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?'