BRUEL & KJAER VIBROCONTROL 8000 - 7.2.5 Using Plant-Wide +24 Vdc Power; 7.2.6 Designating a “Primary” Power Supply; 7.2.7 Power Redundancy (Do I need a PCM?); 7.2.8 Power Wiring Cable Lengths

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7.2.5 Using Plant-Wide +24 Vdc Power
Occasionally a site will have a main +24 Vdc line that is used by all +24 Vdc devices. In this case a 24
Vdc isolator would be required for the VC-8000 rack.
The isolator is needed because the VC-8000 rack power common is the same as the UMM common;
and connecting the plant-wide +24 Vdc to the RCM may cause a ground fault. If this is your scenario
– the site/plant may simply prefer for you to use a standard power supply (i.e. 120-230 Vac to
+24 Vdc) – rather than using an isolator.
IMPORTANT
The rack power connector (COM terminal) is not isolated from UMM signal COM. When using
plant-wide (+24 Vdc) power, a 24 V to 24 V isolator will be necessary (BKV #100549)
7.2.6 Designating a “Primary” Power Supply
The VC-8000 draws power from the power supply with the highest (in specification) voltage. To
prefer a primary supply over a secondary (redundant) supply, adjust the voltage of the primary supply
to be 1 V higher than the secondary.
7.2.7 Power Redundancy (Do I need a PCM?)
Power supply redundancy is external to the rack. The (single) RCM distributes the power from the two
redundant power supplies.
The PCM card was designed (rare cases) as a temporary backup power source when an RCM needs
to be replaced without losing power to the rack. A blank slot would be required to install the PCM. The
PCM is not designed as a permanent redundant power card.
7.2.8 Power Wiring Cable Lengths
The following table shows the maximum wire length for fully loaded racks when powered with a +24
Vdc power supply.
Wire Size 16P Rack 8P Rack 4P Rack
12 AWG
23 m (75 ft.)
61 m (200 ft.)
104 m (340 ft.)
14 AWG
18 m (50 ft.)
46 m (150 ft.)
76 m (250 ft.)
16 AWG
9 m (30 ft.)
24 m (80 ft.)
41 m (135 ft.)
18 AWG
6 m (20 ft.)
16 m (50 ft.)
26 m (85 ft.)
Table 7-2) Maximum Power Wire Length at +24 Vdc Input Power