On Wed, 24 Dec 2008 21:04:26 -0600, jvpoll@dallas.net wrote:
>b) History, practice and more importantly, mistakes in
>practice (accidents) have made important contributions
>to the NEC than simple theory would or could predict;
>take for iinstance grounding practices. What _is_ the
>rationale for grounding the secondary circuit (the
>service to the home) of a power transformer for instance?
>This isn't strictly neccessary for that service to
>function. (I am asking this for the purposes of bringing
>forth an example; I can cite cases where, in practice, this
>has saved property and/or life, but that is different than
>a statement or the treatment a textbook might give.)
>Could you cite a textbook wherein that rationale is brought
>to light?
One reference is the tutorial cited below. While it's written
for sound and video contractors, the fundamentals apply to
hams.
http://audiosystemsgroup.com/SurgeXPowerGround.pdf
It all comes down to safety. The secondary is bonded to provide
both lightning safety and, with the equipment (safety) ground
conductor (green wire) provide a solid path to blow a fuse or
breaker if a fault develops that could shock someone or start a
fire. The lightning protection comes from because the bond to
earth limits the potential that can exist in the event of a
strike. The concept behind lightning protection is to have the
whole building rise in potential by the same amount.
NEC can be purchased in annotated form -- that is, with
explanations and commentaries interspersed with each paragraph.
73,
Jim Brown K9YC
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