Resistance Welding Installation Requirements

As with arc welding and cutting equipment, all resistance welding equipment must be installed by a qualified electrician in conformance with Subpart S of CFR 29 1910. There must be a safety-type disconnecting switch, circuit breaker, or circuit interrupter to open each power circuit to the machine; this switch must be near the machine and readily accessible, so that the power can be shut off when the machine or its controls require maintenance. Ignitron tubes (a type of gas-filled tube used as a controlled rectifier) used in resistance welding equipment must have a thermal protection switch.

When there is a possibility of an operator's fingers being placed under the point of operation during hot work, the equipment must be effectively guarded using a device such as an electronic eye safety circuit, two hand controls, or protection similar to that prescribed for punch press operation in 29 CFR 1910.217, Mechanical Power Presses. All chains, gears, operating bus linkage, and belts must be protected by adequate guards in accordance with 29 CFR 1910.219, Mechanical and Machine Guarding. Two or more safety emergency stop buttons must be provided on all special multispot welding machines, including 2-post and 4-post weld presses.

Whenever feasible, the hazard of flying sparks must be eliminated by installing a shield guard made of safety glass or a suitable fire-resistant plastic at the point of operation. Additional shields or curtains must be installed as necessary to protect any passing and nearby persons from flying sparks. Foot switches must be guarded as well to prevent accidental start-up of the machine.

On large machines, four safety pins with plugs and receptacles must be installed at each corner of the machine so that when a safety pin is removed and inserted in the ram or platen, the press becomes locked out from operation.

If it is practical, the secondary, or welding circuit, of all welding transformers used in multispot, projection, and seam resistance welding machines must be grounded. This may be accomplished by permanently grounding one side of the welding secondary current circuit. Where it is impractical, a center tapped grounding reactor connected across the secondary or the use of a safety disconnect switch along with the welding control are acceptable alternates. The safety disconnect must be able to open both sides of the line when welding current is not present.

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