Epson 214D-1 - Manual (Page 51)

Installation 43
HP289
should be as short as possible and connected to the grounding lug on
the side of the case.
In order to comply with the requirements for Electromagnetic
Compatibility as per EMC-Directive 89/336/EEC of the Council of
European Community, this wiring practice is mandatory.
Although it is also possible to connect shields to the signal ground
(terminal 2) this practice is not in accordance with EMC directives.
RC Networks for Interference Suppression
When driving highly inductive loads with the control relays, it is
recommended that RC suppression networks (often called "Snubbers")
are used for two reasons:
§ To limit the amount of electrical noise caused by arcing across
the relay contacts which may, in extreme cases, cause the
microprocessor to act erratically.
§ To protect the relay contacts against premature wear through
pitting.
RC suppression networks consist of a capacitor and series resistor and
are commonly available in the electrical industry. The values of R and
C are dependant entirely on the load. However, if the user is unsure of
the type of snubber to use, values of 0.25µF and 100 ohms will usually
suffice. Note that only AC voltage approved RC suppression networks
should be used.
The basic principle of operation is that the capacitor prevents a series of
sparks from arcing across the contact as the contact breaks. The series
resistor limits the current through the contact when the contact first
makes