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Reduced tariff contactor control.

wessex
Further to a previous post and single phase storage heaters being spread over a three phase supply.

The utility company have provided three phase metering which controls a 100A single phase contactor provide by them and is supplied from one of the line phases being controlled by a switch neutral from the metering unit.

The main post metering supply has a four pole isolator provided. The relay feed is taken from before the isolator and has no isolation after having being switch by the contactor. I,m looking to control two indpendantly DB mounted contactors each having a four pole main switch.

My issue is a matter of isolation within the DB as effectively a separate switched supply, controlling the DB contactor would not be isolated by the DB mainswitch. Also would an independent neutral have to be taken to the contactor or could the neutral with the db used. Borrowed neutral comes to mind. Perhaps the addition of an aux contact mounted to the main switch would be a solution.

Your thought please.
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    The French way of doing this side-steps the isolation problem quite neatly I think. What the metering arrangement does there is to supply a pair of volt-free contacts (rather than a switched supply). The electrician then uses a low rated MCB in the DB to power whatever contactors they want, switched by the meter's volt-free contacts. Turning off the main switch then automatically isolates everything as everyone would expect. They then repeat the same scheme when there are two or more tiers of DBs - each DB provides a pair of volt-free contacts to each DB it supplies - so again each local simple incomer isolates everything within that enclosure.


    So you could emulate that approach by using the off-peak switched supply to operate just a contactor (in its own little enclosure say) - and use the contacts of that to control the DB mounted contactors which are powered from an MCB in the same DB.


    Otherwise, you could do something equivalent to the traditional "dual-tariff CU" - i.e. two separate main switches in the same enclosure and lots of labelling!


       - Andy.
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  • 0
    The French way of doing this side-steps the isolation problem quite neatly I think. What the metering arrangement does there is to supply a pair of volt-free contacts (rather than a switched supply). The electrician then uses a low rated MCB in the DB to power whatever contactors they want, switched by the meter's volt-free contacts. Turning off the main switch then automatically isolates everything as everyone would expect. They then repeat the same scheme when there are two or more tiers of DBs - each DB provides a pair of volt-free contacts to each DB it supplies - so again each local simple incomer isolates everything within that enclosure.


    So you could emulate that approach by using the off-peak switched supply to operate just a contactor (in its own little enclosure say) - and use the contacts of that to control the DB mounted contactors which are powered from an MCB in the same DB.


    Otherwise, you could do something equivalent to the traditional "dual-tariff CU" - i.e. two separate main switches in the same enclosure and lots of labelling!


       - Andy.
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