This document provides an overview of ampacity testing of fire protected raceways conducted by Kent W. Brown of TVA. It describes the test program which was based on IEEE 848 and aimed to determine ampacity derating factors for various cable and raceway configurations protected by fire barriers. The testing covered single and multiple conduits, covered and open trays, and upgrades from 1-hour to 3-hour fire ratings. Final ampacity correction factors are reported for different protected raceway systems based on the test results.

1. AmpacityAmpacity Testing of Fire Protected RacewaysTesting of Fire Protected Raceways
Kent W. Brown, TVA
St Petersburg, FL – March 2008

2. Purpose of the Presentation
Provide overview of the test program
– Make earlier data available to ICC
» Originally published in IJPG Conference Proceedings
Describe supplemental work
– Additional configurations
– Approach to defining bounding test specimens
Test results provided in the associated paper
– To be included with the Subcommittee D minutes

3. Cable Ampacities – UG vs Station
Underground
– Duct bank
– Buried conduit
– Direct burial
– Known cable locations
– “External” factors dominant
» Soil rho
» Moisture content
Station
– Conduit
– Tray
» Maintained spacing
» Random filled
– “Internal” factors dominant
» Depth of fill
» Covers or coatings
» Barriers

4. Station Ampacities – Background
70’s and 80’s
– Many barrier and coating
systems added
» Response to the 1975
Browns Ferry fire
Ampacity impact of
barrier systems was
unknown
– No two tests used the same
protocol
– Claimed results were
suspect

5. Resolution – IEEE 848
Based on IEEE 848
– Procedure for the
Determination of the
Ampacity Derating of Fire
Protected Cables
Standard protocol for
– Trays (coating or barrier)
– Conduits (barrier)
– Free-air (coating or barrier)
– Through-wall firestops

6. IEEE 848 – Test Setup
Configurations defined
– Cable construction
– Raceway construction
– Raceway fill
– Thermocouples
» Placement
» Instrumentation accuracy
– “End-effects”
– Thermal-breaks at supports T/C Installation in Middle Layer

7. Original WG Objectives
Tray
– Three layer fill
– Cable which provides max
typical depth
Conduit
– Smallest and largest typical
power cables
– Load conduits at maximum fill
– Results in:
» Highest heat generated
» Smallest radiating surface
Conduit
Barrier

8. IEEE 848 – Procedure
Baseline current established by testing
Equilibrium conditions clearly defined
– Time
– Allowable temperature drift
» Max 0.2oC/hr rate of change based on a linear regression
analysis of data over 60 minute period
– Test current stability

9. Protected Raceways – Test Objectives
No original manufacturer deratings used
TXU derating used for single open top trays
TVA test programs address
– Single conduits
» 1-hour rated
» Upgrade of 1-hour design to 3-hour rating
– Multiple conduits in common enclosure
– Covered trays
– Multiple trays in common enclosure

10. TVA Test Configurations
Conduit, 1-hr
– Baseline (7)
– Thermo-Lag (21)
– 3M (2)
Boxed conduits, 1-hr
– Baseline (3)
– Thermo-Lag (5)
Conduit, 3-hr
– Baseline (2)
– Thermo-Lag (3)
Conformal coating
– Baseline (1)
– Flamemastic (11)
Tray, 1-hr
– Baseline (2)
– Thermo-Lag (2)
Tray, 3-hr
– Baseline (2)
– Thermo-Lag (3)
Air Drop, 1-hr
– Baseline (2)
– Thermo-Lag (2)
Diversity
– Baseline (2)
– Alternate loading (9)

11. TVA Program – Conduit Issues
Conduit
– Effect of conduit emissivity
– Effect of number of
conductors
– Non-standard
configurations
– Three-hour systems
Typical Test Enclosure

12. Multiple Conduits – Common Enclosure
Possible configurations
– Barrier directly on conduits
» Single row
» Multiple rows
– Barrier on Unistrut frame
» Single row
» Multiple rows
Selected test configuration for:
– Maximum power
– Minimum surface area

13. TVA Program – Tray Issues
Tray
– Non-standard
configurations
– Multiple trays in a common
enclosure
– Three-hour systems
Protected Tray on Test Stand

14. Multiple Trays – Common Enclosure
Possible configurations
– Side-by-side
– Vertical stack
» 2 power
» 1 power & 1 non-power
» 2 power & 1 non-power
» 2 power & 2 non-power
» 2 power & 3 non-power
Selected test configuration for:
– Maximum power
– Minimum surface area
– 1 non-power layer
Instrumentation
Instrumentation
Control
LV Power
MV Power

15. Multiple Trays – Common Enclosure
power tray
power tray
non-power tray
Wrapped enclosureEnd View

16. Final Ampacity Correction Factors
Single conduits
– Includes 5% margin to address emissivity
» 5/8”, 1-hour - 0.93
» 3/8” + 3/8”, 1-hour – 0.93
» 5/8” + 3/8”, 1-hour – 0.92
» 330-1/770-1, 2” and larger, 3-hour – 0.82
Boxed conduits
– Unistrut frame, 1-hour – 0.88
– Direct mounted, 1-hour – 0.74

17. Final Ampacity Correction Factors
Tray
– Open top, 1-hour (TXU test) – 0.68
– Sheet steel covered, 1-hour – 0.60
– Multiple trays common enclosure, 1-hour – 0.59
– 1-hour to 3-hour upgrade system – 0.52

18. Questions?
Thanks for Your Attention!