Completing MWC properly as DIY'er

Mmmm.

Perhaps, then, the other ought to be Electrical Installation Works Certificate, then Minor would be the only difference.


I'm still not convinced.
Doesn't Engineering/Irrigation/Road-works refer to the site rather than the work done there? Sewerage Works.
 
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I prefer the term workery

After making a u-turn and starting on it this evening I'm excited to say I'll be posting up more silly questions and long held misconceptions in completing my Workery Certificates.

Yes I should've probably tested it first but as I've committed to get a full EICR done anyway (to get the proper RCD readings at least, bugger buying one of those things) now it'll be tickety boo by the time we're done. Looks like this install was checked over last a few years back anyway with no recorded issues. To be honest nigh on all of it looks stock from when it was built.

I also called building control who confirmed as it's non notifiable they won't be needing to see any certification, which takes significant time pressure off me.

Can anyone make a recommendation for a good book to de-tangle the specific terms I need to be able to confidently fill in one of these forms (either EIC or MEIWC) and just generally get up to date on electrical regs? I know what an ohm is, what the guy's law states and what I^2R does to things, but just need to peg specific measurements from here-to-there to the terms and abbreviations in the rules and forms. I figured maybe this this or this. Maybe you have other recommendations though...
 
Mmmm. Perhaps, then, the other ought to be Electrical Installation Works Certificate, then Minor would be the only difference.
Maybe, but perhaps their thinking (and intention) that 'Minor' would not be the only difference - maybe they thought/intended tha EICs should only be used in relation to 'installation wiork', whereas, by using the words "works", if they subscribed to the definition I posted above, that would also include 'repairs'?
I'm still not convinced. ... Doesn't Engineering/Irrigation/Road-works refer to the site rather than the work done there? Sewerage Works.
Although, as you previously said, 'site' is one of the meanings (as you say, as in "Sewage Works"), that is clearly not the case with the defined meaning I posted above - since that refers specifically to activities, not the place where those activities are carried out.

Kind Regards, John
 
The RCD test as said 6 tests in all, in pairs positive and negative, so first tested at half the rated leakage and the RCD should not trip, then at rated leakage and it must trip there is a time limit but off hand can't remember how long, then at 5 times the rating it must trip within 40 mS.

As said can't measure 40 mS with a stop watch, and so a RCD tester is required, there are two types, some you select the test current, others ramp up the test current so you know exactly how much leakage before they trip, there are special RCD's which light a warning lamp 50% to 90% and only trip between 90% and 100% which need the ramp up type to test them.

This
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multi-test meter does all the tests at just under £400 hunting I found
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this one at just under £120 but for insulation tester got one at £35 as to loop impedance/PFC tester
martindale-ez2500-non-trip-impeance-tester-front-side.jpg
just over £130 so we are looking at just under £300 for test equipment. When I came to rewire my mothers house, I realised test equipment and LABC fees would mean around £800 on top of actual cable, CU, sockets etc. I think I got whole lot done for £2,500 and all done in the week, when paying for mother in a care home, speed means money saved, in spite of having all the qualifications and skill, it still worked out cheaper getting some one in to do the work.

OK not the best re-wire, I wanted to either be able to get mother home again, or rent out the house, she had already put a extension socket in a bucket of water as she thought the red neon was it was on fire, so RCD protection was essential.
 
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Thanks for the pointers on the kit. I can get my paws on Meggers and Flukes I trust (with my life, regularly) but the RCD trip time tester is proving harder. Might be worth the investment if I consider it offset against all the EICRs I might not need to get done by a spark in the future if I should doubt the operation of the thing. Or maybe it goes in the "I love gadgets" cash-write-off category. Either way I'll get the EICR done after, this time round.

she had already put a extension socket in a bucket of water as she thought the red neon was it was on fire, so RCD protection was essential.

Hilarious!

Well obviously being a pilot light for the main burners I suppose it is technically on fire, though
 
But electrics is all about maths, so a B rated MCB is designed to trip at just above its rating for thermal release, and between 3 and 5 times rating for magnetic release, so a B32 MCB will trip at 5 x 32 = 160A so simple ohms law 230/160 = 1.4375Ω give 5% margin to allow for volt drop so 1.37Ω corrected to two decimal places.
What's the 5% accounting for? To my mind the 230V is the EMF at the transformer and in a dead short scenario is dumped entirely as I*R over a resistive load of incoming + ring worst-case-resistance (I guess "ring final" in the proper parlance) - i.e. it's all voltage drop. Is it just a safety margin? Tolerance on the supply? Heating of conductors?

Volt drop is not as easy, as there is a complex formula to give correction figures, and one has to decide what to use as the design current with a ring final, most consider 20A centre and 12A even spaced, so use 26A as the design current, so allowed 5% volt drop = 11.5 volt so again ohms law, so 0.44Ω plus the incoming impedance so around the 0.94Ω mark, I don't think many worry about volt drop.
I hadn't previously but intend to. Clearly something going on in the background here as the 26A is coming from some function of centre + even space loads which I don't have a ref for. I'll look into it but any specifics appreciated.

There are tables in the BS7671 to help you, but you need to understand what you are testing
do you know if these points are summarised in any of the books I linked to above (e.g. OSG) or do I need an actual copy of the BS with me?

Thanks again
 
The 26 amp design current was got from IET lectures, not a book, I was a member for a good few years. The
'Rules and Regulations for the Prevention of Fire Risks Arising from Electric Lighting' was really a on site guide, and until the 16th edition it was not a British standard and the main book had examples like now found in the on-site guide, in 1992 it became BS7671 and at that point the examples went into a separate book, the Unions did produce a guide, as did the IEE as it was then, and it had things like the distance between sink and socket, was more than a meter, and electric kettle leads always less than meter, so you had to unplug before filling kettle. However with waste disposal units and like you have to have a socket very close to sink think mine was around 3 inches, however it is below the sink so can't get wet. So the rule was dropped, this has happened many times, at one point bonding went daft, now with RCD protection bonding is not required.

The IET website lists the books, one for PAT testing, one for installation testing, one for electric vehicle charging points, there must be 100's of them, when I was at collage we had to buy Book 3 which showed how to inspect and test, today there is a lot on line.

The electrical safety council has a series of on line best practice guides, and the IET do a mag which back issues available on line called wiring matters both are helpful, however I do think the best practice guides seem to have lost the remit, to fail an installation because what is plugged in to my mind is wrong.

And this is a good point, one has to use ones skill to read some of the books, for example BS7671:2008 (I don't have current on) says you should have RCD protection for cables buried in a wall, it does not say low voltage cables, so reading the book it would seem you need an RCD for the 12 volt cable feeding the door bell, that's daft, and in the main they have no reference to earth it is an IT supply and you can't to best of my knowledge buy a 12 volt RCD even if you wanted on. It is not a case of just reading the book but also using common sense.

The scheme providers generated by Part P to replace what the Unions had done until closed shop was outlawed required as membership for BS7671 to be adhered to. So for scheme member electricians BS7671 is now law, if they don't abide by BS7671 they are in breach of contract. I always felt the scheme providers were breaking the law on closed shop, as unless you join you can't do much of the work.

So today BS7671 is the electrical bible, not a bad thing in a lot of ways, but one does need to interpret what it says, one needs a degree in English to work it out some times.

So back to basics, is it safe, we use to call is EBADS or something like that, it is the automatic disconnection of the supply should a fault occur. It's also down to the speed at which it disconnects, in the old days of a fuse, if you went a little over the mark with cable length, it could take a second or so longer, who was worried! But with the MCB it jumps between the magnetic part disconnecting and the thermal part disconnecting and you want the magnetic part to work, so loop impedance is now far more important.

Also the other rules, height of sockets, how far along a beam to drill a hole, how close to a corner you can put things, we have the building regulations split into Parts, I can't remember all the names, there is M, L, and J I think as well as Part P where they give socket positions, and even when a fan is required in a bathroom, they keep changing, and Welsh and English are not the same. Rules are dropped, but unlike BS7671 there is not a preamble telling you of the changes, I remember reading how if a bathroom has a window which does no open, you must be able to turn on fan without turning on the light, however now can't find it, seems rule was dropped?

I was competent, however no longer, that category of skill has been dropped.
 
What's the 5% accounting for? To my mind the 230V is the EMF at the transformer and in a dead short scenario is dumped entirely as I*R over a resistive load of incoming + ring worst-case-resistance (I guess "ring final" in the proper parlance) - i.e. it's all voltage drop. Is it just a safety margin? Tolerance on the supply? ...

If I understand what he's talking about (which seems to work out numerically), I think eric gave you an incorrect (or, at least, misleading) explanation of the reason for the "5%".

As you say, voltage drop within the installation is simply a consequence of part of the total loop resistance (which is what determines the fault current in the case of a dead short).

Your "tolerance on the supply' is the closest to the proper answer. For decades, calculation of the maximum loop resistance to allow the circuit's fuse/MCB to operate as rapidly as required in the event of a 'dead short' was based on the 'nominal' supply voltage (formerly 240V, now 230V). That meant that, if the loop resistance was just low enough per the standard calculation, then that loop resistance would be too high for any installation (maybe up to half of installations) whose supply voltage was less than the nominal.

After all those decades of the standard approach being 'wrong', very recently the Wiring Regs introduced the concept of what they call "Cmin", by which one multiplies the nominal supply voltage before dividing by the relevant trip current (e.g. 160A for a B32 MCB, per eric's example). The value of Cmin is currently set at 0.95 (i.e. 95%), so the calculation of max loop resistance for a B32 becomes 230 x 0.95 / 160 - which, as with eric's calculation, gives 1.37Ω.

The regulations are still slightly 'wrong'. The UK supply voltage is allowed to be as low as 6% below 230V - hence 216.2V - so "Cmin" really ought to be 0.94 (not 0.95). That means that if loop resistance is'right at the limit' (per calculation performed with Cmin=0.95, or eric's "5%%), then anyone with a supply voltage between 216.2V and 218.5V (admittedly unusual) would theoretically be 'underprotected.

I hop that makes sense.

Kind Regards, John
 
Not quite as bad as John paints it, as a B type is between 3 and 5 times rated current to trip, so only if the volt drop on maximum and the tolerance on maximum would it actually fail to trip within the required time with a short circuit, it would trip on the thermal part, just not on the magnetic part, so all it would mean in real terms is it would take a little longer.

But of course we have a load of tolerances, including the meter, many designed for 230 volt only, so if voltage not 230 volt then there is an error, and to be frank I normally measure twice, if nearly the same, then assume correct, however items switching while on measures can cause false readings, I spent ages writing a program to work out volt drop using the loop impedance, however the readings are to 2 decimal places only, and even not accounting for switching while measuring the incomer has to be +/- 0.01Ω and the socket outlet also +/- 0.01Ω likely a little more to allow for items switching on/off, so really need to allow +/- 0.03Ω with reading, so with in incomer of 0.35Ω and a reading line - neutral at a socket centre of ring final of 0.94Ω the cable should be 106 meters long and have a volt drop of 11.5 volt. But allowing for error volt drop is between 11 volt and 11.9 volt allow for meter to be out as well and one could not really say some one got it wrong even when one calculates at volt drop of 12 volt.

We also have variations in supply, many supplies are in a ring, not like the ring final, but to allow a section to be isolated so it can be worked on without switch off supply, so the loop impedance is not a static valve, it can vary, the DNO normally consider 0.35Ω as the limit, over that they could not guarantee the voltage would stay within limits, but often measured it can be 0.25Ω or lower, so if the pass mark is 1.37Ω question is should one allow for the supply to reach the limit? If so then 1.27Ω is required to allow for when people are working on the supply and the loop impedance is at the limit. We don't allow for a change in supply loop impedance, if it does raise the thermal part would still protect us, and if you consider a shower supply of 45A your only allowed 0.62Ω.

If you buy the EZ150 plug in tester with loop test, it has 8 lights to tell you the earth loop impedance, remember pass mark is 1.37Ω and the lowest the tester goes to is 1.5Ω it did not even cover the 1.44Ω pass mark.
 
I know the rules allow anyone with the knowledge to do notifiable works, isn't the issue whether you can prove that? In the event of a fatal electrical fire, you would need to be able to show that you have the level of knowledge required to justify whatever you put on whatever form. If all you have is this thread and a youtube play list, I can't imagine that would play out very well.
 
Not quite as bad as John paints it, as a B type is between 3 and 5 times rated current to trip, so only if the volt drop on maximum and the tolerance on maximum would it actually fail to trip within the required time with a short circuit ...
That's obviously true, but one really has no choice but to consider 'worst case scenarios' - otherwise one is just gambling.
... it would trip on the thermal part, just not on the magnetic part, so all it would mean in real terms is it would take a little longer.
Again true, but again, the authors of the regs have, for better or for worse, decided (albeit essentially arbitrarily) that the requirement should be for a disconnection time (in response to a 'short circuit') that requires magnetic tripping. As you imply, in reality "a little longer" would probably make no material difference, but it is not really for us to over-ride the regs in that way.

Kind Regards, John
 
I know the rules allow anyone with the knowledge to do notifiable works, isn't the issue whether you can prove that? In the event of a fatal electrical fire, you would need to be able to show that you have the level of knowledge required to justify whatever you put on whatever form.
True, but that's as much of an issue in the case of 'electricians' who have been 'trained' in just a few days as it is for a non-electrician.

The only 'knowledge' (in addition to 'skill') one needs is knowledge/understanding of the requirements of BS7671. If one can demonstrate that what one did was compliant with the requirements of BS7671 then, if one did it 'competently' (in a 'skill' sense), that would be deemed to demonstrate compliance with the law.

Kind Regards, John
 
I know the rules allow anyone with the knowledge to do notifiable works, isn't the issue whether you can prove that?
Yes, I suppose it is.
For notifiable work, unless you are a registered electrician, you must, by law, notify the Local Authority before you start the work. It is up to them whether they accept that you are able to do the work. If you, as a DIYer have no test equipment, I presume they will not deem you competent.

In the event of a fatal electrical fire, you would need to be able to show that you have the level of knowledge required to justify whatever you put on whatever form. If all you have is this thread and a youtube play list, I can't imagine that would play out very well.
Probably true.

Registered electrician means registered with one of the 'self-certifying' schemes (self-certifying is a misnomer and actually means self-notifying). There are many hugely qualified life-long electricians who are not registered because they don't need to be for their work and conversely many totally inexperienced 'electricians' who are registered. In England now there are so few notifiable jobs that it is virtually pointless, however, whatever anyone is doing Part P of The Building Regulations applies.

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That's it - such is life.
 
There is only one organisation who can decide if you have the skill, and that is the courts. When you look at past court cases they seem to come up with some odd ideas. To my mind an electricians mate is an instructed person, and I would in the past have had no qualms sending one to plug in a tester and write down the results. However the court did not agree, they seemed to say the electricians mate did not have even that amount of skill, I suppose the events leading up to the court case showed the mate in fact did not have the skill to do the job, as instead of writing down what the meter said, he fudged up some results after talking to others in the mess hut.

I am talking about the Emma Shaw case. Where the foreman was found guilty, and this would be the same if either a scheme provider authorises some one without the skill or LABC authorises some one without the required skill.

I think it is easy in hind sight to say some one did not have the skill, if they got it wrong, then they clearly do not have the skill, where the problem lies is before anything goes wrong, and some one has to decide if the guy doing the work has the skill. Of course some one may have the skill, but does not use due care and attention. Or simply just in a hurry and greed takes over, the what can I get away with workman.

As to BS7671 it is also down to how you read it, one would need a degree in English, take the "Every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation." Clearly you can use as many MCB's as you like, if it's all being fed from the same RCD it will not reduce the possibility of unwanted tripping, and the RCD does measure the current which is not balanced, and if the current goes over a set limit it will trip, so I would say it is an over current device.

Remember "Circuit. An assembly of electrical equipment supplied from the same origin and protected against overcurrent by
the same protective device(s)."

However many argue a RCD does not form a circuit.

314-01-01 with old 16th Edition had no reference to RCD but 314.1 in 17th did, and at that point the duel RCD consumer unit came on the market, manufacturers seemed to consider it was good enough to have just two main circuits, feeding multiple sub circuits, they also produced the all RCBO consumer unit, and it is up to the skill of the designer to decide what is required, there is no cut and dried answer. Where the stairs are in the centre of a house with no window directly lighting them, it could be argued they need a RCBO supply, however that does not help if the incoming supply fails, so an emergency light would be better.

But the whole point I am making is there is no cut and dried answer, the regulations have reduced in some ways the skill required, but they are not law, you can fit German sockets if you really want, even if they don't comply with regulations. So to make the decision you need to understand to some extent the why, and not just try and follow what it says, but what you think it is intended to say.

If some one says they are going to decimate the work force, it may technically mean getting rid of 1 in 10, but often it means something very different, so one has to learn to read between the lines.

So if you modified a ring final and once complete you tested each socket with an EZ150 Martindale plug in tester, although it passes at 1.5Ω and the limit is 1.37Ω should at a latter date some one was injured the big question is, would the court decide it was due to using unsuitable test equipment, or would they consider you had done what could be reasonably expected, I would hope the latter, or there is really no point in Martindale making the tester.

We will of course have to let the courts decide.
 
and the RCD does measure the current which is not balanced,
Exactly.
It measures the residual current, hence its name, so it in fact measures the under-current in the Neutral conductor compared with the Line.
Obviously an under-current greater than a set value cannot be an over-current.

and if the current goes over a set limit it will trip, so I would say it is an over current device.
In any case, that is clearly NOT what is meant by an over-current device.
 

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