split load configuration help needed

[cjb121]

Hi,
I have an older style 7way MK consumer unit which is all RCD protected and the whole house goes down when anything happens.
I have purchased an new MK 12way split load unit complete with breakers, but now wonder which circuit to connect to main breaker and which to the RCD breaker.
I currently have 1 cooker, 1 shower, 2 Ring, 2 light, 1 immersion circuits, all from the original 20 yr old build.
I want to connect a additional ring for the kitchen and as the immersion circuit is currently used to feed the garage, I want to supply the outside separately and regain the immersion.
Incidentally, the current shower is a 9.5 KW Triton, on a B45 breaker. The supplied breaker is B40.. will that be OK or should I use the original 45, which being all MK looks about the same size although very slightly differnt in looks.
I have been quoted between £300 - £ 750 to do the job and upgrade earth to 10mm.
Thanks

 

[Chri5]

If you've been quoted to have the work done , why are you not leaving the sparks to do the design / placement, for you?

On the assumption that the property is a standard house.

Non RCD

Light radials Grd and 1st floor 6 amp
1st floor ring
cooker (without socket outlet)
immersion

RCD

New garage radial
G/f ring
kitchen ring
shower

9.5kw shower / 230v = 41.3 so 45 amp

 

[sm1thson]

all RCD protected

alarm bell rings!!!
firstly are you sure you installation isnt a TT earth? that needs answering before anything else see here for an explaination of a TT and how to spot it from the others)

 

[cjb121]

If you've been quoted to have the work done , why are you not leaving the sparks to do the design / placement, for you?

On the assumption that the property is a standard house.

Non RCD

Light radials Grd and 1st floor 6 amp
1st floor ring
cooker (without socket outlet)
immersion

RCD

New garage radial
G/f ring
kitchen ring
shower

9.5kw shower / 230v = 41.3 so 45 amp

Ok Many thanks for that. I have just seen a similar POST //www.diynot.com/forums/viewtopic.php?t=82469.
I get the idea now.

So far, every electrician who has quoted me has given a different opion and thereby quote on what needs to be done. ( the last one £750 thought he should rebuild my house )
A fair pay for a fair job but I can see a ripoff here.

 

[cjb121]

all RCD protected

alarm bell rings!!!
firstly are you sure you installation isnt a TT earth? that needs answering before anything else see here for an explaination of a TT and how to spot it from the others)

Ok, from that link it appears I do not have a TT, as I have a separate earth from the fusebox to the CU, but it could be either of the other types

 

[davy_owen_88]

If you mean there's an earth cable from the consumer unit to the main service fuse then you don't have to worry about a TT supply.

9500w / 240v = 39.58A - your shower will just about run on a B40 breaker.

Since you have read my reply in the other post, could you read it again especially the last part and ask yourself if you are competent to do this work. If the answer is yes, then remember to inform your BCO BEFORE you start work and pay all applicable fees.

Are you aware of the safe zones regarding cable routing? Are you aware of ALL current regulations (BS7671)? Main/supplementary bonding? How do you intend on isolating the tails before you can change the CU?

To add to that: what size is the main earthing conductor? What size are the tails from meter to CU?

Davy

 

[cjb121]

If you mean there's an earth cable from the consumer unit to the main service fuse then you don't have to worry about a TT supply.

9500w / 240v = 39.58A - your shower will just about run on a B40 breaker.

Since you have read my reply in the other post, could you read it again especially the last part and ask yourself if you are competent to do this work. If the answer is yes, then remember to inform your BCO BEFORE you start work and pay all applicable fees.

Are you aware of the safe zones regarding cable routing? Are you aware of ALL current regulations (BS7671)? Main/supplementary bonding? How do you intend on isolating the tails before you can change the CU?

To add to that: what size is the main earthing conductor? What size are the tails from meter to CU?

Davy

From what the electricians who have looked at the installation have said, my main earth is OK at 10mm... I don't know the size of the tails but they have not said there is a problem here.
What they have said is I need to upgrade the earth to the stop cock ( both CU and Stop are in the same cloakroom) and earth bond the radiator in the bathroom ( other end of bungalow). One said I could use the shower cable earth, bond the bathroom light to the shower earth and run a bond to the radiator.
This is the main area for disagreement as to how much work needs to be done. Even if I do get a sparks to do the CU change, I thought I could run the bonding to save time and some money here.

If I did do it myself, I have read elsewhere that supply companies are not too worried about taking out the main fuse as long as u don't tamper with the meter. I have recently changed supplier almost yearly and the current ATLANTIC have no service facility anyway in my area.
Any thoughts on that

 

[davy_owen_88]

What they have said is I need to upgrade the earth to the stop cock ( both CU and Stop are in the same cloakroom)

This is main equipotential bonding. Should be a continous length of 10mm² green & yellow cable. You should have this bonding to gas and water supply pipes within 600mm of the meter or as close to their point of entry if there is no meter.

earth bond the radiator in the bathroom ( other end of bungalow). One said I could use the shower cable earth, bond the bathroom light to the shower earth and run a bond to the radiator.
This is the main area for disagreement as to how much work needs to be done. Even if I do get a sparks to do the CU change, I thought I could run the bonding to save time and some money here.

This is supplementary bonding. Connect the earth conductor of every fitting in the bathroom to every conducting part (pipes, rads etc) using 4mm² g&y cable. Supplementary bonding does NOT go back to the MET. You can use the earth conductors of cables and the pipes within the bathroom for supp. bonding.

If I did do it myself, I have read elsewhere that supply companies are not too worried about taking out the main fuse as long as u don't tamper with the meter. I have recently changed supplier almost yearly and the current ATLANTIC have no service facility anyway in my area.

You are not supposed to remove the main fuse but if you remove all load (open isolator at CU) and the fuse carrier is in good condition you should be ok - although I really don't suggest you do it. Contact your DNO and tell them you want an isolator fitted, you may have to pay but it will be worth it.

Davy

 

[cjb121]

What they have said is I need to upgrade the earth to the stop cock ( both CU and Stop are in the same cloakroom)

This is main equipotential bonding. Should be a continous length of 10mm² green & yellow cable. You should have this bonding to gas and water supply pipes within 600mm of the meter or as close to their point of entry if there is no meter.

earth bond the radiator in the bathroom ( other end of bungalow). One said I could use the shower cable earth, bond the bathroom light to the shower earth and run a bond to the radiator.
This is the main area for disagreement as to how much work needs to be done. Even if I do get a sparks to do the CU change, I thought I could run the bonding to save time and some money here.

This is supplementary bonding. Connect the earth conductor of every fitting in the bathroom to every conducting part (pipes, rads etc) using 4mm² g&y cable. Supplementary bonding does NOT go back to the MET. You can use the earth conductors of cables and the pipes within the bathroom for supp. bonding.

If I did do it myself, I have read elsewhere that supply companies are not too worried about taking out the main fuse as long as u don't tamper with the meter. I have recently changed supplier almost yearly and the current ATLANTIC have no service facility anyway in my area.

You are not supposed to remove the main fuse but if you remove all load (open isolator at CU) and the fuse carrier is in good condition you should be ok - although I really don't suggest you do it. Contact your DNO and tell them you want an isolator fitted, you may have to pay but it will be worth it.

Davy

OK many thanks.. I'm really getting to the point where I wish I hadn't bothered now.. not for £300+ anyway..
Whats the current opinion on how to break into an existing ring... are junction boxes OK ?
anyone want an unused CU ??

 

[scousespark]

9500w / 240v = 39.58A - your shower will just about run on a B40 breaker.

Davy

Assuming there are no correction factors.

CJB
For the sake of £300 let a pro do the job. If money is an issue you may drop the price by doing some of the graft yourself.

 

[davy_owen_88]

9500w / 240v = 39.58A - your shower will just about run on a B40 breaker.

Davy

Assuming there are no correction factors.

Correction factors don't effect the load, only the cable feeding it. If the cable runs through insulation it will still draw the same current the only difference is the cable might melt in the process

Whats the current opinion on how to break into an existing ring... are junction boxes OK ?

Junction boxes are fine so long as they are kept accessible.

Davy

 

[scousespark]

Davy,

It was the cable I was thinking of with this, but for the calc I've always used 230V and fitted 50A breakers with 10 mill (minimum).

If this is wrong let me know

 

[EddieCurrent]

I.

 

[davy_owen_88]

Davy,

It was the cable I was thinking of with this, but for the calc I've always used 230V and fitted 50A breakers with 10 mill (minimum).

If this is wrong let me know

Ah, I thought you meant that correction factors would effect the load, but you are correct about the cables.

Most loads assumed to be purely resistive such as showers give their ratings for both 240v and 230v. The highest rating obviously belonging to the 240v rating.

9.5kW @ 240v = 39.58A
8.7kW @ 230v = 37.82A

Nothing wrong with installing higher rated cables and higher rated MCB's but for this guys case, 40A should do.

 

[Adam_151]

Davy,

It was the cable I was thinking of with this, but for the calc I've always used 230V and fitted 50A breakers with 10 mill (minimum).

If this is wrong let me know

The 'headline' rating on shower boxes is generally at 240v, at least on the ones I've seen, it says something like "9.5kw@240v, 8.7kw@230v" I suppose strictly speaking you should use the 230 rating and calc using 230 (as you would do if you only had a 230v rating), but that just seems a tad daft when the voltage is 240v in the real world, using the headline (240v) rating and using 230 in your calculation won't do any harm though, just gives you a design current figure a tad bigger than the real world one and leaving breakers with some 'headroom' is good practice because they can run cooler, etc (I believe the NEC across the pond calls for the design current to be no more than 80% of the nominal current of the breaker for reasons upon this line of thought)

EDIT: So after all that, I'd say use the rating @240v and use 240 when you find the design current