Member postings for Toby

I didn't want to disappoint

Thanks Nigel and Steve for that warning. At the moment I am probably limited by the size of my drills but no doubt that will change

You forgot to mention that you also did a loop impedance test to check the C type will trip correct....

Umm... John, some of what you say is perhaps confusing. so.......

> I think that the rcd is generally right next to the big on off switch

actually, often in a modern consumer unit there are two RCDs. Often one at each end (or one at the end and one in the middle). On mine I only have one but it is the half way along the row

For the record, an RCD is generally easy to identify by the fact it has a test button and is double width. An RCBO has a test button but is normally single width.

> I believe your rcd should be a 30ma type. In the early days much much lower values were often fitted

I don't think I have ever seen an RCD with less that 30mA rating in a domestic consumer unit. Perhaps you are thinking of Voltage Operated Earth Leakage Circuit Breakers? They were a menace and I think the recommendation is to change them wherever they are found.

> Maybe they can go wrong. Probably will if tripped frequently.

They do go wrong and can be damaged if they trip when there is too high a current flow. They should be tested every 6 months using the test button and every 5 years using a proper tester. And replaced if they are known to have taken a full fault current. Not that either generally happens.....

> I think some consumer units use a combined master switch and rcd

Sometimes, but it is not common in the UK. I think (although I will stand corrected...) that RCDs do not meet the BS standard required for a main isolator switch. It is more common in garage consumer units where the RCD is not the main isolator (that is in the main board in the house).

I am assuming your reference to plug in units refers to the old plug ins that replace cartridge or wired fuses in the likes of MEMs or Wylex boards. I am not aware of any modern boards that use plug in breakers, assuming you don't count the crabtree starbreaker boards that have a plug in busbar connector.

hth. Toby

I am surprised you didn't then conveniently forget to pay them

Thanks for that Mike, so possibly Nigel's is actually a MF5 rather than an MF4?

unfortunately mine does not have a lifting rack but I am already thinking about ways of adding one, perhaps a vertical threaded rod, motor driven, although I have not worked out how to do that and still allow the table to rotate sideways. Perhaps a rotating collar between the head and the existing chuck-key collar? Anyway, maybe a simple limit collar is the most pragmatic solution short term at least.

I am keeping my fingers crossed the gears ok. It was certainly smooth and quiet when turned by hand but I guess I will not know for sure until I get it and have a proper play with it. I don't suppose spares from Meddings are cheap.

I am not sure why but that link gives me a file not found error. If others have the problem you want guide 1, issue 3 from here.... **LINK**

To avoid confusions though, that quote refers to upgrading the existing installation. If the new work done relies on the existing installation to meet the regulations (eg bonding, earthing, RCD protection) then the existing stuff does need to be upgraded to support it. Sorry, I am labouring the point but I have talked to electricians who do not understand the distinction and think it is ok to add a new socket to a circuit without adding RCD protection or worrying about loop impedance and disconnect times.

According to the manual Mike sent me this one is greased rather than oiled so I am hoping that is not a problem.

Thanks Nigel and Steve,

There is a chance I might be on my own when picking this up (apart from auction staff but I doubt they will want to help) so I think I will definitely try to drop it down the column first and then slide the whole thing onto my sack truck. If I need to separate it I might try the opposite of what Steve did when re-assembling it.

I certainly don't fancy standing on a workmate and hefting a 70kg weight so I think that approach is out.

I am curious that yours has a 3mt spindle Nigel. Everything I have read says the M4 range has a 2 MT. I will have to pull mine out and check when I get it.

Ah, in which case take care how you handle him. If he has not yet been paid for the fuse box change he might be reluctant to get too involved in discussions of the current problem, perhaps thinking he will be blamed for "breaking it, because it worked before" and being told he has to "fix it" before he gets paid. Neither of which is likely to be fair as it is probably a pre-existing problem.

Best case, he is keen to sort it out but perhaps needs your understanding it might not be for free, worse case he just wants his money and shot of the problem. In which case you might get a "can't find anything wrong guv" type response.

There again, I might be over thinking it

I am assuming Martin was responding to Johns comment

"our fuse box was not up to code and required replacing, though it had been OK for the 30 years"

Strickly that is wrong, as Martin said, there is no need to update a unit just because it doesn't meet the current regs. However if new work is being done (eg adding a socket or circuit extension) it can often be more cost effective long term to update the fuse box to gain the RCD protection etc. Plus it is no bad thing as safety has come along way in 50 years!

I think the book you linked to is the building regs guide, for the wiring regs you want this one: **LINK**

I agree though, both are excellent summaries (although my copies have some minor errors).

Any registered electrician should understand (and own) the full regulations as they have to pass an exam on the subject before being accepted by a registered body.

That said, that highlights a problem with the Part P registration schemes and larger companies. It is completely within the rules for a company to have one "qualified supervisor" who has past the exams and registered supervising a number of "electricians" who have not. So there is no guarantee the guy that turns up at the door has even read the regulations, let alone understood them

EDIT: just re-read your post and I might have misunderstood your meaning. Yes, fitting a new consumer unit but bypassing the RCD etc is definitely not allowed, all new work needing to meet the current regulations.

Edited By Toby on 06/01/2017 13:26:26

ok, thanks, that is good to know. I might do that then as I already have a solid ply box in my van. Saves me taking it out

yes, you should. Unfortunately, as in all walks of life, there are "electricians" and "electricians". Meaning some are experienced enough and have the will to do it right, some either do not have the experience or just don't see there is enough money in it to bother so will just fob you off.

I understand you don't want to get too involved in this yourself but I am guessing that, as an engineer, you have a logical mind and understand how to problem solve. Given that I would advise you get an electrician in, explain the problem and ask for his advice. If he doesn't suggest an initial investigation to find out if there is a fault then I would be suspicious but otherwise I would expect a clear explanation of what he intends to do and why. If you don't get that then I would suggest trying another electrician.

Btw. often the one man bands are better than someone from a big company. They have more incentive to do it right.

Oh, and unfortunately you need to expect to pay a reasonable amount to get it sorted. Eg, to turn up at your house and spend a few hours testing circuits and appliances I charge at least £100 with a proposal to review the situation if that money did not find a solution (ie I could not find a fault/problem to fix). From there you are talking anything from no extra (ie I found a problem and fixed it within the £100) to £hundreds to install a new circuit. And I think my prices are on the cheap side (judging by how little money I made as an electrician......)

It is possible but unlikely the problem has been caused by poor work by the guy who changed your consumer unit so unfortunately this is extra cost. I learnt very early on to warn customers about this when changing a consumer unit as it potentially save a lot of "you broke it, no I didn't" type arguements later on!

I agree with most of what Martin has said with a couple of provisos....

1) although I agree on the fireproof consumer bit being a massive over-reaction, I have seen a worrying number of "modern" plastic enclosures where the terminals are loose to the point of overheating and hence causing a fire. I think this a two fold problem. First, too many "electricians" who have not been taught the right technique for "snugging down" a connector. Just tighten it up and leave and you can guarantee it will loosen later. 2nd, the old boxes used to have double screw connections, the modern cage clamps are good if used properly but are easier to get wrong.

2) I would class a metal light fitting without an earth as a code C2, ie potentially dangerous and requiring fixing. This is in line with industry guidance. If it a plastic class II fitting then yes, no problem.

First thing is to make sure the root cause is understood.

1) A simple overload. Solution is to seperate high current stuff onto a seperate circuit. Eg put your workshop on its own circuit, perhaps even with a serperate RCD.

2) If it is start up current problems then perhaps a change of MCB type (or even RCD type) might solve it. But it would need an electrician familiar with your house to advise. Or it could be you need to look at the drive circuits (eg startup caps etc) for your machines.

3) If it is a fault. (eg earth leakage etc) then find and fix the fault.....

fwiw, on my house (given I am qualified as an electrician) I replaced my consumer unit with the following:

Low usage circuits like washing machine, cooker, shower etc on a RCD, lights, sockets on their own RCBOs and garage on a type C MCB without RCD protection. Supply to the garage is armoured cable and it has its own consumer unit that gives separate RCBO protection to power and lights. That way, if I have a particular item (eg my lathes VFD) that will trip a standard RCBO/MCB I can swap that out to a separate circuit with protection to suit.

Basically, you need an electrician prepared to design the installation properly. Unfortunately a fair few are only prepared to fit standard circuits and are not much interested in fault finding!

btw. a type C MCB is one that will cope with a higher inrush current than normal and an RCBO is basically an MCB with RCD protection built in, so it does not need separate RCD protection.

Edited By Toby on 06/01/2017 11:29:35

thanks Mike, I have just measured it and unfortunately I only have 50 to 54" headroom in my van. I did think I might be able to lie it down but with the top of the column supported on a box so the side of the head is held off the ground. I wasn't sure that would be good for the column though.

So yes, I think I will probably end up removing the star wheel as the other side has the gear change plus a lot of switch gear not shown in the picture above or the manual.

Edited By Toby on 06/01/2017 11:09:09

Oh, (and with apologies to Robin for going off topic) I was told by a DNO (supplier) engineer that they use diversity when calculating the requirements for new supplies and that they typically set that at 20A per house. So if they are supplying a new development of 20 houses they will allow 400A total for that development.

Obviously individual houses can exceed that (generally the house supply fuse is 100A nowadays) but if the average use goes above 20A per house they have problems!

btw, to expand on the domestic strife this might cause. Assuming your problem is just too much load causing an over current trip, your problem is diversity. Most circuits are designed using diversity. This is where the designer will tot up the total load but take into account how much a device might actually be used.

So lets say your cooker is a fancy one with multiple ovens etc. It might be 11kW rated (so that is 47A) . But there is very little chance that all the elements will be on together, and if they are they will not be all on for a long time (the thermstatic control will turn them off when up to temperature). So the guidlines say you should treat it as 10A plus 30% of the remainder, so that would be 10A+12.3A=22.3A in this example. Same with heaters, we take 100% up to 10A plus 50% of that over 10A.

Using these sums we can get a "design current" for the circuit which is much less than the sum of all the rated loads.

The trouble is, if you do happen to use all your machines which the wife is using the cooker to its max and the kids are having showers you can be taking well over the design (and hence protective device) current and cause a trip. This gets worse if (for example) your machines have a high startup current as this will like push the whole system over the edge when you start the machine.

To be honest, I am amazed how little problem this diversity system works. For example in my house I have a 11kW rated oven, an 11.5kW rated shower, 2nd shower, in winter sometimes electric heaters running. Total load well over 150A probably. But it all runs fine of a 60A DNO supply fuse.......

Edited By Toby on 06/01/2017 10:46:59

Not quite. I am going to be pedantic here but.....

the IET regulations are BS7671. Part P is a building regulation that does not actually cover the protective devices and wiring requirements.

John, see my edit to my post above but there are a few reasons why it could be a problem now.

1) as shown above, if you were taking over 45A but less than 55A when cooking the xmas dinner it would be ok on a fuse but not ok on a MCB.

2) If any equipment gives a startup spike of current might not be enough to blow a fuse (they are slow acting) but could be enough to trip an MCB. MCBs have two parts to them, a thermal trip which reacts to long term over current and a magnetic trip that reacts to high currents but acts much faster. Hence any current over 5 times the MCB rating will trip it in less than 0.1 seconds.

3) if it is the RCD tripping now then you could always have had a problem but a normal fuse would not detect that and hence protect against it.