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LOAD TESTERS

When electronics technicians and engineers troubleshoot electronic components and systems, they test the boards and components under load because by testing under load, the quality of the components and the characteristics of the system are revealed. A similar reasoning demands that electricians and technicians test the power source under load.

Until recently, routine load tests have been impractical because they were time consuming, required a couple of devices and instruments, interrupted the circuits use and on deficient circuits, could be unsafe to perform. However, easy-to-use, safe and cost-effective plug-in testers that perform a series of basic tests under a 15 ampere load are now available. In little more time than it takes an electrician to test whether a circuit is live, the load tester is plugged into a receptacle which places a full load on the circuit for a fraction of a second. The microprocessor system measures the line voltage under no load and then under a 15 ampere load and calculates the impedance of the total circuit and displays it as a % voltage drop. The impedance (resistance) of the entire circuit includes the receptacle, the building wiring, the panel box, the meter - all the way to the transformer on the utility pole. If there is a high resistance in any connection in that circuit due to a bad splice or loose connection, or because of a damaged conductor, its condition will be revealed in this test.

Excess voltage drop may also indicate undersized wires. Excess voltage drop decreases the efficiency of some devices and the reduced voltage can possibly cause damage to the equipment. In addition to wasting energy, the generation of heat in the fixed wiring can be a fire hazard if the cause of the excess voltage drop is a point source such as a loose connection or bad splice - and is in contact with a combustible material.

Based on NFPA data, surveys(1) and investigations(2) during the period 1988-1993, more than 600,000 fires occurred every year in residential and non-residential buildings. As many as 25,000 of those fires were caused every year by high resistance connections in electrical distribution systems - in the form of poor connections, bad splices, and damaged conductors. The high resistance conditions that caused these fires could have been identified as hazards with a load test. The load test reveals high resistance connections and splices in branch circuits that otherwise would go undetected because they are hidden - in the receptacle, wall or panel box

The NEC recommends (as a footnote) that the impedance (resistance) of a branch circuit be no more than that which causes a 5% voltage drop in a circuit for reasonable efficiency.

It is suprising that the concept of voltage drop is not more readily understood as the impedance of the circuit. Testing wiring circuits under full load is taught at the OSHA Technical Institute, by the International Association of Electrical Inspectors, the Instrument Society of America, National Technology Transfer, and several universities who teach the use of the load test in courses on electrical safety and proper grounding.

After using this test for eight months, Stephen Scully of the National Assoc. of Home Builders Research Center stated "Because the SureTest is able to quickly and safely apply a full load test to the circuit, we can test all circuits in a house for hidden, sometimes deadly, flaws within minutes".

Based on the availability and ease of use of this test, the Consumer Product Safety Commission recommended inclusion of the 15 ampere load test in NFPA 73, the inspection procedure for one and two-family dwellings.

The Philadelphia Housing Development Corp requires contractors to perform the voltage drop-under-load test prior to installing blown insulation in existing homes(3). If the voltage drop is 10 % or higher (they found that 70% of the older homes failed the NEC's 5% criteria), the contractor must replace/repair the circuit prior to proceeding with the

insulation. Prior to instituting the test, half a dozen smoldering fires resulted from the blown insulation installations. In the 2,500 homes insulated during a two-year period after this electrical integrity test was instituted, there were no fires reported. Lou Porcella of the PHDC stated "The SureTest is the electricians friend. There was a lot of electrical work done as a result of this testing - that otherwise would have been neglected". As of this date, at least 15 municipalities have followed the PHDC's lead in requiring the load test as part of their weatherization programs.

In addition to standard tests of correct wiring and polarity, testing under load will reveal false grounds (the illegal connection of ground-to-neutral at the outlet), bad splices, loose power and ground connections, undersize wire (overlong circuits) and damaged conductors. Since the entire circuit is tested back to the power source at the utility pole transformer, high resistance circuit breakers, meter connections, and transformer connections will also be made evident.

During 1995-1996, Industrial Commercial Electronics, Inc. in Buffalo, NY conducted an evaluation program of the load tester they manufacture. SureTest circuit analyzers were sent to electrical inspectors in 250 municipalities throughout the U.S. for a 30-60 day evaluation, resulting in an overwhelming acceptance of the load test. More than 90% of the inspectors who evaluated the hand-held load testers, purchased them after the evaluation period, and indicated their intention to integrate the load test into their inspection procedures.

As a troubleshooting tool, the load test can save hours of time trying to locate the source of a problem. Load testing can identify deficiencies in a buildings wiring system that static non-load testers cannot. Simple to use, the load tester identifies branch wiring deficiencies and isolates hazards as the electrician moves along the branch circuit. Like a divining rod dowses for water, the load tester "points" to wiring deficiencies and receptacle hazards.

Testing ground impedance under load is also important. Static non-load "ground testers" may indicate that a ground continuity exists, but only a load test will measure the quality of the ground. Loose ground connections or other causes of inadequate grounding can be serious shock hazards because of inadequate fault current paths. An inadequate ground may render useless the protection of expensive equipment by devices that rely on a good ground. These testers measure ground impedance in ohms, and also measure the exact trip point of a GFCI (in mA), independent of line voltage variations.

A routine medical examination by a doctor or nurse will always include the patients temperature and pulse. It would be unprofessional to omit these easy and basic tests because they quickly reveal abnormal conditions.

To an electronics technician/engineer or electrician, the load test confirms the availability, quality and safety of power supplied to the electronics device or appliance. This simple load test quickly reveals abnormal (often hazardous) conditions in a circuit.

Because of the safety ramifications of loose connections, bad splices, false grounds, inadequate grounding, and damaged conductors, in the authors opinion, it would be unprofessional to fail to use this basic test in all electrical repair and installation work.

FOOTNOTES

(1) 1989-1993 NFIRS and NFPA Survey

(2) Smith, Linda & McCoskrie, Dennis "What Causes Wiring Fires in Residences" Fire Journal Jan/Feb 1990: 19-24, 69

(3) Kinney, Larry "Assessing the Integrity of Electrical Wiring" Home Energy Sept/Oct 1995: 5,6

This article was written by Kenyon Riches and is brought to you compliments of IDEAL INDUSTRIES