Fixed voltage indicating systems (VIS) on medium-voltage switchgear

The guide on the two-pole voltage tester (duspol) covers why step 3 of the five safety rules (verifying absence of voltage) requires a specifically EN 61243-3-approved instrument, tested before and after the measurement — and why a non-contact tester is unsuitable for that purpose. This article covers a different instrument that appears in the same context but has a different function: the fixed voltage indicating system (VIS) on medium-voltage switchgear.

What a VIS is

A VIS is a system permanently mounted on the switchgear that continuously indicates, without a technician needing to connect a separate test instrument, whether voltage is present on a part of the installation — typically with a simple light indication (for example a three-state indication: half, full, or a drawn flash arrow). The system is capacitively coupled to the live part via a dedicated coupling connection that the switchgear manufacturer supplies as standard.

IEC 61243-5: scope

IEC 61243-5 ("Voltage detecting systems — Part 5: Voltage detecting systems (VDS)") applies to single-pole, capacitively coupled voltage detecting systems for medium-voltage networks from 1 kV up to and including 52 kV, at mains frequencies from 16⅔ Hz to 60 Hz — this is explicitly a medium-voltage application, not the low-voltage environment in which the duspol of step 3 of the five safety rules is used. The principle relies on a capacitive coupling whose current is proportional to the voltage present; the standard links an indication current above a fixed threshold (on the order of a few microamperes) to the "voltage present" indication.

Note: since 2021, the first edition of IEC 61243-5 (1997) has been merged with IEC 62271-206 into the new standard IEC 62271-213 ("Voltage detecting and indicating system"), specifically for systems integrated into the switchgear itself. The term "VDS/VIS to IEC 61243-5" is still widely used in practice, but for new-build switchgear IEC 62271-213 is the current reference.

Why this is not a replacement for step 3 of the five safety rules

A VIS provides a continuous, passive indication that a technician can consult before carrying out an action — but it is not a portable voltage tester, tested before and after the measurement itself, like the duspol required for step 3 of the five safety rules. The reason is fundamental: a VIS indication cannot be verified on the spot, immediately before contact, for its own correct functioning in the way a duspol is tested before and after the measurement on a known live point (see the duspol guide for that procedure). A VIS is therefore an additional aid — for example to quickly see remotely or from a control panel whether a feeder is still live — and not a replacement for the formal verification of absence of voltage that the five safety rules prescribe immediately before a contact or earthing action.

Practical relevance

When working on medium-voltage switchgear fitted with a VIS, it must be clear that the VIS indication is a useful, permanently available aid for a quick status check, but that the actual verification of absence of voltage immediately before a contact or earthing action must still be carried out with the instrument prescribed for that voltage and that work, tested on the spot — not solely on the basis of the VIS indication.

Common mistakes

Treating a VIS indication ("no voltage") as sufficient verification of absence of voltage for carrying out an action — the VIS does not replace the on-the-spot, before-and-after tested measurement.
Confusing IEC 61243-5 with EN 61243-3 — the former concerns a fixed, capacitively coupled medium-voltage system; the latter concerns the portable two-pole low-voltage tester (duspol) for step 3 of the five safety rules.
Not knowing that IEC 61243-5 has been merged, for new switchgear, with IEC 62271-206 into IEC 62271-213 — for new-build that is the current standard, even though the old designation still circulates widely in practice.
Applying a VIS to low-voltage equipment — the scope of IEC 61243-5/IEC 62271-213 is explicitly 1 kV up to and including 52 kV.