The Non-Negotiable Foundation: Electrical Safety
Siemens industrial control panels — housing PLCs, drives, contactors, circuit breakers, and power supplies — operate at voltages that can cause serious injury or death. No maintenance task, regardless of urgency, is worth compromising on electrical safety. This guide outlines the mandatory safety practices and compliance requirements that apply when servicing these systems.
This article provides general guidance only. Always follow your organisation's specific safety procedures, applicable national regulations, and manufacturer documentation. Work on live or hazardous electrical systems must only be carried out by qualified and authorised personnel.
Core Safety Principles
1. Assume Live Until Proven Dead
Never assume a circuit is de-energised because a switch is in the OFF position or a breaker is open. Always verify with a calibrated voltage tester before touching any conductor or terminal.
2. Lockout / Tagout (LOTO)
Lockout/Tagout is the most critical safety procedure in electrical maintenance. Before working on any Siemens panel:
- Identify all energy sources (mains supply, UPS, capacitor banks in drives)
- Isolate using the main isolator switch or circuit breaker
- Lock the isolator in the OFF position with a personal padlock
- Tag the lockout point with your name, date, and reason for isolation
- Verify the absence of voltage using a voltage tester at the point of work — test the tester before and after on a known live source
- Discharge — allow time for DC bus capacitors in drives to discharge (check drive manual; typically 5–10 minutes after power-off, verify with a DC voltmeter)
3. Personal Protective Equipment (PPE)
Select PPE appropriate to the arc flash risk level of the panel, determined by an arc flash hazard assessment:
- Insulated gloves rated to the working voltage
- Arc flash face shield or arc flash suit (where arc flash risk is present)
- Safety glasses
- Non-conductive footwear
- Natural fibre clothing (cotton, wool) — avoid synthetic fibres that melt
Regulatory Compliance Framework
Maintenance of Siemens industrial electrical equipment must comply with the relevant regulations in your jurisdiction:
| Region | Key Regulations / Standards |
|---|---|
| European Union | Low Voltage Directive (2014/35/EU), EN 50110-1 (Operation of electrical installations) |
| United Kingdom | Electricity at Work Regulations 1989, IET Code of Practice (BS 7671) |
| USA | NFPA 70E (Electrical Safety in the Workplace), OSHA 29 CFR 1910.333 |
| International | IEC 60204-1 (Safety of machinery — electrical equipment), IEC 62443 (industrial cybersecurity) |
Working on Siemens Safety-Rated Systems (Fail-Safe)
Siemens SIMATIC Safety (S7-F), SINAMICS Safety Integrated, and other SIL/PLe-rated components carry additional requirements:
- Any modification to a safety-rated program or hardware configuration must be authorised by the safety system designer or competent person
- After any change, a safety validation test must be performed and documented before returning the system to service
- Parameter changes to safety functions in SINAMICS drives require a password-protected safety commissioning procedure
- Maintain a safety change log as required by IEC 62061 or ISO 13849
Practical Safety Checklist Before Starting Work
- ☐ Work permit issued and signed (where required by site procedures)
- ☐ All energy sources identified and documented
- ☐ LOTO applied — isolator locked and tagged with personal lock
- ☐ Voltage absence verified with calibrated tester
- ☐ Drive DC bus discharge time elapsed and verified
- ☐ Appropriate PPE donned
- ☐ Adjacent live circuits identified and guarded if required
- ☐ Emergency contacts and first aid location confirmed
- ☐ Communication established with supervisor/control room
After the Work Is Complete
Before re-energising the panel:
- Confirm all tools, test equipment, and foreign objects are removed from the panel
- Ensure all covers and shrouds are refitted
- Notify all affected personnel before restoring power
- Remove LOTO devices in the reverse order they were applied
- Complete and file maintenance records, noting what was done and by whom