By continuing to use this site, you agree to our use of cookies. Find out more

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?
06/01/2017 20:19:15
Posted by David Standing 1 on 06/01/2017 19:35:27:
Posted by Toby on 06/01/2017 19:33:04:
Posted by David Standing 1 on 06/01/2017 19:19:50:

I put a C curve mcb in a spare way in the garage consumer unit myself, and took a direct feed via a switched outlet for the compressor off this.

Voila, no more tripping.

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

I have been sitting here expecting a comment/question from you wink 2.

I didn't want to disappoint

Thread: removing the head/table from a meddings MF4?
06/01/2017 20:17:01

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

Thread: Consumer units -how do they work?
06/01/2017 19:33:04
Posted by David Standing 1 on 06/01/2017 19:19:50:

I put a C curve mcb in a spare way in the garage consumer unit myself, and took a direct feed via a switched outlet for the compressor off this.

Voila, no more tripping.

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

06/01/2017 19:31:26
Posted by Ajohnw on 06/01/2017 17:21:44:

You need to know what is tripping out. I think that the rcd is generally right next to the big on off switch. The others will be current trips.

A 1kw motor may take a lot of current when it starts ac or universal dc which is what you have.

There can be several reason for the rcd to trip especially on brushed motors. Effectively they are detecting a miss match between the current going to the motor compared with what's coming back.

The insulation in the motor may be past it's best.

It might be full of dust including dust from the brushes. Sometimes this can be cured by stripping it and cleaning it very thoroughly.

These types of motors sometimes have suppressor capacitors built in. They can cause this sort of problem. So replace both with new ones or remove them. I didn't mention removing them.

I believe your rcd should be a 30ma type. In the early days much much lower values were often fitted.They caused all sorts of problems with lots of things. They are pretty simple things really. Maybe they can go wrong. Probably will if tripped frequently. They usually plug into the consumer unit so can be changed. I think some consumer units use a combined master switch and rcd. Those are likely to plug in as one unit as well. So will the current trips. None of this sort of stuff is intended to do it's thing very often.

John

-

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

06/01/2017 19:13:31
Posted by Vic on 06/01/2017 17:01:40:

I need a C type CB in my box to stop occasional trips but I can't seem to get anyone to fit one. The last two sparkles that have done work for us conveniently forgot to do it.

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

Thread: removing the head/table from a meddings MF4?
06/01/2017 16:40:13

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.

Thread: Consumer units -how do they work?
06/01/2017 15:30:50
Posted by Martin 100 on 06/01/2017 15:18:55:

To add futher fuel to the fire

"There is no legal requirement, and no regulation in BS 7671, requiring an existing electrical installation to be upgraded to current standards. However, there is a requirement under the Building Regulations for England and Wales to leave the installation and the building no worse in terms of the level of compliance with other applicable parts of Schedule 1 to the Building Regulations than before the work was undertaken. (Schedule 1 gives the requirements with which building work must comply,)

From electricalsafetyfirst.org.uk Best Practice Guide 1 (Issue 2)

Replacing a consumer unit in domestic premises where lighting circuits have no protective conductor

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.

Thread: removing the head/table from a meddings MF4?
06/01/2017 15:11:03

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

06/01/2017 14:53:37

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.

Thread: Consumer units -how do they work?
06/01/2017 13:57:14
Posted by John Flack on 06/01/2017 13:44:15:

Thanks again Toby,

Fortunately he has yet to invoice me for the work. He has agreed to return and have a look.

I shall, within reason, attempt to astound him with my (your? ) expert teachings.

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

06/01/2017 13:19:41
Posted by Muzzer on 06/01/2017 13:02:16:

Hi Martin - my comments were really aimed at John Flack's post where he said he had had his CU replaced by an electrician. In which case, the regs should be adhered to in terms of 30mA RCDs, surely. The alternative would be to bypass or respecify the RCDs that came in the replacement CU, which would be very dodgy territory. I doubt you'd recommend that?

Murray

BTW, there's a handy electrician's guide to implementation of the wiring regs, published by the IET. Doesn't cost much and it explains the practical implementation of the regs. I doubt most electricians would understand the formal document which costs £70-90.

Edited By Muzzer on 06/01/2017 13:08:54

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

Thread: removing the head/table from a meddings MF4?
06/01/2017 12:45:44

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

Thread: Consumer units -how do they work?
06/01/2017 12:35:41
Posted by John Flack on 06/01/2017 12:16:36:

Toby

Thanks again that explanation suggests a solution, however should I not have confidence in a professional and qualified electrician to work this all out for me?

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!

06/01/2017 11:54:50
Posted by Martin 100 on 06/01/2017 11:39:56:
Posted by Muzzer on 06/01/2017 10:24:11:

According to IEE (now called IET) Part P regulations, you are required to fit 30mA RCDs (that term includes RCBOs and SRCDs) to any circuits connected to sockets, so if the problem is due to earth leakage, that needs to be fixed.

The wiring regulations (BS7671) are not retrospective so, unless this a is a property subject to a periodic inspection regime (rented) then rewireable or cartridge fuses, no RCD and without earthing to ceiling pendants and light switches is permitted on an original installation dating to say the late 1950's where PVC insulation became the norm.

Sadly Part P of the Building Regulations (a separate document to the wiring regulations) and probably the £250 cost of building regs approval for standalone wiring changes has appeared to have driven the general public away from any permanent wiring installations towards multiway socket extensions that, along with multiway adaptors the fire brigade now deem a new potential source of fire in the home. (despite them generally all being constructed and fused to BS1362 & BS1363)

Also with the introduction of the 17th edition 3rd amendment to BS7671 somehow the tens of millions of plastic (and wood) enclosures that have been used for decades for consumer units are also now 'unsafe' and new installations have to use a metal enclosure or be housed in a fireprooof cupboard. The cynical would suggest they only become unsafe when wired for intensive indoor horticultural purposes when operating at 300% of their intended design rating.

Edited By Martin 100 on 06/01/2017 11:42:31

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.

06/01/2017 11:24:32
Posted by John Flack on 06/01/2017 11:14:35:

OK Toby and Nick

I am a dum dum where electrical definitions are concerned , so I employ a professional electrician to solve my problems of ignorence , if I can't use domestic and workshop equipment after paying for his services what are my options to remedy what seems to be a 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

Thread: removing the head/table from a meddings MF4?
06/01/2017 11:06:59

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

Thread: Consumer units -how do they work?
06/01/2017 10:52:49

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!

06/01/2017 10:46:36
Posted by Toby on 06/01/2017 10:24:18:
Posted by John Flack on 06/01/2017 10:17:42:

Thanks toby

But exactly what is the problem that causes the fuse to trip. The concept that I and my good lady have to liaise as to what 'Ration' of the power supply each wishes to use is not my idea of wedded bliss!!!!!!!!!

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.

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

06/01/2017 10:31:28
Posted by Muzzer on 06/01/2017 10:24:11:

According to IEE (now called IET) Part P regulations, you are required to fit 30mA RCDs (that term includes RCBOs and SRCDs) to any circuits connected to sockets, so if the problem is due to earth leakage, that needs to be fixed.

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.

06/01/2017 10:24:18
Posted by John Flack on 06/01/2017 10:17:42:

Thanks toby

But exactly what is the problem that causes the fuse to trip. The concept that I and my good lady have to liaise as to what 'Ration' of the power supply each wishes to use is not my idea of wedded bliss!!!!!!!!!

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.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Email News - Join our newsletter

Love Model Engineering? Sign up to our emails for the latest news and special offers!

Support Our Partners
Expo Tools July 14
Ausee.com.au
Eccentric Engineering
Allendale Electronics
ChesterUK
Sarik
emcomachinetools
SPG Tools October Seventeen
Warco
Shapiro
TRANSWAVE Converters
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

Visit the Model Engineer
Exhibition website

Model Engineer Exhibition