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   © Dr. Ray Franco, PhD, PE  -  208 Fairways Dr., Vicksburg, MS 39183

Electrical Distribution Panels & Circuit Breaker Fires

Table of Contents:

General

Most circuit breaker problems are due to loose electrical connections. breakers.

When a circuit breaker trips, it releases a cocked spring mechanism that separates the electrical contacts. Circuit breakers have two means of tripping:

(1) An electromagnet that trips almost instantaneously when the current is between nine (9) and 15 times the rated current of the circuit breakers (USA),

and

(2) A temperature sensitive bimetal strip that bends and releases the spring mechanism at a calibrated temperature. Usually, the temperature of the bimetal strip is proportional to the amount of current passing through the circuit breaker. However, the bimetal strip will react and bend to any rise in temperature. The rise in temperature may be due to a loose wire connection, misalignment of the circuit breaker contacts, or the heat from a fire.

Circuit breakers are sized to protect the integrity of the wire insulation; they are not sized to protect human life.

If a circuit breaker is over loaded to a value of 135% it rated current, it must trip within one hour.
If a circuit breaker is over loaded to a value of 200% it rated current, it must trip within two minutes.

Tripped Position

All circuit breakers do not trip to the center position. The following circuit breakers do not have a center position, and they trip to the "off" position: Cutler Hammer, Bryant and Murray.

Zinsco Panel Boxes

Zinsco circuit breakers are notorious for arcing and welding to the aluminum power buses. The first time I tried to remove Zinsco circuit breakers from a panel box, every circuit breaker in the panel box was tack welded to the power bus. This Zinsco combination Meter Socket / Electrical Distribution Panel just about burned my friend's house down. It melted the power buses, arced through the steel panel box, through the asbestos shingles and caught the wood wall on fire. It occurred a night. My friend's bed was on the other side of the wall. He woke up to the smell of smoke. He went outside to investigate. He called me. When he said the circuit breakers were not straight, I told him not to touch them to immediately call his power company. I arrived before they did. I informed the lineman that he needed to pull the power at the distribution transformer. He thought he could pull the meter without disconnecting power at the transformer. It didn't take him long to come around to my way of thinking.

For Maximum Resolution, Click on the Body of the Picture.

Zinco Combition Meter Socket / EDP
Zinsco Combination Meter Socket / Electrical Distribution Panel.
Zinco Panel with Cover Removed
Zinsco Combination Box Without Cover (F10-073).
Zinco Damaged Circuit Breaker
Zinsco Damaged Circuit Breaker (F10-073).
Zinsco Circuit Breaker with Bus Bars
Zinsco Circuit Breaker with Bus Bars (F10-073).

Another Zinsco - Case History: F09-026

Even though this homeowner worked for an electric utility company, he allowed the electrician to bypass the bad spot in the bus without replacing it. The fire was in the kitchen of this home, but as a forensic engineer that does insurance claims, I always inspect and document the electrical service entrance and all panel boxes.

For Maximum Resolution, Click on the Body of the Picture.

Zinco Panel with Missing Circuit Breaker
Zinsco Panel Box with Missing Circuit Breaker (F09-026).
Zinco Panel with Cover Removed
Zinsco Panel Box with Cover Removed (F09-026).
Zinco Panel with a Section of the Power Bus Melted
Damage to Power Bus as a Result of Arcing (F09-026).
Melting of Power Bus
Melting on the Zinceo Power Bus as a Result of Arcing (F09-026).
GTE-Sylvania/Zinsco Panel Box
In 1973, Zinsco was Purchased by GTE-Sylvania (F10-007).

References: http://www.inspectapedia.com/electric/Zinsco.htm

Infamous Federal Pacific Electric Stab-Lok Circuit Breakers

Almost every electrician I have talked with has had problems with Federal Pacific Electric (FPE) circuit breakers not tripping. In 1979, FPE was purchased by Reliance Electric Co., a subsidiary of Exxon Corporation. In June 1980, Reliance Electric informed the U.S. Consumer Product Safety Commission (CPSC) that many FPE circuit breakers did not fully comply with Underwriters Laboratories (UL) requirements. In 1983, the CPSC issued a letter concerning FPE circuit breakers and closed its investigation: http://www.cpsc.gov/cpscpub/prerel/prhtml83/83008.html. The US CPSC has not issued a recall on any FPE circuit breakers.

For Maximum Resolution, Click on the Body of the Picture.

Federal Pacific Electric Panel Box - FPE Electrical Distribution Panel
Small FPE Panel Box with "Federal" on the Door.
Small FPE Panel Box without Cover
Small FPE Panel without Cover.
Full Size Federal Pacific Electric (FPE) Panel Box with Stab-Lok Circuit Breakers
Full Size FPE Panel Box with Stab-Lok Circuit Breakers (F08-020).
Single Pole, Double Pole and 3-Phase Federal Pacific Electric (FPE) Stab-Lok Circuit Breakers
Single Pole, Double Pole, and Three-Phase FPE Circuit Breakers.
Two Federal Pacific Electric (FPE) Panel Boxes at a Commerical Location
Two FPE Panel Boxes at a Commercial Location (F08-020).
Closer View of Commercial Federal Pacific Electric (FPE) Panel Box
Closer View of Commercial FPE Panel Box (F08-020).

I have only had one fire that was caused by a FPE breaker failure, and it was not a Stab-Lok type.

Old Federal Pacific Electric - Panel Box

This was a large fire loss insurance claim. It occurred one month after Hurricane Katrina in downtown Gulfport, MS. The cause of the fire was a electrical arcing in an old Federal Pacific Panel Box. The roof was being repaired. It is possible that water got into the panel box.

For Maximum Resolution, Click on the Body of the Picture.

FIre at Commercial Building Downtown Gulfport, MS
Commercial Fire - Downtown Gulfport, MS (F05-20).
 .
Side of Commercial Building Downtown Gulfport, MS
Fire First Vented Out This Window - Near the Main EDP (F05-20).
 .
Severe Electrical Arcing in Panel Box
Severe Arcing at the 2nd from the Top Left Circuit Breaker;
Wire Insulation on the Right Consumed by the Fire (F05-20).
Panel Box Cover Plate
Center Cover Plate for Circuit Breaker Screws (F05-20).
 .
Major Damage to Cricuit Breaker
Major Damage to 2nd from the Top Left Circuit Beaker;
Insulating/Separating Strips Burned Out in Top Center (F05-20).
Circuit Breaker Welded to Bus
Breaker Welded to the Bus and Plastic Blistered (F05-20).
 .
Large Copper Ball
Large Copper Ball Covering Breaker Screw (F05-20).
 .
Side View of Copper Ball and Screw
Side View Depicting Copper Ball and Screw (F05-20).
 .
Copper Balls inside Circuit Breaker
Copper Balls Found Inside Breaker's Plastic Housing (F05-20).
 .
Manufacturer's Tag
Manufacturer's Tag - Federal Pacific Electric (F05-20).
 .

GE - Panel Box

This home was under construction. It burned three days after power was connected. There was no door or cover on the Electrical Distribution Panel (EDP). The general contractor had the power cut on. The electrical subcontractor had not been at the site in over a month. He said, he wasn't ready for the power to be cut on. One of the three power connections at the EDP was not tight. I was representing the homeowner insurance company. They sued by the general contractor and the electrical subcontractor. The case settled out of court.

For Maximum Resolution, Click on the Body of the Picture.

Home Under Construction
This Home was Under Construction. The Fire Occurred
Three Days after Power was Connected (F06-016).
Back of Home Under Construction
The Electrical Service was Underground
and Entered on the Side of the Carport (F06-016).
Arcing Hole in Steel Panel Box
One of the Power Cables had Arced and Melted the
the Steel Panel Box on the Left. (F06-016).
Severed Power Cable
Severed Power Cable and Melted Steel (F06-016).
 
Exemplar Panel Box
The Panel Box was Identified as a GE TM2020CCU (200 Amps),
and an Exemplar Purchased (F06-016).
Melted AL Components on Right Side
All of the Aluminum Components in the Circuit Beaker
Panel on the Right Melted (F06-016).
Power and Ground Cable Connections
The Arrows Depict Where the Two Power Cables and
the Ground Cable Connected to the Panel (F06-016).
Severed Copper Bus
The Copper Bus Under the Right Power Lug (PW #2)
has been Severed by Arcing (F06-016).
Cable Not Fanned Out
The cable on the Left Does Not Fan Out, Nor Did the
the Lug Screw Cut into the Same Number of Strands (F06-016).

GE Circuit Breaker Overheating Due to Misaligned Contacts

For Maximum Resolution, Click on the Body of the Picture.

In the ON Position there is no continuity of the Circuit Breaker
No Continuity with GE Circuit Breaker in "ON" Position.
The Internal Heat from the Circuit Breaker has Turned the Paper Barcode Brown
Brown Area on Barcode Label Indicating Excessive Heat.
The Internal Heat in the Circuit Breaker was caused by the Contacts not being Aligned
GE Circuit Breaker with Cover Removed - Contacts Not Aligned.
Better View of Circuit Breaker Contacts not Aligned
Side View of GE Circuit Breaker with Misaligned Contacts.

Square D Circuit Breakers

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Thermal Oven Tests of Square D Circuit Breakers to Determine the Temperature of a 20 amp Breaker Trips at - 550 degrees Fahrenheit
Two Square D Circuit Breakers were placed in an Oven.
The Lens melted at 450°F; the Breaker Tripped at 550°F.
Sqaure D Circuit Breakers with Plastic Lens intact - Tripping was due to Electrical Activity
The Plastic Lenses are intact. The Circuit Breakers in this Panel
tripped because of Electrical Activity and not the Heat of the Fire.
Square D Circuit Breaker with Lenses begining to melt - Tripped Circuit Breakers could be due to the temperature of the fire
The Plastic Lenses in this Panel are starting to melt.
The Heat of the Fire could have tripped the Circuit Breakers.
Exemplar Square D Circuit Breaker with Clear Plastic Back.
Exemplar Square D Circuit Breaker with Clear Plastic Back
 .

Square D Circuit Breakers Fire Damage Due to a Loose Connection at the Power Bus

The day before this fire, the homeowner heard a cracking sound whenever the central air conditioning came on. The next day, a small fire occurred when an electrician was tightening the screws in the panel box

For Maximum Resolution, Click on the Body of the Picture.

There is no Damage to the Front of the Circuit Breakers in the Electrical Distribution Pane
Looking at the Front of the Electrical Distribution Panel,
there appeared to be no Damage (F09-045).
A Loose Circuit Breaker Connetion has melted part of the Power Bus and the Power Clips of two Circuit Breakers
One of the Power Clips on the AC Circuit Breaker was Missing,
Part of the Power Bus was Missing and Melting of a Power Clip.
The Loose Circuit Breaker Connection has melted a section of the Panel Power Bus and there is arcing on the Power Bus Section Immediate below this
Missing Power Bus and Arcing on the Power Bus Immediately below
the Missing Bus (F09-045).
The Loose Circuit Breaker Connection Melted the Top Circuit Breaker Power Clip and Damaged the Bottom Circuit Breaker Power Clip
Missing Top Power Clip and Melting on the Bottom Power Clip
of the AC Circuit Breaker (F09-045).
The Circuit Breaker Oppsite the Loose Connection also Suffered Damage (melting) to its Power Clip
The Circuit Breaker Across form the AC Circuit Breaker shared
the same Power Bus, and its Top Clip was melted (F09-045).

Siemens Circuit Breakers - Recalled

In 2010 the U.S. Consumer Protection Safety Commission (CPSC) and Siemens recalled about 2.2 million molded case circuit breakers due to a defective spring that holds the circuit breaker to the bus [1]. The defect can result in loose connections, resistive heating, arcing and fire. The defect is present on both single-pole (120 VAC) and double-pole (240 VAC) circuit breakers. The circuit breakers have the date codes 0610 or 0710. They were sold from June 2010 through August 2010. The recall was announced in September 2010. Siemens paid electricians that installed the circuit breakers replace them. The collected circuit breakers were returned to Siemens.

For Maximum Resolution, Click on the Body of the Picture.

Seimens Circuit Breaker Date Code
Location of Date Code on Siemen Recalled Circuit Breaker.
Siemens Circuit Breaker Comparison
Comparison of Siemen Circuit Breakers - Not Recalled and Recalled

[1] CPSC Recall of Siemen Circuit Breakers

Cutler-Hammer Circuit Breakers - F09-028 Case History

Ice caused a tree limb to fall on the overhead triplex service cables. The service cables pulled weatherhead and meterbase. After repairs were made, the homeowner complained to his insurance company that his lights were blinking and the dryer circuit breaker was tripping. After six months of complaining, his insurance company reluctantly agreed to have the problem investigated by a forensics engineer. The inside electrical distribution panel was directly behind the meterbase. A loose wire connection at the main circuit breaker caused resistive heating that damaged the circuit breaker. It was my opinion that when the service cables pulled the meterbase the wires to main circuit breaker were also pulled. This caused the loose wire connection at the main circuit breaker. Thus, the homeowner was correct and the problem was related to his original claim.

For Maximum Resolution, Click on the Body of the Picture.

A Loose Electrical Connection has Heated the Screw and Caused it to Oxidized or Rust
Heat on a Screw will cause it to Oxidize or Rust (F09-028).
 .
The Heat produced by Loose Electrical Connection has Cracked the Wire Insulation and is starting to melt the aluminum conductor
The Heat from the Loose Electrical Connection cracked the Wire
Insulation and the Aluminum Conductor is starting to melt (F09-028).
The Heat from the Loose Electrical Connection has Cracked and Discolored the Plastic Housing of the Circuit Breaker
The Plastic on the Bottom of the Circuit Breaker was Cracked
and Discolored (F09-028).
 

Eaton/Cutler-Hammer - F12-052 Case History

There was a grease fire in the kitchen of this apartment. The tenant was burned. In the three months that the tenant lived in the apartment, the power went off two or three times. I was an expert witness for the attorney representing the tenant. There were at least four National Electrical Code (NEC) violations in the electrical distribution panel: (1) The power bus was exposed in the top left corner; (2) all ten (10) of the single-pole circuit breakers were oversized (30 amps instead of 20 amps), (3) three of the circuit breakers had two wires under the same screw, and (4) there were three (3) different brands of circuit breakers in the panel box. In addition, the kitchen range (50 amps) was protected by only a 30 amp circuit breaker, and there was a screw through the center of the back-fed circuit breaker that supplied power to the panel.

For Maximum Resolution, Click on the Body of the Picture.

Home Under Construction
The Power Buses were Exposed, All of the Circuit Breakers except
the Main were 30 Amps and Three Brands of Circuits Breakers.
Panel Box Legend
The Panel Box was Manufactured by Eaton/Cutler-Hammer -
the Legend list Circuit Breakers that can be Installed in the Panel.
Home Under Construction
All Ten (10) of the Single-Pole Circuit Breakers
were oversized - 30 amps instead of 20 amps (F12-52).
Two wires under the same circuit breaker screw
Three of the Circuit Breakers had Two Wires under the Same Screw
(F12-52).
 

Mixed Circuit Breakers in Same Panel Box

Forensic electrical engineers must be knowledgeable of the National Electrical Code (NEC) and Underwriters Laboratories' (UL) certifications, standards and markings. Eaton/Cutler-Hammer, Siemens, GE, and Square D circuit breakers are physical the same size, and they will fit in each other's panel boxes. However, in order to put a different brand circuit breaker in a panel box, the circuit breaker must be classified as a replacement circuit breaker for a circuit breaker that is allowed in the box. To be classified as a replacement breaker it must be tested by UL. Eaton/Cutler-Hammer pays UL to classify their circuit breaker as replacement circuit breakers. This is a one way classification. That is, an Eaton/Cutler-Hammer circuit breaker may be able to replace a Siemens circuit breaker, but no testing has been done to determine if a Siemens circuit breaker can replace the Eaton/Cutler-Hammer circuit breaker. According to UL's White Book, classified circuit breakers must have UL's Classified Mark on the front of the circuit breaker. Note, not all of Eaton/Cutler-Hammer circuit breakers are classified as replacement circuit breakers. Also note, that classified circuit breakers are available for Square D panels, but Square D is against using classified breakers.

For Maximum Resolution, Click on the Body of the Picture.

Home Under Construction
According to the UL White Book, a Circuit Breaker that has been
Classified as a Replacement Circuit Breaker has Marking on its Face.
Three brands of circuit breakers in the same panel box
The Circuit Breakers in this Panel Box were manufactured
by Three Different Companies (F12-52).
Two wires under the same circuit breaker screw
The GE Circuit Breaker is NOT Classified for use in an Eaton /
Cutler-Hammer Panel Box. Hence, a NEC Code Violation (F12-52).
Three brands of circuit breakers in the same panel box
The 5 Siemen Circuit Breakers are NOT Classified for use in an Eaton
Cutler-Hammer Panel Box. Hence, a NEC Code Violation (F12-52).
 

Back-Fed Circuit Breakers

Forensic electrical engineers must know the National Electrical Code (NEC) and have a practical understanding of products that are designed to meet the NEC. The following has been in the NEC since 1990 (Section 384-16(f)) : "Plug-in-type overcurrent protection devices or plug-in-type main lug assemblies that are back fed shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means of the panel." In the 2002 NEC, the identical wording was moved to Section 408.36(f).

The screw through the circuit breaker is part of a hold down kit designed specifically for Cutler Hammer, Type BR, circuit breakers.

For Maximum Resolution, Click on the Body of the Picture.

Screw holding back-fed Cutler Hammer type BR circuit breaker
The Screw in the Back-Fed Circuit Breaker is
Part of a Required Hold Down Kit. (F12-052).
Intentional Hole through Cutler Hammer Type BR Circuit Breaker
The Cutler Hammer Circuit Breaker, Type BR, has a Hole
Through it for a Screw that is Part of a Hold Down Kit.
Hold Down Kit for Cutler Hammer type BR Circuit Breaker
The Screw is Part of a Hold Down Kit (Part #: BRHDK125).
 
 
 

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