I do have a "control transformer" which can be identified by the three
fuses on top. One for X1 (secondary) and one each for L1 and L2. I went
back and found out which was X1 and X2 and will correct my wiring today.
My question is I have a filter on X1 and X2 should I ground before or
after the filter?
JT
On 1/1/2016 6:41 PM, John Kasunich wrote:
120V transformer secondaries (in the USA) need to be grounded on
one side, even if they are part of a machine control panel.
Such transformers are referred to as "control power transformers"
and traditionally powered electro-mechanical control devices such
as relays and contactors. Today they still power those things, and
they also power AC-to-DC supplies that run the electronic parts of
the control. The low voltage DC power distribution (typically 24V)
is sometimes un-grounded, sometimes single-point grounded, for
exactly the noise reasons Berthos mentions. But the 120V "control
power" isn't used a the "reference" for anything - it is still "dirty"
power, although not as dirty as the main power that might be going
to a VFD or whatever.
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