Here's one example:

Consider the 'appliance' below:

+-----------------+
| | Open Fault
Hot o---------o-o----/\/\---------+------ X -----o Neutral
| Switch Load | |
| (On) |----+ Case should be G but is connected to N
+-----------------+


With the appliance 'on', current passes through the internal
wiring/motor/etc. of the appliance to the N but this is now connected
to the case as well. If the house wiring opens (or even if the plug is
loose, it is possible to have line voltage on the case.

The 'appliance' can actually be *all* loads on the circuit upstream of
the the Open Fault - all those with a grounded cabinet have it then
become live! Testing installed GFCIs

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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