Questions regarding Ring Circuit

Don001 · Apr 29, 2016

Hi Everyone

I have recently started a C&G 2365 level 2 course and seem to be stuck on, a few things are unclear hope you guys can shed a little light on the queries below.

Regarding Radial & Ring Circuits
The questions I am a little confused with are below

"State the number of spurred sockets allowed on a non fused spur connected to a household ring circuit. (A1 ring)"
My Answer: 1 socket the number of sockets should not be greater than the socket on the ring (If the spur is coming off of a twin then a twin socket can be used)

"State the number of spurs allowed on a household ring circuit. (A1 ring circuit)"
My Answer : I can not find this information is there a number or is it worked out on the amount of appliances and load on the circuit, I know that you can have unlimited Fused spurs

"State the maximum floor area, the number of socket outlets and the minimum size of cable which may be supplied by a radial circuit from a 20A re-wirable fuse. (A3 radial)"
My Answer : A3 radial Max floor = 50M Minimum cable size = 4mm PVC and 2.5mm mineral insulated Max sockets = ?? I can not find the information in the Table H2.1 On Site Guide page 182

Apologies for asking but ive been looking at this for some time, have emailed the tutor waiting for his reply but will probably only be Monday.

Rpa07 · Apr 29, 2016

Don, check out appendix 15 in the BS7671 for all of this information and a crackin' little diagram of the ring and radial circuit allowances. I'm still training and using a BigGreen which has no different info regarding this but obviously differs with AMD 3. Keep asking the questions . . .

Sent from my iPhone using Tapatalk

Pete999 · Apr 29, 2016

Don001 said:
Hi Everyone

I have recently started a C&G 2365 level 2 course and seem to be stuck on, a few things are unclear hope you guys can shed a little light on the queries below.

Regarding Radial & Ring Circuits
The questions I am a little confused with are below

"State the number of spurred sockets allowed on a non fused spur connected to a household ring circuit. (A1 ring)"
My Answer: 1 socket the number of sockets should not be greater than the socket on the ring (If the spur is coming off of a twin then a twin socket can be used)

"State the number of spurs allowed on a household ring circuit. (A1 ring circuit)"
My Answer : I can not find this information is there a number or is it worked out on the amount of appliances and load on the circuit, I know that you can have unlimited Fused spurs

"State the maximum floor area, the number of socket outlets and the minimum size of cable which may be supplied by a radial circuit from a 20A re-wirable fuse. (A3 radial)"
My Answer : A3 radial Max floor = 50M Minimum cable size = 4mm PVC and 2.5mm mineral insulated Max sockets = ?? I can not find the information in the Table H2.1 On Site Guide page 182

Apologies for asking but ive been looking at this for some time, have emailed the tutor waiting for his reply but will probably only be Monday.

Appendix 15 BS7671 is your best source of information required.

Richard Burns · Apr 29, 2016

You will also find useful guidance in the on site guide, chapter seven, under standard final circuits.
The table may also help with some of your last question.

Don001 · Apr 30, 2016

Hi Guys thank you for the information

I have both books the Green BS 7671 and the Yellow On Site Guide

Appendix 15 is useful but there is no information regarding the total amount of sockets allowed on the ring circuit, it mentions non-fused spurs and fused spurs

On Site Guide Chapter 7 has a lot of information regarding the ring circuit and the table Protective Device - Cable Size - Installation Methods and Max length. It does not mention anything about the total amount of sockets

Appendix H On Site Guide has a lot of clear information on Final circuits as well as an easy to use table H2.1 but it lacks the information regarding amount of sockets. There is a table H7 page 186 that refers minimum number of sockets.

I feel as though the question may be a red herring and that there is no official number for the amount of sockets on a ring A1 circuit. it all depends on the load required and access points.

After all this time looking through both books I have noticed two very different statements regarding the same standard and am curious how both of them could be so very different.

Example : BS 7671 553.1.6 (Green Book) "A socket out-let on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket out-let or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug"

the On Site Guide A3 (Yellow and White) States 553.1.6 "Switches and socket-outlets in new dwellings to be installed so that all persons including those whose reach is limited can easily use them. Install switches, socket-outlets and controls through the dwelling in accessible positions at a height of between 450mm and 1200mm from floor level"

Is it possible that regulations could have changed that much ? or does the on site guide only show a brief outline of 553.1.6

Richard Burns · Apr 30, 2016

"State the number of spurred sockets allowed on a non fused spur connected to a household ring circuit. (A1 ring)"

One double or single socket. OSG 7.2.2 page 71

"State the number of spurs allowed on a household ring circuit. (A1 ring circuit)"

The total number of fused spurs is unlimited but the number of unfused spurs should not exceed the number of points of utilisation on the circuit. OSG 7.2.2 page 71.

"State the maximum floor area, the number of socket outlets and the minimum size of cable which may be supplied by a radial circuit from a 20A re-wirable fuse. (A3 radial)"

The historical limit on floor area is 50m², BS7671 Fig 15B page 454.

The number of socket outlets is unlimited but constrained by the floor area covered. OSG 7.2.2 page 71 (based on the number of fused spurs is unlimited).

There is a reason why you cannot find a limit on sockets, there is no limit on sockets, but practical considerations mean that on a standard installation the circuit will not be overloaded. OSG H2.1 page 181.

Minimum cable size is 4mm² live conductors. OSG Table 7.1(i) pages 64 and 65.

BS7671 Fig 15B page 454 states 2.5mm² but the rewirable fuse (BS3036) reduces the clipped direct current carrying capacity from 27A to 19.5A which therefore theoretically requires the next size up of cable (4mm²). An alternative installation method may require even 6mm² cable.

Richard Burns · May 1, 2016

Don001 said:
After all this time looking through both books I have noticed two very different statements regarding the same standard and am curious how both of them could be so very different.

Example : BS 7671 553.1.6 (Green Book) "A socket out-let on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket out-let or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug"

the On Site Guide A3 (Yellow and White) States 553.1.6 "Switches and socket-outlets in new dwellings to be installed so that all persons including those whose reach is limited can easily use them. Install switches, socket-outlets and controls through the dwelling in accessible positions at a height of between 450mm and 1200mm from floor level"

Is it possible that regulations could have changed that much ? or does the on site guide only show a brief outline of 553.1.6

553.1.6 only states the information you have in the BGB, they are using that regulation inappropriately to allow themselves to draw your attention to Part M of the building regulations requirements for accessibility in new builds.