Attached Document Summary

This document describes the fundamentals of the secondary DC distribution system operation to help you understand general installation requirements. This document does not establish a standard for engineering design, but it does reference existing standards that point to the best practice methods used throughout the industry.

Adhering to best-practice methods promotes the safe installation and operation of a robust power distribution system. Best-practice power distribution and wiring practices help protect the system investment over its service life. As the system changes, these practices can also help the operating company control lost revenue due to power-related downtime.

Attached Document Table of Contents

1.0 Purpose and Scope 

2.0 The Secondary DC Distribution System Description 

Distribution Fuse/Breaker and Alarm Panel 

3.0 DF/BAP System Criteria 

3.1 DC Power Plants 

3.2 Total Plant Power 

3.3 Battery Backup 

3.4 Plant Polarity 

3.5 Nominal Voltage 

3.6 Float Voltage 

3.7 Operating Voltage 

3.8 Operating Current 

3.9 DC Distribution 

3.9.1 Primary Distribution 

3.9.2 Secondary Distribution 

3.9.3 Single and Dual Feed 

3.9.4 Equipment Load 

3.10 Constant Power Supplies 

3.11 Constant-Load Equipment 

3.12 Paralleled Constant Power Devices 

3.13 Class 1 Amperage 

3.14 Class 2 Amperage 

3.15 Fault Currents 

3.16 Over-Current Interruption Protective Devices 

3.17 Operating Environment 

4.0 DF/BAP Operational And Component Criteria 

4.1 Input Rating 

4.2 Input Power 

4.3 Distribution Panels Equipped With Input Fuse/Breakers 

4.4 Output Ratings 

4.5 Output Power 

4.6 Load 

4.7 Fuse Types 4.8 Breakers 

4.9 Thermal 

4.9.1 Magnetic Trip 

4.9.2 Time Delay 

4.9.3 Operation 

4.10 Sizing Fuses and Breakers 

4.10.1 Output Amperage 

4.10.2 Input Amperage 

4.10.3 Low-Voltage Conditions 

4.11 Spacing Fuses or Breakers in the Distribution Panel 

4.12 Inherent Voltage Drop 

4.12.1 Typical Voltage Drop 

4.12.2 Maximum Voltage Drop 

4.13 Wire Size and Composition 

4.14 Terminations 

4.14.1 Compression 

4.14.2 Screw-Tight 

4.14.3 Wire-Binding 

4.15 Double Crimp Lugs 

4.16 Half-Taps 

4.17 Bonding 

4.18 Grounding 

4.18.1 Common Bonding Network 

4.18.2 Isolated Bonding Network 

4.18.3 Ground Window 

4.18.4 Preparing Ground Connections 

4.18.5 Ground Loop 

4.18.6 C-Taps 1 

4.18.7 Grounding Summary 

4.19 Alarm Systems 

4.19.1 Color Codes 

4.19.2 Relay External Contacts 

4.19.3 Relay Contact Ratings 

4.19.4 Power Input Alarm 

4.19.5 Fuse/Breaker Alarm 

4.19.6 Bay Alarms 

4.19.7 Alarm Circuits 

4.20 Options 

4.20.1 Disconnects 

4.20.2 DC Mains Disconnect 

4.20.3 Battery Disconnects 

4.20.4 Load Disconnects 

4.20.5 Battery/Load Disconnect Conflict 

4.20.6 Filtering 

4.20.7 DC Power Line-Noise Filtering 

4.20.8 DC Bulk-Capacitance Filtering 

4.20.9 C-Source Circuit 

4.20.10 C-Sourced Input Configuration 

5.0 DF/BAP Electrical/Mechanical Engineering Considerations 

5.1 Available Power 

5.2 Spacing Considerations 

5.3 Mounting Brackets 

5.4 Polarity Markings 

5.5 Input Terminals 

5.6 Output Terminals 

5.7 Corrosion-Reducing Agents 

5.8 Fire Stops 

5.9 General Cabling Practices 

5.10 Half-Tap Installation 

5.11 C-Taps 

5.12 Installing Compression Lugs 

5.12 Sizing Compression Lugs 

5.13 Double-Crimp Lugs 

5.14 Screw-Tight Terminals 

5.15 Wire-Binding Terminals 

5.16 Connecting Inputs to the DF/BAP 

5.17 Connecting to Primary Distribution (BDFB, BDCBB) 

5.18 DF/BAP Output Connections 

5.19 Grounding Connection Guidelines 

5.20 Fuse Installation Guidelines 

5.21 Fuse Designation Labels 

5.22 Breaker Installation Guidelines 

5.23 Breaker Label Designation 

5.24 Internal Office Alarms 

5.25 Securing With Twine 

5.26 Nylon Cable Ties 

5.27 Fiber Protection 

5.28 Tape

5.29 Shrink Tubing 

6.0 DF/BAP Testing And Maintenance Requirements 

6.1 Alarm Testing for Fuses 

6.2 Alarm Testing for Breakers 

6.3 Maintenance Requirements 

6.4 Alarm Card Replacement 

6.5 Fuse Replacement 

6.6 Breaker Replacement 

7.0 DF/BAP Electrical And Component Charts 

7.1 Wire Charts 

7.1.1 Inherent Voltage Drop Formulas 

7.1.2 Desired Voltage Drop 

7.2 Ground Cable Guide

Attached Document List of Figures

Figure 1 - Overview 

Figure 2 - Examples of DF/BAPs

Figure 3 - Subsystem 

Figure 4 - Distribution Systems 

Figure 5 - Breakers 

Figure 6 - Inherent Voltage Drop 

Figure 7 - Lug Types 

Figure 8 - Screw-Tight Terminals 

Figure 9 - Grounding Summary 

Figure 10 - C-Source Configurations 

Figure 11 - DC Distribution System Schematic 

Figure 12 - Connection Examples 

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