B&B Electronics 711FX3-ST - Manual - Manual (Page 15)

(Revised 2010-2-24) Page 15 of 155
N-TRON SWITCH GROUNDING TECHNIQUES
The grounding philosophy of any control system is an integral part of the design. N-Tron switches are
designed to be grounded, but the user has been given the flexibility to float the switch when required. The
best noise immunity and emissions (i.e. CE) are obtained when the N-Tron switch chassis is connected to
earth ground via a drain wire. Some N-Tron switches have metal din-rail brackets that can ground the
switch if the din-rail is grounded. In some cases, N-Tron switches with metal brackets can be supplied with
optional plastic brackets if isolation is required.
Both V- legs of the power input connector are connected to chassis
internally on the PCB. Connecting a drain wire to earth ground from
one of the V- terminal plugs as shown here will ground the switch and
the chassis. The power leads from the power source should be limited
to 3 meters or less in length.
As an alternate, users can run a drain wire & lug from any of the Din-Rail screws or
empty PEM nuts on the enclosure. When using an unused PEM nut to connect a
ground lug via a machine screw, care should be taken to limit the penetration of the
outer skin by less than 1/4 in. Failure to do so may cause irreversible damage to the
internal components of the switch.
Note: Before applying power to the grounded switch, you must use a volt meter to
verify there is no voltage difference between the power supply’s negative output
terminal and the switch chassis grounding point.
If the use of shielded cables is required, it is generally recommended to only connect the shield at one end to
prevent ground loops and interfere with low level signals (i.e. thermocouples, RTD, etc.). Cat5e cables
manufactured to EIA-568A or 568B specifications are required for use with N-Tron Switches.
In the event all Cat5e patch cable distances are small (i.e. All Ethernet devices are located in the same local
cabinet and/or referenced to the same earth ground), it is permissible to use fully shielded cables terminated
to chassis ground at both ends in systems void of low level analog signals.