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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Rcds,mcbs jcbs? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1084999130 Message started by cupid on May 19^th, 2004, 9:38pm

Title: Rcds,mcbs jcbs?
Post by cupid on May 19^th, 2004, 9:38pm

Proberly like lamb to the slaughter,pleeeeeeeeeeese help,just ran a new 10mm cable from CU to new extention to supply cooker,what of the above and what amp do i need? :-*

ps:I have got a good idea its not the last one ;)

Title: Re: Rcds,mcbs jcbs?
Post by plugwash on May 19^th, 2004, 10:43pm

aren't JCBs the things you worry about digging through your armoured runs ;)

rcds are not needed on cooker cuircuits and i would suggest using the non-rcd side of your cu especially if the rcd is small

the mcb should be sized to cope with the rating of the cooker and the socket (if present)

Title: Re: Rcds,mcbs jcbs?
Post by L.Spark on May 20^th, 2004, 1:53am

oval shaped cable 10mm rated at current of ~43A+

Title: Re: Rcds,mcbs jcbs?
Post by cupid on May 20^th, 2004, 9:04pm

Many thanks:plugwash,L.spark.

Title: Re: Rcds,mcbs jcbs?
Post by L.Spark on May 21^st, 2004, 1:14am

no probs, feel free to post back here with any further problems you encounter as were here to help afterall.

Title: Re: Rcds,mcbs jcbs?
Post by The_Trician on May 24^th, 2004, 12:58am

Nobody has asked what rating the cooker is in KW?
So how do we know what mcb is required?

10.00mm T+E is rated at more than 40A but what is the cooker rated at?

Come on lads, pull your socks up here!

TT

Title: Re: Rcds,mcbs jcbs?
Post by L.Spark on May 24^th, 2004, 1:10am

no MCB was suggested it seems, and without the kW you couldnt fuse it correctly anyway, i could have asked when i gave the rating of 10mm, but didnt appear obvious ::)

Title: Re: Rcds,mcbs jcbs?
Post by rabbit_rabbit on May 24^th, 2004, 6:51pm

Depending on installation method 10mm able to carry up to 64 amps but more likely it will be 44 amps for standard installation. So assuming 44 amps thats 10,560 watts - so if ya installing a big 12kW cooker (hob and oven) then rip out that 10mm and fit 16mm! Else a 45 amp MCB will do the trick and dont fit RCD side.

By the way if its an oven ONLY its probably fitted with a 13 amp plug, if this is the case ya need a much lower value MCB and do fit a lower value MCB.

RR

Title: Re: Rcds,mcbs jcbs?
Post by The_Trician on May 24^th, 2004, 7:42pm

Yep - too many variables eh? We need to ask more questions to get more info before replying chaps.

Not having a go here but you can see what might happen.

TT

Title: Re: Rcds,mcbs jcbs?
Post by rabbit_rabbit on May 24^th, 2004, 9:07pm

Well yes TT. Indeed it is a big problem with forums really. It is not possible, when ya think about it, for any non-experienced person or DIYer, to put into writing the data that a pro actually needs. Almost by definition were they able to then they would not be asking the question coz they will know the answer.

Ray

PS. Ya have a PM mate.

Title: Re: Rcds,mcbs jcbs?
Post by L.Spark on May 24^th, 2004, 10:39pm

thanks for point that out Ray, yea you have a PM from me too Trician, it's Rays actualy, it's all PM's flying about tonight eh lol ::)

Title: Re: Rcds,mcbs jcbs?
Post by bright_spark on May 30^th, 2004, 12:37am

It should be feed from the rcd side of the board if the cooker control switch has a 13a outlet on it!!!

BS

Title: Re: Rcds,mcbs jcbs?
Post by plugwash on May 30^th, 2004, 12:41am

there comes the old "feasiblly supply equipment outside the equipotential zone" argument again ;)

Title: Re: Rcds,mcbs jcbs?
Post by L.Spark on May 30^th, 2004, 1:53am

super sparks gotta get a new avatar bad, thats 3 sparks including him now.... ::)

Title: Re: Rcds,mcbs jcbs?
Post by cupid on May 30^th, 2004, 3:47pm

just to say many THANKS again everyone :-*

cupid

Title: Re: Rcds,mcbs jcbs?
Post by unphased on Jun 1^st, 2004, 1:04am

Tut tut lads

Dont forget ya can use diversity on a cooker circuit!!!

First 10A plus 30% remainder plus 5A for socket. Hardly ever need owt bigger than 6mm!
In fact just done a "theoretical" cable size on a 6kW cooker with 15m cable and 2.5mm2 is plenty! I can show calcs if ya dont believe me!

Roy

Title: Re: Rcds,mcbs jcbs?
Post by plugwash on Jun 1^st, 2004, 11:26am

yes according to regs you can
BUT
remember the breaker should be specced to protect the cable so on 2.5mm you can't fit more than 20A
AND
while this is allowed there is a significant chance of a trip and it is likelhy to come at the worst possible time (when prepareing for a large party or similar)

most sparkys i have spoken to reccomend specifying cooker cuircuits to the full rating of the cooker

Title: Re: Rcds,mcbs jcbs?
Post by ban-all-sheds on Jun 1^st, 2004, 3:22pm

wrote on May 20^th, 2004, 1:53am:

oval shaped cable 10mm rated at current of ~43A+

Cupid - I know it's v.unlikely you'll make this mistake, but JIC - this doesn't mean you need to find some twin & earth cable that measures 10mm across...

wrote on May 24^th, 2004, 9:07pm:

Yes - but it's not hard for a pro, or even a DIYer, to ask the questions like "what is the rating of the appliance, does the CCU have a socket, how long is the cable, is it buried/clipped, do you have fuses or MCBs" etc...

Title: Re: Rcds,mcbs jcbs?
Post by ban-all-sheds on Jun 1^st, 2004, 3:25pm

wrote on May 30^th, 2004, 12:41am:

there comes the old "feasiblly supply equipment outside the equipotential zone" argument again ;)

Yup, and with it comes the old and undeniable fact that unless you live in a flat such a socket could feasibly etc etc, and the old and undeniable regs require an RCD...

Title: Re: Rcds,mcbs jcbs?
Post by cupid on Jun 1^st, 2004, 9:11pm

I am taking on board some realy good information here guys and i thank each and every one of you THANK YOU.
This is just a thought when you wire a new build (house/flat) ect, how you no what rating cooker is going to be? i am not being picky one little bit,as i said just a thought.

Title: Re: Rcds,mcbs jcbs?
Post by plugwash on Jun 1^st, 2004, 9:17pm

then you put in 10mm or even 16mm to be safe

Title: Re: Rcds,mcbs jcbs?
Post by Lectrician on Jun 2^nd, 2004, 7:46am

I think it is almost getting to the stage where 2x6mm or 2x10mm are needed, on some new houses we have done recently, there has been a 6Kw Hob, 4.5Kw Oven, and a 4Kw Microwave.

You really do need the info on the appliances before we you start first fixing, there is so much on the market nowadays.

Strange aint it that we now have to install a couple energy saving pendents in a new build, but the cooking appliances are getting unbelievably large :-)

Title: Re: Rcds,mcbs jcbs?
Post by ban-all-sheds on Jun 2^nd, 2004, 9:45am

How long, I wonder, before we start to see 3-phase appliances?

Title: Re: Rcds,mcbs jcbs?
Post by Lectrician on Jun 2^nd, 2004, 9:54am

Fitted a large washer dryer into a house last year (fitted meaning free standing but hard wired.)

It was an american style one, and was 28amp. (you could wash and dry at once.

This model had the links inside it so you could either use it as 28amp single phase, or 10amp 3phase.

Title: Re: Rcds,mcbs jcbs?
Post by plugwash on Jun 2^nd, 2004, 1:14pm

yeah the latter means of connection is included for countrys where low current 3 phase suppplies are around

like a know someone in the netherlands who has 3 phase 25A per phase to his house

also from what fwl-engineer has said i think it will be more efficiant on 3 phase

also if you do have a high current 3 phase board (ie big enough to wire it as either single or 3 phase) it would almost certainly save on cable size to use 3 phase

Title: Re: Rcds,mcbs jcbs?
Post by Lectrician on Jun 2^nd, 2004, 3:25pm

I know some properties near me that have 3ph, with a maximum demand of 30amp, although fused at 100amp.

The REC did this because the houses where at the end of a long run of supply cable (existing), with no HV around to supply them.

Title: Re: Rcds,mcbs jcbs?
Post by ban-all-sheds on Jun 2^nd, 2004, 3:31pm

So are the houses actually wired with 3 different phases?

Title: Re: Rcds,mcbs jcbs?
Post by Lectrician on Jun 2^nd, 2004, 3:36pm

Each house has a 3 phase intake. Its lucky they are large, there is a fuseboard on each floor fed fromm a 3phase board at the intake (so no 400v labels needed which would be awfull!!).

Also good, cause he has a 3phase swimming pool pump, and 3phase calorex dehumid for the pool.

Title: Re: Rcds,mcbs jcbs?
Post by ban-all-sheds on Jun 2^nd, 2004, 4:06pm

So presumably no multi-gang 2-way or intermediate light switches for lights on different floors, otherwise some switches would have 2 or 3 different phases present.

Or are the lights all on 1 phase for all floors?

Title: Re: Rcds,mcbs jcbs?
Post by Lectrician on Jun 2^nd, 2004, 4:11pm

We thought of this in the design. Switches at the bottom/top of the stairs for the large chandelier lights (which light all floors cause its an open stair well).

Lights for each floor are switched by the doors of rooms. Therfore no switches can ever be touched simultaneously. Difficult to explain exact positions, and what lighs are switched, but it works fine. When you come down to the ground floor, you have a short walk before you can turn on the ground floor lights. This doesn't matter as the chandelier on the upper floors lights the gnd floor aswell.