Raidial and Ring from same fuse?

oldshrimpyeyes · 23 Aug 2010

Hi there,

i have been reading a lot here but cant seem to find a answer to this.. so hello here's my (probably stupid) question.

recently brought a house.. and has an oild style rewireable fuse type consumer unit, I have 2 x 30amp fuses one for down stairs plugs and one for upstairs plugs. the cooker has its own 45amp fuse.

the plugs in the plugs in the kitchen appears to be a radial circuits, one of them powering the fridge comes from the consumer Unit straight through the wall to the fridge on the othersde.

The second im not so sure about but it's not part of a ring i know that much.

So my main question is "Can one 30amp fuse at the consumer unit have the Lounge ring circuit and these apparant radials from the kitchen?"

Thanks

Gregg

BigJon · 23 Aug 2010

You can only have one socket "spurred" from your 30A fuse.
Are there any spare ways in your fuse box that you could connect the radial circuit to?
One way to make it safer is to put the lot in a 20 fuse, not ideal and may not be suitable for your power consumption but that way the cables will be protected from overload.
You may want to get a PIR on your instalation to ensure its safety.

Chri5 · 23 Aug 2010

4mm TE cable supports a 30 amp radial, but is the kitchen radial run in 2.5mm or 4mm ?

If in 2.5mm it's wrong.

As for sharing the same fuse, it's not really right- The whole idea of seperate fuses for seperate circuits is to avoid 'eggs in the same basket' when the fuse pops it should only pull down it's own circuit, not others.

A 2.5mm radial spur froma 30 amp fuse is sort of okay for 1 x d/socket, but if there's more than 1 x d/socket theres a good chance demand via appliances could overload the cable which is rated (at best) at no more than 26 amps.

oldshrimpyeyes · 23 Aug 2010

Hi BigJon,

Thers no spare ways on the fuse box.. it's really old and i plan to have replaced soon.

I just confused as to the layout at the moment.. the Socket the fridge runs from is coming directly from the consumer unit as i can see the wire.. howeve the other socket in the kitchen just comes out of the wall.. It's not on a ring and could be a spur but i'm not sure.. i was hoping i'd be able to add another socket from it if it was a radail but no im not so sure?? the whole downstairs runs from on 30amp fuse from the consumer unit.

I was just under the impression that a spur in the kitchen wouldn't be great seen because of the loads???

gregg

oldshrimpyeyes · 23 Aug 2010

Hi Chi5,

Im not sure of the cable type i'll check tonight...

As for all this running via one Fuse is this just a quirk with old techniques? Im guessing wired in the 70's/80's

Chri5 · 23 Aug 2010

It's more a bodge than a quirk.

Fuse units based on wired fuse tended to be small 2/3/4/5/6 way. So once all the ways were used they should have added more fuse units.

Hence why on some better elder sites you might see 2 or 3 boards which have been provided over the years the property developed. Whoever added to yours hasn't added fusing they have just tapped into other circuits at the board. If a fuse is designed for 1 x circuit at 30 amp load, then if 2 circuits use that load the 30 amp limit is across both.

Generally wired fuses have got towards there sell by date. If you throw on a picture or two showing:-

The board, the meter area, where the earth wires go and if the cabling is surface a snap of that we could advise further.

It's unlikely to be dangerous, but if you do intend to decorate or revamp the property do consider that the cabling is likely 60's and will need doing soonish.

oldshrimpyeyes · 24 Aug 2010

Hi Guys,

Thanks for all the input.

Here's a few pics of the meter/board area..

the wire coming down from the right of the consumer unit going through the wall is is the "known" radial as it ends there.

the earth goes outside the house and back in again to the gas pipe.

Missing Fuse is for the old immersion heater.. (on another note can this be reconnected to provide a outlet in the bedroom for occasional use?)

Had a Sparky look at this when we moved in and was advised that the wiring is ok but consumer unit needs changing??

I've not had the chance to look at the gauge of the wire in question.. but think i might have the floor boards up at the weekend and see if i can work out what situation is.

i have a few more questions but i'll see what you guys come back with..

thanks for your help on this.. much appricated

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[GALLERY=media, 25544][/GALLERY][img]

ban-all-sheds · 24 Aug 2010

Chri5 said:
4mm TE cable supports a 30 amp radial.

Not with rewirable fuses.

A 2.5mm radial spur froma 30 amp fuse is sort of okay for 1 x d/socket, but if there's more than 1 x d/socket theres a good chance demand via appliances could overload the cable which is rated (at best) at no more than 26 amps.

Or at worst 9.8A....

ban-all-sheds · 24 Aug 2010

oldshrimpyeyes said:
the earth goes outside the house and back in again to the gas pipe.

Do you have an earth connection coming from the sheath of the supply cable?

If not then your "plan to have replaced soon" should become "plan to have replaced ASAP as a matter of extreme urgency".

Had a Sparky look at this when we moved in and was advised that the wiring is ok but consumer unit needs changing??

Did he say anything about it being a TT supply, and you not having an RCD?

Missing Fuse is for the old immersion heater.. (on another note can this be reconnected to provide a outlet in the bedroom for occasional use?)

Not in a way which complies with the Wiring Regulations.

Even if you do have a TN-S supply, and aren't therefore in danger from the lack of a proper earth, you really should get that fuseboard replaced.

oldshrimpyeyes · 24 Aug 2010

Hi ban-all-sheds,

Thanks for stopping by.. have noticed you seem to be an authority on this sort of thing.

Im sure there must be an earth from the supply i'll check.. (I hope so).

Whats a TT supply?? he did mention a RCD as we wanted to have a powershower wired in (it was on the wall when we moved in but not attached) we have a mixer shower now as the new boiler has helped with pressure.

Gregg

oldshrimpyeyes · 24 Aug 2010

Right so a tt supply is where the earth is at the consumer end rather than the generator???

wouldn't all homes in the uk be TT??

so does this mean i should get all the circuits covered by an RCD?

Questions Questions sorry.

Gregg

ban-all-sheds · 24 Aug 2010

oldshrimpyeyes said:
Right so a tt supply is where the earth is at the consumer end rather than the generator???

No. The star point of the transformer where the LV supply originates will be earthed with TT as well as with TN- supplies.

wouldn't all homes in the uk be TT??

No.

//www.diynot.com/wiki/electrics:earthing-arrangements

so does this mean i should get all the circuits covered by an RCD?

Yes - this is very urgent.

See why here:

//www.diynot.com/wiki/electrics:mcb2

http://www.tlc-direct.co.uk/Book/5.3.1.htm

http://www.tlc-direct.co.uk/Book/5.9.1.htm

With a TT supply your fault loop impedances will be 10's or 100#s of times larger than they should be, and your fuses will not work properly with a L-E fault.

oldshrimpyeyes · 25 Aug 2010

Okey dokey..

So a new consumer unit covered by an RCD is needed.. as a matter of urgency.

what would a avg quote be?

Also as for installing a new socket in the kitchen.. could a Spur be taken from the 45amp cooker outlet? or is this another no no?

..and the circuit that was formally for the immersion heater (15a) could that be upgraded to 30a when the new consumer unit is installed so it could be used in the main bedroom?

sorry for all the questions.. i only have a basic knowlege of household electrics and your insight is really appriciated.

Gregg

Electrifying · 25 Aug 2010

ban-all-sheds said:
Chri5 said:

4mm TE cable supports a 30 amp radial.

Click to expand...

Not with rewirable fuses.

Not getting this comment, BAS

I'm not having a go, I just don't get what you are trying to say.

4mm cable won't carry 30A because it's overload protection is via a 30 A fuse?

A 30 A fuse can't protect 4mm cable from overload? - but it can protect a 2.5mm ring final?

If a 32 A MCB is suitable overload protection for a 2.5mm ring final or a 4mm radial, then it stands to reason that if a 30 A BS3036 is suitable overload protection for a 2.5mm ring final, it must be suitable for a 4mm radial.....

...or do you know something I don't?

I've never actually done the calcs, but does the fusing factor affect the 4mm radial, but not the 2.5mm ring final?

To the OP, there's nothing wrong with 2.5mm spurs off your 30A BS3036 Fuse - as long as each spur only feeds one single or one double socket outlet.

- overload protection then comes from the fact that the spur can't be overloaded, not from the 30 A fuse

(Subject to installation/reference methods, of course - before anyone starts

)

ajrobb · 25 Aug 2010

Electrifying said:
To the OP, there's nothing wrong with 2.5mm spurs off your 30A BS3036 Fuse - as long as each spur only feeds one single or one double socket outlet.

What is Iz for a 2.5mm² spur running in conduit in plaster?

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Raidial and Ring from same fuse?

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