Underfloor Bus Bar Systems

Humm, interesting question.


In the case where the underfloor busbar system feed floor boxes that containing (usually) BS 1363 sockets, I think I would have automatically have thought as the sockets in the floorboxes as being the end of the "fixed wiring" and so "sockets" in the usual sense, so the tap off points on the busbar system as just some proprietary connector system. As some types of floor boxes contain local overcurrent - or more to the point RCD - protection (e.g. to provide the additional protection that most sockets require these days) it would undermine that approach if the tap-off points were treated in the same way as ordinary sockets and so had to be provided with 30mA RCD protection for instance (especially in situations where loads were large, discrimination important or high protective conductor currents present).


I do see your point that the exact wording of BS 7671's definitions don't obviously support that position though. A lot of these definitions go back many many years and it's not uncommon to find that they've been overtaken by changes in technology. I am tempted to think that they've had this problem before - someone's pointed out that lighting track systems would be caught in the ordinary definitions and so they've had to add an exception.to take them out again - so maybe the same reasoning should be applied to underfloor systems. There's probably a similar issue with prefabricated wiring systems used in some modular buildings - as they have a kind of "plug & socket" connections between wall panels or other large units of the building that are bolted together on site.


Remember that most of the regulations' wording is made up by committees and then later amended by more committees - which isn't always the best way to produce clear and succinct prose. So sometimes you need to think beyond the actual wording to understand what was really intended - and then apply that reasoning to your particular application (which is almost certainly at least slightly different to anything those committees had in mind all those years ago). Often precise adherence to the letter of the regulations isn't required - just as long as you produce a solution that's no less safe.


  - Andy.

Humm, interesting question.


In the case where the underfloor busbar system feed floor boxes that containing (usually) BS 1363 sockets, I think I would have automatically have thought as the sockets in the floorboxes as being the end of the "fixed wiring" and so "sockets" in the usual sense, so the tap off points on the busbar system as just some proprietary connector system. As some types of floor boxes contain local overcurrent - or more to the point RCD - protection (e.g. to provide the additional protection that most sockets require these days) it would undermine that approach if the tap-off points were treated in the same way as ordinary sockets and so had to be provided with 30mA RCD protection for instance (especially in situations where loads were large, discrimination important or high protective conductor currents present).


I do see your point that the exact wording of BS 7671's definitions don't obviously support that position though. A lot of these definitions go back many many years and it's not uncommon to find that they've been overtaken by changes in technology. I am tempted to think that they've had this problem before - someone's pointed out that lighting track systems would be caught in the ordinary definitions and so they've had to add an exception.to take them out again - so maybe the same reasoning should be applied to underfloor systems. There's probably a similar issue with prefabricated wiring systems used in some modular buildings - as they have a kind of "plug & socket" connections between wall panels or other large units of the building that are bolted together on site.


Remember that most of the regulations' wording is made up by committees and then later amended by more committees - which isn't always the best way to produce clear and succinct prose. So sometimes you need to think beyond the actual wording to understand what was really intended - and then apply that reasoning to your particular application (which is almost certainly at least slightly different to anything those committees had in mind all those years ago). Often precise adherence to the letter of the regulations isn't required - just as long as you produce a solution that's no less safe.


  - Andy.