switching.
They will detect N/E faults but not disconnect them which might not be a good thing in aTNC-S system with loss of PEN or in a TT system.
If only they were DP switching, but they would then be double module width.

Oh and another thing,
if you try to keep kitchen on it`s own ring for power then that can beggar up the split of a dual RCD board.
I've only used Hagers so far for new 17th CU and they are no taller than the 16th ones. Crabtrees I don't think are any taller but I'm sure others can comment better on other makes.

Plenty speak highly of GET accessories - I know they badge some up as own label for Homebase which kinda puts me off when I saw a woman spending £13 on a double switched surface socket and patress today in Homebase.
One of the new Regs under the 17th requires you to consider what happens to other circuits if one fails.

Thought that was in the 15th too, and expanded upon in the 16th??

Section 314 in the 15th and 16th.
I'm glad I'm not the only one who cringes every time I see that posted on here and I still struggle to understand how the CU manufactures can still get away with selling a concept that does not meet the regs.

Why anyone would use those CU's and design an electrical installation where an earth fault on one sub circuit is guaranteed to take out other circuits is beyond me.

The same installers wouldn't dream of ignoring discrimination but the result is the same.

..taxi for pensdown...
There is no such thing as a 17th Edition consumer unit, just as there is no such thing as a 17th Edition fuse, circuit breaker, cable, enclosure, etc, etc, etc...

So long as people continue to use such terminology they will fail to understand the actual requirements.
The situation is not helped by the manufacturers themselves.

Look in PE, there are loads of mentions of these CU's, headed "17th Edition Boards" or "17th Edition Consumer Units"

Even in my QVS catalogue there is mention of one. Also noticed they are still selling the "16th Ed." split-load CU's....That'll confuse 'em...
Hi ebee
When you say the RCBO will detect N/E faults, are you saying it will only detect and disconnect L/E faults, because as you say they are not double pole.

Keeping the kitchen on its on ring for power can beggar the split on a dual RCD board, I assume you mean the loads would not be balanced on each RCD.

Please don’t say they have to be balanced with tool room precision, I don’t think my wife will be too happy if I tell her she will have to plug the tumble drier and dish washer in the lounge and the washing machine and cooker in the kitchen lol.

I’ve since had time to look at the price of RCBOs, one word springs to mind ouch, the ones I was looking at are £40 a pop.
Thanks for your comment Dingbat, I’ll stand correcting having looked at the screwfix catalogue again it does say “Consumer Units & The 17th Edition” and not “Consumer Units to the 17th Edition”

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