Schedule an Inspection

Electrical Systems

One of the most crucial components of a home is its electrical system, which may pose some safety hazards if not properly maintained. Do you know some of the issues and concerns that surround a home’s electrical system?

Method of Inspection

Incoming Power Line(s)

  • Determine the type and number of conductors in the incoming service.
  • Evaluate the height of the incoming service cables above the ground or grade level.
  • Observe obstructions such as tree limbs in the area.
  • Determine if the service head is correctly oriented and properly secured to the structure.
  • Count the number of service conductors attached to the weather head. The number of service- entrance conductors determines the voltage of the service.
    • A 120-volt, single-phase system consists of two conductors—an ungrounded phase (hot) conductor, and a grounded (neutral) conductor. The 120-volt single-phase service can only supply power to single phase loads (i.e., 120 volt circuits only).
    • A 120/240-volt single-phase system consists of three conductors—two ungrounded phase (hot) conductors, and one grounded (neutral) phase conductor. This system will supply both 120-volt loads and 240 single-phase loads to a dwelling.
  • The size and material of the individual conductors determine the ampacity of the service conductors (ie., copper or aluminum). More than 95% of modern day services are stranded aluminum conductors.
  • An underground (lateral) service extends from the transformer to the meter base of the dwelling. An underground service must be at least a #8 copper or #6 aluminum SEC. The cables must be buried a minimum of 24 inches from finished grade to the top of the cable. (Check local requirements for burial depths).
  • Determine the ampacity of the service. Ampacity is determined by the smallest of three components: (1) type and size of the service entrance cable; (2) rating of the panel; and (3) size of the main disconnect.
    • Ensure that the cables are properly secured to the structure.
    • Is the drip loop properly formed? Are wall and/ or roof penetrations properly sealed against water and air intrusion?
    • Locate the main overcurrent protection (panel box). Examine the service cable to determine the service ampacity capability. (Note: The panel box must be located within 5 feet from the point that the SEC enters the dwelling.)

Main Panel Box and Subpanels

  • Remove covers and examine all enclosures for ampacity ratings.
  • Determine size and material of service and feeder cables, and compatibility with main disconnects.
  • Compare the wire sizes to the fuse or breaker sizes to determine if the ampacity of each breaker/fuse is correct.
  • Report the presence of more than one wire connected to a breaker/fuse (double tap). NEC article 110-14 requires that any breaker/fuse designed for more than one conductor must be clearly and permanently identified for that usage.
  • Report presence of single conductor aluminum wiring in branch circuits (120-volt).

Locate the service-grounding conductor connected in the panel box. Trace the conductor to its point of termination (i.e., a driven rod, connection to a metal water service pipe, or a foundation-grounding conductor). Examine termination connections. The grounding conductor should be securely fastened to the building. A #6 copper or aluminum or larger conductor may be used if not exposed to physical damage. If the conductor is exposed to damage, it must be protected in a conduit. Insulated or bare aluminum or copper-clad aluminum conductors cannot be used where they will be in direct contact with masonry or earth or where subject to corrosive conditions.

Determine type of wiring (i.e., 2-wire with armored cable (BX); 3-wire plastic coated (non-metallic, typically called Romex); knob and tube (copper wire), with cloth insulation, in a loom for protection, and installed on porcelain insulators and through tubes in joists and floors.

Determine the panel box ratings. There are three types of panels used for service equipment and distribution:

  • Main panels generally contain service and distribution wiring and equipment.
  • Lighting and appliance panels (typically referred to as sub-panels), and
  • Split-bus panels are typically main panels found in older homes.

Split-bus panel boards have 1 to 6 two-pole mains in the top section with one of the mains used to supply the bottom section of the panel board. The bottom section of the panel board is used for the lighting and receptacle outlet loads. Split-bus panel boards are required to have a separate main disconnecting means ahead of them if installed after 1981.

Each panel board is rated and tested by the manufacturer. Located either inside the panel box or on the rear side of the front cover is the manufacturer’s listing data label. This label provides the maximum voltage and ampacity ratings for the panel board. The main disconnect (breaker/fuse) cannot exceed the listed ratings.

Determine panel box condition, such as missing or loose covers, interior rust, open knockouts, improperly connected boxes to the wall, or obstructions to the panel box.


  • Examine all accessible areas of the residence for unsuitable wiring, lack of sufficient receptacles, use of extension cord wiring in lieu of permanent wiring, junction boxes or outlet boxes without covers, improper or unprotected splices, defective fixtures, and any other unsafe wiring practices.
  • Inspect all wet location areas, such as the basement, garage, and bathrooms and kitchens for proper wiring with GFCI devices. Depending on the age of the house, GFCIs may not be required. Code-related dates:
    • Exterior outlets below 6’6” – 1973
    • Bathrooms and powder rooms – 1975 and 1978
    • Garages – 1978
    • Kitchens – within 6’ of a sink –1987
    • Unfinished basements and crawl spaces – 1990
    • Wet bars – 1993
  • Check for wall switch controlled outlets in habitable rooms, bathrooms, hallways, stairwells, attached garages and outdoor entrance.
  • Operate all accessible wall switches. Check for current in accessible receptacles in each room. Check polarity in each accessible receptacle, and check for ungrounded circuits.
  • Look for discolored, loose or worn switch plates or receptacle covers, and any other unsafe wiring concerns or problems.
    • Look for knob and tube wiring, corroded or worn armored cable (bx) or defects in any other wiring that may exist. Look for missing or broken fixtures
    • There are a number of wiring types that qualify for wet locations, however, the most common type seen in residential construction is Underground Feeder (UF). This wire is acceptable for underground use, including direct burial in the earth. It should not be embedded in concrete or exposed to the sun, unless identified as sunlight-resistant.
  • Check for approved weather-tight exterior boxes.
  • Check that all exterior wiring is permanently marked sunlight-resistant. Underground Feeders are not approved for outside usage when exposed to the sunlight.
  • All interior/exterior boxes, fixtures and related electrical equipment should be properly secured.

Evaluating Electrical Wiring

  • Electric current travels through a circuit at a constant rate. Current travels at the speed of light, or 186,000 mps. (A light bulb remains at the same intensity the entire time that it is on. This indicates that the current must be the same, or the intensity of the bulb would change.) GFCIs also operate on the balance of current.
  • If an overload occurs in a circuit, the entire wire is instantly affected (or at the speed of light). Failure will be exhibited by the most vulnerable part of the wire, which is the insulation. It does not matter whether it is cloth or plastic. (The filament in a light bulb glows red hot, but it does not burn or fail since there is no oxygen in the bulb to support combustion.) If we were to wrap the hot filament in the bulb with wiring insulation, it would immediately melt and turn to ash. This would indicate that the insulation is more vulnerable than the conductor.

If the conductor is exposed it is considered unacceptable. If the wire insulation is missing it is not difficult to conclude that the wire is in poor and unsafe condition.

  • To evaluate older wiring, follow the wiring in the basement until it goes into the walls or floor. If it changes from new to old wire, there may be concerns.

Common Defects

  1. Aluminum single conductor wiring on 120-volt circuits
  2. Broken fixtures or devices
  3. Loose or inoperative ceiling fans
  4. Double tapped circuits in service or distribution panels
  5. Permanently installed extension cords or temporary wiring
  6. Frayed, deteriorated or melted insulation
  7. Missing or inoperative GFCIs
  8. Grounds loose, wire connections/clamps corroded or not properly connected
  9. Improper junctions or splices
  10. Improper main disconnect
  11. Improper exterior wiring
  12. Loose outlets and switches
  13. Knob and tube wiring (age and condition concerns)
  14. Lights not functional
  15. Missing cover plates
  16. Outlets with open grounds
  17. Inadequate overhead cable clearances
  18. Oversized breakers or fuses
  19. Inoperative smoke detectors
  20. Reversed polarity at outlets
  21. Unsecured or inadequately secured electrical cables
  22. Subpanel grounds and neutrals not separated
  23. issing knock out in panel/boxes
  24. Bath lights on GFCI circuit

Electrical Clearances and Fastener Requirements

Service entrance cable should be secured:

  • Within 12 inches of the masthead
  • At intervals not to exceed 30 inches

Service drops required building clearances:

  • 18 feet over public roadways
  • 15 feet over alleys
  • 12 feet over private driveways
  • 10 feet over finish grade and sidewalks
  • 10 feet over platforms, decks, and porches
  • 8 feet over roofs with less than a 4 in 12 pitch
  • 8 feet over flat roofs
  • 3 feet over roofs with more than a 4 in 12 pitch
  • 3 feet horizontally from fire escapes, porches and decks
  • 3 feet from windows
  • 18 inches over roofs where there is a 4 foot or less overhang

Clearances in closets for light fixtures:

  • 18 inches between fixtures and where combustibles may be stored
  • 6 inches between flush mounted fixtures and where combustibles may be stored

Recessed lighting (typically inspected from the attic):

  • One half inch spacing of recessed portion of the fixture from combustible materials
  • 3 inch spacing of thermal insulation between recessed light fixtures and combustible materials with nothing above the fixture (Non-thermally protected)

Special appliances (such as laundry equipment):

  • 6 feet maximum distance from outlet to appliance

Supply cords for air conditioners:

  • 10 feet maximum for 120 volt wire
  • 6 feet maximum for 208/240 volt wire

Items of Inspection

Service Voltage

The service voltage can be determined by counting the number of wires connected to the mast or weather head. A 2-wire drip loop indicates a single-phase, 120-volt electrical service. A 3-wire drip loop indicates a single-phase, 240-volt electrical service. A 4-wire drip loop indicates a 208 or 240-volt three-phase service. Three-phase electrical systems are typically found commercially, such as in a supermarket or someplace with commercial refrigeration equipment. Two-phase services have 5-wire drip loops and are typically found in industrial applications. A licensed electrician should evaluate three and two phase systems.

Typical Service Entrance Cables
Wire Size Amperage Rating Width
#4/0 200 Amps Aluminum 1 7/16 inches
#2/0 150 AmpsAluminum
(AL)200 Amps Copper (CU)
1 5/16 inches
#2 100 Amps Aluminum
125 Amps Copper
1 5/16inches
#4 100 Amps Copper 3/4 inch
#6 60 Amps Aluminum 3/4 inch

Note that some commercial and industrial systems do not carry standard 240-volt services, and may not be compatible with ordinary 240-volt household appliances.

Service Entrance Amperage

The service entrance amperage is sometimes difficult to determine. The amperage can be derived from the size of the service entrance cable (SEC) by: (a) looking for the size printed on the cable insulation; or (b) comparing the cable sizes to the chart listed below, using a gauge to determine size.

Electric Meter

Although the meter is usually owned by a service power company, it should be checked for defects. The following are some areas that should be evaluated.

  • Look for broken meter seals, or other evidence of tampering. Check to make sure all openings for the meter are properly closed and sealed to keep moisture out.
  • Check that the meter and meter box are properly secured to the building. · Evaluate the location of the meter installation. Provisions should be made to prevent damage from cars, etc.
  • Check for rust at the bottom of the meter socket box/enclosure, which is typically located on the exterior of the house. When the service entrance cable enters at the top of the meter box, and the seal is not water tight, water may cause rust that is evident at the bottom of the box.
  • If the service entrance cable enters at the top of the meter socket/box and the cable that services the main panel comes out of the bottom of the meter socket/box, there is a possibility that water may follow the SEC from the meter box to the main panel. Check the main panel for rust at terminals inside the box and especially on the bottom of the panel.

Service Disconnect Inspection

When the service disconnect is located on the exterior of the structure, the following areas should be closely evaluated:

  • Check for excessive rust or corrosion on the interior and exterior of the box.
  • Check for rust or corrosion at the terminals on the inside of the box.
  • Ascertain that the enclosure is a proper, approved, weather-tight box and is suitable for exterior installation.
  • Check to determine that the meter box is properly secured to the building.

Service Panel Inspection

After locating the main disconnect, main service panel and sub-panels that may be present, remove the covers very carefully and evaluate the interior components for the following items:

  • Check for signs of corrosion on both the panel and all of the interior connections. Corrosion on the interior of the panel may indicate water penetration via the service entrance cable or a condensation problem in the area.
  • Look for circuit breakers/fuses that have more than one electrical conductor attached to them. Double or triple tapping is normally prohibited, both by local jurisdictional requirements and the National Electric Code (NEC).
  • Splices are allowed only to extend the lengths of the wire inside the panel. Splices are never allowed for the connection of more than one line to a circuit breaker/fuse. · Anti-corrosive gel should be found on aluminum cable connectors.
  • Check that branch circuits are not wired before the main service disconnect.
  • Circuit breakers or fuses without conductors may lead someone to believe that the panel has more circuits than it actually has.
  • Low voltage transformers are usually not allowed inside the service panel due to the heat that they create.
  • Check for loose and unattached conductors inside the panel. All conductors inside the panel must be properly terminated.
  • Check the two-pole (240-volt) circuit breakers. Two-pole breakers must trip together, so that they provide total safety for the circuit. The use of nails or pins to hold two breakers together is not acceptable. A properly designed connector should be utilized.
  • All ground wires should be properly secured to the ground wire or the neutral/ground buss, depending on the panel.
  • Neutral wires should be properly secured to the neutral wire buss. · Check wires for signs of arcing, charred metal, or burnt wire insulation.
  • Evaluate all cables entering the panel box to ensure that they are properly protected and secured. BX or metal armor cables must have special plastic bushings inserted between the conductor and the outer shield of the cable to protect the wiring. Wire retainers should secure non-metallic wire.
  • Check all the wiring sizes and their respective fusing. Make sure all the wires are properly sized for the respective fuse or breaker to which they are attached.
  • Openings in the panel that may present a shock hazard · Check for single conductor aluminum wire sizes smaller than #8. Such wiring needs special consideration, since it has been known to pose fire hazards even when properly installed.
  • All panels must have their interior connections covered to prevent shock.Check that the main disconnect for the service is marked “main.”
  • Report inaccessible electrical service panels.
  • The NEC requires a minimum headroom of 6’6″ at the service panel, and 30″ around the panel area, as well as a 36-inch clear area in front of the panel for servicing.
  • The panel must be securely attached to the wall or other structural components.
  • There should be no missing screws in the panel cover. The screws should be blunt-ended.
  • There must be either a single means of disconnecting the electrical service system, or there must be no more than six disconnects in order to shut down the entire electrical system. (Six finger pulls or hand throws) Modern systems will have a single means; older split buss panels may have 6 disconnects.
  • Check the compatibility of the service entrance cable to the rating of the main panel enclosure box. If the service entrance cable is rated for 100 amps maximum and the main service panel contains a 200-amp main disconnect, it poses a potential fire hazard.
  • Adequacy of the electrical service should be determined. By today’s standards, 100-amp service is considered minimal service.
  • Identify the materials used for branch circuit wiring inside the service panel. Copper is preferred wiring material for all circuits 30 amps and under.
  • Check for circuit breakers that are not properly secured or are loose. Some circuit breakers are not compatible with the box they are installed in, and some of the older Federal Pacific panels had this problem with the prescribed breakers. In these cases, the panel cover may be holding some of the breakers in place. Arcing is common with this situation, but it may not be readily visible until the insecure breaker is removed
  • Check the outside of the panel to see if it is warm or hot. This should be a cause for immediate concern.
  • Do not operate any breakers, main disconnects or fuses to check operation. However, be aware of corrosion rust evidence of previous condensation that might indicate operation problems.

Bonding of Service Equipment

Noncurrent-carrying metal parts and equipment, such as the panel, service cable, armor or sheath, equipment enclosures, meter boxes, and fittings are required to be bonded to the metal enclosures which are enclosing electrical components. They may be bonded with approved connectors or locknuts. Bonding jumper size is based on the size of the over-current protection device. They are the same size as the equipment grounding conductors. Other systems with current-carrying potential (i.e., water and gas piping) should be bonded back to ground. Sub-panels should be bonded to the main panel box to ensure a single, low impedance ground. Bonding should be provided where necessary to ensure electrical continuity and the capacity to safely conduct any “fault current” that is likely to be imposed. Equipment and/or piping that may become energized should be bonded to the service equipment, the grounding conductor at the service, the grounding electrode conductor where it is of sufficient size, or to one or more grounding electrodes.


Systems and circuit conductors are grounded to limit voltages due to lightning, line surges, or unintentional contact with higher voltage lines, and to stabilize the voltage to ground during normal operation.

Equipment grounding conductors are bonded to the system grounded conductor to provide a low impedance path for fault current that will facilitate the operation of over-current devices under ground fault conditions.

The protective devices should be selected and coordinated to permit the circuit protective devices that are used to clear a fault without the occurrence of extensive damage to the electrical components of the circuit (i.e., circuit breakers, GFCIs, proper grounding and bonding).

Grounding should: (1) Be permanent and continuous; (2) Have the capacity to safely conduct any fault current that is likely to be imposed on it; and (3) Have sufficiently low impedance (resistance) to limit the voltage to ground and to facilitate the operation of the circuit protective devices.

Driven rods are the typical choice for grounding conductors when a plastic water service pipe is present, since plastic does not conduct electricity.

How Much Amperage Is Enough?

The NEC outlines ways to calculate the service load requirements. The following information is an outline of one of the options, and an understandable way to determine the load requirements from a home inspector’s perspective.

Article 220 of the NEC provides the necessary information for calculating loads. This is a summary using assumptions in an effort to understand the general requirements of developing load calculations.


Small appliance circuits should be calculated at 75% of the circuit rating. A 20-amp branch circuit would be computed at 1500 volt-amps or 15 amps. A 15-amp branch circuit would be computed at 1125 volt-amps or 11.25 amps.

General lighting and general use receptacles are calculated at 3 volt-amps per square foot (SF) of living space.

Appliances that are fastened in place, permanently connected or located on a specific circuit, ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers and water heaters should be counted as the actual nameplate rating. Motors should also be counted at the nameplate rating.


On-Site Method Watts = Amps X Volts


Watts divided by Voltage = Amps, or a 100 watts (ie., a light bulb) divided by 120 volts (typical circuit voltage) = 0.8 amps. (amount of draw)

You should also understand that 60-amp or higher single-phase services allow you to access 120 and 240-volt circuits. A 100 amp single-phase service will allow you to access 100 amps at 240 volts, or 200 amps at 120 volts, or a combination of 120 and 240-volt circuits. The latter is commonly found in most residences.

Simply add the wattage or amperage required by the existing or probable appliances.

Assume a house with 2000 SF of living space, a fossil fuel heating system, central air, electric range/oven, electric dryer and an electric water heater.

120-volt appliances and equipment:

  • Refrigerator – depends on size and model – approx. 4 amps
  • Microwave – depends on size and model – approx. 10 amps
  • Hair dryer – 1500 watts – 12.5 amps
  • Curling iron – 1200 watts – 10 amps
  • Toaster – 1000 watts – 8.3 amps
  • Lighting – approx. 1200 watts – 10 amps
  • TV – 21 to 30 inches – approx. 150 watts – 1.25 amps
  • Portable heater – 1500 watts – 12.5 amps
  • Washing machine – approx. 1000 watts – 8.3 amps
  • Furnace blower – approx. 400 watts – 3.3 amps
  • Miscellaneous items – stereo, exhaust fans, blender, disposal, iron, additional TVs, etc.– 1500 to 4000 watts – 25 amps

Total of the 120-volt circuits = 130.15 amps

240 volt appliances and equipment:

  • AC – 36,000 BTU – approx. 19 amps
  • Range/oven – approx. 10,000 watts – approx. 41.66 amps
  • Dryer – 4800 watts – 20 amps
  • Water heater – 4500 watts – 18.75 amps

Total of the 240-volt circuits = 99.41 amps

These items represent many of the appliances normally contained in a home. There will be other items such as: well pumps, freezers, saunas, welders, generators and multiple systems, etc. Such items can be added, as long as you know the voltage and wattage.

The 130.15 amps will be distributed across both of the 120-volt poles. This means that the 130.15 has to be divided by 2, suggesting that 65.07 will be taken from each side. We know that the distribution will not be even, however, it will be reasonably close.

If we add the approximate 65 amps from the 120-volt circuits to the approximate 99 amps from the 240-volt circuits, we get 164 amps at 240 volts. This suggests that the maximum current that could be drawn in this sample house, assuming every electric device was on simultaneously, is 164 amps. We know that it is nearly impossible to have a situation where every electric component in the house will be on at the same time. This situation will provide a design cushion. An arbitrary figure would be in the 20% range. 164 amps x 80% = 131 amps.

The example above, according to the Summary method, requires 131 amps to service this house. You will typically find a 200-amp service in this situation, however, 150 amps would be adequate. 100 amps would not be acceptable.

Electrical Concerns

There are many specific deficiencies that may be encountered during the inspection of an electrical system. The following are some of the more common concerns:

  • Open junction boxes – All junction boxes must be properly covered.
  • Exposed wires outside the junction boxes – All terminations of electrical wiring must be made inside an approved junction box.
  • Improperly spliced wire – All connections must be made inside a junction box or in a panel box. Exception: knob and tube wire that has been soldered and taped. Splices, which are in the panel, are only allowed to extend a wire.
  • Improperly wired outlets – Use your receptacle analyzer to check the outlets in the residence. Note any defects, such as reversed polarity, open ground, etc.
  • Improperly hung or secured electrical wires – Wire must be secured to studs or passed through drilled holes in studs/beams/joists.
  • Lack of GFCI control devices – Current code requires that all exterior circuits, bathrooms, kitchens within 6′ of sink, garages and basements must be protected by Ground Fault Circuit Interrupters. Check with the authorities in your area for local requirements.
  • Improperly stapled wiring – All staples should be an improved type, insulated, and must not dig into or otherwise damage the insulation of the wiring.
  • Extension cord wiring – Extension cord wiring is considered temporary, and should not be used as permanent wiring.
  • Wiring that rests on heat pipes, heat ducts, or other pipes
  • Wiring passing through or over sharp metal objects, fireproofing or heat ducts, must be properly secured/protected to prevent damage
  • Frayed, brittle or fragile wiring insulation or other deterioration that could create a hazard
  • Knob and tube style wiring – Knob and tube wiring is an older wiring system which does not have a ground. Any receptacle or fixture tied to this older wiring would be ungrounded and may be unsafe. Evaluate the older 2-slot outlets. Note that these outlets do not provide a third ground slot. Upgrading to 3-slot outlets should be considered, if proper grounds can be installed without a disproportionate amount of work. Knob and tube wiring was the most widely used type in frame buildings until the 1920s and had virtually disappeared by the early 1930s when BX wiring systems replaced it. The dangers of knob and tube wiring lay in a combination of problems of both exposed and concealed systems. By 1907, the NEC began to recognize the inherent problems with concealment of this type of wiring. They began to require placement of the wires in dry areas only and a separation distance of 5 inches between the wires. Extreme caution should be used when encountering this type of wiring due to its age and very possible damaged or deteriorated insulation.
  • Wiring smaller than #6 in size should pass through holes in joists when running perpendicular to them
  • Wires running across the ends of joists need to be fastened to running boards
  • Wiring running across the joists must be installed so that the wire is not at the exposed end of the joist
  • Staples and hangers should be no more than 4½’ apart, and no less than 12″ from any enclosure or junction box.
  • Overcrowded junction boxes. This can be established by determining the number of conductors entering and leaving the junction boxes. Junction boxes are sized in accordance with NEC 370-16. The determination is beyond the scope of a visual home inspection. However, a prudent inspector would note the presence of a large number of circuits in any system. It is not recommended that the covers to the junction boxes are removed for this analysis, however, it is the best way to evaluate older wiring.
  • A lack of sufficient outlets. This is typical in older homes and it may not be a problem or a situation that can be enforced.
  • Evaluate conditions in closet areas. Check to insure that there is 18 inches of clearance between incandescent lighting fixtures, and 6 inches of clearance between florescent fixtures, and combustible materials. Note any bare or exposed light bulbs that may exist in a closet area.

Most of the items listed above may create serious safety concerns. Others, such as, the lack of a ledger or label, anti corrosive gel or the presence of a low voltage transformer in the panel, may not pose the same urgency.

Single Conductor Aluminum Wiring

Small, single conductor aluminum wiring, such as 10 gauge, rated 20 amps and 12 gauge rated 15 amps, was used from 1965 to 1974. In 1975, the NEC prohibited the use of single conductor aluminum wiring.

The main concern with small gauge, single conductor aluminum wiring is its expansion characteristics when it is heated. If the wire is in a situation where the amount of current that is being drawn does not heat the wire, there will be no typical aluminum wire related concerns (i.e., if an aluminum wire circuit only serves a lamp and a TV, it will not draw enough current to cause expansion problems). A 15-amp circuit that is serving a lamp and a TV will have a maximum load of only about 3 or 4 amps. This is not nearly enough to cause aluminum wire concerns due to heat.

To determine how much current a circuit is drawing, divide the wattage rating of the lighting and or appliances on the circuit and divide by the voltage. Watts = Amps X Volts so a 100 watt light bulb divided by 120 volts equals .8 amps.

When almost anything is heated, expansion will occur. Materials of different densities will expand at different rates. When an aluminum wire is attached to a steel alloy contact with a similar steel screw, and the contact, screw and wire is heated by the current moving through the circuit, everything expands. During this process, the density of the steel will tend to distort the aluminum wire. When the contact cools, the steel alloy will return to its original size, while the aluminum, because it was distorted, will not.

When aluminum is exposed to air, a film of aluminum oxide forms on the metal’s surface. The oxide formation causes the wire to loosen under the mounting screws. When the screws are worked loose, the oxidation of the aluminum wire under the screws heat and create a fire hazard.

When there is enough distortion, the aluminum wire will become loose at the contact. It may not appear loose, because it may not come off, as you would expect from a loose wire. The loose aluminum wire may function with micro arcing, which will cause more heat at the contact and make the problem worse. The additional heat causes stress on the wire, and may cause a slight fracture in the run of the wire about 1/8 inch from the contact. This fracture causes additional micro arcing and even more heat. Fractures occur at this point because this is the point of maximum temperature difference or change. When multiple arcing occurs, the potential for excessive heat and possibly a fire may be present.

The apparent solution to the problem would be to remove the aluminum wire from the steel alloy contacts. The original suggestion was to pigtail the aluminum wire with a piece of copper wire and to attach the copper wire onto the steel contact. This would have been acceptable, except for the fact that the aluminum and copper, being dissimilar, corrode due to oxidation when they are in contact with each other.

To help eliminate the problems and concerns, device manufacturers developed switches and outlets designed to receive copper or aluminum. These devices were called co/al devices, however, they were not as effective as the manufacturers had anticipated, and were revised. The revised devices are called co/alr, the “r” meaning revised.

With the co/alr devices, the switch and outlet concerns were addressed, however, there is still a concern with fixtures that are wired directly, such as a chandelier. In most cases, and assuming they are wired correctly and the loads are properly calculated, there should be no problems, because the amount of heat generated by these fixtures is not enough to stress or overload the wire. The concerns are related to situations that are unknown or where the wiring or calculations are incorrect.

AMP Corporation designed a wire crimping tool and system that will provide dependable results with aluminum to copper connections. The crimp is designed to ensure that air does not come between the aluminum and copper. After the connection is crimped, it is covered with a sleeve, which is shrunk around the connection. This process minimizes oxidation at the contact. This is the only system that the Consumer Product Safety Commission (CPSC) has accepted. 1. The CPSC does not recognize any other system or correction as acceptable. This creates legal concerns for anyone who may recommend a different solution. 2. AMP Corporation does not sell the crimping tool; they have patents pending and only allow users to lease the equipment. This limits access for residential or small work, because it is difficult to justify leasing costs for one house. 3. The number of “qualified” electricians that have gone through the AMP training creates further limitations. There are very few electricians in the country that have gone through the training, and most are commercial electricians. Based on this situation, we as home inspectors cannot recommend this as a solution, because most of our clients will not be able to find a qualified electrician in their area. 4. Our posture is to explain the aluminum wire situation so that our client understands the concerns, and recommend a licensed electrician to determine the best action.

The NEC and most jurisdictions recognize twister wire nuts and co-alr device usage. The CPSC has not required the removal of the other two methods from the marketplace. This would suggest that there is insufficient research to ban the use of these products.

ASHI standards and the ERC inspection guide require us to report the presence of single conductor aluminum wire as a defect.

18 Typically lampcord wiring and low voltage applications
16 Typically lampcord wiring and low voltage applications
14 15 Amps
12 20 Amps 15 Amps
10 30 Amps 20 Amps
8 50 Amps 30 Amps
6 65 Amps 50 Amps
4 100 Amps 70 Amps
3 110 Amps 80 Amps
2 125 Amps 100 Amps
1 150 Amps 110 Amps
1/0 175 Amps 125 Amps
2/0 200 Amps 150 Amps
3/0 175 Amps
4/0 200 Amps