Consumer units -how do they work?

[John FlackParticipant @johnflack59079]

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?

[TobyParticipant @toby]

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!

[MuzzerParticipant @muzzer]

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

[TobyParticipant @toby]

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

[John FlackParticipant @johnflack59079]

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.

[John FlackParticipant @johnflack59079]

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.

[TobyParticipant @toby]

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

[Ex contributorParticipant @mgnbuk]

Bear in mind with RCDs that they also trip on Neutral to Earth faults as well as Live to Earth -something a fuse or MCB doesn't do.

I had one of these faults at work late last year, which turned out to be a neutral wire having been sheared off at a connector block by the screw & the loose end had sprung to contact the side of the earthed adaptable box containing the connection. So it is necessary to check all the neutrals, as well as all the lives, for shorts to ground with an insulation tester if an RCD is tripping.

I had the CU changed at home as part of having a kitchen extension built – it was easier (and hence cheaper) for the electrician to fit one, larger, CU rather than add a small suplementary CU for the extension. He initially had some difficulty getting the new CU to stay set, which turned out to be a Neutral to Earth fault in a dining room light fitting, wahich had not shown up on the old CU. A while after the extension was completed, the kitchen circuit RCD started tripping, which I eventually traced to the washing machine. First thoughts were that the several years old washing machine immersion heater element was getting "leaky", but it turned out to be that the plumber had not properly tightened the washer waste trap, which was dripping. Unfortunately, the waste trap was positioned above the washer 13A socket, which had filled with water ! So the RCD tripping was as a result of a dodgy situation & it did the job it was intended to do. These things trip for a reason – it is best to get to the bottom of that reason & fix it properly.

Nigel B

[MuzzerParticipant @muzzer]

Yes, I've had that problem with loose Neutral wiring shorting to earth. You can isolate the power by flicking the NCB to make it safe while you install wiring etc but if the Neutral connection brushes against an earthed box etc while you are doing so, the RCD can trip.

[Clive IndiaParticipant @cliveindia]

And all this has been generated because Robin needs to replace a fan motor?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive India on 06/01/2017 14:48:31:

And all this has been generated because Robin needs to replace a fan motor?

.

Yes … that's the joy of conversation

[Martin 100Participant @martin100]

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,)

Electrical Safety First Best Practice Guide No. 1 (Issue 3)

 

Replacing a consumer unit in domestic premises.

Link replaced  (quote is taken from the best practice on consumer unit replacement where lighting wiring historically does not not have an earth connection) 

Edited By Martin 100 on 06/01/2017 15:36:57

[TobyParticipant @toby]

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.

[Martin 100Participant @martin100]

Yes the OP has a problem and as you pointed Toby out quite early in this thread it could be existing leakage on the existing installation, I agree entirely!

My point immediately above was not all the installation nor indeed the entire consumer unit requires replacement for the sake of one new circuit, or additions or modifications to an existing circuit

Like for like requires nothing more than what was there originally. Indeed by 'improving things' such as extending RCD protection to lighting circuits it removes shock risk but increases the risk of falling down the stairs in zero lighting conditions. The former could be survivable, the latter quite possibly not.

[Nick_GParticipant @nick_g]

Posted by Clive India on 06/01/2017 14:48:31:

And all this has been generated because Robin needs to replace a fan motor?

.

Yes. But the title of the OP was "How does a consumer unit work"

Once this had been explained the thread developed and expanded. – Have you never been to the pub with a crowd of like minded guys.?

Nick

[VicParticipant @vic]

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.

[AjohnwParticipant @ajohnw51620]

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

–

[TobyParticipant @toby]

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

[David Standing 1Participant @davidstanding1]

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 asked the OP if he had a capacitor start motor way back in this thread, and if he was running it off a B curve or C curve mcb, but didn't get an answer.

At my previous house I was running a single phase compressor with a 3hp motor and capacitor start, and these are notorious for tripping out B curve mcb's.

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.

Edited By David Standing 1 on 06/01/2017 19:22:36

Edited By David Standing 1 on 06/01/2017 19:23:51

[TobyParticipant @toby]

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

[TobyParticipant @toby]

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….

[AjohnwParticipant @ajohnw51620]

The OP said it's a dc motor David. Or universal. There may be capacitor in it but only for suppression.

If starting current is causing his problem the C curve might help.

It seems that garage CU's should only have on lighting and one power connection !

Vic If the electrician wont do it you could try pulling it out and fitting one yourself. It very probably will pull out just like wire fuse blocks do. We can change those ourselves – or at least replace the fuse.

John

–

[David Standing 1Participant @davidstanding1]

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 .

[David Standing 1Participant @davidstanding1]

Posted by Ajohnw on 06/01/2017 19:33:54:

The OP said it's a dc motor David. Or universal. There may be capacitor in it but only for suppression.

If starting current is causing his problem the C curve might help.

It seems that garage CU's should only have on lighting and one power connection !

Vic If the electrician wont do it you could try pulling it out and fitting one yourself. It very probably will pull out just like wire fuse blocks do. We can change those ourselves – or at least replace the fuse.

John

–

 

John

As mentioned by Toby, the mcb's will probably be screwed to the CU busbar.

 

Oh, and another thing to mention (I think Toby might have done earlier) is that there is no standardisation with CU's and mcb's across different manufacturers, so a Wylex C curve mcb probably won't fit the cutouts in a Crabtree CU, and so on.

Edited By David Standing 1 on 06/01/2017 19:40:00

[AjohnwParticipant @ajohnw51620]

Posted by Toby on 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

Thanks Toby. I'm surprised that they don't all plug in. I thought that all consumer units were like this one under the cover.

**LINK**

They tried rather low current rcd's in factories early on and I thought some also found their way into houses. Fridges and all sorts tripped them.

John

–

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