5. Electrical Grounding
The principal point of connection to the main grounding means for an xDAP is through the ground connection on the power
receptacle, which uses IEC 60320 type C14 connectors. xDAP products follow the accepted practices for grounding
computing equipment such as PCs. The case is solidly connected to the receptacle earth ground. There is a low impedance
connection between the case and the DC power supply ground. There is a similar connection, with much lesser current
capability, between xDAP low-power signal converter electronics and the same common ground. Generally, this grounding
strategy will provide a high degree of grounding safety for desktop units, but for industrial equipment in a rack, beware that
it can introduce unanticipated electrical ground connections between equipment through the case and rack. This can be
beneficial, but it could also allow stray ground current to use the rack as a bypass path or ground coupling link. There is
usually no danger from this, but there could be implications for how the affected equipment operates, and for conformance
with EMC directives.
There can be exposure to damage from connecting xDAP systems to signal sources that are referenced to a “floating
ground.” The analog inputs on xDAP products cope well with small shifts in common mode voltage levels, since the signal
inputs are differential and high impedance, but the inputs can be damaged if either input voltage exceeds the maximum
voltage range limits relative to the xDAP ground, even for a short time.
There are ground-reference pins on analog connectors, intended for equalizing small voltage differences that might exist
between sensors and signal inputs. There are also ground-return pins on digital input and output connectors. If any of these
are incorrectly connected to power current source, it is possible that too much current will attempt to flow back to the power
supply ground through the delicate ground reference connections of the signal pins. This more or less guarantees damage to
the xDAP unit.
Be particularly careful when wiring signals. It is best to have all systems turned off and unplugged from power sources when
wiring. It is easy to accidentally short-circuit signal lines to incorrect pins or to the strongly grounded case, damaging the
signal inputs, the sensors, or both. Signals lines that you think are not powered could pack a damaging level of static charge,
so anti-static precautions are strongly advised.
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