I have a board that I recently redesigned that contains nine
T90 relays that switch 110VAC. The board goes in an
industrial controller and switches lights and contactors
(mag starters). The relays all have flyback diodes across
the coils and snubbers across the contacts.
On the old version of the board (not my design), the 110VAC
traces were mixed on the board with signal traces. It
worked, but as you can imagine, we had problems in the
field. I tried to eliminate the problem by aligning the
relays so that the 110VAC traces were all on the lower area
of the board and all other traces were along the upper.
There is a "no trace zone" about .6" wide that runs under
the relays between the coil pins and the contact pins. This
is the dividing line between the 110VAC area and the rest of
This layout helped a lot, but I'm still getting a few spikes
back in the signal traces. It is sometimes enough to lock up
the NE5090 mux on the board, especially when the contactors
fire. I have bypass caps on the chips on the board, but I
really would like to eliminate the spikes.
The whole point of this long-winded explanation is to ask if
filling the "no trace zone" with a ground plane would do any
good. If so, should it be earth ground or circuit ground? Is
there any way to hack a current board (adding foil or
something) to simulate the ground plane that would give
meaningful test results before we redo the board? The board
is two-sided, through hole.
See also: www.piclist.com/techref/index.htm?key=120vac+traces
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