What is the science behind the 1 MOhm minimum insulation resistance? What is the basis for this particular value?
The value was chosen because it is a nice round figure and easily remembered. 98759.3k Ohms just would not do. It was set to limit current leakage to safe levels and not waste electricity. In fact in the 14th edition wiring regs. fixed wiring was to have an insulation resistance of at least 1 Meg Ohm, but disconnected apparatus could have a minimum insulation resistance of 0.5 MegOhms if the apparatus had no British Standard. Actually our "modern" regs some years ago also specified just a 0.5MegOhm value. (16th Edition, 2001, Table 71A.
What is the science behind the 1 MOhm minimum insulation resistance? What is the basis for this particular value?
The value was chosen because it is a nice round figure and easily remembered. 98759.3k Ohms just would not do. It was set to limit current leakage to safe levels and not waste electricity. In fact in the 14th edition wiring regs. fixed wiring was to have an insulation resistance of at least 1 Meg Ohm, but disconnected apparatus could have a minimum insulation resistance of 0.5 MegOhms if the apparatus had no British Standard. Actually our "modern" regs some years ago also specified just a 0.5MegOhm value. (16th Edition, 2001, Table 71A.
