A Complete Guide to Pushbuttons and Pilot Lights for Industrial Use


Posted on Wednesday Jan 22, 2025 at 06:44PM in Educational Resources



Pushbuttons and Pilot Lights: A Practical Field Guide for Panels and Machines

Read More summary: Tired of mystery buttons and dead pilot lights killing uptime? Here’s the jobsite guide to pick, wire, label, and prove your operators safe so your crew stops guessing and your line stops idling.

TL;DR

  • Use 22 mm or 30 mm operators from proven families and match control voltage to the plant standard. Size and fuse the control transformer per UL 508A and NEC 450.

  • Follow color rules. Red mushroom with a yellow background for emergency stop. Use white, gray, or black for general actuation. Reserve green for normal run status. Tie your choices to IEC 60073 and ISO 13850 where applicable.

  • Pick the right enclosure rating for the environment. NEMA 4 or 4X for washdown, NEMA 12 for oily dust, NEMA 3R outdoors. Verify IP codes if you coordinate with OEMs.

  • Prove safety. Emergency stop circuits need direct opening (positive opening) NC contacts and must meet the stop function performance defined in NFPA 79 and IEC 60204-1. Lockout/tagout steps come from OSHA 1910.147.

  • Document everything. Label devices, keep drawings current, and mark the panel SCCR and nameplate to meet NEC Article 409 and UL 508A.

  • Stock smart. Standardize lenses, contact blocks, and lamps. Keep a spare kit on the truck. Order from Revco and use your online account to see branch inventory, build job lists, and pick up same day.


Why this matters on the job — risk, time, cost

A wrong button color or a dim pilot light looks small. It is not. It slows crews, hides faults, and can create unsafe actions. Poor choices lead to callbacks, operators who bypass safeties, and inspectors who flag panels. Good choices reduce training time, speed troubleshooting, and prevent downtime. Right parts, right colors, right enclosures, and proven wiring save hours on every install.

To keep work moving, standardize the hardware and the rules. That lets your teams wire and test faster. It also makes spares simple to carry and order. Revco keeps stocked lines of pushbuttons and pilot lights with real-time inventory, so you can plan the panel and pick up parts the same day.

Fundamentals — what these devices do and the outcomes you need

Pushbuttons send control signals. Use momentary for jog or start. Use maintained for selector functions or latching actions where allowed by your risk assessment.
Pilot lights show state. Use steady lights for normal status. Use flashing for higher priority alerts.

Common diameters are 16 mm, 22 mm, and 30 mm. Most plant standards rely on 22 mm or 30 mm devices for robustness and glove use. Modern families include modular contact blocks, LED light modules that run on 24 V AC/DC or 120 V AC, and accessories like legend plates and guards. See proven lines such as Schneider Electric Harmony XB4/XB5 and Siemens SIRIUS ACT. Eaton’s M22 platform is another widely used option with multicolor indicators.

Match control voltage to your plant standard. Many panels use 24 V DC for control safety and LED life. Others use 120 V AC with a control transformer. If you use a transformer, size and protect it correctly and keep the control circuit isolated and fused as required. A stocked example is Square D’s Type TF control transformer, available from Revco, such as the 9070TF300D32.

Codes and standards you must follow in the United States

You do not need to quote code text, but you must design and install to the rules. Key references:

  • NEC 2023 (NFPA 70). Article 409 covers industrial control panels, including nameplate markings and cross-references to other articles for loads controlled by the panel. Article 450 covers transformers and their protection. You can review NFPA public reports and panel statements that clarify Article 409 scope and references, and Article 450 updates on overcurrent protection. Start with NFPA’s Article 409 public inputs and comments and Article 450 second draft material on the NFPA site.

    • Article 409 overview and scope in NFPA public documents: see NFPA code panel materials summarizing 409.1 Scope and 409.3 Other Articles.

    • Article 450 public materials explain transformer protection changes and committee statements.

  • NFPA 79 (Electrical Standard for Industrial Machinery). Defines the stop and emergency stop functions and documentation for machinery electrical equipment. See the NFPA 79 standard overview page for purpose and scope.

  • OSHA 29 CFR 1910.147. Lockout/Tagout for control of hazardous energy. This is your rule set for servicing and maintenance and for training requirements. See OSHA’s standard and overview pages.

  • UL 508A. Construction and evaluation of industrial control panels, including component usage, spacings, SCCR determination (Supplement SB), and marking. See UL’s 508A summary and the UL 508A standard catalog page.

  • Ingress protection. NEMA 250 defines enclosure types. IEC 60529 defines IP codes. Use NEMA 4/4X for washdown, 12 for oily dust, 3R outdoors. Reference the NEMA enclosure types guide and IEC’s IP ratings overview.

  • Color coding and operator design. IEC 60073 provides coding principles for indicators and actuators. ISO 13850 defines the emergency stop function. IEC 60204-1 sets electrical equipment rules for machinery and references the stop function.

    • For color of safety signs, ANSI Z535.1 provides the safety color system and harmonizes with ISO 3864.

Jurisdiction note: State and local adoption can lag. The Authority Having Jurisdiction has the final say. Confirm the adopted NEC edition and any local amendments before you submit or install.

Action plan — step by step with checklists

Step 1: Define the control functions and risk

  • List each required function: Start, Stop, Jog, Mode, Reset, E-Stop, Alarm Acknowledge.

  • Decide momentary versus maintained for each function.

  • Decide if you need guarded operators or keyed selectors.

  • Select control voltage: 24 V DC or 120 V AC with a control transformer.

  • Identify environment: washdown, oily dust, outdoor, hazardous area.

  • Confirm the enclosure rating: NEMA 12, 4, 4X, or 3R. Use Revco’s quick primer on NEMA ratings to align your choice with conditions.

  • Determine safety category and performance level for stop functions using your risk assessment. Align with NFPA 79 stop functions and IEC 60204-1.

Checklist
[ ] Function list approved by operations
[ ] Voltage standard set
[ ] Environment and NEMA/IP determined
[ ] Safety and stop function defined
[ ] AHJ edition confirmed

Step 2: Select hardware that matches code and the plant standard


  • Pick the operator family and diameter. Standardize across panels to simplify spares.
  • Choose contact blocks. Use positively driven NC contacts where required for safety chains. Direct opening (positive opening) contacts are called out in IEC 60947-5-1 for safety devices.

  • Choose pilot lights. Prefer LED modules. Define steady versus flashing states. Use flashing for higher priority alerts. IEC and industry notes specify two flash rates when two priority levels are needed.

  • Select the control transformer if needed. Size VA for steady loads plus inrush. Fuse both primary and secondary as required. Example: Square D 9070TF series like the 9070TF300D32.

  • Match enclosures to NEMA 4/4X for washdown, 12 for oil and dust, 3R outdoors. Reference NEMA 250 enclosure guidance and IEC IP code basics.

Checklist
[ ] Operator family and size set
[ ] Contact blocks specified with positive opening where required
[ ] Pilot lights and flash logic defined
[ ] Transformer VA and fusing calculated
[ ] Enclosure rating confirmed

Step 3: Apply color and legend rules that operators understand

Follow IEC 60073 for indicators and actuators and align with ANSI Z535.1 safety color system for human factors.

  • Emergency stop: Red mushroom head with a yellow background plate. Latch to stop. Twist or pull to release, per device design. This aligns with ISO 13850 and IEC 60204-1 expectations for the emergency stop function.

  • Start or enable action: White, gray, or black are preferred. Green can be used for actuation in some schemes but avoid mixing rules.

  • Stop or off: Black, gray, or white are preferred. Red is allowed for stop but should not be confused with E-Stop locations.

  • Status lights:

    • Green for normal operation.

    • Red for fault or stop.

    • Yellow for abnormal or warning.

    • Blue for special conditions or reset required.

    • White for general status.
      Use manufacturer families with clear color options and matching legend plates. See Schneider Harmony XB4 pilot light examples and Eaton M22 indicators.

Checklist
[ ] E-Stop red with yellow background
[ ] Color rules documented
[ ] Legend plates defined and engraved
[ ] Flashing logic documented

Step 4: Build to UL 508A and NEC, then prove it

  • Layout: Keep operator spacing for gloves. Group by function.

  • Wiring: Land conductors per manufacturer torque values. Route safety circuits cleanly and in separate duct where practical.

  • Direct opening: Use positive opening NC contacts in emergency stop circuits per IEC 60947-5-1. Manufacturer datasheets will state conformity.

  • Transformer protection: Fuse primary and secondary per the transformer table and UL 508A guidance.

  • Nameplate and SCCR: Mark the panel per NEC Article 409 and determine SCCR using UL 508A Supplement SB.

  • Test: Verify each operator action and pilot light logic. Prove E-Stop removes power as designed and releases only with intended action.

  • LOTO: Write and follow lockout/tagout steps per OSHA 1910.147 for all commissioning and service work.

Checklist
[ ] Torque logs completed
[ ] Positive opening safety contacts verified
[ ] Transformer fusing installed
[ ] Panel nameplate and SCCR marked
[ ] Functional test sheet signed
[ ] LOTO procedure used

Step 5: Document, stock spares, and train

  • Drawings: Update schematics and bills of material after any field changes.

  • Labels: Use durable legend plates. Keep a legend key on the door.

  • Spares: Stock lamps, contact blocks, lenses, and E-Stop operators.

  • Training: Teach operators to read colors and flashing logic.

  • Service notes: Record failure modes and part numbers in the CMMS.

Checklist
[ ] As-built drawings saved
[ ] Spare kit list on door
[ ] Operator briefing done
[ ] CMMS entries complete

Two worked examples

Example 1: Downtime payback from standardizing pilot lights

  • Current state: A mixing line loses 10 minutes per fault because operators cannot tell if the stop is a trip or a normal stop. Four events per week. Labor and lost throughput cost is 600 dollars per hour.

  • Loss per week: 4 events × 10 minutes = 40 minutes = 0.667 hours × 600 = 400 dollars/week.

  • Fix: Rebuild the operator station with a standard set of indicators and flashing red for faults. Parts and labor total 1,500 dollars.

  • Result: Events still occur, but diagnosis time drops to 2 minutes. New loss per week: 4 × 2 = 8 minutes = 0.133 hours × 600 = 80 dollars/week.

  • Savings: 400 − 80 = 320 dollars/week.

  • Payback: 1,500 ÷ 320 ≈ 4.7 weeks.

Example 2: Transformer sizing for a panel with mixed lights

  • Loads:

    • Three 22 mm LED pilot lights at 24 V DC, 20 mA each.

    • One horn at 24 V DC, 0.3 A.

    • Two relay coils at 24 V DC, 50 mA each.

  • Total steady current: 0.02×3 + 0.3 + 0.05×2 = 0.49 A.

  • Add 25% margin for inrush and future: 0.49 × 1.25 = 0.61 A.

  • VA at 24 V: 24 × 0.61 ≈ 14.6 VA.

  • Choice: A 50 VA control transformer gives margin and supports add-ons. Protect primary and secondary per NEC 450 and UL 508A. A stocked option is the Square D Type TF like 9070TF300D32.

Implementation notes aligned to standards — pitfalls to avoid

  • Do not use green for emergency devices. Reserve red with yellow background for E-Stop per ISO 13850 and IEC 60204-1.

  • Do not mix color schemes between lines. Publish a plant color standard based on IEC 60073 and train to it.

  • Do not run safety circuits through software decisions unless your risk assessment and architecture allow it. Use hardwired E-Stops with direct opening contacts first.

  • Do not undersize the control transformer. Respect inrush and accessory growth. Follow UL 508A and NEC Article 450 for protection.

  • Do not ignore enclosure ratings. Check NEMA 250 and IEC 60529. Match washdown and corrosive environments with NEMA 4X and compatible operators.

  • Do not skip LOTO. Use OSHA 1910.147 for every service task.

  • Do not forget SCCR. Determine and mark it on the panel per UL 508A and NEC Article 409.

Measurement plan — KPIs, cadence, instrumentation

  • Mean time to diagnose (MTTD). Target under 2 minutes for common stops.

  • Mean time to repair (MTTR). Track before and after a standardization project.

  • Downtime hours per line per month. Normalize by shifts.

  • Panel punch-list defects per inspection. Aim for zero.

  • Color compliance rate during audits.

  • Spare consumption and stockouts for lamps and contact blocks.

  • Training completion for operators and maintenance.

Review monthly in your maintenance meeting. Tie improvements to dollars saved using the downtime rate from operations.

Troubleshooting and common mistakes

  • Wrong lamp voltage. A 120 V lamp installed on 24 V will look dead. Confirm module voltage.

  • NO vs NC mislanded. Check schematic symbols. Use a meter to confirm action before energizing.

  • No direct opening in E-Stop. Verify positive opening NC contacts on emergency devices per IEC 60947-5-1.

  • Legend plates missing or vague. Install engraved plates and keep a legend list in the door.

  • Enclosure rating mismatch. NEMA 1 or 12 in washdown leads to failures. Use NEMA 4/4X where needed.

  • No transformer secondary protection. Add fusing per UL 508A.

  • No SCCR or nameplate. NEC Article 409 requires it.

  • LOTO skipped. Enforce OSHA 1910.147 every time.

Resources and related Revco pages

When to escalate

  • Legal counsel if your machine risk assessment raises product liability questions or state rules differ from your corporate standard.

  • AHJ or electrical inspector when panel markings, SCCR, or local amendments are unclear.

  • UL 508A Panel Shop or UL engineer when you need third-party certification or help with SCCR and component choices.

  • Platform technical support from the operator device manufacturer if you are mixing blocks or need an IP69K solution.

  • Safety officer if the emergency stop function or guard circuits change during a retrofit.

Short legal disclaimer

This guide is for licensed professionals. Always follow the adopted NEC edition, NFPA 79 for machinery, OSHA 29 CFR 1910, manufacturer instructions, and the Authority Having Jurisdiction. Standards content is copyrighted. Purchase and apply the current editions.

FAQ

1) Which diameter should I pick, 22 mm or 30 mm?
Use the plant standard. If none exists, pick 22 mm for compact panels and good glove usability, or 30 mm where heavy gloves and high visibility matter. Stick to one family to simplify spares.

2) Can I use green for a Start button?
You can, but many plants choose white, gray, or black for Start per IEC 60073 coding principles. Keep green for “running” status lights. Reserve red with a yellow background for emergency stop per ISO 13850 and IEC 60204-1.

3) Do emergency stops need special contacts?
Yes. Use devices with direct opening (positive opening) NC contacts per IEC 60947-5-1. The datasheet should say “positive opening” and show the symbol.

4) Do I need a control transformer?
Use one if your control voltage differs from supply. Size it for steady load plus inrush and fuse per UL 508A and NEC Article 450. See Revco for Square D Type TF examples like the 9070TF300D32.

5) What enclosure rating should I use in washdown?
NEMA 4 or 4X depending on corrosion risk. Check operator IP ratings as well. Match the weakest link to the environment.

6) How do I mark the panel?
Follow NEC Article 409 for nameplate data and SCCR marking. Determine SCCR using UL 508A Supplement SB and list it on the nameplate.

7) What about lockout/tagout?
Write and follow procedures under OSHA 1910.147. Train workers and document each step. Never rely on a pilot light alone to prove isolation.

8) Where do I start if I have to standardize across a site?
Publish a one-page spec: operator family, colors, legends, enclosure ratings, control voltage, transformer sizing rules, and test procedure. Stock matching spares at the crib and in service trucks. Use Revco job lists and branch inventory to keep kits ready.

About Revco Lighting & Electrical Supply

Since 1978, Revco Lighting & Electrical Supply has been helping professionals bring their projects to light—literally. As a go-to source for lighting and electrical products across Long Island, NY and nearby areas, we specialize in supporting contractors, builders, and industry experts with practical solutions and dependable service. Whether it’s a complex commercial build or a simple residential upgrade, we’re here to make sure you have what you need, when you need it.























































Pushbuttons and pilot lights