Light reading

First question


Ohm's Law and the "voltage divider rule" tell us that the larger the resistance to earth, the greater the touch voltage.

Since fatal shock current is measured at the most in 10s of mA, and load resistances are very low, even with very large earth electrode resistances in the extraneous-conductive-parts, is it now possible to see how someone can receive a fatal shock from this?

Second question


50 V AC is generally taken in BS 7671 to be a relatively safe touch voltage (some "zones" in special locations in Part 7 are obvious exceptions to that rule).

100 V is used by DNOs as their "safe" limit.


Section 722 uses 70 V for particular reasons (both hands-to-feet shock risk, large contact area, water-wet conditions, persons clothed and wearing shoes).

First question


Ohm's Law and the "voltage divider rule" tell us that the larger the resistance to earth, the greater the touch voltage.

Since fatal shock current is measured at the most in 10s of mA, and load resistances are very low, even with very large earth electrode resistances in the extraneous-conductive-parts, is it now possible to see how someone can receive a fatal shock from this?

Second question


50 V AC is generally taken in BS 7671 to be a relatively safe touch voltage (some "zones" in special locations in Part 7 are obvious exceptions to that rule).

100 V is used by DNOs as their "safe" limit.


Section 722 uses 70 V for particular reasons (both hands-to-feet shock risk, large contact area, water-wet conditions, persons clothed and wearing shoes).