A 110V mains supply

I doubt that a transformer suitable for "several computers" will fit into a consumer unit.


An external transformer will be required but these are available from several suppliers. An RCD on the primary circuit of a isolating transformer will not protect against an electric shock from the secondary side.


You will need either a special RCD for 110 volts, or possibly a risk assessment that justifies omitting RCD protection in view of the lower and less dangerous voltage. If the transformer has an earthed center tap, then the shock voltage is only 55 volts and in MY VIEW RCD protection could then be omitted for normal dry indoor conditions.

Japanese computers and games consoles that require a 110V AC mains supply.

I thought Japan used 100V rather than 110V (or are these "US" versions of Japanese games, or just a case of 110V is 'close enough'?)


If you're going to have several devices on the same supply then you'll need something pretty 'stiff' to cope with the switch-on surges (a.k.a. inrush currents) - otherwise you'll likely find that switching one on causes all the ones already switched on to crash or restart as the supply voltage momentarily collapses. Older PSUs where particularly poor in that respect - often drawing many tens of times their nameplate rating when switched on.


If the 110V socket outlets are going to be part of the fixed installation then you'll probably find that most traditional "foreign" types don't meet UK safety regs for domestic use (mostly due to not being shuttered) - although if you look hard enough it's usually possible to find shuttered versions these days (I think they're just becoming a requirement in the US now).


Be careful too about how the secondary is arranged. Many UK 110V systems will be 55-0-55V centre-tapped Reduced Low Voltage systems (RLV), but US style 110V equipment will usually expect N to be at close to earth potential and so may have single pole switching etc in the L only. Even US style 2-pin plugs are polarized (by the rather subtle method of making the N pin slightly wider than the line) and socket terminal screws are often identified by different colour metals (brass for L, tinned for N) rather than any obvious L and N markings that you might have expected.


  - Andy.

The available transformers will be autotransformers with a single winding that doesn't provide separation and BS7671 doesn't like those .

Japanese 100V can be anywhere from about 90 and a bit to a touch under 110, and is often without earth, on plugs with both pins 6mm, an OK if loose fit in the US sockets, and 50 or 60Hz depending on which district.

The easiest is probably to buy a yellow building site transformer, and wire a Japanese extension lead ( Enchō kōdo ) to  a yellow BS4343 plug, but attach it to a board or table, so not to make it part of the fixed wiring. example of extension lead  https://www.ebay.com/itm/ELECOM-power-strip-lightning-guard-swing-plug-4-ports-2-5m-white-T-K1A-2425WH/173472717532?hash=item2863c79adc:g:xz8AAOSwtMFbc-Bq note the hinged plug - all rated for 15A, but of course the cable is better cooled than ours with it's thicker over jacket.

Specialist hobby installations like this, as with Ham radio, and the works of the more enthusiastic HiFi types, are not a comfortable fit to the letter of BS7671, and some creativity may be needed, or a temporary installation that the user takes with them when they move out.