How to Inspect Residential Electrical Panels - Part 7
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How to inspect electrical panels - the main panel
Inspecting the electrical distribution panel
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This article summarizes inspection of the building electrical panel, main panel, or electrical distribution and sub panels. This document discusses procedures for safe and effective visual inspection of residential electrical systems including electrical panels and other components, when the inspection is conducted by trained building
inspection professionals, home inspectors, electrical inspectors, and electricians. It was presented by
Daniel Friedman - InspectApedia.com, at the Hudson Valley chapter of the American Society of Home Inspectors -
HVASHI Seminar 12 Sept 2002, Updated April 2006, April 2009.
Match wiring gauge to ampacity - the following describe copper wire sized or gauges and the matching circuit ampacity or overcurrent protection that is required to be provided by fuse or circuit breaker:
14 gauge - 15Amps
12 gauge - 20 Amps
10 gauge - 30 Amps
8 gauge - 40 Amps
Exceptions to these wire sizes and fusing occur for special circumstances such as air conditioners whose motors produce a brief current surge during startup.
Aluminum electrical branch circuit wiring size guide: for a circuit of the same amperage, an aluminum solid conductor branch circuit wire must be 1 size larger than copper. Currently (since the 1970's) aluminum electrical wiring is used only in the form of 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
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 ELECTRICAL 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)
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
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.
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.
"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.
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