3 Installation
28 | 266 MODBUS® multivariable transmitter User manual 2105216 Rev. AB
Electrical connections
Protective conductor and grounding
A terminal is available on the transmitter exterior for connection to an earth ground or potential equalization (PE) grid (Figure
24). A connection for attaching wiring shields is located inside of the rear housing cover. For additional field wiring requirements
see the following publications:
— For European applications, see Standards IEC60364 and IEC60079-14 for installation of electrical equipment.
— For United States or Canada Division or Zone rated applications, see NEC (NFPA 70) section 500 or CSA C22.1.
Figure 24: Ground connections
In order to fulfill the requirements of the low-voltage guidelines and the relevant EN 61010 rules for the installation of electrical
equipment, the housing must be provided with a protective circuit (for example: grounding or protective conductor) if voltages
greater than 150 Vdc could occur.
Integrated surge protector
The 266 MODBUS
®
transmitter terminal block includes transient suppression circuitry built in. The circuitry is based on a four-
tier protection design that protects the power inputs and communications.
For correct operation of the suppression system a high-current path to earth ground or potential equalization (PE) grid is
required (Figure 24). Section 3.6.1, Protective conductor and grounding, includes additional information on grounding the
transmitter.
IMPORTANT NOTE: The grounding (PE) should be kept as short as possible with a minimum wire size of 12
AWG.
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