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Testing if supplementary bonding is required.

MrJack96
I have read some bits stating we can measure between the two metallic parts in question and referring to the formula 


50/ia will give you the resistance needed to keep touch voltage to less than 50v 


my questions can we do the same test to determine if the part has a high enough resistance to not require bonding and what sort of figures we should look for?
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    yes, in some cases. The problem is that exactly which electrode (may be a deliberate one, or an accidental one like a security camera mounted on a metal fence post) carries the most current, and where exactly the volts pile up to a dangerous level is horribly variable with the exact local circumstances. The bulk of the voltage drop is almost never along the copper, as that is pretty low resistance.

    Things are rarely as cut and dried as the C and G blackboard model (or whiteboard nowadays probably, or power point) in real life.

    To illustrate what I mean -

    An example of an incident from a few years ago - can you work out what happened?


    I think it would be a brave designer who had anticipated this scenario, or anything like it.

    Here they had (I assume) installed  metal doors and frames connected to the building metal work, and folk standing on the floor at not the same voltage.

    Mike.
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  • 0
    yes, in some cases. The problem is that exactly which electrode (may be a deliberate one, or an accidental one like a security camera mounted on a metal fence post) carries the most current, and where exactly the volts pile up to a dangerous level is horribly variable with the exact local circumstances. The bulk of the voltage drop is almost never along the copper, as that is pretty low resistance.

    Things are rarely as cut and dried as the C and G blackboard model (or whiteboard nowadays probably, or power point) in real life.

    To illustrate what I mean -

    An example of an incident from a few years ago - can you work out what happened?


    I think it would be a brave designer who had anticipated this scenario, or anything like it.

    Here they had (I assume) installed  metal doors and frames connected to the building metal work, and folk standing on the floor at not the same voltage.

    Mike.
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