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This article discusses moisture movement methods, provisions of the National Electric Code intended to reduce the potential for intrusion, and three home inspections of wet electric service panels, each with a different method of water entry: flow along an overhead service drop, flow through an underground conduit, and condensation induced by humid air entering a panel in an air conditioned basement. Photographs are included to illustrate the causes and paths for the moisture intrusion. References to other cases are included, along with references to further information on the movement of moisture in buildings and corrosion in electrical panels.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Roger Hankey, ASHI® Certified Inspector #269, October 2010
Field study of sources of moisture & causes of corrosion in residential electrical panels.
ABSTRACT: The intrusion of moisture at electric service panels has the potential to cause corrosion and water damage to electrical equipment. While the design and installation of most systems keeps them dry, roughly 10% of residential systems suffer from moisture intrusion and corrosion1.
Home inspectors are tasked with examining electric service panels, typically in existing homes, for potential home buyers. This article discusses moisture movement methods, provisions of the National Electric Code intended to reduce the potential for intrusion, and three home inspections of wet electric service panels, each with a different method of water entry: flow along an overhead service drop, flow through an underground conduit, and condensation induced by humid air entering a panel in an air conditioned basement. Photographs are included to illustrate the causes and paths for the moisture intrusion. References to other cases are included, along with references to further information on the movement of moisture in buildings and corrosion in electrical panels.
Introduction to Water Problems in Electrical Equipment
The presence of water, except in plumbing components designed to provide, receive, store, or remove water, and on exterior components designed to shed water, has the potential to damage building systems and components. Given the widespread presence of water in the environment, building components and systems usually are designed to reduce the potential for moisture intrusion.
Manufacturers of electrical equipment recognize this omnipresence of water and specify product installation methods and maintenance to reduce the potential for moisture intrusion and remove water that enters the system. Success in diagnosing moisture intrusion begins with understanding the ways moisture moves. The four moisture transport mechanisms predominant in building science are:
Liquid flow water movement is primarily influenced by gravity and wind. This method of moisture movement requires an entry point and path for the water flow to reach electrical components.
Capillary suction causing water movement is an important factor in moisture movement in many porous building materials but rarely occurs on non-porous metallic or plastic electrical components. Capillary suction can dampen a basement foundation wall. Many interior service or distribution panels are mounted on foundation walls. If the panel is not isolated from the foundation wall by an air space and a suitable mounting board, the moisture in the foundation wall can corrode the panel.
Moisture movement from air flow can occasionally be a factor leading to condensation in electrical equipment. The air flow can be caused by air pressure differentials, convection currents such the “stack effect” of rising warm air being displaced by falling cooler air, or by mechanical equipment such as fans and blowers.
Vapor diffusion (water vapor moving directly through permeable solid materials) is the moisture transport method that moves the least amount of water in a building, and is rarely a factor in introducing water into electrical systems which are composed primarily of non-permeable materials.4
Home inspection standards: The American Society of Home Inspectors® (ASHI) Standards do not require the inspector to determine compliance with regulatory requirements, (Sec. 13.2A8). However, a general knowledge of long standing regulatory requirements can serve as a basis for understanding why identifying and reporting moisture intrusion and corrosion in electrical equipment is an important aspect of a home inspection.
Wet or corroded electrical equipment are “components inspected that, in the professional judgment of the inspector, are not functioning properly”, as stated in ASHI® Standards 2.2C1, and therefore must be reported. The Standards also require opening the electric service panel.
The National Electric Code & moisture intrusion:
The National Electric Code (NEC) requires metallic electrical equipment be protected against deteriorating agents, including corrosion. NEC section 100 defines terms including:
Rain tight: Constructed or protected so that exposure to a beating rain will not result in the entrance of water under specified test conditions.
NEC 110.11 states “Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations”; and NEC 110.12(C) states “There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating.”
NEC 300-6 (A) states: “Ferrous raceways, cable trays, cable bus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material such as zinc, cadmium, or enamel. Where protected from corrosion solely by enamel, they shall not be used outdoors or in wet locations…”
Many interior metallic electrical components are protected solely by enamel and therefore are not designed for contact with water. Moisture in electrical equipment can lead to:
The following cases illustrate three ways moisture can enter electrical components.
Most electric service installations incorporate good workmanship and follow generally established practices. Therefore these systems stay dry. The infrequent presence of moisture in electrical panels creates a challenge for those who investigate water intrusion.
While multiple adverse conditions often lead to the moisture intrusion, those conditions are often subtle variations from normal. The first indication of trouble is usually found at the service panel
Water Entry into Electrical Panel Case #1 - Leaks at SEC
The white grounded conductor was slightly shorter and entered the mast head horizontally rather than from below.(Photo below-left). Looking into the end of the mast head you can see how readily rain would follow the in-sloping white wire into the interior of the service entry conduit.
A further inspection of the service revealed staining on the bottom of the elbow where the conduit penetrated the wall. Our next photo (below, left) shows the under-side of the conduit elbow cover.
There was no drain hole in the bottom of this elbow.
Therefore, the probable moisture path was along the service drop, into the mast head on the white neutral conductor, down the mast, through the meter box, through the elbow and into the main panel to the neutral bus and finally onto the bottom of the panel.
Water Entry into Electrical Panel Case #2 - Snow Melt
Water Entry into Electrical Panel Case #3 - Negative Air Pressure & Moisture Condensation
Also see SEWER GAS ODORS where we describe sewer gas leaks through electrical conduit.
Water Entry into Electrical Panel Case #4 - Mouse Infestation in the Electrical Panel
Other conditions which can lead to water intrusion and corrosion in electric panels as well as other forms of damage include:
The following NEC sections, if implemented, reduce the potential for moisture intrusion and corrosion:
230.8 Where a service raceway enters a building or structure from an underground distribution system, it shall be sealed …
300.7(A) Sealing. … where passing from the interior to the exterior of a building, the raceway or sleeve shall be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve.
-- © Roger Hankey, text and illustrations adapted with permission from the author. Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - email@example.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
Most Common Water Enter Points into Electrical Meter Bases and Panels
Research of a large number of homes documented at CORROSION in ELECTRICAL PANELS found that at many electrical meters and panels the common leak points for water entry were found originating at the masthead, at frayed leaky service entry cable (SEC) insulation, at a poor seal of the SEC at its entry to the electrical meter base, or where the SEC penetrates the building wall passing to an electrical panel located lower than that pint, such as in a basement.
For those cases, the best repair would have been proper SEC installation details so that water was not entering the conduit and following the SEC cable in the first place.
In good building science it's generally better to keep water out of where it is not wanted than to let the water in and then let it run out.
White stains or "water tracking" marks sometimes found on SEC wires entering the top of an electrical panel or at other wiring in an electrical enclosure or conduit may be caused by mineral deposits or debris left from water running down inside the SEC cable jacket or conduit into the enclosure or conduit. Examples of these conditions are found in photographs that track water moving inside the SEC, visible at CORROSION in ELECTRICAL PANELS. - Ed.
Frequently Asked Questions (FAQs) About the cause & repair for water leaks into electrical conduit, panels, boxes, etc.
Question: pulling wires through wet conduit
Electromotive action when : Electrical wires are pulled into conduit where the conduit has substantial level of standing water and the three wires are submerged in water!
Can this cause excessive current return on the natural wire from power company and causes excessives heating in all equipment running in the system ?
There is not any current on the ground wire at all ---- is just 3 - 5 mili-amps !
Honestly, Travis, I don't know. I don't think the water itself is ever a cause of induced electrical current, though water inside conduit could, depending on level of impurities in the water, help conduct stray currents into wires that might be nicked or have damaged insulation.
I have found low levels of induced-electrical current in electrical wires in a variety of locations and installations where such wires ran under or even parallel to high current power transmission lines or service entry cables.
And all of us amateurs as well as pros working on electrical systems run across nicked or damaged wires that can then be measured to show unexpected currents.
A brother in law, a theater electrician, in wiring his New York City apartment with armored cable, over-tightened all of the BX-to-Box connector clamps and omitted the plastic wire protectors that should have been inserted into each BX wire end. The result was that as he over-tightened the box connector clamp he squashed the cut-end of the BX cable armor enough that every single wire set in the apartment at every single junction box was nicked and connected (inadvertently) to the building ground. All of the nicked hot wires were found immediately when he tried to turn on power. His GFCI breakers in the panel kept tripping - which was when he gave me a call. We found that the circuit neutral wires were also shorted to ground by the same clamp-cut mistakes.
I would inspect the system for damaged wires, and I'd look for a hot wire nick or leak. If no defects of that type are found I'd do some field tests to see if nearby power sources are inducing a current into the wire run.
Investigating a case of unexpected shock to workers who were rebuilding a garage (after an electrical catastrophe) we found that wet plywood roof sheathing was acting as a giant capacitor picking up a current induced by very close overhead power transmission lines.
Question: how do I stop water from pouring out of electrical conduit into the electrical system?
What is the permanent fix for this situation? I have built a sluice to catch the water that spills out of top of the wire conduit (into a 5 gal bucket) but I am worried about having so much constant water near an electrical source. I look forward to your answer. Thanks. - T.M. 12/31/2012
Reply: find the water source, direct it away, seal leaky conduit fittings
I agree that the conditions you describe are unacceptable and dangerous. A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem, though in this case, some detective work on your own part, as long as you can avoid getting shocked or killed, should be adequate.
To fix the problem you describe - water pouring out of an electrical conduit into an electrical box, panel, or control (any of these is unacceptable) we need to identify the water source as well as to identify all of the places (there may be more than one) where water is entering the conduit. The fix depends on what water sources and leak points we find.
Intercept & Direct Surface or Subsurface Water Away from Electrical Components
For example, where I found water entering a building electrical panel mounted on a basement wall, inspecting ouitside we found an in-slope grade towards that building wall and a buried electrical trench bringing the SEC feeders to the building. The trench, cutting a diagonal across the hill, was operating as a catch trench for both surface and subsurface water, aiming all of that water right at the building wall where the foundation wall was in turn penetrated by the entering electrical conduit.
Water was not actually entering the conduit in this case; water was simply following the conduit through the wall into the electrical panel.
The "fix" that worked to stop this wet electrical panel involved:
Find & Fix Leaks into Electrical Conduit to stop water from entering electrical boxes & panels
A different and common example that may better fit your case is a leak, or more than one leak into an electrical conduit that is buried in ground exposed to surface or subsurface water, or rain entering an electrical conduit from above-ground, for example following an SEC down through the electrical meter box and from there into the interior of the conduit that in turn entered the building.
Some fellows think that if they just route the conduit "up" in a reverse drip loop they will stop this leak hazard. Some other wannabe electricians whose work I've inspected figured it was enough to drill a hole into an outdoor electrical conduit elbow bottom or junction box to let water in the conduit drain out before the wires enter the building.
I do not agree with either of these band-aid approaches to electrical conduit leaks.
Outdoor electrical boxes and conduit are expected to be weather-tight, not to serve as pipes that move water from one place to another.
And depending on water source, elevation, and pressure, such a loop is no guarantee that water doesn't enter the electrical system, and further, the wiring routed inside conduit and various junction boxes is not normally intended for exposure to water or flooding. (Conversely, continuous, un-spliced UF underground feeder, outdoor exposure-rated electrical wiring may be buried outdoors, underground without protection by conduit.)
For leaks into electrical conduit, if the water quantity is small and the leak limited to one entry point, we might successfully expose and seal with proper fittings the leak into the conduit. But preferable is to direct water away from that point as well.
In your case, as you do not describe any investigation to pinpoint the water source, that's where I'd start. From the quantity of water you are describing I suspect that there may be a section of conduit buried outside in flooded soils and lacking proper connections, possibly even with one end open to the soil). You want to to assure that the conduit is all water-tight throughout its length. Any outside junction boxes that may have been required are either brought above-ground and also sealed, or are rated for below-ground water-tight use. .
Send along some photos of your installation and we may be able to offer further comments or suggestions, and keep us informed of what you find, as doubtless your own work will help other readers.
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