Transformer question (only slightly OT)
ard at p850ug1.demon.co.uk
Tue Sep 5 18:33:23 CDT 2006
> Is one side of your mains grounded? Here in the US, the most common
Yes. The 'neutral' side of our mains is connected to ground at some point
(normally at the secondary of the last distribution transformer -- note
that over here a single transformer supplies many houses, we don't have
the equivalent of your 'pole pigs').
But no device may assume that the neutral side of the mains is 'safe' to
touch. It muse be inaccessible without the use of the tool. Single-pole
switches and fuses must be in the live (hot) side of the mains. It is
against the rules to put a protective device (fuse/breaker) in the
neutral side at all unless you use one where a fault on that side will
turn off the live as well (e.g. a double pole circuit breaker, but not 2
independant single pole ones). Oh yes, the outer cap of an ES or similar
light bulb is the neutral side.
> distribution is a 120-0-120v distribution transformer with the center tap
> connected to ground. So, for common 120v wall receptacles, one side (in
Yep. My Tekky curve tracer's manaul gives transformer primary winding
connection diagramss for 3 configurations : 115V, 230V with one side
grounds, and 230V with the centre tap grounds. I believe it's to reduce
noise, etc, it's not any safety problem
> addition to the grounding prong) is grounded. I've popped the GFI on my
> workbench outlet on several occasions--in every case, it involved a "hot
> chassis" piece of equipment. Sparks are pretty, but I'll take the
> inconvenience, thank you.
Well, when working on a live chassis set, or on the mains side of an
SMPSU, I use an isolating transformer. It means I can connect the 'scope
to points on the device without damage or blowing the breaker.
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