AmpacityAmpacity Testing of Fire Protected RacewaysTesting of Fire Protected Raceways

Kent W. Brown, TVASt Petersburg, FL – March 2008

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

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

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

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

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

Original WG Objectives

Tray– Three layer fill– Cable which provides max

typical depthConduit– Smallest and largest typical

power cables– Load conduits at maximum fill– Results in:

» Highest heat generated» Smallest radiating surface

Conduit

Barrier

IEEE 848 – Procedure

Baseline current established by testingEquilibrium 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

Protected Raceways – Test Objectives

No original manufacturer deratings usedTXU derating used for single open top traysTVA 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

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)

TVA Program – Conduit Issues

Conduit– Effect of conduit emissivity– Effect of number of

conductors– Non-standard

configurations– Three-hour systems

Typical Test Enclosure

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

TVA Program – Tray Issues

Tray– Non-standard

configurations– Multiple trays in a common

enclosure– Three-hour systems

Protected Tray on Test Stand

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

Multiple Trays – Common Enclosure

power tray

power tray

non-power tray

Wrapped enclosureEnd View

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

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

Questions?

Thanks for Your Attention!