TL;DR
PEMDAS (Order of Operations): Mathematical evaluation rule: Parentheses, Exponents, Multiplication/Division (left to right), Addition/Subtraction (left to right).
PEMDAS (Order of Operations)
Definition
Mathematical evaluation rule: Parentheses, Exponents, Multiplication/Division (left to right), Addition/Subtraction (left to right).
Regulatory Context
NEC regulatory requirements for pemdas (order of operations):
Article 480 (Batteries):
- 480.5: battery location ventilation requirements
- 480.6: battery rack requirements and seismic bracing
- 480.9: disconnecting means requirements
Article 240 (Overcurrent Protection):
- 240.4(D): small conductor protection (14AWG=15A, 12AWG=20A, 10AWG=30A)
- 240.6: standard fuse/breaker sizes 15, 20, 25, 30, 35, 40, 45, 50, 60
- 240.21: tap rules 10-foot tap, 25-foot tap
Article 220 (Branch-Circuit, Feeder, and Service Load Calculations):
- 220.12: general lighting 3 VA/sq ft for dwelling
- 220.18: appliance load first 10kVA at 100%, remainder at 40%
- 220.55: cooking equipment demand factors (Table)
Common Errors
Common mistakes related to pemdas (order of operations) that electricians must avoid:
- Double-tapped breaker
- Two conductors on a single-pole breaker not rated for multiple conductors
- Undersized conductor
- Wire ampacity insufficient for overcurrent device rating per Table 310.16
- Missing GFCI
- Bathroom, kitchen, garage, outdoor, and crawl space receptacles require GFCI per 210.8
- No AFCI protection
- Bedrooms and living areas in new construction require AFCI per 210.12
Patient Communication
Clear communication about pemdas (order of operations) with patients, families, and the healthcare team is essential. Use standardized handoff tools (SBAR) for shift changes and transfers. Verify understanding by asking the patient to repeat key information back to you.
Calculation Methods
Calculations for pemdas (order of operations):
| Formula | Equation | Example |
|---|---|---|
| Power (3-phase) | P = 1.732 x E x I x PF | 480V x 20A x 0.85 x 1.732 = 14,117W |
| Conduit fill | 1 wire=53%, 2 wires=31%, 3+ wires=40% of conduit area | 4 x 12AWG THHN (0.0133 sq in) = 0.0532 sq in. 3/4 inch EMT allows 0.213 sq in (40%). OK. |
Safety Considerations
Safety requirements relevant to pemdas (order of operations) in electrical work:
- Lockout/tagout (LOTO): de-energize, lock, tag, try, verify zero energy before working on equipment
- Working space clearances per 110.26: minimum 3ft depth, 30 inch width, 6.5ft headroom for under 600V equipment
- PPE categories 1-4 based on incident energy level (cal/sq cm): Cat 1 = 4 cal/sq cm, Cat 4 = 40 cal/sq cm
- Ground fault protection of equipment required on 480Y/277V services over 1000A per 230.95
Why It Matters
Tested directly on the IBEW aptitude exam. Incorrect order of operations leads to wrong answers.
Related Terms
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