I beleive that in the early days of electricity when they were using metal conduits
It was considered ok to use the metal conduit as a earth/ground.
Electrical systems in houses were much smaller then,
A few lights and a radio was the norm.
How ever now days electrical systems in houses are MUCH bigger
And using metal conduit would probably not cut it,
under a full fault current situation.
And the chances of the metal conduits path being compromised is higher.
Therefore it is no longer best practice and also NOT code in some area's.
Probably a good thing too.
if you look at it from a safety stand point.
It was considered ok to use the metal conduit as a earth/ground.
Electrical systems in houses were much smaller then,
A few lights and a radio was the norm.
How ever now days electrical systems in houses are MUCH bigger
And using metal conduit would probably not cut it,
under a full fault current situation.
And the chances of the metal conduits path being compromised is higher.
Therefore it is no longer best practice and also NOT code in some area's.
Probably a good thing too.
if you look at it from a safety stand point.