Arc welding — electrical safety and open-circuit voltage

Repair work on a steel greenhouse structure, a conveyor track, or a mobile frame is often done with a welding machine — right at the workplace, sometimes in a damp or highly conductive environment full of earthed steel. NEN-EN-IEC 60974 is the standard series that governs the electrical safety of the welding equipment itself, separate from the regular NEN 3140 inspection of the rest of the installation.

Open-circuit voltage: higher than it looks

Between welding passes, a welding machine supplies an open-circuit voltage to the welding electrode, needed to be able to strike the arc. This voltage is often above what is generally considered safe to touch. As also explained in the arc flash guide: damp or sweaty skin can reduce body resistance from several kΩ down to just a few hundred Ω — at the same voltage, a much higher current then flows through the body. A welder leaning against an earthed steel greenhouse frame with wet gloves therefore runs a real risk that would be much smaller under dry, insulated conditions.

Mandatory voltage reduction in high-risk environments

For work in confined, damp, or highly conductive spaces (for example a narrow steel greenhouse gutter, a silo, or a damp technical room full of earthed metal), NEN-EN-IEC 60974-1 imposes an additional requirement: a Voltage Reduction Device (VRD) must reduce the open-circuit voltage to below 35 V DC / 48 V AC (RMS) as soon as the arc is not burning. That is well below the open-circuit voltage of a welding machine without a VRD.

Separate inspection: NEN-EN-IEC 60974-4

Welding equipment is periodically inspected according to NEN-EN-IEC 60974-4 — a separate, more specific inspection than the regular NEN 3140 inspection of other work equipment, focused on earth connection, insulation resistance, and leakage current of the welding circuit specifically. After every repair of the welding machine, a renewed 60974-4 inspection is mandatory, regardless of the regular inspection cycle.

Common mistakes

1. Welding without a VRD in a damp or highly conductive space — a continuous steel greenhouse structure with a lot of earthed metal and often high humidity is precisely the type of environment the VRD requirement is meant for.
2. Considering a regular NEN 3140 inspection sticker on the welding machine sufficient — the specific welding standard NEN-EN-IEC 60974-4 tests different, welding-circuit-specific risks than the generic NEN 3140 inspection of other work equipment.
3. Continuing to work after repairing the welding machine without a renewed 60974-4 inspection — a repair can change the electrical safety of the machine, regardless of the remaining validity of the previous inspection.

Related

• Arc flash — risk, energy, and protection
• PPE overview
• RIE work equipment