Water leaking into an electrical panel can cause dangerous conditions. Do not ignore external warning signs such as those pointed to by my client here. Rust and Corrosion in Electrical Panels
A Study and Report on Frequency and Causes of Rust & Corrosion inside of residential electrical panels
     

  • CORROSION in ELECTRICAL PANELS - CONTENTS: cause, effects, frequency of occurrence, prevention, engineering report ib the causes of rusty electrical panels, How to prevent water leaks, condensation, and rust in electrical panels, October 1991 IEEE-Holm Conference on Electrical Contacts, Observations in electric panels include corroded, burned, and damaged connections and corroded and malfunctioning circuit breakers.
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Rust in electrical panels, sources of water leaks into electrical panels:

Field observations of residential service panel connections and components discovered significant occurrences of rust, corrosion, and damage to electrical equipment, risking failure to trip on overcurrent and thus risking building fires.

These observations led to a study of the frequency and cause of water damage, rust, corrosion, or other moisture-related unsafe conditions in residential electrical panels. This report by Daniel Friedman was presented to the electrical engineering community at the IEEE Holm Conference on Electrical Contacts.

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Rust and Corrosion in Electrical Panels - Field Observations of Residential Service Panel Connections and Components

Introduction to the Electrical Panel Corrosion Study

IEEE Holm Conference on Electrical Contacts, Daniel Friedman, Poughkeepsie, NY, October 19, 1992, updated 12 March 2015

[Click to enlarge any image]

ABSTRACT: Visual examination of the electrical service panel is an important element of the procedure followed by professional home inspectors, whose observations are most often made at the time of sale of a used residence. The inspectors' observations can provide a data base on field performance of residential electrical system components that may be valuable toward the development of improvements in both the components and their associated qualification standards.

The observations noted in this paper are derived from a set of more than 1,500 detailed inspection reports by the paper's author and from a survey of members of the American Society of Home Inspectors (ASHI). Professional home inspectors offer a unique perspective of field failures: in performing a comprehensive survey of a building's systems and components, an inspector may discover common external or interactive causes of damage or deterioration. Home inspectors regularly observe field deterioration in progress before hazards or malfunctions are so obvious as to come to the attention of the occupants.

The reported observations in electric panels include corroded, burned, and damaged connections and corroded and malfunctioning circuit breakers. Causative factors noted in the service environment include presence of moisture, damage from overcurrent, and poor installation practices. Suggested improvements, including the need for greater resistance to corrosion and other field and environmental conditions, are discussed. -- This material was first presented at the October 1991 IEEE-Holm Conference on Electrical Contacts. Original text expanded by the author for this online publication 20 February-March 2006.

Rust and corrosion in residential electrical panels is more than a theoretical safety concern. Our friend and contributor to this InspectAPedia.com Steven Bliss reported:

In a heavy rain, water was gushing through my main service panel and subpanel, flowing through the circuit breakers like a waterfall. Very disturbing. The electrician and Burlington Electric both thought water was coming through cracks in the exterior main service entry cable that has very old cloth sheathing. However, I caulked the hell out of the top of the electrical meter where the wire goes enters the meterbox and also at the wall where the SEC passes into the house, and the problem appears to be solved.  One circuit breaker had frozen solid from corrosion and had to be replaced. I don’t know how long this has been going on. I only discovered it when I tripped a breaker with a power tool.

Watch out: for electrical services, panels, breakers, fuses that have been flooded or wet, to avoid dangerous or fatal electrical shock
see HOW TO TURN OFF ELECTRICITY in a building that has been wet or flooded

Visual examination of the electrical service equipment is an important element of the procedure followed by professional home inspectors, whose observations are most often made at the time of sale of a used residence. These observations can provide a data base of field performance of residential electrical system components that may be valuable for the development of improvements in both the components and their associated qualification standards.

Professional home inspectors offer a unique perspective on field failures: in performing a comprehensive survey of a building's systems and components, an inspector may discover common external or interactive causes of damage or deterioration.

Inspectors see in-service field conditions, often before failures occur, and before failing conditions are so obvious as to come to the attention of the occupants. Other studies of connector/component failures in service panels have focused on defects discovered after rather than before actual failures and have not considered corrosion/damage diagnosis based on a comprehensive examination of the entire structure and site for causal factors. (1)(2)(3)(4)

1052 Electric Service Panels were examined in the field, in conditions of actual use. Examination revealed frequent occurrences of corroded, burned, and damaged connections and corroded and malfunctioning circuit breakers. Significant, reportable corrosion/related defects in the panels were observed in 12% of cases - a frequency significantly greater than that anticipated by the electrical industry.

Causative factors noted in the service environment included presence of moisture, damage from overcurrent, and poor installation practices. Suggested improvements, including the need for greater resistance to corrosion and other field and environmental conditions, are discussed.

This information was first presented to industry experts at the 1992 Philadelphia IEEE Holm Conference on Electrical Contacts to suggest that the moisture and corrosion resistance characteristics of electrical panels and their contents should be increased. Information about the common causes and sources of water entry was also of importance to home inspectors who need to be alert for these conditions and for the damage and risks they may cause.

PANEL RUST STUDY PROCEDURE - Study Procedure for Electrical Panel Corrosion

Comprehensive visual inspections for building defects were performed on 1052 private homes between 1987 and 1991. The overhead service drop, service entrance conductors, electric meter, and raceway or cable from the electric meter to the service panel were examined, as were the service panel and all components therein. Inspection was visual, did not normally involve use of test equipment, and followed well established guidelines for professional home inspectors.(5)(6)(7).

Field notes were recorded indicating any defects in each panel. Site conditions which might be a related cause were also noted. Every "defect" was severe enough to merit a report to the building owner or buyer as a safety concern.

Electrical Panel corrosion (C) Daniel Friedman Electrical panel corrosion due to leaks (C) Daniel Friedman

Visible damage or other conditions which might indicate malfunction or unsafe conditions included: significant rust or corrosion on any component; signs of overheating [Such as [Fig-3 above left] overheated electrical ground and neutral wires at a corroded panel bus, and [Fig-15, above right] overheated electrical branch circuit wires which may or may not be due to a corroded circuit breaker which failed to trip], or other damage at connections of the service entrance wires, at wiring connections on circuit breaker terminals or individual fuse terminals, at neutral or ground bus bars or connectors; or rust at the base of the panel enclosure itself.

Light surface rust on the exterior of the panel or minor corrosion in the panel interior were not reported if there were no other indications of malfunction such as evidence of overheating or of past repair work.

The field data were tabulated: estimated year of equipment installation, system ampacity, panel type (breaker, fuse, antiquated), presence of knob-and-tube wiring, presence of rust or corrosion on four common locations in the panel, apparent source of moisture related to corrosion, and other defects (mis-wired device, burned connectors, etc.).

PANEL RUST STUDY RESULTS - for Electrical Panel Corrosion

Frequency of Corrosion in Electric Panels

Table 1. Year of Electrical Equipment Installation and Number of Electrical Panels Studied
'90-'87 '87-'76 '75-'65 '64-'59 '58-'37 Pre-'37 Total
60 244 308 145 201 94 1052

An examination of field notes from more than a thousand private home inspections performed between 1987 and 1991 reveals rust and corrosion of various electrical components in 126 of 1052 service panels. More than one in ten service panels showed sufficient corrosion to merit, in the opinion of the inspector, report to the client of a possible safety or functional concern with the equipment.

The age of equipment varied from brand new to more than 50 years old. [Table 1 above]. Most of these were circuit-breaker type panels (835), with the remainder fused equipment (217). More than one in ten service panels showed sufficient corrosion to merit a report to the client of a concern.[Table 2 below].

Table 2 - Frequency of Corrosion In Service Panels
Number of Defects Percent of Cases Percent of Total Panels
Cases 1 126 100% 11%
Panel Surfaces & Other Steel Components 110 87% 10%
Circuit Breaker Terminals 97 76% 9%
SEC Connectors 46 36% 4%
Bus Bar Connectors 42 33% 3%
Notes to Table 2:
1. 126 service panels examined had one or more reportable corrosion or corrosion related defects. Since some panels have more than one reported defect,, the number of defects will total more than the number of cases.
2. 1052 service panels were examined.

The criteria for reporting such damage in a given panel is subjective, not quantitative, and does not normally involve equipment tests. Two definitions of severity of damage are:

Light corrosion: surface rust spots on panel enclosure parts or on other steel components in the panel. No visible evidence of failure, wet components, arcing, burning, history of repairs, or other clues suggesting, from external visual inspection, that safety components such as fuses or circuit breakers appear at likely risk of malfunction. Light corrosion instances were not tabulated in this study.

Rust on steel electrical panel components (C) Daniel FriedmanSerious corrosion: heavy rusting or other corrosion at connections of the service entrance wires (usually at terminals on a main fuse block or circuit breaker), at wiring connections on circuit breaker terminals or individual fuse terminals, at neutral or ground bus bars or connectors, or at the base of the panel enclosure itself. Exfoliation on steel panel components, or other highly-suspect conditions are present in such cases.

Even if the inspector does not observe serious corrosion on wiring connections in a panel equipped with circuit breakers, the presence of heavy rust, exfoliation, or actual water in the panel enclosure is considered grounds for reporting a serious finding.

This conclusion is based on an untested opinion of many professional inspectors that the presence of sufficient moisture to cause such corrosion raises questions about the condition of hidden safety components such as circuit breaker internal parts or bus-bar components covered by breakers or fuses.

The natural collection point for moisture, the panel bottom, might be reached after droplets have passed over and in some cases through other electrical components and connectors.

Rust on steel service panel components was by far the most common observation, occurring in 110 (10%) of the installations examined. [Fig-1 at left]

rust on screw connectors on circuit breakers (C) Daniel Friedman

Rust on screw connectors on circuit breakers, and less often on fuse terminals, was also common, occurring in 97 cases, slightly less than 10% of the systems examined.

In some cases corrosion was so severe that not only was the connection questionable, but the connector screws themselves were so corroded that the electrician had to cut the wire when preparing to install new breakers. [Fig-2 at left]

Corrosion at the connection of service entrance cable to main breakers or fuse connectors was found in 46 cases. It was common to see severe corrosion at this location when water was present.

Evidence of overheating (burned insulation and discolored wire and in some instances partially melted aluminum wire) was observed at those connectors in several instances. Corrosion on neutral and grounding bus bars and connector screws was found in 42 cases.

Evidence of overheating was seen in two of these cases. [Fig-3 below left] , [Fig-4 below right]

Neutral bus overheating (C) Daniel Friedman Neutral bus overheating (C) Daniel Friedman

WHERE CORROSION OCCURS - in Electrical Panels?

Rust on steel service panel components is by far the most common observation, occurring in 110 (10%) of the installations examined. [Table 2 above]

Rust on screw connectors on circuit breakers, and less often on fuse terminals, was also common, occurring in 97 cases, slightly less than 10% of the systems examined. In some cases corrosion was so severe that not only was the connection questionable, but the connector screws themselves were so corroded that the electrician had to cut the wire when preparing to install new breakers. When severe rust is present we report that the operation of the circuit breakers might be suspect.

Corrosion on neutral and grounding bus bars and connector screws was found in 42 cases. However field data indicates that bus-bar connector corrosion so severe as to offer visual suggestion that the connection is highly questionable is rare. Evidence of overheating (possibly related to corrosion) was seen in only two of these cases, detected as discolored copper wires at the connector.

Corrosion at the connection of service entrance cable to main breakers or fuse connectors was found in 46 cases. However this connection gives cause for greater concern, as it is not uncommon to see severe corrosion at this location when water is present. we have observed evidence of overheating such as burned insulation and discolored wire and in some instances partially melted aluminum wire at such connectors.

MOISTURE SOURCES leaking or condensing in Electrical Panels

A significant advantage accrues from having a service panel inspected as part of a more comprehensive property inspection: home inspectors are concerned with the building envelope, with water entry, and with damage to building components from moisture.

In normally damp climates moisture is a major factor in building damage; identifying moisture sources and controlling moisture is important both in diagnosing failures and in protecting buildings from future failures. For each panel reported as a "problem" the inspector logged the apparent source of water entry. (For each of the 126 services for which defects were reported, the apparent sources of water entry was recorded.) [Table 3 below]

Table 3. Apparent Entry Source(s) of Moisture - #Cases - Percent of Total
Service Entrance Cable Defects 310 66%
Condensation 83 17%
Surface/Roof Runoff Leakage 79 17%
Notes to Table 3:
1. For a given panel in some instance more than one possible source was recorded
2. High interior moisture levels from any condition could cause condensation. Naturally a major source of high interior moisture levels is the third item listed, surface and roof runoff leakage into the building.
3. Percent of total possible sources observed (472)

The most common sources of water and moisture entry were: through service entrance conductor cables which were old and damaged, or which were improperly sealed at meter boxes or building sidewalls; from condensation from high interior moisture levels; and from other building leaks or surface water which passed down building walls where panel enclosures were mounted.

ENTRY CABLE LEAKS - Service Entrance Cable (SEC) Leaks into Electric Panels

By far the most common source of water entry in service panels, 310 out of 472 possible sources observed, is associated with the passage of an above-ground service entry cable from outside, through the building wall, into panels which are located in basements or at a location lower than the point of penetration of the cable through the building wall.

There was often strong visual evidence that water had entered service enclosure, including: water stains and drip marks on components directly below the center of the entry cable when it enters the service equipment; water stains, sometimes rust marks, down the exposed face of circuit breakers; water droplets present on connectors and other components at the time of inspection.

Frayed SEC causes electrical panel rust (C) Daniel Friedman Water tracking marks show leaks into electrical panel (C) Daniel Friedman

Water, often in large volumes from wind-driven rain, followed the entrance cable into the building on three paths:

  1. Frayed electrical service entry cable and bad seal at meter box top when the SEC is located above and enters the electric meter box top, when mounted outside (exposed to weather). [See [Fig-6 above left ].] Water entered the meter enclosure and traveled down the interior of the plastic-covered electrical service entrance cable into the building, often entering the service entry cable where that cable exited at the meter base. Notice the frayed SEC which also admits water into the cable itself as wind-blown rain strikes it.
  2. Inadequately sealed electrical service entry cable connector: While frayed fabric-type SEC covering lets wind-blown rain enter the cable, meter box, and electrical panel, plastic-covered SEC wires form a virtual "water pipe into the electric panel," conducting water from the electric meter box into the electrical panel, as shown in , [Fig-5 above right] This occurs when there is a leak into the electric meter box (frayed SEC cable or bad seal at top of the box where the cable enters), and where the electrical panel is mounted in the building at a level lower than that of the meter box.
  3. Inadequately sealed opening where the cable passed through the building wall. A "drip loop" is not generally used at this location. Water followed the outside surface of the cable into the building panel. Capillary action may be a factor.[Fig-7 below]
  4. Deteriorated, (worn, frayed fabric-covered) service entrance cables. Water entered the cable from wind-driven rain and followed a natural capillary path into the service panel.

Water leak at building wall (C) Daniel Friedman

Figure 7, water follows electrical service entry cable exterior into the building and into the electrical panel through an un-caulked opening in the building exterior wall.

WATER ENTRY PATHS - into Electric Panels from the SEC

Water, often in large volumes from wind-driven rain, follows the entrance cable into the building on three failure paths:

  1. Failure to adequately seal the opening where the cable passes through the building wall. [A "drip loop" is never seen at this location, probably for aesthetic reasons.] Water follows the outside surface of the cable into the building panel. Capillary action may be a factor.
  2. Failure to adequately seal the connector at the top of the electric meter, mounted outside. Water enters the meter enclosure and travels onward down the entrance cable into the building, often moving inside the service entry cable where that cable exits at the bottom of the meter base.
  3. Failure to replace worn, frayed fabric-covered older service entrance cables. Water enters the cable from wind-driven rain and follows a natural capillary path into the service panel.
Visual Evidence: There is often, but not always, strong visual evidence that water takes these routes into the panel:
  1. Water stains and drip marks atop panel components, usually the main breaker, directly below the center of the entry cable when it enters the panel from the top.
  2. Water stains and drip marks on panel components and on panel base directly below the entry cable when it enters the panel from one side.
  3. Water stains, sometimes rust marks, down the exposed face of circuit breakers
  4. Visible droplets present on connectors and other components at the time of inspection.

OTHER BUILDING LEAKS - Affecting Electric Panels

A surprising number of occurrences of water entry appear to be due to other building leaks, 79 of 472. These sources include roof leaks (water passing from leaks into soffits through building walls and down basement wall - rare), and basement water entry associated with improper handling of roof runoff (leaky gutters) or surface drainage. Water concentrated around a building from roof runoff or surface drainage often results in moisture seeping through the foundation wall.

It's an interesting coincidence that service panels are often mounted in the corner of a basement, just where water may be concentrated outside from a faulty downspout. On a typical modern home with a single downspout at front and rear roof edges, chances are one in four that a service panel and a downspout will find themselves sharing a damp corner.

In such cases we've occasionally observed water entering the rear of the service panel at points of contact with the basement wall, even when the panel is actually affixed to plywood or nailer boards which themselves are fastened directly to the foundation. However the principal path from roof/surface runoff to panel is probably interior condensation due to high moisture levels caused by general basement water entry, discussed next.

The most common mechanism by which moisture entered these panels was from roof/surface runoff, causing basement water entry and high indoor moisture levels which in turn lead to condensation. This finding is discussed below. In a few other cases there were indications of water entering the rear of the service enclosure at points of contact with the basement wall, even when the enclosure was actually affixed to plywood or nailer boards which themselves were fastened directly to the foundation.

INDOOR CONDENSATION - Affecting Electric Panels

When water, corrosion, or signs of a history of wetness in service equipment were found and when there were no obvious contact-paths for droplets to travel in to the panel from outside, condensation inside the panel was recorded as the apparent source. In 83 of 472 cases there were wet-basement conditions but the service panel was mounted well away from points of outside water entry through walls or cables.

When moisture is observed primarily at specific panel locations, such as below the entrance cable or on the panel base, and when most other panel components are not corroded, we suspect specific points of outside entry such as described earlier.

But in many inspections we observe water, corrosion, or signs of a history of wetness in panels where there are no obvious contact-paths for droplets to travel in to the panel from outside.

In these cases, when corrosion is fairly uniform over panel enclosure sides and top, and over other panel components, we suspect that moisture is occurring as condensation inside the panel. Often the inspector will find such indications. This was so in 83 of 472 cases, when there were generally wet-basement conditions but when the service panel was fortunate to find itself mounted well away from points of outside water entry through walls or entry cables. While not a part of this study, we have observed this pattern of rust and corrosion on panel components even in very dry climates (Tucson and Phoenix) where electrical equipment was installed against masonry walls in service closets accessed from outside the building.

From these observations we suspect that the combination of high interior moisture levels in many basements, combined with temperature changes, results in movement of moisture to the interior of service panels on a regular basis during humid weather.

Also see Backdrafting & Sewer/Septic Odors for an explanation of how negative air pressure in buildings can cause unexpected air and moisture movement, condensation, and moisture-related problems such as rust, corrosion, or odors, or mold.

OTHER LEAKS - and Related Damage in Corroded Electrical Panels

Burned connectors:Among other common panel "defects," any burned connectors observed in service panels were recorded and tabulated. There were 23 such cases out of the 1052 panels observed, a 2% occurrence. In at least two of these 23 cases, the evidence of an actual fire in the panel was found. Other Observations:The following incidents, observed one or more times during the 1052 inspections are reported:
  1. during rainy weather, water visibly dripping into the panel through the entry cable See [Fig-5] ; white streaks down both black hot leads were deposited by water running inside the service entry cable.]
  2. droplets clinging to interior panel breaker terminals and bus bars
  3. standing water completely filling the panel base when a steel lip is installed thereon
  4. moisture in small droplets, apparently condensation, soaking all panel components
  5. circuit breaker terminals so completely rusted and corroded as to make removal of the terminal screw impossible [See previous Figures [Fig-1], [Fig-2], [Fig-3], [Fig-4]]
  6. evidence of corrosion at aluminum entrance cables, regardless of use of anti-corrosive flux, sufficient to cause overheating of the cable and partial melting of its insulation
  7. in an unheated basement subject to freezing, a Bakelite fuse pullout which had been damaged by moisture, cracked, and disintegrated when the inspector attempted to pull the main fuses, leaving one fuse in place, one fuse half-removed<196>an exciting moment for the inspector
  8. burnout at connection between breaker, steel connecting screw, and aluminum bus-bar, resulting in loss of power in half the electric panel
  9. unintended "connections" between sheet metal screws, very commonly used to replace lost machine-thread panel cover screws, and electric wires in the panel, in two cases resulting in a fire in the service panel.

PANEL AGE vs FAILURES - Electrical Equipment Age vs. Failure Rates in the Studied Population

The age of equipment varied from brand new to more than 50 years old. Most of these were circuit-breaker type panels (835), with the remainder fused equipment (217).

Service panel age did not necessarily match the age of the building. For many older homes historical and other evidence indicated that the service had been upgraded. For homes constructed before 1937, electric panels had often been upgraded two or more times.[Table 1]

Table 1. Year of Electrical Equipment Installation and Number of Electrical Panels Studied
'90-'87'87-'76 '75-'65 '64-'59 '58-'37 Pre-'37 Total
60244 308 145 201 94 1052

No relationship was observed between type of equipment (fuse systems versus circuit breaker equipment) and the ability of water or moisture to enter the enclosures.

In this study, older equipment, subject to the same history of water entry, almost always looked less damaged from moisture. On such connectors and devices less extensive corrosion was found than on newer aluminum and steel screws, connectors, bus bars, and other components exposed to the same conditions.

Better data regarding actual failures might be surveyed among electricians performing replacements. Meese and Beausoleil have looked at failures in branch circuits.(3)

A common opinion among some experts was that fused equipment might be more reliable in damp/corrosive conditions than circuit breaker equipment. That view is based on the premise that electromechanical parts are more vulnerable than a fused link. However it's possible that the easier abuse of fuses (overfusing and bypassing) may offset the reliability advantage. (2)(3)(4) However other work by Keyes (1) and Popper (2) indicates that fusible panels may be more dangerous.This study did not test these opinions.

We did not tabulate the occurrence of corrosion, presence of defects, or evidence of failures, as a function of equipment age. However a subjective opinion is that older equipment, subject to the same history of water entry, almost always looks less damaged from moisture. We suspect that a factor is the use in older equipment of heavy copper and plated components. On such connectors and devices we see less extensive corrosion than on newer aluminum and steel screws, connectors, bus bars, and other components exposed to the same conditions.

Home inspectors rarely observe electrical equipment immediately after a catastrophe. It is common, however, for these specialists to find equipment in various states of deterioration of which the most severe might be just before a hard failure which would lead the homeowner to take corrective measures.

Occasionally the inspector will encounter new equipment in a property for sale and will observe the old devices abandoned (as trash) in the building. In these uncommon instances there may be opportunity to observe first hand the evidence of failure which led to equipment replacement. Better data regarding actual failures might be surveyed among electricians performing replacements. Meese and Beausoleil have looked at such failures in branch circuits.(5)

These views are confounded by the observation that in the geographic area studied service panel equipment is often 1960's vintage or newer. Older equipment has been replaced for several reasons: desire of owners to improve service ampacity, necessity to replace damaged or failed equipment, and requirements of lending institutions and recommendations from local power utility companies which cause services of less than 100 Amps to be replaced when houses are sold.

CORROSION-RELATED FAILURES - Evidence of Corrosion-Related Malfunction in Electrical Panels

Inspection practices exclude functional testing of electric panels

Normal home inspection practice does not include performance of many tests on electrical equipment. It is common for inspectors to operate switches and controls which are provided for the homeowner (circuit breakers) or for use by service personnel (disconnects at HVAC equipment).

The Standards of Practice of the American Society of Home Inspectors require that every GFCI device be tested, that light switches and receptacles be sampled for proper operation and correct polarity and grounding. Inspectors may also verify that 240 volts is provided by the service. By contrast, testing for proper operation of a circuit breaker under load conditions requires special equipment, training, and procedures which are beyond the scope of a normal home inspection.(6)

Many inspectors are reluctant to operate circuit breakers, particularly main fuses or breakers, in occupied buildings. Often they will not do so without owner permission, because of risks of losses associated with unexpected power outage (e.g. computer was turned on upstairs, kidney dialysis machine was in operation). we have field reports of loss of building heat, with concomitant risks of freeze damage, when power was turned off as part of an inspection, only to discover that a faulty circuit breaker or main fuse could not be restored to power. Inspectors approach this topic with caution.(7)

As an incidental study, we tabulated frequency of certain very common "defects" observed in service panels, of which one, burned connectors, could possibly relate to the presence of corrosion. There were 23 such cases out of the 1052 panels observed, a 2% occurrence. In at least two of these 23 cases, the inspector noted evidence of an actual fire in the panel. (The number of panel defects will exceed the number of panels examined, since multiple defects may have been reported for individual installations.)

ANECDOTAL EVIDENCE - of Electrical Panel Malfunction from Corrosion

We did not tabulate severity of corrosion. Every case reported however was severe enough to merit having been reported to the building owner or buyer as a potential safety concern. As anecdotal evidence, we report having found:

  • during rainy weather, water visibly dripping into the panel through the entry cable
  • droplets clinging to interior panel breaker terminals and bus bars
  • standing water completely filling the panel base when a steel lip is installed thereon
  • moisture in small droplets, apparently condensation, soaking all panel components
  • circuit breaker terminals so completely rusted and corroded as to make removal of the terminal screw impossible
  • evidence of corrosion at aluminum entrance cables, regardless of use of anti-corrosive flux, sufficient to cause overheating of the cable and partial melting of its insulation
  • in an unheated basement subject to freezing, a Bakelite fuse pullout which had been damaged by moisture, cracked, and disintegrated when the inspector attempted to pull the main fuses, leaving one fuse in place, one fuse half-removed<196>an exciting moment for the inspector
  • steel screws connecting main breakers to aluminum bus-bars failed at the point of connection resulting in loss of power in half the electric panel
  • sheet metal screws, very commonly used to replace lost machine-thread panel cover screws, have been found to pierce electric wires in the panel, in two cases resulting in a fire in the service panel.
  • In 1991 the author participated in investigation of a fire (Pok NY Arnold Road) which was attributed to SEC cable fraying, leaks, corrosion, and a burn up at the electric panel in the building.

PANEL CORROSION CONCLUSIONS - Conclusions and Recommendations Regarding Electric Panel Leaks and Corrosion

Moisture from exterior leaks and interior condensation must be accepted as a very common hostile environment for service equipment in homes throughout a good part of the United States. Based on a large sample of electric service panels found in homes ranging from new to more than 100 years old in Southern New York, at least one of every ten units examined showed evidence of corrosion and moisture. One might expect worse conditions in more humid regions.

The most common sources of water and moisture entry appear to be: through service entrance conductor cables which are old and damaged, or which are improperly sealed at meter boxes or building sidewalls; from condensation from high interior moisture levels; and from other building leaks or surface water which pass down building walls where panel enclosures are mounted

Electric service components are not adequately protected from corrosion. In this study, corrosion was found at main entry cable connections, wire connectors on circuit breakers, wire connectors on neutral and grounding bus bars, and on the panel enclosure itself. Steel and aluminum components more often showed significant corrosion than do heavy solid copper components.

As a result of moisture and corrosion in service equipment, hazardous conditions may be expected. At some service cable connectors there was visual evidence to strongly suggest that corrosion had led to overheating and damage to the conductors. The observation of corroded circuit breaker and other panel connectors, and the presence of highly visible water marks and even water itself on circuit breakers raises serious questions: what is the corrosion resistance of internal parts? What conditions might be found on critical parts inside those devices?

Improvements in the design of electric service panel enclosures might include drainage and ventilation for service equipment enclosures and moisture-entry-resistant panel enclosure or panel backs and fastening methods. Similar improvements, possibly by minor design changes in the stamping of steel back and base plates of electric meter enclosures might be considered.

Leaks at and through contemporary service entry cables might be reduced by: reliable weather tight connectors at the top of exposed electric meters; use sealant to encapsulate the stripped cable end (inside the meter enclosure) whenever a service cable passes out the bottom of a meter enclosure to service equipment located below the meter; use improved sealant at the building wall opening made for passage of the cable to the building interior, or use of a weather tight bib designed for a variety of uneven and often flexible wall surfaces.

Steps to increase the corrosion resistance of entrance and breaker wire connections, bus bar connectors, screw terminals, might compensate for very common field conditions which continue to place this equipment at high risk of damage from moisture. St-Onge, addressing copper services, has made other suggestions for corrective measures, (11) and other studies have made more broad suggestions for design and installation improvements.(9) Improved materials are available and have been discussed in the literature by Breedis and Hauser.(10)

Effective corrosion resistance should be added to the present standards for qualification of electrical service equipment.

Perhaps it's not startling to note that we omit from these suggestions a greater emphasis on field training for installers. When electrical work is performed by a trained qualified electrician, it's generally obvious immediately when a device cover is removed. Unfortunately we are not the first observe a broad range of skill and training in electrical work, particularly in rural areas where building code enforcement may be lax and "improvements" are made by property owners and untrained mechanics. (9)

Combined with demanding field conditions which we've described in this article, improvements in component design may be a more successful step to reduce water entry, moisture, corrosion, and failures in electric service panel connectors and components.

MORE STUDY TOPICS - Additional Study of Electrical Panel Defects Is Needed

The author is continuing and expanding this study to allow examination of additional variables

  1. Inspection field note forms have been modified to allow collection of pertinent details including manufacturer and model of service equipment.
  2. A more aggressive attempt will be made to obtain failed and removed older equipment in order that it may be provided to professionals interested in testing for actual reliability of the devices which were removed as "suspect."
  3. Effort will be made to extend the scope of collection of field data to other geographic regions: warm-dry regions of the Southwest where use of cooling equipment and a more casual attitude towards protection from weather are common; colder-more dry regions of northern regions.
  4. Effort will be made to obtain survey results from a wider selection of professional inspectors, within guidelines to provide consistency of "opinion" regarding reportable defects.

Readers who have suggestions for critical observations which should be collected during field work are urged to contact the author, Dan Friedman - contact information is given at the end of this document.

PANEL PHOTO LIST - List of Illustrations of Electrical Panel Corrosion

The original illustrations and photos, available by clicking on the links below, are called-out in the article text by individual [Figure #].

Also see GALVANIC SCALE & METAL CORROSION

 

Continue reading at CORROSION & MOISTURE SOURCES in PANELS or select a topic from the More Reading links shown below.

Or see MOISTURE CONTROL in BUILDINGS

Or see ELECTRIC PANEL INSPECTION

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CORROSION in ELECTRICAL PANELS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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