suplimental questions:
1) As a non technical person can some one please explain to me the limiting factors in preventing sockets (plug sockets?
) being fitted to and being able to operate on all rail vehicles.
2) Further, how do the sockets provided on some trains draw provide their power? From what source is suitable electricity created or converted and distributed
If you don't mind I'll answer the 2nd one first to provide some context for the 1st.
There are two or three (main) ways to create the 230/400V AC for sockets.
The first has been used for many, many years on trains, this being the Motor Alternator. It is what it says on the tin. Provides nice isolation from the supply current but is not a clean supply.
This type of supply is suitable for:
Carriages Mk2. Mk3a (1000V DC Supply), Carriages Mk3 (415V Supply), DC EMUs, AC EMUs, and DMUs.
Transformers can be used on services powered by an AC, such as the class 390. But this would be by a secondary winding on the primary transformer, sitting behind the DC bus, this would therefore not be protected from when the VCBs open at current gaps, so is not preferable.
HSTs use a 3 phase 415V distribution for ETS, so this can simply be fed through an isolation transformer and remain within the spirit of BS7671. However, this is not a clean supply and would usually feed 'cleaners' sockets'
The most modern way is using power electronics to take a DC input and make a fake AC output that is actually formed of a quazisquarewave, rather than a true sine wave. These are not an issue for power supplies but can be a problem for wound equipment like motors, or florescent tubes. (Hence why MA sets are used.) But in my opinion this is the most likely method for supply used on most rolling stock as it provides a very nice level of isolation and redundancy to current gaps if a parallel battery is provided on the DC bus (it usually is).
To answer part one, space and cost I imagine are big factors. But not just the equipment cost, but how much of the train you need to stip out to harness up these sockets that are only there as a matter of convenience, not a safety critical item. Also while we're on that, the use of 230V@50Hz on some trains can interfere with LV DC systems that provide control so would require protection, adding more expense...
My point wasn't about whether the sockets should or shouldn't be there, but about the response to the question 'why are there only sockets at the tables' being 'because that's how they were built'.
But in response to your points above, if there is no space for a socket, how did they fit them in by the table seats? Also, I tend to agree that there is no point in putting sockets in when there is no perceived requirement for such things.
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Because on the Class 390 they're part of the table assembly and not built into the wall.
And it's not a case of perceived requirement, there simply wasn't any perception at all, no-one knew how they would be used at all on services and the equipment likely to be used at the time, by the perceived passengers at the time, was business laptops and equipment not dissimilar, therefore, due to the size of the aforementioned equipment, why would you want facility for it fitting at airline seats, where space for it is dubious and would likely add significant additional cost.
Also, not fitting them into walls is surprisingly common in modern stock, take a look at the Class 395...
