GRASS VALLEY KARRERA, Installation & Service Manual

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Installation & Service Manual
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systems are matched to the destination country’s standard. For example, in the USA C19 to
NEMA 5-20P cables are provided.
USA Power Cable Example
About High Line (208V-240V) Versus Low Line (120V) Operations
North American users usually have a choice to use low line (120 volts) or high line (208-240
volts) as the AC source. If Low line is used, an 8RU Compact Frame with all options installed
and running at 120 volts will draw a total of approximately 15 amps from the line cords. At
100 volts, this increases to approximately 18 amps. This load will be evenly distributed
among the line cords.
IMPORTANT:
Each line cord must be serviced by a dedicated 20 amp
circuit. Two power supplies on the same circuit could exceed 20 amps.
With a fully loaded system, a third power supply is needed for
redundancy.
The possibility of drawing as much as 15 amps from a line cord explains the 20 amp
(NEMA 5-20P) plug on the line cords supplied. The NEC in the US specifies that the
ubiquitous 15 amp outlet be de-rated to 12 amps for continuous loads. A 20 amp outlet is
needed for the rare case of a 15 amp load experienced during a fault condition.
Most of the above is not an issue if high line (240V) operation is used. Since AC line currents
are approximately half of those at low line, exceeding the current rating of a circuit should
not be a problem. In areas where there is a choice between high line or low line operation,
the user should consider the advantages and disadvantages of each power sourcing
scheme.
About Low Line (120V) Operational Considerations
If low line (120V) operation is used (mostly in North America) three characteristics of the
switcher should be kept in mind when provisioning AC power for the system, which will
result in the most reliable system possible:
• Consider brown-out—Modern switching power supplies are constant power devices
and as such, unlike resistive loads, the input current increases as the input voltage
decreases.
• Consider power supply failure—If two or three power modules are present, they will
load share. For instance, if two modules are fitted and the total AC line current is 10
amps, each of the two line cords will draw about 5 amps. If one supply fails, the other
supply takes up the entire load. At this point, one line cord will draw 0 amps and the
other cord will draw 10 amps.
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