mapj1:
...IMO these values need to be revisited and discussed further.


I'd like to know why you say that, though you may well be right, after all 

"because another fancy document you have not read says so" is no guarantee of validity.  (*)


Ideally such tables should indicate their sources, but that is not much good if that too is another reference or unavailable.

In the favour of the current situation, there are not enough electrocutions to indicate that the current assumptions are widely off the mark, or if they are, then not in a dangerous direction.


Mike.


*

I am reminded of the fiasco of "coefficient of friction", the idea being that the friction force is proportional to contact area and pressure there is a constant factor for any  given material.

Some numbers were tabulated by some lazy experimenters in the late 1800s, and copied without imagination into many engineering textbooks well into the 2nd half of the 20th century..

For nearly a century school children grew up learning about this "fact", and also learning that in practical labs, that in some way they could never re-create the data book values except for one very contrived experiment.  Not until the late 1960s and part of the work for the US space program were tests re-done and the whole idea of linearly pressure dependent friction largely discredited. It is just vastly more complex than that. Some things are sticky with no applied pressure (jam and glue come to mind), and some are almost independent of it up to some critical value then bind, almost anything with an oily feeing surface, most things take more to get them moving than to keep them in motion, once the starting 'stiction' is overcome.. Oh there are many errors to the simple model.


 

These values seem to be based on 0.8 multiplier relying on the sag at the trafo's terminals plus the MET being bonded to any conductive parts within the premises. However, the calculations I'm running show only a few volts difference of exposure between remote earth vs bonded metal like pipes and rebar.


It is funny you mention hidden inference- AFDDs come to mind but that is a different thread altogether.


 

mapj1:
...IMO these values need to be revisited and discussed further.


I'd like to know why you say that, though you may well be right, after all 

"because another fancy document you have not read says so" is no guarantee of validity.  (*)


Ideally such tables should indicate their sources, but that is not much good if that too is another reference or unavailable.

In the favour of the current situation, there are not enough electrocutions to indicate that the current assumptions are widely off the mark, or if they are, then not in a dangerous direction.


Mike.


*

I am reminded of the fiasco of "coefficient of friction", the idea being that the friction force is proportional to contact area and pressure there is a constant factor for any  given material.

Some numbers were tabulated by some lazy experimenters in the late 1800s, and copied without imagination into many engineering textbooks well into the 2nd half of the 20th century..

For nearly a century school children grew up learning about this "fact", and also learning that in practical labs, that in some way they could never re-create the data book values except for one very contrived experiment.  Not until the late 1960s and part of the work for the US space program were tests re-done and the whole idea of linearly pressure dependent friction largely discredited. It is just vastly more complex than that. Some things are sticky with no applied pressure (jam and glue come to mind), and some are almost independent of it up to some critical value then bind, almost anything with an oily feeing surface, most things take more to get them moving than to keep them in motion, once the starting 'stiction' is overcome.. Oh there are many errors to the simple model.


 

These values seem to be based on 0.8 multiplier relying on the sag at the trafo's terminals plus the MET being bonded to any conductive parts within the premises. However, the calculations I'm running show only a few volts difference of exposure between remote earth vs bonded metal like pipes and rebar.


It is funny you mention hidden inference- AFDDs come to mind but that is a different thread altogether.