Non-contact voltage tester

How it works

The tip contains an antenna and sensing circuit. Held near an energized ac conductor, the tip senses the electric field around it, and the circuit lights an indicator at the tip and, if enabled, sounds a buzzer. Fluke’s 2005 announcement describes testing by touching the tip to a terminal strip, outlet or cord, with no need to touch a bare conductor. A 1999 patent describes such testers as typically pen-like, pocket-held and battery operated.

Because the tester responds to a field and not to a measured current, anything that weakens the field can silence it. Fluke’s instruction sheet lists shielded cable, the thickness and type of insulation, distance from the voltage source, a user who is fully isolated from ground, recessed receptacles and the condition of the tester and its batteries.

Anatomy

Tip: The sensing end, which glows when the tester detects a field; the instruction sheet tells the user to examine it for cracks or breakage.
Tactile barrier: A ridge between the grip and the tip; Fluke tells the user to hold the product behind it.
Body and battery compartment: Holds the batteries; the 1AC II takes two AAA cells.
Power button and self-test indicator: The 1AC II is switched on with a button and its VoltBeat indicator flashes to show it is working; the 1999 Applied Power patent describes a switch clip that serves both as pocket clip and as the actuator for its self-test.
Indicator and buzzer: A light at the tip and an optional audible signal.

Variants

Pen-style detector: The common form, powered on by a button and held in the hand; Fluke’s 1AC II is an example.
Low-voltage model: Fluke’s instruction sheet lists a model for 20 V to 90 V ac (LAC) in North America, for control circuits.
Regional ranges: Fluke lists detection ranges of 90 V to 1000 V ac for North America, South America and Asia, and 200 V to 1000 V ac for Europe.
Detector built into a meter: Fluke says its FieldSense technology has been included in electrical testers and clamp meters so that voltage and current can be measured without touching a live wire.

Specifications

Voltage detection range · V ac: 90 to 1000Fluke 1AC II models A1 and A2; other models differ by region (see variants).
Measurement category rating · CAT and volts: CAT IV 1000 VMarked on the Fluke 1AC II under IEC 61010-2-030; the rating is a property of the product, not a statement that it can prove absence of voltage.
Operating temperature · degrees C: -10 to 50Fluke 1AC II.
Auto power off · minutes: about 5Fluke 1AC II.

Made to

IEC 61010-1
IEC 61010-2-030

Safety and care

Safety

The manufacturer’s sheet says not to rely on the tester to detect the presence or absence of voltage for safety purposes. It states that a single-pole non-contact detector is not suitable for determining whether a circuit is hazardous, and that a voltmeter or two-pole voltage detector is necessary to confirm the absence of hazardous voltage before work begins.
If the tip does not glow, voltage could still be present; the field may be too weak for the tester to sense it, for the reasons the sheet lists.
Hold the tester behind the tactile barrier, do not use it around explosive gas or vapor or in damp or wet places, and use caution above 30 V ac.
Do not use the tester if the indicator is not flashing, if the tester appears damaged, or if the tip is cracked.
Wear personal protective equipment, including approved rubber gloves, face protection and flame-resistant clothing, where hazardous live conductors are exposed.
Fluke recalled the 1AC-I VoltAlert, first sold on 29 September 2009, because the testers could fail to give an indication of live voltage and the operator could falsely believe the power was off.

Care

Replace alkaline batteries with fresh batteries of the same manufacturer and type, and remove them if the tester will be stored for a long period or above 50 degrees C, to prevent leakage.
Clean with a damp cloth.

Tips

Treat the self-test flash as the working signal
Fluke’s VoltAlert instruction sheet tells the user not to use the tester if its VoltBeat self-test indicator is not flashing.1
Prove the tester on a known live source before and after
The instruction sheet directs the user to test on a known live source within the product’s rated ac voltage range both before and after use. A tester that does not respond to the known source is not working, whatever it showed at the circuit in question.1
Treat a glow as a prompt to measure with a meter
Fluke explains that energized wiring next to unused wiring, as in the same conduit, can couple a voltage onto the unused conductor, and recommends the low-impedance input of a multimeter to tell such ghost voltage from real voltage.1

History

Earliest documented

filed 13 November 1972 (division of an application of 3 May 1968)

United States

The earliest source located for sensing an ac field without contact is US Patent 3,826,981 of Hugh C. Ross, whose abstract describes a high-input-impedance meter that may be used with a proximity probe for direct sensing of ac fields. A pocket-sized contact voltage tester with a glow lamp was patented earlier by David N. Lauder (filed 1947, issued 1952). Neither is the pen-style non-contact detector in its present form; the earliest patent located for that form is US Patent 5,103,165 of 1992.1 2 3

The non-contact tester grew out of the pocket test lamp. Lauder’s patent, filed in 1947 and issued in 1952, combines a voltage tester and a continuity tester in a case the size of a pencil or fountain pen, carried in a vest pocket. It still required two test prods on the conductors, so the user touched the circuit.

The sensing method came from instrument work. Ross’s patent, filed in 1972, concerns a high-impedance solid-state meter and mentions a proximity probe that senses ac fields directly. The pen form reached the patent record later: Strattz’s 1990 application describes a hand-held probe with an antenna, a battery and a light-emitting diode in the tip, built with an all-plastic casing and clip so that no part of the tool is conductive. His patent states that probes used around live naked wires, such as those in junction boxes, were known.

By 1999 the form was settled enough that the Applied Power patent calls it well known, pen-like and battery operated, and adds a self-test that gives one blink and beep when the user actuates the clip switch. Self-test also appears in Fluke’s own product line: its 2005 announcement for the 1AC-II names VoltBeat continuous self-test and a CAT IV 1000 V rating, and the later instruction sheet makes a flashing VoltBeat a condition of use.

The tool’s limits are now part of its documentation. Fluke recalled the 1AC-I in cooperation with the US Consumer Product Safety Commission because it could fail to indicate live voltage, and offered a 1AC-II or LVD2 as replacement. The current instruction sheet states that a single-pole non-contact detector is not suitable for determining whether a circuit is hazardous. Separately, OSHA 29 CFR 1910.333 requires a qualified person to use test equipment to verify that circuit parts are deenergized and to test for induced voltage and backfeed. O*NET’s Tools Used table lists non-contact voltage detectors for 2 of the 9 occupations mapped to this tool in the archive’s crosswalk, in a commodity class that also includes voltmeters and test lamps.

Timeline

1947
David N. Lauder files the application for a pocket-sized penlite voltage and continuity tester, issued as US Patent 2,616,952 in 1952; it tests by contact, with test prods, and signals with lamps.1
1968
Hugh C. Ross files the parent application (3 May) of the patent later issued as US 3,826,981.1
1972
Ross files the divisional application (13 November) that issues in 1974 as US Patent 3,826,981, covering a solid-state high-impedance meter system usable with a proximity probe for direct sensing of ac fields.1
1990
James M. Strattz of Raleigh, North Carolina, assignor to Static Control Components, files (19 November) for an insulated hand-held non-contacting voltage detection probe with an antenna and a light-emitting diode that glows in the probe tip.1
1992
Strattz’s patent issues on 7 April as US Patent 5,103,165.1
1999
US Patent 5,877,618 (Luebke et al., Applied Power) issues on 2 March for a non-contact voltage tester with a self-test feature, stating that hand-held non-contact testers are well known.1
2005
Fluke introduces the 1AC-II and 1LAC-II VoltAlert detectors with VoltBeat continuous self-test and CAT IV 1000 V rating.1
2009
Fluke first releases the 1AC-I VoltAlert on 29 September; it is later recalled in cooperation with the US Consumer Product Safety Commission.1

Gaps in the record (5)

The first non-contact voltage detector, its inventor and its date have not been identified; no patent located describes the pen-style detector before 1990.
The year Fluke first sold a VoltAlert (the original model before the 1AC-II) has not been sourced.
The date of the 1AC-I recall is not stated on Fluke’s notice and has not been sourced.
The 1990 Strattz patent and the 1999 Applied Power patent are the earliest pen-style non-contact patents found, not necessarily the earliest in existence.
No independent test data on sensitivity or failure rates has been located, so no quality judgment is made.