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Protective Earth in a 710 medical location with ELV & PoE circuits

Peter69

Is there a requirement to earth back boxes and/ or metal plates in a medical location when the wiring system is ELV or PoE (normally rated at 24vDC)?

Looking at 414.4.4 states exposed parts of SELV circuit shall not be connected to earth. 

Does this apply to all ELV?

The system will be used in all medical locations

Thanks for any help

  • +1

    Looking at 414.4.4 states exposed parts of SELV circuit shall not be connected to earth. 

    Does this apply to all ELV?

    No - it's a speciality of SELV to keep the circuit Separated (hence the initial S). With PELV and FELV there's no such limitation (but if you do so there's an additional risk of importing a fault voltage from elsewhere - hence SELV is often preferred in some situations)

    As I read 710.411.7, FELV isn't permitted, and 710.414.4.1. seems to ask for exposed-conductive-parts of PELV systems to be connected to protective conductor.

    Whether a back box or metal faceplate constitutes an exposed-conductive-part may depend on the detail of the situation - i.e. whether it's credible that a breakdown of basic insulation or a loose wire could result in the part coming into contact with a live conductor. A lot of RJ45 systems have a plastic module with punch-down terminations that leave a minimal amount of basic insulation (or potentially free wire) exposed after the end of the cable sheath - so I could see a point of view that it might not be.

       - Andy.

  • +1
    Peter69 said:
    Is there a requirement to earth back boxes and/ or metal plates in a medical location when the wiring system is ELV or PoE (normally rated at 24vDC)?

    What type of source is used for the DC?

    Peter69 said:
    Looking at 414.4.4 states exposed parts of SELV circuit shall not be connected to earth. 

    Products to BS EN 62368-1 Audio/video, information and communication technology equipment. Safety requirements  are not guaranteed to provide SELV or PELV. You would need to check with the manufacturer of the equipment. 

    This might limit what can be provided in Group 1 and/or Group 2 medical locations ... see Regulation 710.414.3.

    If the source of power does not meet all the requirements of SELV or PELV then you might have to treat it as FELV, in which case it's not permitted in medical locations period (Regulation 710.411.7).

    If the system is PELV, the system has a protective conductor, and it would make sense to bond accessible conductive parts as part of the bonding system in Group 1 and Group 2 locations. 

    For SELV, it would be best to understand whether there is a risk of static charging, that can occur with datacomms systems. (For example, Ethernet has a controlled static discharge path to Earth across the isolation barrier ... although this is not widely known.)

    There are other provisions for SELV and PELV, such as basic insulation being necessary in Group 1 and Group 2 medical locations (Regulation 710.414.1) ... this may preclude the provision of IT outlets and patch leads (RJ45 jack plugs and socket-outlets) in Group 1 and Group 2 locations, as particularly RJ45 jack plugs might not provide IP2X/IPXXB unless the outlets are in suitable enclosures?

    It could be a good idea to contact a consultant who specialises in medical locations and has knowledge of datacomms etc. in such locations.

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