Consumer Unit Replacement time.

[MasterAbacus]

Right guys, time to replace my Consumer Unit, But im after some advice.

Currently Its a Fused / Wired consumer Unit, and i want to change it to a more modern MCB Type.

Ive not looked into the Fused Comsumer yet, but i can tell you it has 6 Fuses as follows:

1 x (Green) that has a Mcb pluged into it 45 Amp (Labled COOKER)

2 x (White) 5 Amp (Labled LIGHTS)

2 x (Red) 30 Amp (Labled Sockets)

1 x (Blue) Unknown amp (Labled Emergence Heater)

Also the Standard ON /OFF Switch.

Ive Noticed nothing is labled Shower, and we have an electric shower, so where that goes i will need to check. This will be possble as im going ot be fitting a new shower soon, hence the reason i want to do the consumer Unit too.

Currently Im thinking along the lines of :

Source from Meter to an RCBO

RCBO to Consumer Unit, then wire accordingly.

32 Amp RCB for Mains

6 Amp for Lights

The cooker , Shower and Emergance heater Id like advice on what to use please????

Im also thinking of running 2 x 2.5mm and 2 x 1.5mm from the new consumer upto the loft, (Not connected to anything) In the hope that when we Extend the house back, We can use these for the Mains and lighting supply. At that time Ill conect them to seperate mcbs, Is this a good idea?

One last thing, Any Advice on Earthings would be nice, Theres an earth to what i think is sheld at the source, but our water into the house is plastic, we dont have gas either, so am i right in thinking all earths need to link to the source earth, and the water pipes internaly should be bonded and linked to the source earth too???

REALLY SORRY FOR WAFLING ON HERE GUYS, BUT WOULD BE NICE TO HAVE A BIT OF HELP ON THIS ONE....

2 more things... the Source fuse seal is already broken, so a nice pair of pliers should help that come out, and lastly, once ive done it all, i will be getting a Propper sparks to come and sign it all off.... I think

Many Thanks In Advance


MA

 

[industryspark]

probably you need to post some more information.

by emergence heater do you mean immersion heater or have i misunderstood?

definetly you need to find where the circuit origanates for the shower and whats protecting it, the size of the shower supply cable will dictate what protection is needed. what power is the shower and what size cable is suppling it currently?

Source from Meter to an RCBO

do you mean RCD?

do you know anything about split load boards?

the Source fuse seal is already broken, so a nice pair of pliers should help that come out,

be carefull when doing this, it can be more hazardous than you think depending on age of installation. see previous posts.

 

[MasterAbacus]

Hi, Sorry, I get things a little mixed up when typing... brain goes quicker than fingers sometimes....Oh and my spelling aint that good either....

I did mean immersion ....

I did Mean RCD


and as for split load boards.... Is that a posh name for a consumer units inside bits....ie the rails etc the mcbs attach to???

 

[industryspark]

Oh and my spelling aint that good either....

thats ok, i have a habit of using text abreviations all the time!

split load board is a type of CU where you have a main incomer/isolator/ RCD (usually 100mA) where the bussbar for the mcb's attaches to. this then feeds circuits that dont need RCD protection really such as lighting.

you then have a seperate 30mA RCD (within the same CU) which provides protection for circuits that require this i.e shower, sockets.

 

[MasterAbacus]

OK, so does it have to be a split load board? Im now asuming the RCD is part of the CU? and all the other MCB`s just go in along the rails, Starting with the higher rated nearer to the RCD???

 

[Adam_151]

1) this work will be notifiable to building control, and you can't just get a sparks to sign it off for you unless you can find one willing to take the risk and break the rules

2) you should work out where the shower is fed from, pull fuses and check out what stops working, I have a nasty feeling it might be piggy backed onto the cooker circuit, if that is indeed the case then you ought to find out where the connection is made, if its in the CU then sorting it out when thats replaced is a piece of cake, if its anywhere else...

a) I'm not sure that unit is designed to take a 45A circuit, doesn't matter too much as its being changed....

b) its possible that its a 30A circuit on the wrong size breaker because the shower has been connected to it, if done at the CU its possible that no wiring has been overloaded, but if done further downstream, then the cooker circuit might need replacing

3) more comments, I'm sure, but that'll do for now

 

[MasterAbacus]

Ive just a a quick bit of investigating.... the shower runs the the same (Green) Fuse that the cooker Aparently runs on.... and the cable looks about 5mm if that....

The earth wire from the shower runs to the cold water pipe in the lower bathroom, but i cant find an earth link from the Pipework to the Source..... Sounds dangerous to me.....

 

[industryspark]

doesnt have to be split load no but its a common method, depends on your installation and what you want running from it.

dont take this the wrong way but from your questions the best advice i can give you is to get an electrician in for this job.

changing a CU isnt a DIY job ( even though many attempt it) its crucial that you get it correct.

what if you install it wrong and the spark you intend to get in wont sign it off?

get plenty of qoutes and make sure the spark you choose is a member of a scheme, i.e NICEIC or NAPIT. they should provide you with all the correct certs and test results

but best of all you'l have piece of mind.

 

[MasterAbacus]

Looking a bit further.... I just Turned off the Green 45amp, LAbled cooker... and guess what.... the cooker still works..... but it kills the shower.....

Oh what fun....!!!!.....

 

[MasterAbacus]

doesnt have to be split load no but its a common method, depends on your installation and what you want running from it.

dont take this the wrong way but from your questions the best advice i can give you is to get an electrician in for this job.

changing a CU isnt a DIY job ( even though many attempt it) its crucial that you get it correct.

what if you install it wrong and the spark you intend to get in wont sign it off?

get plenty of qoutes and make sure the spark you choose is a member of a scheme, i.e NICEIC or NAPIT. they should provide you with all the correct certs and test results

but best of all you'l have piece of mind.

Thanks for that, But i will be doing this myself.... there are enough helpfull people online and plenty of books or online information about, that I refuse to pay a Sparks hourly rate.... Im not a complete novice, Its just been a while since ive done this kind of work....Ill make sure the work is done to the regs, and checked accordingly.

 

[MasterAbacus]

Thanks Adam, I think this is all going ot come down to a little investiagtion work.... Next job is to find what fust the cooker is on, cn as its not on the (Green) as i expected....

Any Ideas about the earthing?

 

[Adam_151]

Ideally you would have a 16mm² earth from the service intake to the MET (main earthing terminal) from there continue in 16mm² to the CU earth bar, also from the MET there should be 10mm² earths to utility entrance points... gas and water should be bonded on the consumers side of the meter and within 600mm of entrance to the Equipotential zone (this covers the whole house... so within 600mm of where in enters the house)

EDIT: (you can get away with smaller, but those sizes future proof things (even if you don't have a 100A service now...) and are the sizes from tables, you can sometimes calculate smaller, but you need to know more details and its not really worth the hassle just for something like this

EDIT: forgot to mention, the MET and the earth bar in the CU are combined, with the CU earth bar acting as the MET as well, but this is not always the case, it is a tidy way to do things though, and I'd do it this way unless there was a reason why not, like the main earth was non-replaceable (sweated onto TN-S intake for example) and it was too short or not big enough (would like to keep it out of the CU in this case, and also would be easier for the DNO to replace it [as I would request them to do if it was too small])

The purpose of this is to keep everything at the same potential, so the electricial system earth is at the same potential as pipe work so you can't get a shock between them

The bathroom is defined as a special location because it represents additional electrical shock risk due to lack of clothes and presence of water (likewise swimming pools are another special location... but unless you are loaded and your house reflects this...) anyway we create a mini equipotential zone in the bathroom, we bond all pipe work entering the bathroom in 4mm² earth cable along with all the electrical earths of circuits supplying equipment in the bathroom zones (this for most bathrooms counts as the whole bathroom).

Its simple in theory, but where plastic pipework is involved things get more complicated... for bathrooms mostly in copper but maybe the odd little bit in plastic, its easiest to take the bonding cable to each of the bathroom 'appliances' bath, sink, etc, and bond the pipes at each, even though this might not be strictly neccesary because one continous piece of copper might be bonded at the sink and bath for example... but this doesn't do any harm, and takes care of the fact taht it might have two inch of pvc spliced in...

The earth wire from your shower to the pipework is probably an incomplete attempt at bonding (in some cases this can be more dangerous than not bonding at all!) and your shower should have the normal earth in its supply cable back to the fuse board as well...

Hope this helps...

 

[MasterAbacus]

Hi Guys thanks for the Advice so far....

Currently im moving along nicely....But a little more advice would go down well...

The new consumer im looking to install already comes with a 100A DP switch, and here is what i intend to install Mcb wise...

3 x 6 Amp for Lights

3 x 32 Amp for Ring main

Thats the easy bit as its pretty much like for like replacement with the existing....

Now ill have the Cooker and Imersion heater feeds.... WHAT Mcbs will i need for these?

Then Onto the Shower... New cable going in when i replace the unit as im not so sure the existing is thick enough.... What recomendations for the cable and Mcb, or is RCBO?

Lastly back to the earthing, Im following ok i think, basicaly there should be a link between the copper pipework and the earth to the house? AM I RIGHT IN THINKING THIS?
the pipework in the bathrooms if copper is used then they should be bonded together....ie Hot and cold Linked with Clamps and cable? Same for bath? Ive replaced some copper with Plastic in the lower wash room, but used copper "ups" to the units.... do these still need an earth? How about the radiators?

IM REALLY SORRY FOR ALL THE QUISTIONS, BUT TO BE HINEST IM ENJOYNG LEARNING HERE.... IVE STILL NOT DONE ANYTHING, BUT IM BUILDING UP A PICTURE AS TO WHAT NEEDS TO BE DONE QUITE NICELY.... IF I EVETUALLY DECIDE ITS TOO BIG OF A JOB ILL GET SOMEINE IN , BAT AT THE MINUETE I THINK IF I FOLLOW COMMON SENCE, I SHOULD BE FINE....

Thanks again guys.... look forward to the responces...

 

[Adam_151]

Immersion heater goes on a 16A circuit, shower, depends on shower rating, but somewhere around 45A would be normal.

Sockets which may resonably be expected to supply equipment outside should be RCD protected, and its strongly recommended that showers should be too, and its also a good idea to have all 'convience outlets' on RCD (sorry, term I've borrowed from the yanks... any socket thats not for a specific purpose)

The most cost effective way of acheiveing this is with a split load board... the main switch feeds a non RCD protected bus bar, and the RCD the RCD then feeds a non RCD protected bus bar. The downside of a split board is inconvience, if it trips a lot goes off, also the more circuits you have on it, the more likely it is to nuisence trip because some equipment has earth leakage when there is nothing wrong with it, the better way would be a straight forward switch controlled board fitted with RCBOs (mcb and RCD in one unit), but this would be expensive... a compromise might be a split load box with high leakage circuits (eg kitchen ring) on RCBOs on the non RCD side

See my last post above for information on earth bonding

 

[securespark]

OK, so does it have to be a split load board?

Almost certainly.

Contrary to advice otherwise, to comply with regulations, a split-load board (or SIMILAR arrangement) is necessary to comply with regulation 314-01-02.

This means you have to have a split-load board, or an incomer board with RCBO's for those circuits requiring RCD protection.

Any socket outlet that can supply equipment to be used outdoors has to be protected by the RCD, as do showers, if the manufacturer's instructions say so.

Further, if you have a TT supply, you MUST use a splitload board (or SIMILAR arrangement) where the main incomer is a (minimum) 100mA S type RCD and the normal 30mA G type on the split side.