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andson

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My friend wants some work doing, firstly a new consumer unit. he has an old 8 way domino fuse type and want's to upgrade? do i have to install a 17th edition type consumer unit or can i get away with a conventional 10 way split, 100dp isolator, 30ma rcd,and so on.. if i can use one of these is the idea to check the infeed of cables and see what direction they are coming from and mount the new unit further up the cable run to allow you the length of cable to connect, as there will probably be no slack in the existing cable? also i have got to power a new granny flat, so i have got to share the load out in the consumer unit,

what i will need is 5x32A for two cooker feeds, 1 main house and 1 for the granny flat. 1 socket up (main house) 1 socket down (main house) and 1 sockets granny flat. is this acceptable?

3x10A lights up, lights down, lights granny flat. (again is this ok)

and 2x6A for smoke alarm and extractor fan in new granny flat kitchen, can these run to the same 6 amp breaker? and am i right in saying that this is a must for building regs regarding the new kitchen i have got to install the smoke alarm and extractor fan?

as these consumer units come with 1x40,4x32,2x16 and 3x6, does this mean i am going to have to dissregard some off the breakers and buy new ones or can i get away with using these?

where the granny flat is going there was already a sizable extension to which they are increasing and i was called in after the builder had kindly dissconected(ie some ripped out, and some knotted and shoved in the roof space its a proper mess, thats why i want to run a new socket and light circuit!!! the cable in the roof and bits that have been removed are of no use too me, so the best way for me to go on this one is to remove that part of the radial light circuit and reconnect accordingly to the exsiting lighting circuit, and does the same apply to the ring circuit, as i beleive it was spurred of the original ring.

damn confusing i know.. but just trying to pick some your brains, as you always seem to come up with sound advice...

cheers all, and sorry for the length of the post

andy...

 
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I thought it was conventional to wire smoke alarms into the lighting circuit so they were not switched off?

My kitchen extractor fan is run of a Sw FCU off the kitchen radial.

Thought you couldn't spur a ring off a ring (if that's what your origional post said about the granny flat)? (circuit diagram would look like bumbells)

Anyways I shouldn't even attempt to answer these proper electrical questions

Naughty me :^O

I'll step down and leave it for them that know :|

 
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My friend wants some work doing, firstly a new consumer unit. he has an old 8 way domino fuse type and want's to upgrade? do i have to install a 17th edition type consumer unit or can i get away with a conventional 10 way split, 100dp isolator, 30ma rcd,and so on..
Hello Anderson...

because of the length of the post I am going to split it up into more manageable chunks...

(I was going to say.. are you sure you are competent to do this..

but just had a quick look at some of your previous posts.. & I understand you are recently qualified looking toward working for yourself but still doing old job ?? )

Any way

GENERAL RULE NO 1.

ALL work should comply with the wiring regulations current at the time that the work is carried out.

So your CU change should comply with the current 17th edition..

when changing a CU you are altering every circuit, (cuz different overload protection) so 'IMHO' ALL circuits should now comply with 17th.

Just as a side note:-

What you call a conventional 10-way split load board.. 'could' be 17th compliant IF all of the non RCD circuits were wired in earthed metal conduit & supply NO circuits to bathrooms or outside.

The CU wholesalers call 17th are normally FULLY RCD protected on all circuits.

Personally I would fit a fully RCD protected CU, High integrity job probably?

if i can use one of these is the idea to check the infeed of cables and see what direction they are coming from and mount the new unit further up the cable run to allow you the length of cable to connect' date=' as there will probably be no slack in the existing cable? .[/quote']

Personally I don't look at the the position in relation to cable runs..

If cable need extending then extend them!!!

often they come through a wall with no slack anyway!!

My first concern is How accessible is the fuse box.. Can it be easily reached in the event of a fault.. house in darkness, elderly person fumbling around to find switch..

we don't want stuff too high up the wall needing stepladders!!!

e.g. reg 132.12 (ii) accessibility for operation!
 
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First off any new work must comply to current regs - So yes you must use 17th CU

The loading does not look to be too bad for what you propose so long as you have gas ch and no electric showers...

But why 10A for the lighting???

Smoke alarm circuits burried <50mm still need RCD protection and must not be protected by the same RCD as a socket circuit, so RCBO for the smokes!! (in smoke alarm regs) also as new extension smokes will be a requirement, also extractor in new bathrooms & kitchens will be required aswel as the correct ratio of low energy lighting (part L1 fo building regs)

Just remember your protective earthing!

 
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1.18 A smoke alarm, or smoke alarm system, that includes a standby power supply or supplies, [ie AC with battery back up], can operate during mains failure. It can therefore be connected to a regularly-used local lighting circuithttp://www.tlc-direct.co.uk/Technical/Regulations/Fire1.htm

I was bound to pick something up :D
personally this isn't what I would recommend as first option..

O-S-G pg 56 smoke alarms:

recommends they be wired into a separate way in the CU. OR supplied from local lighting circuit..

I always try to run separate circuit wherever possible!

Power consumption is not and issue,

I just prefer less rick of power being tripped off smokes cuz of bulb blowing..

and ease of maintenance & isolation if needed later? :|

 
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also i have got to power a new granny flat, so i have got to share the load out in the consumer unit, what i will need is 5x32A for two cooker feeds, 1 main house and 1 for the granny flat. 1 socket up (main house) 1 socket down (main house) and 1 sockets granny flat. is this acceptable?

3x10A lights up, lights down, lights granny flat. (again is this ok)
Do you need 32a for all of the rings? most likely 20A would do..

e.g. I person in granny flat are they going to be running over 4.5kW of power on their sockets???

Also as Noz said why 10A for the lights.. wont 6A do?

Obviously without seeing plans & actual dimensions it is very hard to give specific answers..

i.e. one persons granny flat may be another persons granny mansion!!! :| ?:| :eek:

 

andson

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thanks all, as usual you all have honest excellent advice and thats why i use this forum, to skip through after the information you have all gave me and update my situation, i am qualified but newly, this is why some of you guys are probably cringing.. but i got to learn and start somewhere. anyway i dont want to get side tracked.so..

it is possible for me to run my smoke alarm, of my lighting circuit , but will i have to install one in the main house if there is not one present and interlink them?

can i use the 40 amp breaker for a cooker to free up a 32 amp on the board, i get all my sockets off the remaing 32's i can use my 3 6amp for the lights, so im getting there, there would be 2 16amp, what would these normally be used for?

and finally, you mention extending cable runs to connect in to a new c.u, how is this acheived?

thanks all, and keep them rolling..

andy..

 
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thanks all, as usual you all have honest excellent advice and thats why i use this forum, to skip through after the information you have all gave me and update my situation, i am qualified but newly, this is why some of you guys are probably cringing.. but i got to learn and start somewhere. anyway i dont want to get side tracked.so..
When considering all these circuits and changes etc.. Get back to the basic design consideration..

if I remember we used to be taught..

1/ Calc load current

2/ Select protective device

3/ Consider cable installation method

4/ Select suitable cable size/capacity

5/ Ensure max volt-drop complied with

6/ Check for shock protection Max Zs

7/ Check other correction factors e.g. high ambient temp environments.

If all these satisfied then each final circuit should be ok!

Also need to check your MAX demand for whole installation is still ok for incoming cable size main cut out rating?

(unlikely to exceed in domestic environment) but you do need to check it to put on your electric certificate!!

it is possible for me to run my smoke alarm' date=' of my lighting circuit , but will i have to install one in the main house if there is not one present and interlink them?

[/quote']

If putting smokes off lights..

I would still make sure there is a FCU 3a to allow safe maintenance at a later date..

e.g. keep lights on but turn smokes off to remove back-up batteries or temp remove whilst painting decorating etc..

If the property is still only two stories high.. on refurb work you are under no obligation to have to put smokes in rest of property..

(New build or loft conversion YES)

refurb it would still be very wise and prudent to install mains powered interlinked around the rest of the property though IMO. :) ;)

can i use the 40 amp breaker for a cooker to free up a 32 amp on the board' date=' i get all my sockets off the remaing 32's i can use my 3 6amp for the lights, so im getting there, there would be 2 16amp, what would these normally be used for?

[/quote']

See answer to first point above.. what are your cable sizes & prospective load currents????

REMEMBER!

you dont have to use all of the rated fuses that came with the CU..

you can swap for more appropriate ratings. ?:|

Some older cooker circuits were wired in 4.0mm so 40A would be a NO NO

e.g. if you don't NEED 40A supply.. I would drop it down to a 32A..

As I said on earlier post.. Do you REALLY need all rings to be 32A..

your average upstairs sockets in most domestic properties is quite happy with a 20A..

and with 17th ed. cable ratings and possibility of new insulation being involved.. 20A may be more appropriate? :)

I would suggest you sit down with a pen & paper..

make a note of all the circuits you need.. and what the actual load currents are likely to be..

Then check your cable sizes then what fuse ratings you need..

If necessary replace some of the ones on the CU with new MCBs!!

and finally' date=' you mention extending cable runs to connect in to a new c.u, how is this acheived?[/quote']

Any method you feel suitable that is.......

Electrically safe.

No adverse mechanical strain on joints.

Appropriately protected from external influences.

If screw connections/jbox accessible for Test & Inspect.

DOESN'T END UP LOOKING LIKE A RATS NEST!!!

(good workmanship & proper materials 134.1.1! ;) )
 

andson

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yes i will have to sit down with my pen paper and calc,

could you give us a link to the method of extending the cables please, i am still un sure of the method?

cheers andy..

 

Admin1

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Agree with the guys on this one apache. Dedicated circuit for the smokies (where possible) on additions, and definately so on a re-wire.

I did it this way on the 16th regs anyway. I also wondered why the 10 A on lighting. :|

 

Theorysparky

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Agree with the guys on this one apache. Dedicated circuit for the smokies (where possible) on additions, and definately so on a re-wire.I did it this way on the 16th regs anyway. I also wondered why the 10 A on lighting. :|
58 50w downlighters is my guess :^O :^O:^O

 

cheggers

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First off any new work must comply to current regs - So yes you must use 17th CUThe loading does not look to be too bad for what you propose so long as you have gas ch and no electric showers...

But why 10A for the lighting???

Smoke alarm circuits burried <50mm still need RCD protection and must not be protected by the same RCD as a socket circuit, so RCBO for the smokes!! (in smoke alarm regs) also as new extension smokes will be a requirement, also extractor in new bathrooms & kitchens will be required aswel as the correct ratio of low energy lighting (part L1 fo building regs)

Just remember your protective earthing!
with reference to your post, smokes must not be on the same rcd as sockets I saw that on a hagar consumer unit advise leaflet but have not seen it in the regs do you think hagar have miss printed that or is it in the regs

 
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Last post first:

Cheggers - it is in the regs, but whether 7671 or 5839 I misremember (too much beer)!

Ring final circuits: Once you`ve left the kitchen / utility, I`d have no issue putting the rest of the house on a 16/20 radial. A few years back, as an experiment, I dropped the mcb in my parents, in-laws, kids and own house to 20A on the house ring, instead of 32A.

NONE of them has EVER managed to trip it!!!!!

Swap the breakers you don`t need ( or put `em into stock - soon you`ll be able to fill your own CU, instead of buying the mcb`s THEY want you to have:)

SL`s posts, as usual, full of well thought out, sensible advice.

:)

 

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