Phase Testers

A phase tester (phase comparator) checks whether two power sources, or the two ends of a line, are in phase and whether the phase sequence is correct. In tasks such as paralleling two sources, closing operations in ring networks, commissioning after a new cable joint, or generator and transformer connections, mismatched phases can cause short circuits, equipment damage and injuries. Phase checking is therefore a routine step in commissioning for DSO operations crews, maintenance departments of industrial sites and electrical contractors.

How to choose the right model

• Network voltage: For low-voltage panels and distribution installations, the HPL-200W (AC 70 V – 1 kV) is used. For medium voltage, the HPI-S20W (AC 22 – 42 kV) or the HPR is considered.
• Link between the detectors: At medium voltage, the two measuring points are checked with separate detectors. In the HPI-S20W the detector pair is isolated by a fibre-optic link; the HPR is a wireless pair. The layout of the measuring points and whether you want to carry a connecting element on site influence the choice.
• Function required: The HPL-200W checks same phase and different phase with a single device. The HPR offers voltage detection with one detector and phase and phase-sequence checking with two.
• Confirmation of the voltage range: Send us your network's nominal voltage and the place of use (cubicle, overhead line, cable termination); for the HPR in particular, we confirm the operating range against your network at the quotation stage.

Model	Subcategory	Operating voltage	Key feature
HPL-200W	Low-Voltage Phase Testers	AC 70 V – 1 kV (three-phase)	Same phase / different phase check with a single device
HPI-S20W	Medium / High-Voltage Phase Testers	AC 22 kV – 42 kV	Detector pair isolated by a fibre-optic link
HPR	Medium / High-Voltage Phase Testers	Confirmed against your network	Wireless pair; voltage detection with a single detector

Safe use

• Phase checking is carried out on a live system; use personal protective equipment suited to the voltage class and observe approach distances.
• Use the device only within its defined operating range; do not rely on a result obtained on a network outside that range.
• Check that the device and detectors work before measuring; record the results in the commissioning records.
• Phase checking does not replace the pre-work check for absence of voltage; use a voltage detector suited to the voltage class for that.

For step-by-step application, read our article What Is a Phase Tester and How Is It Used?.

Frequently Asked Questions

What is the difference between a phase coincidence check and a phase sequence check?

A phase coincidence check shows whether the conductors at two points belong to the same phase. A phase sequence check verifies the rotation order of the three phases; both matter for the direction of rotation of motors and for paralleling sources.

Can a single phase tester be used for both low and medium voltage?

In the range, these two levels are covered by separate devices: the HPL-200W for low voltage (AC 70 V – 1 kV), and the HPI-S20W and HPR for medium voltage. Teams working at both levels need to carry both devices.