Electrical Safety
Air compressors are high electrical power equipment. Electrical safety is critical to prevent electrocution, fires, and equipment damage.
Electrical Risks
Risk Classification
┌─────────────────────────────────────────────────────────┐
│ ELECTRICAL RISKS IN COMPRESSORS │
│ │
│ ELECTRIC SHOCK │
│ ├─ Direct contact with conductors │
│ ├─ Indirect contact (ground fault) │
│ └─ Step voltage │
│ │
│ ARC FLASH │
│ ├─ Plasma explosion │
│ ├─ Thermal radiation (up to 35,000°F) │
│ ├─ Pressure wave │
│ ├─ Material projection │
│ └─ Intense light (eye damage) │
│ │
│ FIRE │
│ ├─ Conductor overload │
│ ├─ Loose connections │
│ ├─ Short circuit │
│ └─ Insulation failure │
│ │
└─────────────────────────────────────────────────────────┘
Typical Voltages
| Equipment | Voltage | Risk Level |
|---|---|---|
| Small compressor (<5 HP) | 208-230V | Medium |
| Medium compressor (5-50 HP) | 460-480V | High |
| Large compressor (>50 HP) | 460-4160V | Very high |
| Controls | 24-120V | Low-Medium |
| VSD | Input + DC Bus | High |
Arc Flash
Risk Categories
Incident energy levels:
cal/cm² Category Required PPE
─────────────────────────────────────────
0-1.2 1 Basic FR clothing
1.2-4 1 Basic FR clothing
4-8 2 FR clothing + face shield
8-25 3 FR suit + hood
25-40 4 Full flash suit
>40 -- Working energized prohibited
Arc Flash Analysis
Arc flash study:
┌─────────────────────────────────────────────────────┐
│ 1500 kVA Transformer │
│ │ │
│ [====╪====] Main breaker │
│ │ Arc Flash: 8.5 cal/cm² │
│ │ Flash boundary: 48" │
│ │ PPE Category: 2 │
│ │ │
│ [====╪====] Compressor MCC │
│ │ Arc Flash: 4.2 cal/cm² │
│ │ Flash boundary: 36" │
│ │ PPE Category: 2 │
│ │ │
│ [====╪====] Compressor 1 Starter │
│ Arc Flash: 1.5 cal/cm² │
│ Flash boundary: 18" │
│ PPE Category: 1 │
└─────────────────────────────────────────────────────┘
Warning Labels
┌─────────────────────────────────────────────────────────┐
│ ⚡ WARNING - ARC FLASH HAZARD ⚡ │
│ │
│ Incident Energy at 18": 4.2 cal/cm² │
│ Arc Flash Boundary: 36 inches │
│ PPE Category: 2 │
│ Working Distance: 18 inches │
│ │
│ REQUIRED PPE: │
│ • FR clothing (min 8 cal/cm²) │
│ • Safety glasses │
│ • Hard hat with face shield │
│ • Leather gloves │
│ • Hearing protection │
│ │
│ Equipment Name: MCC-COMPRESSORS │
│ Study Date: 01/15/2024 │
└─────────────────────────────────────────────────────────┘
Protective Equipment
PPE by Category
| Category | cal/cm² | Required PPE |
|---|---|---|
| 1 | 4 | FR shirt/pants, glasses, gloves |
| 2 | 8 | + Face shield, hard hat |
| 3 | 25 | + FR hood, hearing protection |
| 4 | 40 | Full flash suit |
Dielectric Gloves
Glove classes by voltage:
Class Max Voltage Color
────────────────────────────
00 500 V Beige
0 1,000 V Red
1 7,500 V White
2 17,000 V Yellow
3 26,500 V Green
4 36,000 V Orange
| Requirement | Frequency |
|---|---|
| Visual inspection | Before each use |
| Air test | Before each use |
| Dielectric test | Every 6 months |
| Replacement | If test fails or visible damage |
Electrical Installation
NEC/NFPA 70 Requirements
Compressor room - Electrical requirements:
┌─────────────────────────────────────────────────────┐
│ │
│ ┌─────────┐ │
│ │ │◄── Panel in accessible area │
│ │ Panel │ 36" clear space front │
│ │ │ 30" minimum width │
│ └────┬────┘ │
│ │ │
│ ═════╪═════ Conduit (mechanical protection) │
│ │ │
│ ┌────┴────┐ │
│ │Compressor│◄── Visible disconnect │
│ │ │ within line of sight │
│ └─────────┘ │
│ │ │
│ ═════╧═════ Ground (green or bare) │
│ │
└─────────────────────────────────────────────────────┘
Working Clearances
| Voltage | Front Clearance | Side Clearance |
|---|---|---|
| 0-150V | 36" | 30" |
| 151-600V | 36" | 30" |
| 601-2500V | 48" | 36" |
Grounding System
Ground connections:
Main panel
│
├──► Ground bar
│ │
│ ┌────┼────┬────┬────┐
│ │ │ │ │ │
│ ▼ ▼ ▼ ▼ ▼
│ Eq1 Eq2 Eq3 Eq4 Eq5
│
└──► Ground electrode
│
════╧════ (Buried rod)
Maximum ground resistance: 25 ohms
(Preferable < 5 ohms)
Safe Procedures
De-energized Work (Preferred)
De-energization sequence:
1. Notify affected personnel
│
▼
2. Identify all energy sources
│
▼
3. Shut down normally
│
▼
4. Operate disconnecting device
│
▼
5. Apply LOTO (lock and tag)
│
▼
6. Verify absence of voltage
(Verify test equipment works,
test, verify equipment works)
│
▼
7. Apply temporary grounds (if applicable)
│
▼
8. Work
Energized Work (Only if Necessary)
| Requirement | Description |
|---|---|
| Justification | Document why cannot de-energize |
| Authorization | Energized work permit |
| PPE | Per arc flash category |
| Limits | Establish work zone |
| Attendant | Dedicated person |
| Tools | Insulated and certified |
Absence of Voltage Verification
Live-Dead-Live procedure:
1. LIVE: Verify multimeter works
on known source
│
▼
2. DEAD: Test circuit that should
be de-energized
│
▼
3. LIVE: Verify again that
multimeter still works
⚠ If meter shows no voltage but
you didn't verify it works,
you might have a damaged meter.
VSD - Special Considerations
VSD-Specific Risks
┌─────────────────────────────────────────────────────────┐
│ VARIABLE FREQUENCY DRIVE RISKS │
│ │
│ DC BUS CAPACITORS │
│ ├─ Retain charge after power off │
│ ├─ Voltage: 650-900 VDC typical │
│ ├─ Discharge time: 5-15 minutes │
│ └─ ALWAYS verify with multimeter │
│ │
│ HIGH FREQUENCY OUTPUT │
│ ├─ Don't measure with normal multimeter │
│ ├─ Non-sinusoidal waveforms │
│ └─ Can damage instruments │
│ │
│ UNEXPECTED START │
│ ├─ May start automatically │
│ ├─ Remote signal can activate │
│ └─ Apply LOTO at power supply │
│ │
└─────────────────────────────────────────────────────────┘
Capacitor Discharge Time
| VSD Size | Minimum Wait Time |
|---|---|
| < 10 HP | 5 minutes |
| 10-50 HP | 10 minutes |
| 50-200 HP | 15 minutes |
| > 200 HP | Check manual |
Inspection and Maintenance
Electrical Checklist
ELECTRICAL INSPECTION - COMPRESSORS
Date: _________ Inspector: _________
PANELS
[ ] Doors close properly
[ ] No overheating (thermography)
[ ] Arc flash labels present
[ ] Working space clear
WIRING
[ ] No visible insulation damage
[ ] Connections tight
[ ] No exposed conductors
[ ] Conduits in good condition
MOTORS
[ ] No abnormal noises
[ ] Ventilation unobstructed
[ ] Ground connections verified
[ ] Amperage within nameplate
CONTROLS
[ ] Stop buttons work
[ ] Indicators operate correctly
[ ] Alarms tested
Observations: _________________________________
Infrared Thermography
| Temp Difference | Action |
|---|---|
| 1-10°C above normal | Monitor |
| 10-25°C above normal | Schedule repair |
| 25-40°C above normal | Urgent repair |
| >40°C above normal | Immediate action |
Training
NFPA 70E Requirements
| Work Type | Required Training |
|---|---|
| De-energized work | Basic electrical |
| Energized work | Qualified electrical + Arc Flash |
| Supervision | Hazard awareness |
| Operation | Safe equipment operation |
Golden Rule
Always assume a circuit is energized until you personally verify it is de-energized. Never rely on others' word or visual indicators.