Electrical Service Entry Wire Inspection & Service Ampacity: How to Inspect InspectAPedia® -
How to inspect the electrical service entry wiring for components that limit the electrical service ampacity available to the building - a 200 Amp main panel does not itself assure that 200A is available.
How to determine electrical service ampacity - how much electrical power do we have at a building?
Electric meter defects that can be determined by visual inspection
Questions & answers about electrical service ampacity determination for buildings
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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.
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
Readers of this section should see AMPS & VOLTS DETERMINATION for a detailed article on how to determine the amps and volts of a building's electrical service.
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
AMPS
Copper
Aluminum
30
10*
8*
60
6*
6*
70
6*
4*
100
4
2
125
2
1/0
150
1/0
2/0
200
2/0
4/0
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
Electric Meter Defects
Loose electric meter - watch for attachment screws falling inside, shorting, causing a fire (Arnold Rd. Pok)
Water Leaks into electric meter top from frayed SEC or defective seal at meter top
Water leaks from electric meter pan into service conductors into main electrical panel - see RUST in ELECTRICAL PANELS
Obsolete electric meters - change out required by utility company in some circumstances
Electric meter rated only for copper wire connected to aluminum SEC
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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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