Regulation 710.411.6 (Group 2 Medical Locations)

[eveares]

Just been reading my copy of BS7671 in my spare time, regulation 710.411.6 says that an IT earthing system with a IMD must be used for group 2 medical locations.

Does that mean that expect for devices covered by reg 710.411.4 in group 2 locations, all medical devices must and always be fed from an system with an IT earthing arrangement?

If true, does this not mean that earthed devices could potentially become live with in respect not to the ground (what is isolated) but to one and other (like a earth fault loop) should a earth fault develop in two or more devices.

Also, why is the IT system used under such circumstances for Group 2 locations, is it purely for continuity of electrical service/operation in the most power critical areas (i.e. Life support) in the event of a single earth fault?

Regards: Elliott.

 

[John D v2.0]

Well since it's IT, neither side is intentionally connected to earth. So what were really saying is would it be dangerous if we have a supply with two conductors with 230v AC between them, and one side is inadvertently shorted to some metal work and the other side is touchable at the same time. The metal work happens to be connected to earth but that's not relevant here.
In that kind of double fault situation you're always going to end up with the full supply voltage available to touch.
There's no way to protect against this kind of double fault against touch without lowering the voltage to elv or lower.

 

[ban-all-sheds]

AIUI, the double-fault scenario is why we don't generally have IT systems.