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How to Inspect Residential Electrical Panels
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• Class on how to inspect electrical panels
• Home inspection procedures and safety

© Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

COURSE SUMMARY - Electric Panel Inspection Course Summary

SAFETY WARNING: Inspection of electrical systems risks death by fatal electrical shock. The procedures discussed in this class require that the cover of the panel be removed in order to expose the panel interior. Homeowners should not attempt this step, and no one lacking proper electrical safety training should remove the electrical panel cover nor attempt to perform the tasks discussed in this class. ELECTRICAL CODE COMPLIANCE WARNING: these inspection procedures are designed to assist in the detection and reporting of electrical service defects which can be recognized by visual inspection. This inspection is not for the purpose of determining compliance with local or national electrical codes. Guidelines given here, such as overhead wire clearances, are based on widely-accepted codes and standards, but local building codes may specify other or different restrictions.

Part I - Electrical Panel Defect Identification - Principles

• Safety Procedures for Electrical Inspectors
• Electrical Power Delivery System
• Common Electrical Panel and Wiring Defects

Part II - Electrical Panel Defect Recognition - Photos of Electrical Defects & Examples

This section of the class contains annotated field photographs of certain electrical panel defects which can be recognized by visual inspection. That is, no instruments, no measurements, and no insertion of any device into the electrical panel are required to perform these tasks. I have these photos on file and will add them to this presentation if readers request.

ELECTRICAL INSPECTION SAFETY - Overview of the Residential Electrical System and Electrical Inspection Hazards

• The Electrical System Function is to power home systems/appliances, providing safe distribution of electrical power throughout the building.
• Costs: operation, repair, updating/expansion

Safety Procedures for Residential Building Electrical Inspectors

SAFETY WARNING: Inspection of electrical systems risks death by fatal electrical shock. The procedures discussed in this class require that the cover of the panel be removed in order to expose the panel interior. Homeowners should not attempt this step, and no one lacking proper electrical safety training should remove the electrical panel cover nor attempt to perform the tasks discussed in this class.

Electrical Panel Inspection Safety - Critical Warnings

Do not:

• touch SEC or other wires
• insert probes/tools into panel
• remove suspect panel covers (more later)
• touch electrical equipment from unsafe location (wet, off balance, grounded, etc.)

Protect nearby observers, clients, etc. from hazards [added by DF 2/13/2006]

• Do not permit observers to touch the inspector while that person is working on or at the electrical panel.
• Do not permit observers to touch the electrical panel nor to insert any tool, pencil, or other object into the panel.
• The inspector should stand with his/her body between observers and the panel, and should be prepared to physically block an attempt by the observer to reach towards or touch the electrical panel while its cover has been removed.
• Explain, calmly and without exaggeration, but accurately, the shock and fire hazards to observers and instruct the observers on what to do if the inspector him/herself is being shocked by the panel. [Don't touch the person being shocked. If a wooden board or stake is nearby, one might attempt to push the inspector away from the panel using that device or to turn off the main breaker or fuse. Call for help immediately.

More Reading on Electrical Inspection Safety

Electrical inspectors planning to examine residential electrical panels, in addition to obtaining proper training, should read the following:

• Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Determining Electrical Service Ampacity, Dan Friedman and Alan Carson, the ASHI Tech Journal Article, Vol.2. No.1, Winter 1992 p. 14-19. (Online, and original reprints available from the American Society of Home Inspectors). Sidebars provided with this article include a table of Electric Wire Sizes provided for the article by ASHI professionals Jules Falcone and Matthew Pinto.

Electrical Vocabulary for Residential Electrical Inspectors

• Service Drop/Service Laterals (overhead/underground from street) - Insp. not required; [note clearance/tree/condition/number of wires]
• Service Entrance (masthead, service entrance conductors, meter/meter)
• Service Voltage
• Service Amperage
• Service Equipment
• Service disconnect - main overcurrent dev.
• Service box, main panel, service panel
• Grounding equipment - rod/electrode, grounding conductor
• Grounding wire: the "ground wire," normally inactive, alternative path from various devices to ground, exercised in abnormal conditions to permit fuse to blow and reduce shock hazard
• Grounded wire: neutral wire, normally carries return current, in daily use, gives flow path of current from source to earth
• Grounding electrode conductor: "the ground wire" from service equipment to ground at water pipe or electrode(s)
• Equipment grounding conductors: "ground wires" on each branch circuit throughout the house
• Grounding: connect something to earth (0 potential)
• Bonding: joining two electrical conductors so will be at same electrical potential (FYI: gas piping not used for grounding, is bonded to the grounding system)

Inspecting the Electrical Service Drop or Service Lateral bringing electrical power to a building

• Lateral - underground (mostly not visible)
  Look For: settlement, conduit damage ?
• Drop - overhead
  Look For: number of wires -2/120V, 3/240V, 4/3-phase
  Look For: drip loop - present?
  Look For: service cap - secure, facing down, present?
  Look For: service mast - secure, straight, flashed, present? Lateral - underground (mostly not visible)
  Look For: settlement, conduit damage ?

Electrical Service Drop Wire Clearances and Other Defects

Inspecting the Electrical Service Entry Wiring bringing electrical power to the electric meter

• Mast, conduit, cable: weather tight
• service cap
• roof flashing
• conduit required at roof penetrations
• conduit joints
• top and base of meter
• at wall penetration
• well connected to service entrance cable (SEC)

A study by the author (Reporting Extent and Sources of Rust and Corrosion in Electrical Panels, HOLM Conference) showed that very common sources of water leaks into and damaging electrical panels include frayed SEC, leaks at the top of the meter, and leaks at the building wall where the SEC passes from the bottom of a meter pan into the building electrical panel.

How to Determine Residential Electrical Service Ampacity

Do not rely on the ampacity printed on the main fuse or breaker, though that information is important. Examine the following:

• service drop wire size
• mast diameter
• 1-inch 60A mast
• 2-inch 200A lateral
• meter base size
• meter rating
• service box rating
• distribution panel rating
• total of all fuses or breakers in panel (the sum is NOT the service ampacity as % utilization applies)

So what determines the actual service ampacity at a building?

• Smallest link in the chain determines
• Best indication is size of SEC + id CU/AL
• IF SEC is not visible, look at service disconnect
• Specify if unable to determine, and why

A General Table of Electrical Service Ampacity vs. Service Entry Cable Sizes

More Reading:
Ampacity of an Electrical Service - Details of how to determine electrical service ampacity and voltage by visual inspection and/or safe use of test instruments.

Electrical Service Ampacity Defects

• inadequate / marginal total capacity for the modern use of the building. Some lenders require a minimum of 100A.
• Some utility companies will not replace an old 60A service (and meter) and will require that service be upgraded.
• load calculation of required service ampacity for buildings is not required during a home inspection but the inspector should be familiar with that procedure

Inspecting Electrical Service Grounding Equipment

• Required for safety, lets fuses blow
• Example: toaster falls into metal sink
• Grounding Electrode Conductor wire from service equipment to
• house plumbing (grounds the plumbing)
• Entering metal water pipe (grounds the system)
• Grounding Electrode (two now recommended)
• Continuous, no splices, meter bypass
• Copper
• Aluminum - insulated solid conductor
• Aluminum - insulated multi-strand
• Aluminum - bare vs. insulated (risk of corrosion, break in wire, loss of safe grounding)

Table of Electrical Ground Wire Sizes

Electrical Service Grounding Defects & Conditions

• not found in sub panel feeder
• attached to plastic pipe
• attached to abandoned pipe
• spliced
• loose or missing connections
• inaccessible connections
• no meter bypass
• not found in main box
• not found in sub panel feeder
• attached to plastic pipe
• attached to abandoned pipe
• spliced
• loose or missing connections
• inaccessible connections
• no water meter/water shutoff valve bypass
• neutral bonded to ground downstream of box (or upstream)
• neutral not bonded to ground at box
• main panel not bonded to ground wire
• undersized ground wire
• ground rod cut off or short
• corroded ground wire
• bare aluminum exposed to corrosion
• neutral. bonded downstream of box (or upstream)
• neutral. not bonded to ground at box
• main panel not bonded to ground wire
• undersized ground wire
• ground rod cut off or short
• corroded ground wire
• bare aluminum exposed to corrosion

Inspecting the Residential Electrical Main Disconnect Panel or "Box" for Defects

• Main control center for house
• Integrated or separate service disconnect (main breaker or fuses) - need main disconnect if more than 6 switches

Electrical Service Box Location Defects

• OK indoors our outside (if weather tight)
• NOT OK bathroom, clothes closet, kitchen cabinets
• Should Be at eye level, easily accessible, with 3 ft. working clearance

Inspecting the Electric Service Panel for Condition Defects

The Implications: electrical shock or fire

• Poor access, not secured
• Rust, corrosion
• Overheating
• Over fusing or box rating too small
• Inappropriate. mounting surface / not secure
• Damaged parts
• Poor connections, poor wiring
• Illegal taps
• Neutral wire defects
• fused, bypasses box, fused upstream
• Obsolete
• Exterior, not weather tight
• Specific Electrical Panel Product Defects, see below

SYSTEM GROUNDING - Inspecting Residential Electrical System Grounding for Defects

• This wiring is for Emergency-use only - it should never be wired so as to carry current during normal operation. (E.g. This occurs if a sub panel bonds the neutral to ground wires).
• Provides better path for current than a person, blows fuse/breaker, dissipates static, may dissipate lightning
• Example: loose black in metal box touches side; current flows through person when touched, depends on who is grounded

DISTRIBUTION PANELS - Inspecting Residential Electrical Distribution Panels for Defects

• Main and sub panels, aka "service panels, aux panels, sub panels, fuse boxes, fuse box"
• Fed from meter to main breaker/fuse or fed from separate service connect
• distributes electricity through house branch circuits and special (range etc) circuits
• each sub circuit must be protected (fuse/breaker)

PANEL COVER - Residential Electrical Panel Cover Inspection and Special Safety Hazards - Look before you touch!

• Look (and test?) before touching, open door, look again (rust, burns, gaps, unsafe stance)
• Block client from touching equipment
• May be unsafe to remove upper cover of combination panels (service main at top)
• Sheet metal screw shorts, shocks, fires
• Swing-out covers can pinch wires

CIRCUIT WIRING AMPS FUSING - Electrical branch circuit wiring amps/fusing defects - Copper electrical wiring

Match wiring gauge to ampacity:

• 14 gauge - 15Amps
• 12 gauge - 20 Amps
• 10 gauge - 30 Amps
• 8 gauge - 40 Amps
• Aluminum: 1 size larger, currently only multi-strand on single-use circuits like range /DHW/AC older solid conductor AL may be present in next gauge. (Solid conductor aluminum branch circuit wiring is unsafe, a fire hazard, and requires repair - see The Aluminum Wiring Website

PROBLEM-BRAND ELEC PANELS - Problem-Brand Electrical Panels

• Federal Pacific Electric Stab-Lok breaker panels - see The Federal Pacific FPE Stab-Lok Panel Hazards Website
• Zinsco electric panels
• Bryant electric panels
• Challenger replacement breakers/panels
• Other problem-prone panels or breakers (more research needed)

ELEC PANEL LOCATION - Electrical Panel Location Defects

• Mains: Not in: bathroom, clothes closet, kitchen cabinets, stairwells (same as service disconnect)
• Should be at eye level, easily accessible, 3 ft. clearance
• Subs: may be located almost anywhere (still some Sub panels are improper as above).
• Finding hidden sub panels: Look for feeder-breaker/fuse or wires leaving main

FUSES vs CIRCUIT BREAKERS - Relative Electrical Safety of Fuses versus Circuit Breakers

• Fuses more reliable to "blow" - not mechanical BUT easier to over-fuse (reduce with S-type retro)
• Breakers more convenient to reset can be tested without having to then replace the safety device - less likely to be over-fused (but over fusing still happens - compare wire gauge to breaker ampacity)

MAIN DISCONNECT INSPECTION - Electrical Panel Main Disconnect Inspection - Do you Pull the Main Fuse or Test the Main Breaker?

• may be necessary to get some panel covers off
• may be unsafe or may not want to shut power off to building
• ask occupant/owner before killing power
• report limitations to inspection
• re-set accidentally-tripped breakers and leave note

OTHER PANEL DEFECTS - Other Electrical Panel Defects Discoverable by Visual Inspection

• Obsolete and/or fused neutrals
• Damaged panel/components
• Loose panel
• Inappropriate support material
• Unprotected panel openings/knockouts
• Undersized panel - physical size/crowded
• Overheating - look at mains, breakers, bus, neutrals, wires
• Rust or water - look for rust, corrosion, overheating, subtle spots, suspect hidden damage to bus or breakers, look for water trace marks on entering SEC
• circuits not labeled
• panel overcrowded
• poor access to panel
• panel upside down or switches "on" in down position (obsolete)
• Panel used-with and not suitable for AL wiring

PANEL FUSING/BREAKER - Electric Panel Fusing/Breaker Defects

• Over fusing and under fusing
• double taps
• multi-wire circuits on same bus
• multi-wire circuits not linked (some experts disagree on this point. See Multiwire Branch Electrical Circuits and Split-Wired Receptacles - Electrical Wiring Safety Requirements
• too many breakers and wires for panel size
• wrong breaker type in panel
• loose/damaged breakers (broken, rust, etc)

PANEL WIRING - Electric Panel Wiring Condition Defects

• sheathing not removed
• overheating
• loose
• damaged
• not secured
• wire crosses bus bars
• abandoned wires in panel

Building,home,inspection,environmental,inspect,test,testing,investigation,home inspection,ASHI,American Society of Home Inspectors Air,C)trap Daniel Friedman,environmental inspection,environmental testing,diagnosis,repair,prevention,leak,damage, litigation,lawsuit,lawyer,legal,expert witness,testimony,forensic,engineering,fire,hygienist,industrial,

More expert information on this topic

Reference sources for this Electrical Panel Inspection Class

• * Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
• Ampacity of an Electrical Service: How to determine the electrical service size or ampacity entering a building
• Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
• Electrical Panels, How to Inspect in Buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
• Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
• Lightning Strike Risk Assessment, Protection Systems & Services
• Multi-wire branch circuit inspection and defects
• Zinsco Electrical Circuit Breaker Failures: overheating, failure to trip, burn-ups involving Zinsco and certain Sylvania electrical panel components - page under development March 2006.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
• "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
• "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
• "Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
• Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels


• Directory of Home Inspectors accessible via internet
• Electrical System & Wiring Hazard Inspection, Detection, Cause, Remedy, Prevention - Main Electrical Page

More expert information on this topic

More Information on Electrical Inspections, Building Diagnostic Inspections and Repairs

• * Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
• Ampacity of an Electrical Service: How to determine the electrical service size or ampacity entering a building
• Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
• Electrical Panels, How to Inspect in Buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
• Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
• Lightning Strike Risk Assessment, Protection Systems & Services
• Multi-wire branch circuit inspection and defects
• Zinsco Electrical Circuit Breaker Failures: overheating, failure to trip, burn-ups involving Zinsco and certain Sylvania electrical panel components - page under development March 2006.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
• "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
• "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
• "Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
• Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels


• Directory of Home Inspectors accessible via internet
• Electrical System & Wiring Hazard Inspection, Detection, Cause, Remedy, Prevention - Main Electrical Page

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