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Electrical Service Entry Cable Visual Inspection Can Determine Voltage Range InspectAPedia®  -     How to inspect the electrical service entry cables at a building How to determine the size, capacity, or ampacity of electrical service at a building

This article explains how to estimate the electrical service size, (or "electrical power" or "service amps") at a building by visual examination of the service entry cables, electric meter and meter base, electrical service panel, main switch, and other details. 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

VOLTAGE at the SEC - How to figure out Electrical Service Voltage by visual examination at the service entry

Visual examination of overhead electrical wires at the service entry. This procedure pertains to overhead wires, not underground conduit. Examination is made at the point of connection of the service drop to the service conductors.

In lay terms, the service conductors are also called the service entry cable or SEC. Underground wiring up to the building is called a service lateral. A 240V electrical service [three-wire figure at left] will include three wires connected to the building - the two 120V "hot" legs which together provide 240V, and a third grounded conductor.

A 120V service [second, two wire figure at left] will have only two wires, a 120V power line and a grounded line or neutral.

However simple visual examination from the ground is not a certain proof of voltage available in the building. In a few unusual circumstances, all three wires may be present but one of them may be disconnected at the utility pole or masthead. Such "mistakes" occur during temporary hookups in new construction or renovation.

Could there be 240V service to a building with only two wires? Yes but not normally in the U.S. Some Canadian rural properties served by long private wires may have only two overhead conductors on a 240 volt service. For these systems ground connections are made only at the building, not back to the utility company's lines. In the U.S. this would be unusual but be alert for it, especially at rural properties.

Notes to Table:
1. This could also be a delta 3-phase with 3 120V legs; 3 phase power not common at residential properties.
2. 208 Volt service may be present on 3rd red wire.

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• 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.
• Douglas Hansen, Robert Stead. Mark Cramer. Photographs: Daniel Friedman.
• 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)

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