Watlow Series 965 - Manual (Page 28)

Appendix
28
WATLOW Series 965 User's Manual
• Use twisted pair wire any time control circuit signals must travel over two feet,
or when you bundle them parallel with other wires.
• Select the size or gauge of wire by calculating the maximum circuit current
and choosing the gauge meeting that requirement. Using greatly larger wire
sizes than required generally increases the likelihood of electrostatic (capaci-
tance) coupling of noise.
• Eliminate ground loops in the entire control system. You can spot the
obvious loops by studying the "as-built" wiring diagram. There are also not-
so-obvious ground loops resulting from connecting internal circuit commons
in the manufacturer's equipment.
• Do not daisy chain ac power (or return) lines, or output signal (or return) lines
to multiple control circuits. Use a direct line from the power source to each
input requiring ac power. Avoid paralleling L1 (power lead) and L2 (return
lead) to load power solenoids, contactors, and control circuits. If an applica-
tion uses L1 (power lead) to switch a load, L2 (return lead) has the same
switched signal and could couple unwanted noise into a control circuit.
• Tie all ground terminals together with one lead (usually green wire) tied to
ground at one point. Don't connect ground to the control case if the control is
in a grounded enclosure (preventing ground loops).
• Do not confuse chassis grounds (safety ground) with control circuit commons
or with ac supply L2 (return or neutral line). Each return system wiring must
be separate. Absolutely never use chassis ground (safety) as a conductor to
return circuit current.
Eliminating Noise
• Use "snubbers" (QUENCHARC™ P/N: 0804-0147-0000) to filter out noise
generated by relays, relay contacts, solenoids, motors, etc. A snubber is a
simple filter device using a 0.1
µ
f, 600 volt, non-polarized capacitor in series
with a 100
Ω
, 1/2 watt resistor. The device can be used on ac or dc circuits
to effectively dampen noise at its source.
• The ultimate protection is an "uninterruptable" power supply. This "senses"
the ac power line; when the line fluctuates, a battery powered 60Hz
inverted circuit takes over, supplying power within one-half to one cycle of
the ac line; very expensive.
Wiring Guide