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Distro and the 18th Edition Wiring Regs.

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Jasonstry View Drop Down
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    Posted: 21 October 2018 at 4:54pm
Hi all,

I have spent a Sunday morning looking at the potential impact of 18th Edition wiring regs when it comes to my stage distro but am getting conflicting info. I also notice there is a lot of distro for sale at cheap prices atm, which makes me wonder. Anyway, if I am struggling to get accurate info, I imagine others are as well, so I thought I would pose the question here so any replies will help other people as well as me and maybe stop people wasting money.

In my case, I just have 2 units with 32A single phase in and 2 x 16A out. The input is on an MCB and the outputs are on RCDs. I have been told it will be fine but somebody else says the input needs to be changed to a RCD and the outputs to MCBs and I have also been told that the outputs should now be on RCBOs so I don't need anything on the input! Using RCBOs makes a lot of sense but could get expensive very quickly for some people. On the face of it, RCDs should still be OK but what do I know?

All advice very welcome.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 5:04pm
I've also heard that all final circuits should be on RCBO's but don't take my word for it!

It makes a lot of sense and although it's more expensive I would prefer distro's done that way.  Especially now a lot of modern equipment has high leakage currents due to SMPS.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 7:13pm
There was another thread about this recently, seems to be the case. Does make sense regarding increased leakage over kit
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Post Options Post Options   Thanks (0) Thanks(0)   Quote spongebob Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 7:17pm
Originally posted by Jasonstry Jasonstry wrote:


In my case, I just have 2 units with 32A single phase in and 2 x 16A out. The input is on an MCB and the outputs are on RCDs


The output protection must be an RCBO otherwise they're not correctly limited to 16A output?

Post a photo up perhaps?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote James Tengo Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 7:23pm
As far as I can tell, old kit with just mcb’s will be harder to justify using. RCD on incomer and MCB per outlet still acceptable (like most home distribution units in existence) but new distros should be RCBO per outlet. All the distros we have bought in the last few years are RCBO per outlet anyway, so not much change for us.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 8:03pm
I was working in a hotel recently and while investigating whether the 63/3 I was using had any RCD protection, I came to the conclusion that at best all the 13A sockets around the room were protected by a 100mA RCD, worst case none.  The 3ph DB had no RCD's in it, there were two additional ones in a separate box where obviously some protection had been retro-fitted to some of the circuits but it was impossible to determine whether it was some or all.

What's the actual legal situation for a commercial premises such as a hotel?  Is it ok since it's an old (not antique by any means) installation not to have any obvious and certainly no 30mA RCD protection on the final circuits?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote James Tengo Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 8:34pm
Previously 16th & 17th were not retroactive, not checked if 18th is. There used to be an allowance for physical separation, for example if a truss was 6m in the air then it was deemed acceptable to have it on a supply that didn’t have RCD’s, where as fixtures on the stage, accessible to human touch, were preferred to be covered by an RCD. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jasonstry Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 9:07pm
Cheers all,

Sorry, brain was going round in circles - still is. Of course my distros have an RCD on the input and an MCB for each of the 16A outputs, not the other way around. In theory, the As I understand it, the new regs require that each socket rated up to 32A has to be protected by an RCD, whether indoors or outdoors when it used to be 20A indoors and also that the circuit should disconnect in 0.4 seconds. None of that seems to indicate RCBOs to me now, any more than it did before. I am seeing distros being sold with RCBOs on the input side and MCBs on the outputs as in https://www.stage-electrics.co.uk/shop/sales/stage-engineering---electrical/electrical-hardware/portable-power-distribution/product.aspx?code=353-0663 or https://www.distributionzone.com/Products/Power-Distribution/Portable-Power-Distribution/PCE-IMST-Distribution-Box-32A-230V-2P-E-RCBO-1-X-3. That doesn't make any sense to me either as the socket upstream should be protected by an MCB anyway. Rubber Box have some with RCBOs and some with MCBs suggesting both are OK. All very odd. As I say, I can see merit in using RCBOs but just wondering , partly because I will be investing in another one soon. 

I don't think 18th Edition is retro-active but it won't matter as I am sure that every temporary installation will be classified as a new installation.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JEB88 Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 9:37pm
The 18th edition only comes into force for any circuits designed after 2019. Anything designed before that is ok, otherwise it would lead to a mass expense for everyone, not only does it require RCBOS on every circuit it also requires metal Dist boards and fixings & fastenings.

Literally just completed the course a couple of weeks ago. Although have a funny/frustatrating story about the test!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote James Tengo Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 9:39pm
In the old single RCD to MCB style distros it was common to have a variable RCD that could be set up, for example, as 1a leakage and 2s delay. This might be required for a specific scenario, large LED screen for example, yet would be inappropriate under 18th, hence multiple smaller RCD’s per outlet being the fashion. As you already have an MCB per outlet why not combine them and use RCBO’s. It’s not the exact wording of the regs, but it’s the implied outcome
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Post Options Post Options   Thanks (0) Thanks(0)   Quote James Tengo Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 9:45pm
And the distros you linked to are overall 30ma RCD, and individual MCB per way.
RCD - leakage protection
MCB - over current protection
RCBO - Combined leakage and over current protection

Don’t get to into anti arc protection, that’s another issue we may be facing shortly...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dylan-penguinmedia Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 9:53pm
I’ve been reading a few things on this, and although admittedly I’ve not read the official text yet, the part that isn’t clear is, I’ve seen it stated that circuits up to 63a must be 30ma rcd protected - I’m guessing that’s final circuits? So upstream distribution is still subject to discrimination and higher leakage protection is allowed? Unless the final appliance is for example a piece of equipment with a 63a inlet, where 30ma max rcd is relevant again?
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