In this chapter: how electricity causes harm in a wood pellet plant or feed mill, what electrical panels, grounding and protective devices must have, why dust inside a panel is a double problem, what equipment can be installed in dusty areas, and who may work on an electrical installation.
A hazard that is not just for electricians
A wood pellet plant or feed mill has a lot of installed power: motors for mills and pellet mills, fans, conveyors, boilers or steam generators, compressors. All of it is controlled from electrical panels that, in many plants, share the space with dust, moisture and vibration.
People tend to think electrical hazards are an electrician's problem. The data say otherwise. The Electrical Safety Foundation International (ESFI), which compiles official U.S. data, counted 1,654 workplace electrical fatalities between 2011 and 2024, and estimates that 70% occurred in non-electrical occupations. In 2023 and 2024 there were also 5,180 electrical injuries with days away from work1. In a plant, that means operators who open a panel to reset a circuit breaker, mechanics who replace a motor without cutting the power, or cleaning staff who wipe a push-button station with a damp cloth.
Three ways to get hurt
Electricity causes harm in three ways:
- Electric shock. Current passes through the body. It can happen through direct contact, by touching a part that is energized, or through indirect contact, by touching the frame of a motor or a panel that has become energized because of an insulation fault.
- Arc flash. A fault or a poorly executed switching operation creates an arc that releases intense heat, molten metal and a pressure wave. It causes severe burns even if the person doesn't touch anything.
- Fire and explosion. A loose connection that overheats, an overloaded motor or a spark from unsuitable equipment can ignite settled dust or a dust cloud. This is the ignition source we saw in Chapter 3.
Electrical panels: the basics that cannot be missing
Before getting into technical standards, there are basic conditions any supervisor can check on a walk-through:
- Closed panels. Doors and covers in place, with no holes and no cables entering through makeshift openings. Locked, so only authorized people can open them.
- No energized parts within reach when the door is opened: busbars and terminals must have their protection.
- Labeled circuits. Each breaker labeled with the name of the equipment it feeds. Without this, the lockout we saw in Chapter 4 cannot be done properly.
- Clear space in front. The front of a panel is not a storage area for bags, tools or spare parts.
- No temporary installations that became permanent: extension cords, splices made with tape, overloaded outlets.
- Cables protected from forklift traffic, from rubbing against moving parts and from the heat of steam pipes.
Grounding and protective devices
Two protective measures prevent most shocks from indirect contact:
- Grounding. It connects the metal parts of machines and panels to ground, so that an insulation fault does not leave the frame at a dangerous voltage. Argentina's Decreto 351/79 requires exposed conductive parts to be connected to ground through a continuous and permanent circuit, able to carry the fault current and with adequate resistance2.
- Ground-fault / residual-current devices (RCDs). They detect current leaking to ground and cut the circuit. The same decree requires them to trip in no more than 0.03 seconds at their rated current, of 30 mA or 300 mA depending on their sensitivity2. An RCD that is not tested periodically can be stuck without anyone knowing.
Grounding must be measured. In Argentina, Resolución SRT 900/2015 approved a mandatory protocol for measuring grounding and verifying the continuity of exposed conductive parts; measurements are valid for 12 months, and if parts without a ground connection are found, the employer must have an action plan to correct them3. In Mexico, NOM-029-STPS-2011 sets the safety conditions for the maintenance of electrical installations in workplaces4.
Grounding machines and pipes also serves to dissipate static electricity, which can cause sparks in pneumatic conveying and in filters. Mexico has a specific standard, NOM-022-STPS-20155.
Dust inside electrical panels
In a wood pellet plant or feed mill, dust gets everywhere, and panels are no exception. Dust inside a panel is a double problem:
- It heats. A layer of dust on contactors, drives and terminals acts as thermal insulation: the equipment cannot dissipate its heat and runs hotter. The U.S. National Electrical Code (NEC, NFPA 70) and OSHA's electrical standard take precisely this effect into account: they consider a location hazardous where accumulated dust, even if it is not in suspension, may interfere with the safe dissipation of heat from electrical equipment6.
- It ignites. An arcing contact, a loose terminal that overheats or an arc can ignite that dust. And a fire inside a panel can be the start of the event we described in Chapter 3.
The measures are well known:
- Locate the main panels outside dusty areas, in a separate electrical room and, if needed, with filtered ventilation or slight positive pressure.
- Choose enclosures with the right degree of protection against dust ingress, and keep their gaskets, cable glands and latches in good condition.
- Keep the doors closed. A panel left open "to let it breathe" fills up with dust.
- Clean with the panel de-energized and locked out, by qualified staff, with a suitable vacuum cleaner. Never with compressed air, which drives dust into the equipment and raises it into the air.
- Check periodically the tightness of connections and the temperature of the equipment. Inspection with a thermal imaging camera is a common tool for finding hot spots before they fail.
Equipment suitable for dusty areas
Where there may be a cloud of combustible dust, electrical equipment (motors, sensors, light fixtures, push-button stations, junction boxes) must be built so it cannot ignite it. First the area is classified; then the equipment is chosen.
European Union: the two ATEX directives
As we saw in Chapter 3, Directive 1999/92/EC requires the employer to classify dusty areas into zones 20, 21 and 22, and Directive 2014/34/EU sets how equipment must be built and certified. Directive 1999/92/EC establishes which equipment category corresponds to each zone7:
| Zone | Presence of a dust cloud | Permitted equipment category |
|---|---|---|
| 20 | Continuous or frequent | Category 1 |
| 21 | Likely in normal operation | Category 1 or 2 |
| 22 | Unlikely and short-lived | Category 1, 2 or 3 |
The international technical standards used to apply this scheme belong to the IEC 60079 series: part 10-2 for classifying dust areas (2026 edition), part 14 for the design, selection and installation of equipment (current 2024 edition) and part 17 for its inspection and maintenance (2023 edition)8.
United States: the NEC
The NEC classifies locations with combustible dust as Class II, with two divisions depending on the likelihood of hazardous dust being present. Article 502 of the code sets the requirements for wiring and equipment in those locations6.
Argentina and other countries
Decreto 351/79 requires dusty premises to meet the additional requirements of the electrical installation regulations, requires materials for environments with an explosion hazard to have official approval, and states that the user is responsible for choosing the right material for each hazard2. In practice, many plants in the region use ATEX or IEC 60079 as the reference for selecting and certifying their equipment.
A key point: suitable equipment stops being suitable if a cover is removed, a cable gland is replaced with an ordinary one, or it is repaired with non-original parts. Maintaining this equipment is a specialized task.
Who may intervene
Not just anyone may work on an electrical installation, and the regulations agree on two ideas: work de-energized whenever possible, and whoever intervenes must be trained and authorized.
- United States. OSHA requires live parts to be de-energized before anyone works on or near them, unless doing so creates a greater hazard or is infeasible, and requires de-energized circuits to be locked out or tagged. Only qualified persons may work on parts that have not been de-energized9. The consensus standard NFPA 70E (2027 edition) sets out how to establish an electrically safe work condition, how to perform an arc flash risk assessment and when an energized electrical work permit is required10.
- Argentina. Decreto 351/79 requires electrical maintenance staff to be trained by the company and informed of the hazards. Live work may only be done by staff authorized by the company, with the approval of the person in charge of Health and Safety, and there must be a single person responsible for the job2. For installations above 1 kV, the Argentine Electrotechnical Association's regulation for live work applies, approved by Resolución SRT 11/202211.
- Mexico. NOM-029-STPS-2011 requires maintenance of electrical installations to be done by trained staff authorized in writing by the employer4.
Beyond these rules, many jurisdictions require new installations or alterations to be designed and signed off by a licensed professional. Check what your municipality, province or state requires.
Turning off the breaker doesn't make the machine safe
Decreto 351/79 says it clearly: locking a switch in the open position is not enough on its own to work. You must disconnect all sources, lock out, verify the absence of voltage, ground where applicable, and post signs2. A variable frequency drive or a capacitor bank can retain voltage after the power is cut, and a control circuit can be fed from another panel. That is why electrical lockout is part of the general lockout procedure we saw in Chapter 4.
What to ask of a new machine
The European Machinery Regulation requires machinery to be designed to prevent all hazards of an electrical nature and to avoid or discharge hazardous electrostatic charges12. When you buy, ask for the electrical diagram, the degree of protection of motors and panels and, if the machine will be installed in a hazardous (classified) area, the certification of its components for that area.
Chapter checklist
- Are the panels closed, locked, with no energized parts within reach and with labeled circuits?
- Is the space in front of the panels clear?
- Are there temporary installations that became permanent?
- Do we measure grounding and the continuity of exposed conductive parts, with a current record?
- Are the RCDs tested periodically?
- Are the main panels outside dusty areas, or do they have adequate protection?
- Is there a program for cleaning and inspecting panels, with the equipment de-energized?
- Are dusty areas classified, and is the electrical equipment suitable for each zone?
- Is it written down who may work on the electrical installation and with what authorization?
- Does the lockout procedure include verifying the absence of voltage?
What to leave to a professional
The design of the electrical installation, grounding measurement, the classification of dusty areas and the selection of equipment for those areas must be done by a qualified professional, according to your country's regulations. The same applies to any live work and to the maintenance of equipment certified for explosive atmospheres.
At Meelko, we define the location of panels, the cable routing and motor protection together with the line layout, so the electrical side stays away from dust from day one. If you want to review your project or your plant, tell us about your project.
Chapter sources
- Electrical Safety Foundation International (ESFI). Workplace Electrical Fatalities 2011-2024, March 2026, with BLS and OSHA data. https://www.esfi.org/wp-content/uploads/2026/03/ESFI-Workplace-Electrical-Fatalities-2011-2024.pdf ↑
- Argentina. Decreto 351/79, Annex VI (electrical installations), points 1.1.3, 1.1.4, 1.2.1, 1.2.2, 1.2.3, 3.3.1, 3.3.2.1 and 3.4. https://www.argentina.gob.ar/normativa/recurso/32030/dto351-1979-anexo6/htm ↑
- Superintendencia de Riesgos del Trabajo (Argentina). Resolución SRT 900/2015, Protocolo para la medición del valor de puesta a tierra y la verificación de la continuidad de las masas en el ambiente laboral. Boletín Oficial, April 28, 2015. https://www.boletinoficial.gob.ar/detalleAviso/primera/124220/20150428 — Practical guide: https://argentina.gob.ar/sites/default/files/res_srt_900_15-guia-practica_0.pdf ↑
- Mexico. NOM-029-STPS-2011, Mantenimiento de las instalaciones eléctricas en los centros de trabajo - Condiciones de seguridad, DOF December 29, 2011. https://platiica.economia.gob.mx/normalizacion/nom-029-stps-2011/ ↑
- Mexico. NOM-022-STPS-2015, Electricidad estática en los centros de trabajo - Condiciones de seguridad, DOF April 1, 2016. https://platiica.economia.gob.mx/normalizacion/nom-022-stps-2015/ ↑
- NFPA 70, National Electrical Code, 2026 edition (current), Articles 500 and 502. Official page: https://www.nfpa.org/product/nfpa-70-national-electrical-code-nec/p0070code/nfpa-70-national-electrical-code-nec-2026/7026sb — The definition of Class II, Division 2 (500.5(C)(2)) in the 2023 edition, with the condition of accumulated dust that interferes with heat dissipation: ECM, NEC Requirements for Hazardous Locations, October 11, 2023, https://www.ecmweb.com/national-electrical-code/code-basics/article/21275030/nec-requirements-for-hazardous-locations — The same condition appears in OSHA's definition of Class II, Division 2 location, 29 CFR 1910.399: https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.399 — Summary of Article 502: https://www.ecmweb.com/national-electrical-code/article/21281848/nec-article-502-summary — The text of the 2026 edition is not freely accessible, so its wording is not quoted. ↑
- Directive 1999/92/EC of the European Parliament and of the Council of December 16, 1999 (ATEX workers directive), Annexes I and II, part B. OJ L 23, January 28, 2000. https://www.boe.es/doue/2000/023/L00057-00064.pdf ↑
- IEC 60079-10-2, Explosive atmospheres - Part 10-2: Classification of areas - Explosive dust atmospheres, edition 3.0, June 29, 2026; replaces edition 2.0 of 2015. https://webstore.iec.ch/en/publication/90124 — IEC 60079-14:2024: https://webstore.iec.ch/publication/66049 — IEC 60079-17:2023: https://webstore.iec.ch/publication/90154 ↑
- OSHA. 29 CFR 1910.333, Selection and use of work practices, paragraphs (a)(1), (b)(2) and (c)(2); definition of qualified person in 29 CFR 1910.399. https://www.law.cornell.edu/cfr/text/29/1910.333 ↑
- NFPA 70E, Standard for Electrical Safety in the Workplace, 2027 edition (published in 2026; replaces the 2024 edition). Official page: https://www.nfpa.org/product/nfpa-70e-standard-for-electrical-safety-in-the-workplace/p0070ecode/nfpa-70e-2027/70e27 — The electrically safe work condition (Article 120), the arc flash risk assessment (130.5) and the energized electrical work permit appear in the committee's official documents for this edition: https://docinfofiles.nfpa.org/files/AboutTheCodes/70E/70E_A2026_NEC_AAC_SD_SCRStatements.pdf and https://docinfofiles.nfpa.org/files/AboutTheCodes/70E/70E_A2026_EEW_AAA_FD_FRStatements.pdf ↑
- Superintendencia de Riesgos del Trabajo (Argentina). Resolución SRT 11/2022, which approves the AEA's Reglamento para la ejecución de trabajos con tensión en instalaciones eléctricas mayores a 1 kV (2020 edition) and repeals Resolución SRT 592/2004. Boletín Oficial, March 3, 2022. https://www.boletinoficial.gob.ar/detalleAviso/primera/258260/20220303 ↑
- Regulation (EU) 2023/1230 on machinery, Annex III, sections 1.5.1 and 1.5.2. https://www.boe.es/doue/2023/165/L00001-00102.pdf ↑
