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About phase auditors
When working on low-voltage systems, there must be no voltage to protect employees. Measuring technology is used to check this status. The phase tester is a tool for the initial assessment of zero voltage. Our guide will show you the possibilities and limitations of this voltage tester.
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What was a phase tester?
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Construction of a phase tester
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How does the test process work?
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What was to be observed when using phase checkers?
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What defects can occur on phase checkers?
What was a phase tester?
A phase tester is a purely qualitative measuring device as a single-pole voltage tester. It is used to determine whether an electrical cable in the grounded low-voltage power supply system is live against the ground potential. It allows the measurement result to be "Yes" for "Voltage is present" or "No" for "No voltage in conductor". No statement is possible about the value of the voltage.
The voltage range in which these simple devices operate is between approximately 150 to 250 volts at a power frequency of up to approximately 500 hertz. Some models are already starting from 100 Volt alternating voltage. Phase testers are used as test aids for quickly determining the current voltage supply of the normally live external conductor of an electrical system. It is also used to locate this L-conductor – "the phase" – in an electrical installation.
Construction of a phase tester
The shape of a screwdriver has become established for phase testers. The models available in our online shop are equipped with blades for slotted screws in blade widths of three millimeters. The housing is so insulated that only the tip with the blade and the finger button at the back remain conductive. The blade shaft is insulated and only releases the tip for guiding to the measuring parts. In the housing, a series resistor with a value of approx. 1 megohm follows the end of the shaft of the metallic blade and a glow lamp, which is often screwed in with a spring element for a secure hold in the housing. On the top is the finger button for touching the sides of the user.
The version as a screwdriver is suitable for moving slotted screws. The housings are not designed for large forces. However, spring or luster terminals can be easily operated.
A clip similar to a pen ensures that the phase tester does not accidentally fall out of shirt or jacket pockets.
How does the test process work?
The tip of the phase tester screwdriver is held against a (presumably) live conductor. The testing person holds a finger on the back button of the phase tester and thus "connects" it to the earth via the body contact. If a voltage is applied to the conductor to be tested, a very low, non-hazardous current flows through the device to earth, limited by the series resistor, in the range of less than 1 milliamp, which was the cause of the glow lamp to light up. In this case, the tested conductor carries voltage. If, on the other hand, the tip of the phase tester is touched with the neutral conductor or the protective conductor, the glow lamp does not light up, as the potential of these cables corresponds to the environmental potential. They are therefore voltage-free from the perspective of the phase tester.
What was to be observed when using phase checkers?
The design of the single-pole voltage tester has not changed for decades. The economical device is standardized according to DIN VDE 0680-6 with edition of April 1977. The current state of the standards for electrical installations in industry no longer permits the use of the phase tester to determine the absence of voltage of an electrical system. The reliability of a voltage tester's statement is not 100% reliable. For example, when wearing insulating footwear or working on insulating floor coverings, the device cannot respond and the tested cable can still carry tension. This can be remedied by touching a heating pipe or something similar.
It should also be noted that the luminous intensity of the glow lamp in the phase tester does not make any statement about the actual voltage level. On the other hand, it can occur that the glow lamp of the phase tester does not light up in the case of non-grounded AC voltage networks despite the presence of a high voltage, as there is no potential difference. This can be the case, for example, with small, autonomous IT systems. And the reverse can also occur: An unconnected cable indicates the occurrence of voltage. This can be done, among other things, by scattering other live conductors that run parallel to the actually current-free one.
Moreover, the glow of the built-in glow lamp in the voltage tester can be difficult to detect in very bright ambient light. As no doubt-free statement about the absence of voltage of a conductor is possible, the term "lie pin" has not only become the term "phase tester" among electricians.
What defects can occur on phase checkers?
The most impact-resistant housings can burst due to improper application of force when screwing. A defective series resistor or a broken glow lamp also render the measuring instrument inoperative. With many phase checkers, the housing can be opened for changing these two components on the screw cap.
Practical advice
A phase tester is only a good idea to get a "first impression", but not in any way to make a reliable statement about the absence of voltage in an electrical installation. For example, a first impression can answer the question whether a device that does not work actually receives voltage at the supplying socket or has addressed the safety of the domestic installation. According to standard VDE 0682, Part 401, a two-pole voltage tester is the only permissible test instrument for the statement of the absence of voltage and meets the requirements of the Occupational Safety Act.