MCB Problem - Possibly needs a larger rated MCB?

[Daniel Nolan]

Hello eveyone!

I've recently passed a DEI and 17th Edition course and I've been asked by a friend about an electrical problem and because I don't have any experience I was wondering if someone could check I've come up with the right solution please?

The problem is this. My friend's got a washing machine, a tumble dryer, a microwave and kettle all running from the same socket circuit protected by a 16A MCB. When the washing machine and tumble dryer are running and she turns on the kettle the MCB trips.

That's as much information as I know. My gut feeling was that the MCB is possibly too small for the loads, so I looked in BS7671 and the On-Site Guide for solutions. I think that depending on if the sockets are on a ring circuit (with a line conductor with a CSA of 2.5mm) or a radial circuit (using a line conductor with a CSA of 4mm) then the MCB should be a 32A Type B, or if the circuit is a radial with line conductor CSA of 2.5mm it should be a 20A Type B.

So, my first question is am I right? Or have I gone completely down the wrong road?

Secondly, if you were faced with the same problem, how would you come up with a solution? I'd like to know if I've applied what I've learnt correctly and if I if I haven't (which I suspect is likely if I'm honest :blush2 I'd like to see how it should be done to see where I've gone wrong.

Thanks for your time reading this!

Danny

 

[bugsy]

w/m eleement 3kw, tumble dryer element 3kw, kettle 3kw - what do you reckon?

 

[Engineer54]

A 20A MCB should be OK to install.
Whoever designed a kitchen circuit to supply all those appliances on a 2.5mm radial circuit, clearly has no idea whatsoever!! Maybe a kitchen fitter or another example from the Electrical Trainee boy's!! lol!!!

 

[micknew]

You obviously have not learnt any electrical theory have you?
Get a qualified sparks in to put it right..

 

[Flyingsparks]

Makes you wonder what they actually teach you on these courses !

 

[rich.250]

I think you are overlooking a lot of factors!! Reference method, max zs combined with CPC csa to achieve this.....
The circuit is obviously functioning correctly. Just designed wrong initially.

 

[rich.250]

Makes you wonder what they actually teach you on these courses !

Hmmmmmm, now that is a question...... LOL

 

[tonycoysh]

My Brother-in-Law has this same problem. CU is on the wall above. 2.5mm radial from a 16A breaker down to a dbl socket above the worktop and a dbl socket below running exactly the same, Diswasher, Washer Dryer, Microwave and Kettle. I'm sure with the distance of cable run without measuring that Zs etc will be fine. So for this one I'll make it a ring and increase cb to 32A mainly because iof their setup it's easier in this instance than upgrading to 4mm and changing the cb to 32A.

 

[D80]

Further information is needed on that circuit really.

Is there a socket outlet on the cooker switch plate? Could plug the kettle in there if so.

 

[D80]

Is it sparks or kitchen fitters putting in these 16A radials? Complete idiots!

 

[SimpleSimon]

You obviously have not learnt any electrical theory have you?
Get a qualified sparks in to put it right..

Get a grip. The guys showing he's using his brain and thinking about it than asking the experts for their advice too, we all started somewhere and comments like this just discourage people.

Sent from my GT-I9100 using Tapatalk

 

[Paul.M]

I'm sorry chaps but I have to say something on this. The op has clearly stated his quals and knowledge and has asked for help of seniors. He has given info that he had seen. I don't think we should be so quick to slag off someone that wants to learn. Just my thoughts gents. Help the lad out, I'm in a good mood tonight .

Ask away mate, ask away.

 

[Paul.M]

Thank-you Simon. Well said words.

 

[Des 56]

Hello Daniel and welcome,you have asked in a very polite manner about your conclusions about an installation after doing this course
Your gut feeling and your thoughts on loading exceeding mcb capacity seem probable with the information given to you
mcb ratings for the type of circuits you suggest seem to be correct

I presume that you would not be considering doing this work just yet,because of your admitted lack of experience and are asking for opinions to further your understanding

Take a look at the install and confirm what you have been told
Assess the loading and inspect the current set up with consideration being given to modifying the existing or installing extra capacity which will depend on 131.8 brb being satisfied, procedures for compliance with building regs also to be followed

 

[Paul.M]

I wish that more new comers would ask questions in this manner. I tip my hat to you Daniel.

 

[Guest112]

im agreeing with both sides of this tbh i dont personally agree with domestic installer courses and it seems they dont teach students enough before the scams let them loose in peoples houses but i do agree that by researching and seeking advice your doing the right thing

 

[MarkieSparkie]

I think you are overlooking a lot of factors!! Reference method, max zs combined with CPC csa to achieve this.....
The circuit is obviously functioning correctly. Just designed wrong initially.

Your last sentence is a sweeping statement, remember this is on BS3036 board and therefore is likely to be designed to 16th edition or earlier. Just because this final circuit is not a standard circuit as defined in the OSG does not imply that it is necessarily badly designed. In fact it was probably designed prior to the inception of OSG. The increasing variety and quantity of labour saving kitchen appliances deployed in the modern kitchen has just over whelmed the original design, which was fit for purpose at the time.

 

[Engineer54]

Markie, the OP wasn't referring to a 3036 fuse board, he clearly stated a ''16A type B MCB'' So i think we can consider that the CU is a lot newer than a 3036 board....

 

[Knobhead]

I’m still bemused by this fascination for radials. Once installed you’ve more or less painted your self in to a corner regarding extending circuits. Sorry it’s off topic really but it’s getting under my skin.
(Rant over)

 

[Silly Sausage]

I wish that more new comers would ask questions in this manner. I tip my hat to you Daniel.

Indeed, a refreshing change, lots of info etc., rather than 'I've got a problem, what's the solution?'

 

[Silly Sausage]

I’m still bemused by this fascination for radials. Once installed you’ve more or less painted your self in to a corner regarding extending circuits. Sorry it’s off topic really but it’s getting under my skin.
(Rant over)

I'm sure there's proper debate going on about the Ring v Radial question by the likes of IET or whoever. Can't be &%$&%$ed searching for it now though.

 

[rich.250]

Your last sentence is a sweeping statement, remember this is on BS3036 board and therefore is likely to be designed to 16th edition or earlier. Just because this final circuit is not a standard circuit as defined in the OSG does not imply that it is necessarily badly designed. In fact it was probably designed prior to the inception of OSG. The increasing variety and quantity of labour saving kitchen appliances deployed in the modern kitchen has just over whelmed the original design, which was fit for purpose at the time.

Just meant that they should have thought of loading in the first place Mark.....
People always overlook what's going on the circuit, not
Having a go at the OP here just the previous installer!!

 

[Deleted member 9648]

I’m still bemused by this fascination for radials. Once installed you’ve more or less painted your self in to a corner regarding extending circuits. Sorry it’s off topic really but it’s getting under my skin.
(Rant over)

Given the number of CU changes I do where the ring is not a ring I'd ban rings tomorrow,install more radials and a larger CU to accomodate...Rings are a pain to test,and very easy to abuse. A 20a radial would be far safer in the hands of a DIYer,kitchen fitter,5DW...etc,etc.....none of which can get within 50 yards of a ring without breaking it.
OK.....I can hear the shouts of "Well,they shouldnt effin touch it anyway"....but they do,they do.

 

[QSGAZ]

radial 16amp breaker type b, ring 32amp breaker type b. If it is a type b try chaning MCB for type c. does the MCB trip or does the RCD trip?

 

[Flyingsparks]

radial 16amp breaker type b, ring 32amp breaker type b. If it is a type b try chaning MCB for type c. does the MCB trip or does the RCD trip?

I am not sure that this would be a good idea.
Type C devices are to used to avoid nuisance tripping and are usually on circuits where there are high inrush currents on start up - they are not used for protecting circuits that may be running at a constant overload.

 

[Engineer54]

Given the number of CU changes I do where the ring is not a ring I'd ban rings tomorrow,install more radials and a larger CU to accomodate...Rings are a pain to test,and very easy to abuse. A 20a radial would be far safer in the hands of a DIYer,kitchen fitter,5DW...etc,etc.....none of which can get within 50 yards of a ring without breaking it.
OK.....I can hear the shouts of "Well,they shouldnt effin touch it anyway"....but they do,they do.

So now we design circuits around DIY'ers, Electrical Trainee's, and kitchen fitters?? I'm afraid were going to have to disagree again!! Never heard anything like that, for a reason or excuse to base a sound electrical design on before!!!

 

[telectrix]

throw out the dishwasher, waste of space. dry clothes on radiators, get a kettle that goes on the gas hob. ssssimplessss.

 

[Andy78]

I'm sure I remember picking up a copy of PE a couple of years back with a large article saying how we should be all wiring kitchens in radials and it was the way forward. Came with handy diagrams and pictures. Maybe that has something to do with it. Do kitchen fitters get taught to wire this way ?

DIY radial mischief struck at my brothers new house when I went to upgrade his C/U. The builder who had lived in the house previously had installed a radial socket circuit....... that served every point in the 3 bedroom house !! It went upstairs first to the front bedroom then hit a JB that spidered off 4 ways to serve 4 sockets in the other 2 bedrooms. A spur was taken from one of these sockets downstairs where a ring had been fashioned on the end of the spur to serve downstairs rooms including the kitchen. There was one proper ring in the house at least. It served one double outlet under the kitchen worktop :S

 

[Deleted member 9648]

So now we design circuits around DIY'ers, Electrical Trainee's, and kitchen fitters?? I'm afraid were going to have to disagree again!! Never heard anything like that, for a reason or excuse to base a sound electrical design on before!!!

Used as an example of how rings can become dangerously overloaded due to poor installation and common faults.....I've also come across plenty of rings left/installed by electricians with broken continuity. A radial is not subject to the same issues unless the OCPD rating is incorrect........I was not suggesting 5DW's and so on should be considered,merely that a radial is more forgiving of faults and poor installation which in the real world are inevitable.

 

[Knobhead]

The builder who had lived in the house previously had installed a radial socket circuit....... that served every point in the 3 bedroom house !! It went upstairs first to the front bedroom then hit a JB that spidered off 4 ways to serve 4 sockets in the other 2 bedrooms. A spur was taken from one of these sockets downstairs where a ring had been fashioned on the end of the spur to serve downstairs rooms including the kitchen. There was one proper ring in the house at least. It served one double outlet under the kitchen worktop :S

I didn’t know whether to laugh or cry at that ! ! ! !

 

[Knobhead]

I’ve got to agree with E54, why degrade a good system to accommodate incompetent installation and testing?

 

[Andy78]

You would have been closer to tears if you had to rip it out and start again like I did. I'm just sooooo glad he put laminate floors in every upstairs room too. Made it so much easier.

 

[Knobhead]

Oh Sh*t springs to mind ! ! ! !

 

[Paul.M]

I've just seen the op's new member intro. Avionics technician, that will explain the detailed question he asked. Not as wet behind the ears as we all thought.

 

[Deleted member 9648]

I’ve got to agree with E54, why degrade a good system to accommodate incompetent installation and testing?

My point is only that I'm not sure ring finals are a good system anymore....While I still install rings by default,I wish radials were standard practice in the uk,rather than rings.

 

[rich.250]

radial 16amp breaker type b, ring 32amp breaker type b. If it is a type b try chaning MCB for type c. does the MCB trip or does the RCD trip?

I agree with flyingsparks, this is not a good resolution,
As he said, and also I doubt the circuit would meet the lower Zs for a type c to disconnect as required

 

[murphyosama]

hi how ya doin mate well for a start tumble dryers pull savage current remember its 4.3 amps a kilo watt try a 20 or 25 amp mcb and buy a good ammeter it will tell you how much current is being pulled , when im first fixing i always runs rings especially in a kitchen where most of the power is going in a house and rings are better for testing pre and post connection