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Loss of neutral

lyledunn
I have just been involved in a situation where temporary loss of neutral on a TNCS system caused thousands of pounds worth of damage. It seems this loss of neutral situation, either within or outside the installation, is occurring more frequently. SPDs are now commonly fitted but at DBS  and generally with a Up in the order of 860v, so giving no protection on loss of neutral in a three-phase and neutral system. Cost benefit analysis across the national spectrum might not support a compulsion but is it time designers should be raising the issue with clients and at least offering a solution. On the other hand, is there a packaged solution?
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    AJJewsbury:

    I wouldn't expect SPD to offer any protection from longer-term overvoltage situations like broken neutrals - they operate by creating a low impedance L-PE or L-N and would have to dissipate huge amounts of (heat) energy if the overvoltage lasted for more than a small fraction of a second. The best we can hope for is that the SPD fails safe and disconnects itself before it starts a fire.


    As for other solutions there are plenty of voltage monitoring relays on the market that could be fitted (probably via a contactor) to disconnect the installation if the voltage went outside limits. (e.g.https://uk.rs-online.com/web/p/monitoring-relays/9143945/ )


       - Andy.




    Back to my comment about Malta. 


    Over voltage protection is compulsory, SPDs are optional. The installations are to comply with BS7671.


    Here is an example of a Maltese consumer unit with the over voltage device Andy has suggested linked to a contactor.
    https://www.enemalta.com.mt/electricity-safety/electricity-safety-regulations/


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    AJJewsbury:

    I wouldn't expect SPD to offer any protection from longer-term overvoltage situations like broken neutrals - they operate by creating a low impedance L-PE or L-N and would have to dissipate huge amounts of (heat) energy if the overvoltage lasted for more than a small fraction of a second. The best we can hope for is that the SPD fails safe and disconnects itself before it starts a fire.


    As for other solutions there are plenty of voltage monitoring relays on the market that could be fitted (probably via a contactor) to disconnect the installation if the voltage went outside limits. (e.g.https://uk.rs-online.com/web/p/monitoring-relays/9143945/ )


       - Andy.




    Back to my comment about Malta. 


    Over voltage protection is compulsory, SPDs are optional. The installations are to comply with BS7671.


    Here is an example of a Maltese consumer unit with the over voltage device Andy has suggested linked to a contactor.
    https://www.enemalta.com.mt/electricity-safety/electricity-safety-regulations/


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