USB charger Euro modules

1. As part of the ring main - requires modules which can accommodate 2 x 2.5 sq mm conductors unless they are connected via a switch or fuse that accommodates 2 x 2.5 sq mm conductors.

Yes, at least 2 no. 2.5 sq mm conductors - maybe 3 no. or 2 no. 4 sq mm also?

2. On a spur from a socket on a ring main - is it permissible to spur two or more modules (in any topological combination) from a socket without a series fuse?

See Appendix 15 of BS 7671:2018 or BS 7671:2008+A3:2015 (and also, consider the individual manufacturer's requirements for overcurrent and fault protection). This shows FCUs for appliances - why would a USB charger module behave differently to either a fixed appliance, or any other type of current-using equipment?

3. A separate ring main - is a ring configuration even necessary or can it be a long chain which terminates in the final module? It will be possible to use cables with 1 sq mm conductors.

A choice for the designer? The latter option being a radial?

In terms of 1 sq mm cable, only if it's put on a lighting circuit (Table 52.3), otherwise it's a power circuit and min 1.5 sq mm copper applies. Perhaps 1 sq mm might be OK for connection to a single module, between the module and a short run to adjacent FCU?

4. Radially wired - several possible topological combinations. It will be possible to use cables with 1 sq mm conductors.

Again, only if the radial is for lighting will it be possible to comply with Table 52.3



I'm still of the opinion that these are issues for the designer to assess on a case-by-case basis. If an organisation wants to get a standard design together, there are two broad options to get you to a point where you can choose ring vs radial etc.:


(a) Select the product(s) you will recommend up-front.


(b) Go for the "lowest common denominator" - i.e. connect each one from an FCU with 1 A fuse.

1. As part of the ring main - requires modules which can accommodate 2 x 2.5 sq mm conductors unless they are connected via a switch or fuse that accommodates 2 x 2.5 sq mm conductors.

Yes, at least 2 no. 2.5 sq mm conductors - maybe 3 no. or 2 no. 4 sq mm also?

2. On a spur from a socket on a ring main - is it permissible to spur two or more modules (in any topological combination) from a socket without a series fuse?

See Appendix 15 of BS 7671:2018 or BS 7671:2008+A3:2015 (and also, consider the individual manufacturer's requirements for overcurrent and fault protection). This shows FCUs for appliances - why would a USB charger module behave differently to either a fixed appliance, or any other type of current-using equipment?

3. A separate ring main - is a ring configuration even necessary or can it be a long chain which terminates in the final module? It will be possible to use cables with 1 sq mm conductors.

A choice for the designer? The latter option being a radial?

In terms of 1 sq mm cable, only if it's put on a lighting circuit (Table 52.3), otherwise it's a power circuit and min 1.5 sq mm copper applies. Perhaps 1 sq mm might be OK for connection to a single module, between the module and a short run to adjacent FCU?

4. Radially wired - several possible topological combinations. It will be possible to use cables with 1 sq mm conductors.

Again, only if the radial is for lighting will it be possible to comply with Table 52.3



I'm still of the opinion that these are issues for the designer to assess on a case-by-case basis. If an organisation wants to get a standard design together, there are two broad options to get you to a point where you can choose ring vs radial etc.:


(a) Select the product(s) you will recommend up-front.


(b) Go for the "lowest common denominator" - i.e. connect each one from an FCU with 1 A fuse.