M120 Chassis Grounding Specifications

To meet safety and electromagnetic interference (EMI) requirements and to ensure proper operation, the router must be adequately grounded before power is connected. Two pairs of threaded inserts (PEM nuts) are provided on the right rear of the chassis for connecting the router to earth ground.

Caution: Before router installation begins, a licensed electrician must attach a cable lug to the grounding and power cables that you supply. A cable with an incorrectly attached lug can damage the router.

To ground AC-powered and DC-powered routers, connect a grounding cable to earth ground and then attach it to the chassis grounding points using two screws. The left pair of grounding points fits M6 screws (European), and the right pair fits UNC 1/4–20 screws (American). The grounding points are spaced at 0.625-in. (15.86-mm) centers. The accessory box shipped with the router includes the cable lug that attaches to the grounding cable (see Figure 1) and two UNC 1/4–20 screws used to secure the grounding cable to the right pair of grounding points. (The cable lug shown in Figure 1 is also used for the DC power cables.)

Figure 1: M120 DC Power and Grounding Cable Lug

If the 48 VDC facility is equipped with a circuit breaker rated at 60 A (-48 VDC), then the grounding cable must be minimum 10 AWG, or as permitted by the local code. If the 48 VDC facility is equipped with a circuit breaker rated more than 60 A (-48 VDC) up to 100 A (-48 VDC), then the grounding cable must be minimum 8 AWG, or as permitted by the local code.

Note: Additional grounding is provided to an AC-powered router when you plug its power supplies into grounded AC power receptacles.