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Electric Train Heating

All our Railtour stock are fitted with Electric Train Heating and most with steam heating - for that winter steam excursion! The ETH is powered from the locomotive by a pair of jumpers between coaches. The system operates at 800v, this voltage chosen to reduce the current demand on the cables from the locomotive. A standard Mk1 coach has a heating capacity of around 22kw representing a current of about 28A at 800v. The first coach in the train has to pass all the current for the rest of the train, so for a 12 coach train, this represents a current of 350A or so. The total power absorbed by the train heating is then 264kw or 354hp, quite a chunk out of a 1500hp engine!
There is no such thing as a 'standard' Mk1 coach (we have discovered painfully) and no two coaches seem to be the same. The different works producing the coaches (Wolverton, Swindon, Doncaster, etc.) all had their own variations on the basic theme, hence the diagram below is representative rather than definitive.

ETH schematic

The two inter-coach jumpers carry the "plus" and "minus" power, and a second lighter wire is built into the plug (coaxially) as a safety cut-off. If the second circuit is broken, the ETH automatically switches off in the locomotive. There are switches in the vestibule of each coach for use in an emergency to break this circuit and thus disable the ETH. The last coach in the train must have its ETH jumper correctly "parked" in the spare recepticle so that the safety circuit is completed allowing the ETH to function.

The under-seat heaters are each rated at 800w, 200v and are arranged in banks of four in series, each bank being controlled by a switch in the saloon. The corridor, vestibule and toilet heaters are also arranged in banks of four to match up with the 800v supply. The saloon heaters are fused on both rails at 30A, the vestibule etc. on both rails at 6A.