Why did 405 look so good?

[ppppenguin]

The island of Ireland has a fairly modest grid system, in keeping with its size and population. There are interconnects between Eire and Ulster which I think are AC, so the 2 countries' grids are synchronous to each other.

AFAIK, there have only been interconnects with mainland GB in the last 20 years or so. In common with most undesea electrity cables these are high voltage DC. Hence the GB and Ireland grids are not synchronised.

I'm not sure about the history of BBC and ITV locking their 405 networks to mains frequency. By 1964 and the start of BBC2 I'm pretty sure everything was crystal controlled. By 1967 and the start of colour there was no possibility of mains lock.