Electrical Service Entry Wire Inspection & Service Ampacity: How to Inspect

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
References

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Electrical service entry wiring, service entry cabling (SEC), & the electrical meter: how to inspect for & report service ampacity, service entry defects & hazards. Carson Dunlop's sketch at page top shows where the electrical inspection starts at a residential property.

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

This article series 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.

Readers of this article should also be sure to review Safety Hazards and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems and should pay special attention to the following chapters from that article: Electrical Panel Interior Inspection - Removing Electric Panel Covers - Electrical Panel Cover Screws - Electrical Panel Interior Hazards - Testing Main Breakers or Fuses and Inspect Breakers, Fuses.

Our photo (left) illustrates an unstable and improper passage of electrical service wiring over the roof of a private home. In this case the house was being used to support electrical wiring that was in turn bringing power to a separate home located nearby.

Examples of electrical service defects that can be spotted outdoors at the electrical service entry

Mast, conduit, cable: weather tightness
Service cap, installed, sealed, properly positioned to keep water out of the SEC wiring
Roof flashing errors at standards or masts
Electrical conduit is required at roof penetrations made by the SEC
Electrical conduit joints outdoors must be weather tight - note the damaged electrical conduit, open connections, incomplete conduit, wiring exposed to weather and water at our mobile home electrical inspection photo shown at left.
Top and base of meter must be weather tight, secured,
Leaks at the SEC to building wall penetration
Well connected to service entrance cable (SEC)
Frayed SEC cables expose inner wiring to damage or deterioration and are a source of water entry in the electrical meter box as well as into electrical panels if the panel is located lower than the SEC
Abandoned SEC cables may not have been properly disconnected - electrocution hazard
Readers of this section should also see ELECTRIC METERS & METER BASES for details of additional unsafe electrical service conditions that can be spotted from outside the building.

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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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
"Frequency of Occurrence and Sources of Rust and Corrosion in Electrical Panels," Daniel Friedman, IEEE HOLM Conference, Philadelphia PA, 1992 - see ELECTRIC PANEL RUST for an online version of this article.
Jim Simmons: Personal communication, J. Simmons to Daniel Friedman, 9/19/2008. Photographs contributed to this website by Jim P. Simmons, Licensed Electrician, 360-705-4225 Mr. Electric, Licensed Master Electrician, Olympia, Washington Contact Jim P. Simmons, Licensed Master Electrician, Mr. Electric, 1320 Dayton Street SE
Olympia, WA 98501, Ph 360-705-4225, Fx 360-705-0130 mrelectricwa@gmail.com
Kenneth Kruger: Original author of the sidebar on testing VOM DMM condition: Kenneth Kruger, R.A., P.E. AIA ASCE, is an ASHI Member and ASHI Director in Cambridge, MA. He provided basis for this article penned by DJ Friedman.
"How to Use DMM's Safely," Leonard Ogden, CEE News, 888 Seventh Ave., New York, NY 10106, Dec 1990 p.10.
Dr. Jess Aronstein, consulting engineer, Poughkeepsie NY, 1991 protune@aol.com
Rex Cauldwell, master electrician and contributor to the Journal of Light Construction on electrical topics
New York State Central Hudson Gas and Electric Company, G&E/1-2/85 consumer safety pamphlet
American Society of Home Inspectors, ASHI Training Manual, Al Alk -[obsolete, and includes unsafe practices-DF]

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.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

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)
Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels
"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.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"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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