InspectAPedia ^TM

What are the Limiting Factors That Determine the Electrical Capacity or Size at a Building? ElectricAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• What are the Limiting Factors That Determine the Electrical Capacity or Size at a Building? Answers simplify the process of determining the actual electrical service capacity provided to a building
• How to determine the size, capacity, or ampacity of electrical service at a building

This article explains the Limiting Factors That Determine the Electrical Capacity or Size at a Building? Visual inspection and use of digital multimeters(DMMs), Volt-ohm meters (VOMs), neon testers, and electrical inspection safety are discussed. Photographs and sketches illustrate electrical panels, meter bases, and electric meters. One of the most frequently asked questions at ASHI Education Seminars and Conferences is "How do I determine the service amperage?"

It's not as difficult as one may think to get a reasonable handle on the electrical service capacity at a building without sophisticated analysis. But there are some pitfalls, and the process itself is dangerous. The articles from which much of this online material originated appeared first in the ASHI Technical Journal, Vol. 2. No. 1, January 1992, "Determining Service Ampacity," Dan Friedman and Alan Carson, and the ASHI Technical Journal, Vol. 3. No. 1, Spring, 1993, "Determining Service Ampacity - Another Consideration," Robert L. Klewitz, P.E., with subsequent updates and additions to the original text ongoing to 2/19/2006. Reprints of the originals and reprints of the Journal are available from ASHI, the American Society of Home Inspectors www.ashi.com

AMPACITY - the LIMITING FACTOR - Summary: What is the limiting factor that determines the actual electrical service ampacity at a building?

Remember you're looking for the limiting factor in determining ampacity. Finding the electrical component in this list which has the smallest capacity means that you have found the "weak link in the chain" of components bringing electrical service to the building. Particularly when inspecting older properties, where there is the chance that someone has upgraded some but not all of the components in this list, there may be an inconsistency such as the installation of a larger electrical panel without upgrading the main disconnect.

1. Electrical service entry cable or "SEC" size and amperage rating (we do not generally consider the overhead or service lateral wiring)
2. Electric meter (questionable but may assist, especially if the item's generation, age, and obselesence can be determined)
3. Electric meter base (questionable but may assist, especially if the item's generation, age, and obselesence can be determined)
4. Main electrical power switch fuse/circuit breaker ampacity
5. Electrical panel rated ampacity (and bus design may support only 120V)

Use links at the left of each page or the links given just below to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Technical Reviewers

• The Original Authors: Alan Carson is an ASHI Member, national home inspection educator, author and building failures researcher in Toronto, Ontario. Daniel Friedman, an original author of this article and the editor and producer of InspectAPedia where this article now appears is an ASHI Member, first ASHI Technical Committee chairman, editor and publisher of the ASHI Technical Journal, licensed home inspector, educator, and building failures researcher in Poughkeepsie, NY. Robert Klewitz is a licensed professional engineer, a professional home inspector, an ASHI Member, and has served on the ASHI Technical Committee as well as in other ASHI activities. His practice is in Issaquah, WA.
• Daniel Friedman - InspectAPedia.com ^TM Website Author/Editor
• Douglas Hansen, Robert Stead. Mark Cramer. Photographs: Daniel Friedman.
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
• N. Srinivasan, MSEE, is a senior member of IEEE with 30 years experience in the electrical industry. Mr. Srinivasan is in Vienna VA.
• Louis P. Babin generously contributed technical editing about the effects of doubling ampacity in an electrical circuit (September 2007)

Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

More expert information on Inspecting Electrical Equipment and Electrical Safety for Inspectors

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

InspectAPedia ^TM Home & Site Map - Building Inspection, Diagnosis, & Repair, Environmental Inspection & Testing - Research Website

Home Inspection Construction Consulting Services & advice for home buyers

Contact Daniel Friedman for website content suggestions or for fee-paid consulting

	Enter your search termsSubmit search form
	Search This Website - InspectAPedia.com