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PE advice by Napit (hot tubs)

ebee

There is an article in PE and I have just received it via email.

I am disappointed that the article seems to suggest that it contains all you need to know yet no mention is made of earthing systems

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    AJJewsbury: 
     

    Does BS 7671 really require we keep the touch voltage below 50 V?

    For TT systems that use RCDs, and for ‘persistent’ touch voltages , yes - 411.5.3 (ii).

    The TT systems that have such low loop impedances that overcurrent devices can be used, there isn't a specified limit, but as the system then approximates to TN systems any reasonable leakage current isn't likely to do any harm.

        - Andy.

    Nope … this is effectively the same requirement as 415.2.2 …

    … where the fault current exceeds the residual operating current, the touch voltage may also exceed 50 V until the device trips.

    But also, this is only the earth electrode resistance, not the effective resistance from the transformer earth to the point at which you are standing … 

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  • 0

    AJJewsbury: 
     

    Does BS 7671 really require we keep the touch voltage below 50 V?

    For TT systems that use RCDs, and for ‘persistent’ touch voltages , yes - 411.5.3 (ii).

    The TT systems that have such low loop impedances that overcurrent devices can be used, there isn't a specified limit, but as the system then approximates to TN systems any reasonable leakage current isn't likely to do any harm.

        - Andy.

    Nope … this is effectively the same requirement as 415.2.2 …

    … where the fault current exceeds the residual operating current, the touch voltage may also exceed 50 V until the device trips.

    But also, this is only the earth electrode resistance, not the effective resistance from the transformer earth to the point at which you are standing … 

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