Consumer units -how do they work?

[TobyParticipant @toby]

Posted by Russell Eberhardt on 07/01/2017 14:17:10:

Posted by Ajohnw on 07/01/2017 13:49:14:

The reason for the metal boxes is simple – anything goes wrong in there – rats chewing cables etc can happen and it will most definitely blow a fuse if it causes a problem. The other aspect is fire risk and if so fumes. Fire risk is also now the main reason for rcd's but I feel that they are still a bit bound up on other aspects. In other words how much current to cause a fire?

Our French rats are far too fat to get into a consumer unit. (Most of them are in Parliament ). I doubt if the fire/fume risk is much different when you consider the amount of plastic in all the circuit breakers. I would hope that the enclosures would be made from a fire retardent grade of plastic for these prices I would hope so! **LINK**

Russell.

I think this was one of the reasons the UK went metal only (even though the regs say "made of a non-combustable material). Various tests showed that plastic units from big manufacturers that were made of "fire retardent plastic" actually burnt very nicely! So rather than trust them to use decent plastic in the future they just told us not to use plastic at all…….

[EmgeeParticipant @emgee]

Posted by Muzzer on 07/01/2017 15:10:03:

RCDs have been mandatory on TT systems for several decades, possibly the 60s? They were fitted by the supplier and it would have been a serious offence to tamper with them.

Hi Muzzer

I believe you have stated RCD (residual current device) when you should have stated ELCB (earth leakage circuit breaker), the ELCB as it's name suggests was operated by a voltage passing to earth, there was an earth conductor connected to the earth bar metallic frame of the consumer unit and another seperate conductor connected to an earth electrode.

The ELCB was supplied and fitted by the electrical contractor and left with meter tails connected, connection of the tails to the meter was carried out by the electricity supply company after which the lead security seals were attached. The Wylex brand was usually 60A DP black in colour with a yellow circular trip test button, the Chiltern make was grey in colour with a yellow trip testing bar.

The RCD is operated by an out of balance Line and Neutral current and has no earth/cpc connected in any way.

The more modern term RCCB is now mandatory on TT supplies but with a much greater size earth conductor to the stake/electrode.

Emgee

Edited By Emgee on 07/01/2017 18:36:35

[MuzzerParticipant @muzzer]

Good point. As you say, an ELCB is triggered by the current flowing from the ground electrical connection to the earth rod, whereas an RCD doesn't need any earth connection to operate. Acronyms!!

My Cambridgeshire house was wired in TT (overhead supply) and had a grey ELCB. Sounds as if it may have been a Chiltern brand. However, I discovered that it didn't have a ground rod and the gas and water incomers were plastic. The "ground" circuit floated somewhere between ground and 230V – enough to deliver a nice zing due to the cumulative leakage current – until I installed a 1m ground rod.

Incidentally, in US and Canada, the wiring "code" (aka regulations) specify that garage receptacles (sockets) must not be GFCI (RCD) protected. I believe this was based on the need for something like garage door openers, engine block heaters or similar to function without risk of tripping. It always struck me as questionable practice if the garage is actually used as a workshop, given the damp, concrete floors, lots of mains equipment etc often ffound in basement workshop / garages. I fitted an extra outlet from our hot tub GFCI to run my 220V workshop equipment when we lived there.

Murray

[Robin GrahamParticipant @robingraham42208]

I was being lazy – thought it might be a well known component in brushed motors which someone here would instantly recognise. Googling on Schnaffrner FN2010-01-06 reveals that it is an EMI supressor, basically a C/L/R choke..

I think I have enough info to sort it out now.

Thanks., Rob.

[AjohnwParticipant @ajohnw51620]

Posted by Toby on 07/01/2017 17:30:49:

EDIT: forgot to say, the guidlines DO say test and fix for bonding. Strictly no work should be done unless bonding is present and measures less than 0.05 ohms, but it doesn't necessarily need to upgraded to 10mm2 if it appears ok.

Toby

Edited By Toby on 07/01/2017 17:41:17

Maybe I should fit and earth spike and something simple. If it didn't work out I'd have the enjoyment of seeing them test it.

What I meant actually was that they should test the pipe itself. Part if not the main reason for doing it is shorts in the house to a pipe but I suspect they are up to what I mentioned on the gas pipe as 10mm"2 doesn't make much sense. To get the grounding to work well they would probably need to bond the domestic side to the actual gas feed to the house bypassing the flexible pipe that is fitted to our meter back to the stop cock. They change those every now and again and have also now switched to a style that it incredibly light weight. If it came to the bonding failing before the flexible did I'd back the bonding. This doesn't sound safe to me.

An interesting page on who is responsible for what indicating that electricians can / can't pull fuses as the extra isolation isn't shown very clearly.

**LINK**

I don't think I mentioned the saga of the pulled fuse. We have 2 meters with independent feeds. I've long suspected that they are on different phases, Anyway one day no power on the 2nd floor. Other houses had power so I pulled out the main fuse to check them. No seal on them anyway. Ok so phoned them. They had a phase fail so I mentioned the fuse and said I can put it back in. Muttering in the background and then no there might be a spark to which I said I can turn everything off. No we will send some one out. Using a name for them that many will know what I mean 3 suits turned up in a posh car to put the fuse back in all wearing macs not overalls and one had the bits needed to seal the fuse in his pocket. There was even a discussion about who should put it back in. It was delegated by the man who appeared to the the senior one.

John

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[Nick HulmeParticipant @nickhulme30114]

Posted by Muzzer on 07/01/2017 19:14:23:

Incidentally, in US and Canada, the wiring "code" (aka regulations) specify that garage receptacles (sockets) must not be GFCI (RCD) protected. I believe this was based on the need for something like garage door openers, engine block heaters or similar to function without risk of tripping. It always struck me as questionable practice if the garage is actually used as a workshop, given the damp, concrete floors, lots of mains equipment etc often ffound in basement workshop / garages. I fitted an extra outlet from our hot tub GFCI to run my 220V workshop equipment when we lived there.

Murray

Common sense allows long-term avoidance of electrocution, as would adequate education.

But it's obviously better that we have legislation that protects the ignorant and leaves no leeway for those with niche requirements and adequate intelligence and technical knowledge.

Another plus point is a fat living for those retro-fitting un-necessary equipment to replace adequate existing installations.

Given there's nothing else thinning out the herd these days I'd recommend damp string insulation on live wires with adequate labels and signage

[AjohnwParticipant @ajohnw51620]

RCD's do not provide protection against electrocution Nick. They are there to prevent fires. The claim is that the bulk of fires in the UK are caused by faults in the electrical circuitry in houses.

I have had a kick from the mains at work a couple of times. They feel the same even when there is an RCD there. Peoples immunity varies too. PAT probably has more gain in this area but as far as I know not needed in domestic environments.

Wouldn't surprise me if the bulk of house fire of this nature were down to rubber insulated house wiring that has perished but statistics are statistics and don't always account for cause on things like this – just like the effect of so called safety cameras hidden around corners to catch people for minor speeding offences.

Quick edit. I thought that a range of rcd trip currents were still available

http://www.screwfix.com/p/bg-80a-100ma-double-pole-type-ac-rcd/5948P?kpid=5948P&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&gclid=CPXUvPWRsdECFY8Q0wodbIsE_g

The low limit was either 5 or 10ma – can't remember which. Next step as I understand it is none at all and clear marking but it's hard to see why at this level.

John

–

Edited By Ajohnw on 07/01/2017 23:05:09

[EmgeeParticipant @emgee]

Posted by Ajohnw on 07/01/2017 22:58:26:

RCD's do not provide protection against electrocution Nick. They are there to prevent fires. The claim is that the bulk of fires in the UK are caused by faults in the electrical circuitry in houses.

John

John,

30ma tripping current of the RCCB is so designed to prevent fibrillation and so prevent death by electric shock and is well documented . Prevention of fires by electrical faults can normally be achieved by the use of a 100ma RCCB.

Emgee

Edited By Emgee on 07/01/2017 23:36:19

[Clive IndiaParticipant @cliveindia]

Posted by Emgee on 07/01/2017 23:30:35:

Posted by Ajohnw on 07/01/2017 22:58:26:

RCDs do not provide protection against electrocution Nick. They are there to prevent fires. The claim is that the bulk of fires in the UK are caused by faults in the electrical circuitry in houses. John

John,
30ma tripping current of the RCCB is so designed to prevent fibrillation and so prevent death by electric shock and is well documented . Prevention of fires by electrical faults can normally be achieved by the use of a 100ma RCCB. Emgee

Yes, agree with Emgee. The downside is they breed over-confidence when working on live circuits.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive India on 08/01/2017 09:24:58:

… The downside is they breed over-confidence when working on live circuits.

.

There must be a 'Darwin' joke in there ^^^

MichaelG.

[Rick Kirkland 1Participant @rickkirkland1]

Unfortunately there is a load of inaccurate and somewhat dangerous crap being spouted in this thread by people who obviously know NOTHING about protective devices and their usage. I hope to God none of those spouting said crap have got the nerve to call themselves Electricians. There is also a lot of truthful fact being posted especially regarding the requirements of BS7671, 17th edition to Amd 3, 1st January 2015. THAT is the satandard to which I have to carry out my work. The sad part is I actually work with other Electricians, term used loosely who are unable or too idle to read the book and understand it. And before ANYBODY starts shouting about the onsite guide, that is ALL it is, , a guide. I look at certificates where the column asking for the ” max Zs permitted under BS7671″ is put down as one of the figures from a table in the onsite guide. TOTALLY WRONG. And in the Electricity at work act the legislation forbids working on live circuits unless absolutely impracticable to do so. It is NOT ok to work on live circuits thinking and RCD will protect you from stupidity. For Gods sake STOP messing with things you don’t understand and get someone in who does. IT COULD SAVE YOUR LIFE. What price do you put on your life? ?

Edited By Rick Kirkland 1 on 08/01/2017 09:51:16

[TobyParticipant @toby]

John, you cannot use an earth spike for bonding you will get nowhere close to the resistance required. As to the size of the bonding, don't forget you need to consider faults external to the building as well as internal. And you cannot assume that just because today your water pipe is low resistance to the supply earth it will be so next year.

I agree with the comments about RCDs breeding over-confidence, too many people think they prevent an electric, as in some how magically prevent more than 30mA going through. Whereas in practice all they do is limit the duration of the shock.

[Rick Kirkland 1Participant @rickkirkland1]

Here we go again. LISTEN UP! !! You do NOT earth to a water pipe. Bonding is in fact used to prevent electric shock due to the water pipe PROVIDING EARTH POTENTIAL ! Will you people stop posting inaccurate, dangerous ideas on here. I can see another thread coming up where a person asks, I’ve just bought a new 14inch swing by 40 inch between centres lathe, what kind of things can I make on it? And someone answers “you could make a large cast iron fruit bowl by sitting on the compound slide with the cutting tool taped to your arm, , I’m sure this will be ok as I’ve seen photos of massive industrial lathes with the operator sat in a chair on the saddle as the lathe does its work. Some of you lot are death waiting to happen. I really cannot believe what I’m reading here.

[TobyParticipant @toby]

Posted by Rick Kirkland 1 on 08/01/2017 09:49:29:
Unfortunately there is a load of inaccurate and somewhat dangerous crap being spouted in this thread by people who obviously know NOTHING about protective devices and their usage. ………..

Come on Rick, don't hold back, tell us what you really think

Seriously though, electrics is no different to anything else, for example hobbyists messing with dangerous metalworking machines that they have little experience of

I think the great thing is people can post what they like on forums like this and there will hopefully be someone around to correct them if they mis-understand something. Like you say, there are plenty of "electricians" out there that don't really have a clue what the regs mean or why so it is hard to criticise a non electrician for occasionally getting it wrong.

[TobyParticipant @toby]

Posted by Rick Kirkland 1 on 08/01/2017 09:59:46:
Here we go again. LISTEN UP! !! You do NOT earth to a water pipe. Bonding is in fact used to prevent electric shock due to the water pipe PROVIDING EARTH POTENTIAL ! Will you people stop posting inaccurate,

 

Ok, I cannot resist this- that is not quite accurate

the external potential can be something other than earth

Edit: btw, for those that want to read up on earthing and bonding I can recommend the IET guidance note 8 (earthing and bonding). A riveting read (ok, maybe not…) which gives a lot more info although I think doesn't go far enough in explaining why as apposed to just what…….

Edited By Toby on 08/01/2017 10:24:34

[TobyParticipant @toby]

btw. While I am correcting things, I need to give myself a good slap and correct myself!

Yesterday I said……

Posted by Toby on 07/01/2017 17:30:49:

Bonding is a real can of worms! This is one area where it should be sorted even it was ok against the regs when installed. Hence the gas man giving everyone leaflets saying it must be done. In fact the 10mm2 min is actually for PME/TNC, for TNCS or TT it can sometimes be 6mm2.

That should of course have read " In fact the 10mm2 min is actually for PME/TNCS, for TNS or TT it can sometimes be 6mm2".

[AjohnwParticipant @ajohnw51620]

Ok by me but afraid I don't entirely agree. One of the odd jobs I did was design and help install a large ev battery pack cycling installation. 200v+ packs, lots of them. We had some experts in on this particular subject. Why I don't really know as precautions obviously needed to be taken. There were concerns about the fact that it was DC too and much higher voltages when they were on charge. It turns out that much of the information that is available comes from experimentation with pigs but doesn't really match the reports from actual accidents. It can go either way and is somewhat dependent on the person and also just where the current flows. In one extreme is seems that people have caught fire in electric chairs before they die and on the the other hand much lower currents can kill.

I'd strongly advise people not to stick one hand on a well bonded sink and then poke a finger on the other hand into something live. Sums it up pretty well really. That particular path is worst case. It also looks like there is no specific call for sink bonding in BS7671 or by the IET. This may be why.

One thing for sure when I had to work on a live panel they didn't make me feel over confident. The word panel in my sense though is some box maybe a large one with all sorts of bits and pieces in it.

John

–

[Steven VineParticipant @stevenvine79904]

Posted by Rick Kirkland 1 on 08/01/2017 09:49:29:
Unfortunately there is a load of inaccurate and somewhat dangerous crap being spouted in this thread by people who obviously know NOTHING about protective devices and their usage. I hope to God none of those spouting said crap have got the nerve to call themselves Electricians.

Aw Rick. Is that too harsh? I think I've learned all I need to know about consumer units and electrical equipment from this thread. I am now even confident enough to go change my consumer unit, in case it goes up in flames due to the rubber wiring. I plan to go down the local pub and pick up some more information and 'hearsay' from the drinkers before I start. I'll probably thumb through the Screwfix catalog as well, as it contains a wealth of information for potential installers! And of course I will wear thick heavy gloves as I dismantle the consumer unit, in case the rats get me. LOL. (Ps, I'll probably do it live, as I am one of those with a different immunity to electric shocks).

Steve

Edited By Steven Vine on 08/01/2017 11:18:37

Edited By Steven Vine on 08/01/2017 11:31:02

[EmgeeParticipant @emgee]

Posted by Rick Kirkland 1 on 08/01/2017 09:49:29:
And before ANYBODY starts shouting about the onsite guide, that is ALL it is, , a guide. I look at certificates where the column asking for the " max Zs permitted under BS7671" is put down as one of the figures from a table in the onsite guide. TOTALLY WRONG.

Edited By Rick Kirkland 1 on 08/01/2017 09:51:16

Hi Rick

If the Zs table (A41.1to A41.6?) in the on-site guide is copied from and the same as that included in BS7671 why is it wrong to enter the Max Zs permitted for the cct by reference to a table of values ? provided of course the correct part of the table is selected for the type and rating of the protective device and maximum disconnection time for the cct.

The cct measured Zs value will be written in the relevant column in the test readings to check compliance.

Emgee

[Mark CParticipant @markc]

Just a point regarding the Darwin risk. If you do some stupid thing in your workshop and rip your hand off, you probably will learn a valuable lesson but it will most likely be limited to personal education. If you arse with electrics the collateral damage almost certainly will include OTHERS. This is the distinction between competent persons, they are the ones who know that they don't have the correct information and go find it rather than a quick look on wikipedia and some assumptions about what "they" think should be OK.

Mark

[TobyParticipant @toby]

Posted by Ajohnw on 08/01/2017 10:49:16:

Ok by me but afraid I don't entirely agree. One of the odd jobs I did was design and help install a large ev battery pack cycling installation. 200v+ packs, lots of them. We had some experts in on this particular subject. Why I don't really know as precautions obviously needed to be taken. There were concerns about the fact that it was DC too and much higher voltages when they were on charge. It turns out that much of the information that is available comes from experimentation with pigs but doesn't really match the reports from actual accidents. It can go either way and is somewhat dependent on the person and also just where the current flows. In one extreme is seems that people have caught fire in electric chairs before they die and on the the other hand much lower currents can kill.

I'd strongly advise people not to stick one hand on a well bonded sink and then poke a finger on the other hand into something live. Sums it up pretty well really. That particular path is worst case. It also looks like there is no specific call for sink bonding in BS7671 or by the IET. This may be why.

One thing for sure when I had to work on a live panel they didn't make me feel over confident. The word panel in my sense though is some box maybe a large one with all sorts of bits and pieces in it.

John

–

John, you are going to have to explain what exactly you disagree with. Safe currents and voltages are always going to depend on circumstances and the subject. Just because RCDs don't work sometimes (no surprised to anyone I hope….) doesn't mean they don't serve a purpose. Ditto earthing and bonding.

And why should the regs have something specific to kitchen sinks? The general rules on bonding cover them just fine. We could start a whole new discussion on when to bond and when not to but I don't think that would be appreciated

As to live working, it is clear Rick was talking about domestic electrical work and he is right, there is no excuse for live working there except just lazyness. I know we are all tempted to bend the rules sometimes but that isn't really an excuse. I can tell you from experience that when the DNO fuse goes with a big bang and a flash you feel pretty embarrassed and stupid!

On the other hand, if your job happens to be connecting up a new supply from the road to a house you would be well used to working live (in a hole in the road, half full of water…….)

[Rick Kirkland 1Participant @rickkirkland1]

I’ve just bought a brand new Atomic bomb. It has a detonator which is touch sensitive, like one of those bedside table lamps and a vibration detection detonator that goes off at the slightest movement. I need to get it into the corner of my workshop. Would it be ok to nudge it into the corner using a bulldozer with a rubber sheet covering the blade. Charlie down the pub said he didn’t think it would be a problem and he could guide it with his hands as long as he was wearing leather gloves. What do you think as I’m new to nuclear devices and am not prepared to pay the people who are experts in the field and do this professionally . Ps. It’s four feet wide, nine feet high and my doorway is a standard 6′ x 2’6″. What should I do about that? My wife seems unhappy about the whole project as too.

[AjohnwParticipant @ajohnw51620]

Posted by Toby on 08/01/2017 10:21:28:

Posted by Rick Kirkland 1 on 08/01/2017 09:59:46:
Here we go again. LISTEN UP! !! You do NOT earth to a water pipe. Bonding is in fact used to prevent electric shock due to the water pipe PROVIDING EARTH POTENTIAL ! Will you people stop posting inaccurate,

Ok, I cannot resist this- that is not quite accurate

the external potential can be something other than earth

Edit: btw, for those that want to read up on earthing and bonding I can recommend the IET guidance note 8 (earthing and bonding). A riveting read (ok, maybe not…) which gives a lot more info although I think doesn't go far enough in explaining why as apposed to just what…….

Edited By Toby on 08/01/2017 10:24:34

I'd second that comment Toby. If they want to know why not just buy the IET guide.

Maybe I am a control freak but maybe not. I like to know what should be done who ever does it. It can be useful. For instance the gas pipe bonding. The guide states something entirely different in my situation where the meter isn't in the house so if some one at some point wants to wreck the appearance of the place which seems likely I can point that out.

I understand that the guide may mention things that the building regs don't and the advice is to follow them 'cause if something goes wrong an electrician might find themselves being sued.

Toby has raised an interesting point as to why. For instance if some one has a metal waste pipe that contacts the earth it must be bonded.

The gas pipe needs seems really weird to me though. I'd love to know the reasoning.

As to 100ma RCD's. I have no need. If I did I would take the trouble to find out the why's a wherefores of their use. The only reason I posted the link was to show that they were available.

John

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[Russell EberhardtParticipant @russelleberhardt48058]

This thread is getting silly!

Russell.

[Rick Kirkland 1Participant @rickkirkland1]

Toby. . I’m giving up now. You on the other hand could go on for ever answering comebacks from people with just enough dangerous knowledge in their possession to keep making comebacks. This is one of the reasons I’ve not (and many others that have made themselves known to me) have not posted here for a couple of years.I’m in no way painting everyone with the same brush, but the term ‘babies playing with loaded guns” springs to mind.

[Author]

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