In the UK I have only come across one place where 110 - 0 - 110 was used this was an army base erected for the Americans even then it was still 50 Hz and it did not use the standard yellow sockets they were the flat pin American ones.
The 55 - 0 - 55 volt and 230 volt plugs and sockets only vary is shape with the outer part where the lug is in a different place so I can understand having the N rather than L2 marking however the yellow cable is not in the main rated for 230 volt in fact a lot of the blue cable used with caravans is not rated for 230 either according to
wiring matters so why have a blue core?
For reduced low voltage systems, low temperature 300/500 V thermoplastic (BS 7919) or equivalent flexible cables shall be used. For
applications exceeding reduced low voltage, flexible cable shall be H07RN-F (BS 7919) type or equivalent having 450/750 V rating and resistant to abrasion and water.
The means of connection between the caravan pitch socket-outlet and the leisure accommodation vehicle should be an assembly of the
following:
- a plug as specified in BS EN 60309-2;
- a flexible cable type H07RN-F (BS 7919) or equivalent, with a protective conductor and having the following characteristics:
length: 25 m maximum
- for current rating 16A: minimum cross-sectional area: 2.5 mm2.
For higher current ratings, the cross-sectional area must be chosen so that secure tripping of the overcurrent protective device is achieved at
the lowest fault current calculated at the end of the cord extension set
- colour identification in accordance with Table 51.
- a connector as specified in BS EN 60309-2.
The use of "Arctic" cable for low voltage (230v) supply to boats and caravans is not permitted. Yes we do it but that does not make it right. Do remember 0 - 110 is low voltage not reduced low voltage so question is still valid why is the core blue rather than black?