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Member postings for Toby

Here is a list of all the postings Toby has made in our forums. Click on a thread name to jump to the thread.

Thread: Consumer units -how do they work?
10/01/2017 15:40:10
Posted by Les Jones 1 on 10/01/2017 10:21:59:

Thanks Toby for your quick reply. That was my own view. I was thinking of a situation with an intermitant fault were any clue is a great help. It is like trying to get the OP on threads like this to tell us if it is an MCB or RCD that tripped when all they say is that it tripped the power.


yes indeed, in this case having a separate MCB and RCD was helpful, although he might not have thought so when the RCD took out all the other circuits connected to it

10/01/2017 15:37:22

post deleted as Emgee deleted his post that I was replying to.....

Edited By Toby on 10/01/2017 15:38:12

Edited By Toby on 10/01/2017 15:38:25

10/01/2017 09:29:58
Posted by Les Jones 1 on 10/01/2017 08:43:33:

One thing I have wondered is if it had been fed from an RCBO if there is a way of knowing if it was tripped by over current or earth leakage.


Not easily. You would have to test the circuit/equipment to find the fault. The other disadvantage of RCBOs is they are single pole (mostly in the uk domestic market anyway) so will not interrupt a neutral to earth leakage. Depends on what is energising the neutral of course.

10/01/2017 07:46:21
Posted by David Standing 1 on 10/01/2017 01:44:58:
Posted by Robin Graham on 09/01/2017 23:33:06:

Extractor now working fine. I really only needed to know if it was an over current or earth leak that was tripping the box. Armed with the info that it was an earth leak, I tracked it down to a live wire which must have been trapped between the entry box and the casing, perhaps when the previous owner had fiddled with it. Squashed, but no bare wire so probably a capacitative leak. Rewire without replacing components seems to have sorted it.

End of thread?


Edited By Robin Graham on 09/01/2017 23:36:04

Well Rob, that's taken all the fun out of it! laugh.

but good news it was a easy fix

Thread: removing the head/table from a meddings MF4?
09/01/2017 20:04:42

yes, the MF4 is what I was after and so far looks like it is very good condition, there are a few very minor drill marks on the table but it is much much better than any others I have seen for sale recently. The only strange thing is the depth stop, it is a double nut type rather than the clamp type shown in all the pictures I have seen. I don't know if that is a meddings change but I suspect it is a modification. Anyway, the real test will be when I get it running!

The MB10 looks ok except the big setscrew holding (I assume) the rear pulley looks to be cross threaded. I haven't removed it to see what the damage is though. Apart from that it still turns smoothly although I have let to turn it on. The biggest problems is that I don't think I have much use for a drill with minimum speed of 3000rpm but I am sure it will come in useful one day. I just could not resist it for £30

The belt sander is a bit of an odd one, I sort of fancied one before but don't really have the space. But this one just happened to be in the same lot as the MF4 so I had no choice to take it. All I know so far is that the sanding belt looks usable (if maybe a bit coarse) and the drive belt is in one piece. I think something is wrapped round the motor shaft though (maybe bits of an old belt?) and on the front it says 2HP 3 phase, 440V. The spare inverter I have is 1.5HP so I shall have to see if it is man enough for the job (hopefully yes with a soft start).

09/01/2017 19:06:13

An update. The stuff has been collected and loading the drill was not as bad as I feared. I had a mate with me and we lowered the table and head to the bottom so the CofG was low and then walked it onto a sack truck. Getting it into my van was a bit more fun but we ended up just raising the head and table again then tilted it until it was on its side, half in the van, then lifted the bottom and shuffled it fully in.

In fact the biggest problem was that we had taken my mates engine crane just in case we needed it and that just got in the way!

So thanks for all the help and advice, it certainly made it a lot easier!

Oh, and when I said we "collected the stuff" that included a meddings MB10 and a AJH belt sander. I was just able to lift the MB10 into my van on my own but it is a heavy little thing!

Next job is to check everything out, wire in an inverter and hope they all run! So far all I have done is check the motor on the MF4 can be 240V delta and look at how it is wired at the moment. It looks like it has a NVR in the back of the on/off switch wired back to a E-stop, plus what I assume (not tested it yet) is a reversing switch. At least electrics don't scare me

Lastly, a couple of pics of the new toys in my very untidy garage.....

Edited By Toby on 09/01/2017 19:11:36

Thread: Consumer units -how do they work?
08/01/2017 11:55:43
Posted by Emgee on 08/01/2017 11:30:48:
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.


I have to admit I am not clear what Rick means, the on site guide tables are not the same as BS7671 as the on-site has a 0.8 correction factor to take into account conductor temperature. I wonder if he is referring to Cmin, I don't have the latest copy of the guide to check if that is now included in the tables.

Or maybe Rick is refering to circuits with RCDs where Zs can exceed this figures (but Zln should not....). Actually that is something that has always annoyed me, the certs (and hence what most people test) concentrates on Zs, completely ignoring that it still needs to work with a Line-Neutral fault.

EDIT: but yes, Rick's post above mine and Russell before that are right, I am also going to shut up now

Edited By Toby on 08/01/2017 12:00:05

08/01/2017 11:38:19
Posted by Ajohnw on 08/01/2017 10:49:16:

frownOk 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.

laughOne 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, 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.......)

08/01/2017 10:34:13

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".

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 cheeky

the external potential can be something other than earthwink

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

08/01/2017 10:03:41
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.

08/01/2017 09:51:10

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.

07/01/2017 17:46:28
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 wink). 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**


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.......

07/01/2017 17:34:51
Posted by Gordon W on 07/01/2017 17:19:29:

Way back in 1970 we rebuilt an old house, got grants etc. so had to comply with the regs. .Consumer unit had an RCD.

I am guessing that house had an TT earth system (earth rod, rather than earthed through the suppy). I think that as the only reason for needing one back then.

EDIT, just noticed Muzzer already mentioned the need for an RCD on TT systems.

Edited By Toby on 07/01/2017 17:35:34

Edited By Toby on 07/01/2017 17:35:49

07/01/2017 17:30:49
Posted by Ajohnw on 07/01/2017 13:49:14:

devil I didn't want to mention don't have to be used on here. It's a bit like PAT testing there are variables. I do wonder why an industrial plug though. Suggests there is something wrong with what we usually use. I would also wonder if fixed wiring regs were different to plugs.


The latest addition is bugging me. 10mm^2 bonding on gas pipes just past the meter. If you have one of the people in who can work on the supply side of things they have to leave a card saying this should be done. There are also some cowboys about leaving card saying must do it now. The person who left one here was apologetic about it and shook his head when he told me about the 10mm^2. He said he has to leave them just about everywhere he goes.


Anyway leaves me wondering why regs don't state test it and fix if needed as far as bonding is concerned.


I don't think omitting an RCD is quite like pat testing. Pat testing is there to ensure that something isn't damaged or faulty and unsafe. ie works as designed. It is hard to argue that is not a good idea.

Whether you have an RCD or not is a design issue. There are some circumstances where they are not a good idea as they will cause problems. eg machine tools with out of phase currents, medical equipment where an interrupted supply could cause harm, etc.

Hence the regs say RCDs should be used on socket outlets not exceeding 20A and mobile equipment used outdoors with a current rating of less than 32A. The point being that both of these are higher risk, either because you cannot control their use (eg sockets) or because of the environment (outdoors). For lower risk stuff the need for RCDs is not so important.

In fact there is also a exception - for a specific socket that is for use for a particular item of equipment and labelled as such. So I have one socket in my garage/workshop that is not RCD protected. It is specifically for my door entry system because I would really like to be able to get in, even if a bit of water gets in the electrics

So if someone had a machine that was not faulty but still caused RCD problems I would have no problem fitting a non RCD outlet for it. I would of course want to make sure the machine was wired in such a way there was no chance of cable damage or other accidental access to a live part and that the machine was properly earthed.

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.

Like I say, it is a real can or worms and can actually cause a hazard - I have seen a video of a gas pipe smoking due to a PME system fault being earthed through the bonding! However in general it can save lives if there is a fault somewhere outside the property and can be essential in ensuring an RCD works properly for an internal fault.

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.


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

07/01/2017 12:24:24
Posted by Russell Eberhardt on 07/01/2017 11:55:12:

I thought it strange that plastic consumer units are regarded as unsafe in the UK but are the norm in most of the EU then I noticed that "Electrical Safety First Best Practice Guide No. 1 (Issue 3) " is published by Electrical Safety First whose address is The Metal Box Factory etc.

Am I just being suspicious?


To be fair, I don't think they have made metal boxes there for quite a few years.....

07/01/2017 12:20:10

No, I am not going to pick you up on that John

Yes, conduit is not generally used in houses nowadays unless additional mechanical protection is needed. Even then I think the recommendation is 3mm steel which rules out normal conduit! Although I think that 3mm is a figure picked out of the air by some guy at NICEIC so can be argued about. RCDs and running cables in prescribed zones is the usual way of handling things nowadays.

You are also right that RCDs were around well before the 90's, I wasn't clear but I meant common in houses (ie mandated on sockets etc) which I thought started around 2000.

That said, I have just looked at wikipedia and it says the wiring regs were started in 1882 but I think it was the 16th edition that mandated RCDs on sockets and that was in 1991, so earlier than I thought.

As to whether RCDs stop electrocution. They don't, but they certain reduce the risk dramatically in the most common situations. As you say though, it depends on what you grab! I like RCDs and think that (generally) they are a good idea. However can cause problems, particularly with motors and inverters so I can understand why some people are not so keen.

Actually, on that subject it is worth mentioning that it is still well within the regs to supply equipment without an RCD. It just has to be done the right way (and with a risk assessment) and you certainly cannot use a 13A socket! I am of course not advocating that as a solution when the problem is actually faulty equipment

07/01/2017 09:51:17

I've not much to add except I think that RCDs were around in the 1990s so the fan (and hence the filter) was hopefully designed for them.

But yes, I agree with Mike, the easiest approach is to bypass the filter and see if it still causes a problem. If it is ok then a new filter should sort it.

Thread: removing the head/table from a meddings MF4?
07/01/2017 09:25:02

This one will be going on an inverter/vfd so that will provide motor protection and NVR. It does have an E stop switch but its mounted right at the back where there is no way you would get to it in an emergency! Plus I don't think is a good idea having a e-stop between the inverter and motor.

I'll probably do what I did with my lathe, completely bypass the standard switchgear and wire the inverter direct to the motor. The inverter controls giving all the necessary E stop etc.

Thread: Consumer units -how do they work?
06/01/2017 20:22:42
Posted by Clive India on 06/01/2017 19:54:29:
Posted by Nick_G on 06/01/2017 16:49:17:...... - Have you never been to the pub with a crowd of like minded guys.? laugh Nick

Oh yes, forgot - will try it out with my mates down the pub tonight, although some of the group are power engineers who have little respect for the average electrician.
Just for the record - I didn't say anyone here is an average electrician.wink


Edited By Toby on 06/01/2017 20:23:05

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