Resistance welding requirements

All resistance welding equipment must be installed by a qualified electrician and have a local safety-type disconnect or circuit breaker so power can be shut off when servicing the machine. See the installation requirement in 1910.255(a)(1).

• Place the disconnect or breaker at or near the machine for convenient shutoff.
• Ensure installation complies with subpart S electrical requirements referenced in 1910.255(a)(1).
• Label the disconnect and keep it accessible to maintenance personnel.

Yes. Ignitron tubes used in resistance welding equipment must be equipped with a thermal protection switch. See the thermal protection requirement in 1910.255(a)(2).

• Verify thermal switches are installed, functional, and tested during preventive maintenance.
• Replace or repair thermal protection devices immediately if they fail certification checks.

Workers designated to operate resistance welding equipment must be properly instructed and judged competent to operate that equipment. See the personnel requirement in 1910.255(a)(3).

• Training should cover machine controls, emergency stops, guarding, hazards (electrical, pinch, sparks), and safe work procedures.
• Keep training records and periodically re-evaluate competency, especially after changes to equipment or processes.

Controls of all automatic or air and hydraulic clamps must be arranged or guarded to prevent the operator from accidentally activating them. See the guarding requirement in 1910.255(a)(4).

• Use physical guards, recessed switch locations, interlocks, or two-hand controls as appropriate.
• Ensure guards do not hinder safe operation or maintenance and that operators are trained on their purpose.

All external weld-initiating control circuits must operate on low voltage not exceeding 120 volts for operator safety. See the voltage limit in 1910.255(b)(1).

• Verify control wiring and components are rated appropriately and clearly labeled.
• For portable guns, note 1910.255(c)(4) further limits initiating switch voltage to 24 volts.

Capacitor-discharge welding equipment and high-voltage control panels must be fully enclosed, insulated, interlocked to interrupt power and short-circuit capacitors when panels are opened, and include a manual device to assure absolute capacitor discharge. See the capacitor welding requirements in 1910.255(b)(2).

• Doors must have interlocks wired into the control circuit (similar to elevator interlocks).
• Provide a manually operated switch or positive device, in addition to mechanical interlocks, to guarantee capacitor discharge before access.
• Include procedures and signage for safe panel access during maintenance.

All doors and access panels of resistance welding machines and control panels must be kept locked and interlocked to prevent unauthorized access to live parts. See the interlock and locking requirement in 1910.255(b)(3).

• Use keyed or tool-only access where appropriate and clearly mark authorized access points.
• Wire interlocks so opening a panel interrupts power and, for capacitor systems, discharges capacitors per 1910.255(b)(2).

Where an operator's fingers could be under the point of operation of a press welding machine, the operation must be effectively guarded by devices such as an electronic eye safety circuit, two-hand controls, or protection similar to punch press guarding in 1910.217. See the point-of-operation guarding requirement in 1910.255(b)(4) and the punch press guarding standard 1910.217.

• Evaluate hazards and choose guarding that prevents access during the hazardous stroke.
• Maintain and test safeguarding devices regularly and train operators on safe use.

All chains, gears, operating bus linkage, and belts on welding equipment must be protected by adequate guards in accordance with 1910.219 machine guarding requirements. See the guarding requirement in 1910.255(b)(5) and the general machine guarding requirements in 1910.219.

• Install fixed or interlocked guards that prevent reaching into moving parts.
• Ensure guards are strong, secure, and allow safe maintenance access when locked-out per energy control procedures.

Where practical, flying-spark hazards must be eliminated by installing a shield of safety glass or fire-resistant plastic at the point of operation, and additional shields or curtains must protect passing persons as necessary; 1910.252(b)(2)(i)(C) is cited for related safeguards. See the shields requirement in 1910.255(b)(5) and the cross-reference to 1910.252(b)(2)(i)(C).

• Use nonflammable, impact-resistant materials for shields.
• Position shields/curtains so they do not restrict operator visibility while protecting bystanders and adjacent work areas.

All foot switches on resistance welding machines must be guarded to prevent accidental operation of the machine. See the foot switch guarding requirement in 1910.255(b)(6).

• Use recessed, shrouded, or guarded foot controls or guarded pedal covers.
• Check that guarding does not interfere with intended operator action and is maintained to prevent bypassing.

Special multispot welding machines must have two or more safety emergency stop buttons, including on 2-post and 4-post weld presses. See the stop-button requirement in 1910.255(b)(7).

• Place stops where operators and nearby personnel can reach them quickly.
• Test emergency stops regularly as part of maintenance and keep records of those tests.

Large machines must have four safety pins with plugs and receptacles (one in each corner) so that when pins are removed and inserted in the ram or platen the press becomes inoperative. See the safety pins requirement in 1910.255(b)(8).

• Use pins designed to reliably interrupt the press actuation when engaged.
• Include pin insertion/removal in lockout/tagout and maintenance procedures.

Where technically practical, the secondary of welding transformers used in multispot, projection and seam welding machines should be grounded, and this may be done by permanently grounding one side of the welding secondary current circuit. See the grounding guidance in 1910.255(b)(9).

• Grounding reduces shock risk when feasible; document engineering decisions when grounding is not practical.
• Coordinate grounding methods with electrical code and the qualified electrician who installed the equipment per 1910.255(a)(1).

If grounding the secondary is not technically practical, a center-tapped grounding reactor across the secondary or a safety disconnect that opens both sides of the line when welding current is not present are acceptable alternatives. See the alternate grounding and safety disconnect options in 1910.255(c).

• Ensure the safety disconnect opens both sides of the line when no welding current is present.
• Document the technical basis for choosing an alternate and include it in maintenance records.

All portable welding guns must have suitable counterbalanced devices for supporting the guns and cables unless the gun design or fixture makes counterbalancing impractical or unnecessary. See the counterbalance requirement in 1910.255(c)(1).

• Use spring balancers, trolleys, or fixtures sized to support the gun and avoid operator fatigue.
• Inspect counterbalance devices regularly for wear and proper function.

All portable welding guns, transformers and related equipment suspended from overhead structures must be equipped with safety chains or cables capable of supporting the total shock load if the primary support fails. See the safety chain requirement in 1910.255(c)(2).

• Use rated safety chains/cables with appropriate attachments and inspect them for corrosion or damage.
• Size safety hardware to support dynamic shock loads, not just static weight.

Each clevis must be capable of supporting the total shock load of the suspended equipment in the event of trolley failure. See the clevis strength requirement in 1910.255(c)(3).

• Use clevis fittings rated for dynamic loads and inspect attachment points regularly.
• Replace worn or deformed clevises immediately and document replacements in maintenance records.

Initiating switches, including retraction and dual-schedule switches on portable welding guns, must be equipped with guards to prevent accidental initiation and the initiating switch voltage must not exceed 24 volts. See the switch-guard and voltage requirement in 1910.255(c)(4).

• Use guarded or recessed switches and test guards for durability.
• Label controls and train operators to avoid bypassing guards.

The movable holder must have sufficient clearance at the gun frame entry to prevent shearing of fingers, and the secondary and case of all portable welding transformers must be grounded. See the moving holder clearance in 1910.255(c)(5) and (c)(6) and the portable transformer grounding in 1910.255(c)(6).

• Design gun frames with finger-safe clearances and guards where pinch points exist.
• Ground portable transformers by center-tapped secondary or a center-tapped grounding reactor; verify continuity and bond to equipment grounding conductor.

Flash welding machines must have a hood to control flying flash and, in high-production cases or when materials give off toxic fumes, provide ventilation in accordance with 1910.252(c). See the flash welding hood and ventilation requirement in 1910.255(d)(1) and the cross-reference to 1910.252(c).

• Assess fume hazards and use local exhaust or general ventilation to keep exposures below limits.
• Position hoods to capture flashes without restricting operator tasks and maintain ventilation systems per manufacturer guidance.

Fire-resistant curtains or suitable shields must be set up around flash welding machines to protect nearby operators while not hampering their movements. See the fire curtain requirement in 1910.255(d)(2).

• Use durable, fire-resistant materials rated for the environment and secure them so they won't obstruct safe operation.
• Inspect and replace curtains or shields that show damage or wear.

Periodic inspections by qualified maintenance personnel are required and employers must keep a certification record showing the date of inspection, the inspector's signature, and the equipment serial number or identifier. See the maintenance and recordkeeping requirement in 1910.255(e).

• Keep records for the life of the equipment or per company policy and make them available during audits.
• Include results of functional tests for interlocks, thermal protection, emergency stops, and grounding checks.

When a welding machine must be temporarily re-energized for testing or positioning, employers must follow the sequence of steps in 1910.147(f)(1) to protect employees and use effective guarding during the energized period. See OSHA's Letter of Interpretation on the minor servicing exception and testing procedures and the Control of Hazardous Energy standard 1910.147.

• Required sequence before re-energizing includes clearing tools/materials, removing employees from the hazard area, removing locks/tags as specified, energizing for test while using protective measures, then de-energizing and reapplying lockout if further servicing is needed.
• Document the testing procedure and train authorized employees on the specific steps and protections used during these temporary operations.

Before accessing a high-voltage capacitor panel, the panel doors must be interlocked and locked, power must be interrupted by the interlock, and capacitors must be shorted and absolutely discharged using the interlock and the required manual discharge device. See the capacitor panel requirements in 1910.255(b)(2) and the access panel interlock requirement in 1910.255(b)(3).

• Verify the manual discharge device operates independently of mechanical interlocks and test its function before maintenance.
• Lock and tag the panel per your energy-control procedures and retain records of the discharge operation.

Guarding foot switches and initiating switches on portable guns prevents accidental activation; use guarded or recessed switch housings, switch covers, or two-step actions and ensure initiating voltages meet the limits in 1910.255. See foot switch guarding in 1910.255(b)(6) and portable gun switch requirements in 1910.255(c)(4).

• Fit guards that prevent accidental contact but allow deliberate actuation.
• Use low-voltage control circuits (≤24 V for gun-initiating switches) and periodically inspect guards for wear or tampering.

The certification record must include the inspection date, the signature of the person who performed the inspection, and the serial number or other identifier for the equipment inspected. See the maintenance record requirement in 1910.255(e).

• Add brief notes on items checked (interlocks, grounding, thermal switches, guards) and any corrective actions taken.
• Retain records per company policy and make them available to authorized personnel and inspectors.