053-996-B0 Rev D
Page 12 of 26
5
Wiring
This chapter provides cabling details and notes on cable sizing for DC applications with respect to the product.
WARNING
Ensure that power is removed by turning off converters and removing battery line fuse (if
applicable) or connection before attempting work on the wiring connections. Use a voltmeter to
verify the absence of voltage. Clearly mark the correct polarity of the leads before commencing
work on DC connections.
Refer to the previous (Installation) chapter for safety precautions and tools required.
5.1
Grounding
The isolated power system battery return bus (BRB) should be connected to the building master ground bus
(MGB) or floor ground bus (FGB) in a larger building. This acts as a system reference and as a low impedance
path to ground for surges, transients, noise, etc. The MGB or FGB should have a direct low impedance path to the
building grounding system. The cable from the power system to the MGB or FGB should be sized to provide
sufficient ampacity to clear the largest fuse or breaker on the power system, excluding the battery protection fuse
(if applicable) or circuit breaker. This is the minimum requirement; other factors including length of cable and
special grounding requirements of the load should also be factored in. The insulated cable should be equipped
with two-hole crimp type lugs and should not have any tight bends or kinks.
Power System Ampacity Ground Reference Conductor Size
< 30A
#10
30 – 100A
#6-2
100 – 400A
0000
400 – 800A
350 MCM
> 800A
750 MCM
Table 2. Typical ground reference conductor selection
The power system frame must also be connected to the MGB or FGB. This is done for personnel safety and to
meet many Telco grounding requirements. Each bay should have its own frame or site ground connection. Refer
also to the Customer Connections drawing at the rear of this manual.
5.1.1
Frame Ground
The DCP03 is grounded utilizing screws/bonding washers to the relay rack then to the main grounding bus using
35mm
2
(#2 AWG) insulated cable.
5.2
Calculating Wire Size Requirements
Wire size is calculated by first determining the appropriate maximum voltage drop requirement. Using the formula
below calculate the CMA wire size requirement. Determine the size and number of conductors required to satisfy
the CMA requirement.
CMA = (A x LF x K) / AVD, where:
CMA = Cross section of wire in circular MIL area
A = Ultimate drain in amps
LF = Conductor loop feet
K = 11.1 constant factor for commercial (TW type) copper wire
AVD = Allowable voltage drop
Check again that the ampacity rating of the cable meets the requirement for the installation application. Consult
local electrical codes (NEC, CEC, etc.) for guidelines. If required, increase the size of the cable to meet the code.