Electrical Cheat Sheet

1. Ohm's Law

V = I × R

2. Power

P = V × I

P = I² × R

P = V² / R

3. Energy Consumption

E = P × t

4. Series Circuits

R_total = R1 + R2 + R3 + ...

5. Parallel Circuits

1/R_total = 1/R1 + 1/R2 + 1/R3 + ...

6. Voltage Division (Series)

Vx = (R_x / R_total) × V_total

7. Current Division (Parallel)

Ix = (R_total / R_x) × I_total

8. AC Formulas

V_RMS = V_peak / √2

I_RMS = I_peak / √2

9. Power Factor

PF = cos(ϕ) where ϕ is the phase angle

10. Reactance and Impedance

X_L = 2πfL (Inductive Reactance)

X_C = 1/(2πfC) (Capacitive Reactance)

Z = √(R² + (X_L - X_C)²)

Remember: Always check units and safety factors while designing circuits.

Power Design Guide

Initial Steps Before Low Voltage Power Design

Review Construction/Installation Type

Determine codes to follow: ASHRAE or IBC

Coordinate with state, local, and city ordinances

Determine if LEED Project

Coordinate energy analysis plan

Either with outside consultant OR proceed with internal design

Initial Demand Load Estimating

Need SQ Estimates from Architectural Divisions before continuing

Review NFPA 70 - Article 230 for assistance

Load Estimating Reference

Load Type	NFPA 70 Reference	Notes
Receptacle Loads	220.14, 220.80	~180VA for each receptacle
Lighting Loads	220.12, 220.80
HVAC Loads	220.61, 440
EV Charging	625
Equipment Loads	220.42
Outside Branch Circuits	225	Site Lighting (225.25), EMG/Fire Pumps (225.30 A)

Demand Load Calculator

Service Size Estimating

Ensure proper spare capacity has been accounted for - NFPA 70 Article 220.56

Total Calculated Demand Load (kVA):

Desired Spare Capacity (%):

Service Voltage:

Recommended Service Size:

Standard Service Sizes

Common service sizes: 100A, 200A, 400A, 600A, 800A, 1000A, 1200A, 1600A, 2000A, 2500A, 3000A, 4000A

One-Line Programming

Key Considerations

Determine if service is greater or less than 1200A
Typical cutoff for Switchboard vs. Distribution Main Panelboard
Determine Customer/Project metering requirements
Ensure all loads are properly segregated and assigned metering

Panelboard Sizing Reference

Branch Load Type	NFPA 70 Reference
HVAC	Articles 440 and 220
Lighting	Article 210
Receptacles	Article 210
Emergency	Articles 700 and 701

Panel Configuration

Determine if panels are to be MCB or MLO
Size MCB accordingly - NFPA 70 Article 240 (OCP)

Conductor Sizing

Consider AL or CU conductor type
Determine conductor sizing from estimated load
Determine estimated run length
Determine voltage drop and potential upsizing - NFPA 70 Article 220.55
Determine conduit size - NFPA 70 Annex C
Must be below 30% fill rate

Microgrid Strategies

Strategy	NFPA 70 Reference
BESS (Battery Energy Storage System)	Article 706
On-Site Generation	Article 705
External Microgrid Feed Paralleling Utility	Article 705
Utility Back-Feed	Article 702

Initial Power Layout - SD

Electrical Room Requirements

Requirement	NFPA 70 Reference
Working clearances	Article 110.26
Door/Exit requirements	Article 314.20
Installation requirements	Articles 300, 430
Disconnecting means requirements	Article 225.30

Consider distance to sources of branch circuits when determining locations

Initial Layout Checklist

Ensure all project spaces have defined use

Determine common mechanical loads

Overhead Doors, HVAC, Process Mechanical, Fire Smoke Dampeners, Actuators, Unit Heaters, Make Up Air Units, Condensing units, Pumps, etc.

Receptacle Placement Guidelines

Typically mounted at 18" afg - NFPA 70 Article 210.52(A)(1)
Typically no longer than 6' away from desired use/appliance - NFPA 70 Article 210.52(A)(1)
Determine receptacle use for tables/counters
Determine if space requires GFCI receptacles - NFPA 70 Article 210.8(B)
Determine if space requires floor box receptacle installations - NFPA 70 Article 210.52(A)(3)

Load Estimator

Project Information

Project Name:

Building Type:

Total Building Area (sq ft):

Lighting Loads

Calculation Method:

General Lighting Load by Occupancy - NEC 2020 Table 220.12

Type of Occupancy	Unit Load (VA/sq ft)
Office Buildings	1.30
Parking Garage	0.30
Transportation	1.20
Warehouses (storage)	1.25
Schools	3.00

Unit Load (VA/sq ft):

Area for Lighting (sq ft):

Demand Factor (%):

Calculated Load:

Receptacle Loads

Calculation Method:

Unit Load (VA/sq ft):

Typically 1.0 VA/sq ft for office spaces

Area for Receptacles (sq ft):

Demand Factor (%):

Calculated Load:

HVAC & Major Equipment Loads

Equipment Name:

Type:

Connected Load:

Unit:

Voltage:

Phase:

D.F. (%):

Total Equipment Load:

Summary of Demand Loads

Load Category	Connected Load (kVA)	Demand Factor (%)	Demand Load (kVA)
Lighting	0.0	100	0.0
Receptacles	0.0	100	0.0
HVAC & Equipment	0.0	-	0.0
Total Demand Load	0.0	-	0.0

Recommended Service Size:

Ohm's Law Calculator

Voltage (V):

Current (I):

Resistance (R):

Result:

V = I × R | I = V / R | R = V / I

Power Calculator

Voltage (V):

Current (I):

Phase:

Result:

Single Phase: P = V × I | Three Phase: P = √3 × V × I

HP Conversion

HP Type:

Enter HP (leave blank if using Watts):

Enter Watts (leave blank if using HP):

Result:

Conversion Factors:
• Mechanical HP: 1 HP = 745.7 W
• Electrical HP: 1 HP = 746.0 W
• Metric HP: 1 HP = 735.5 W

Voltage Drop Calculator

Conductor Type:

RMC (Steel)

PVC

Phase:

3-phase

1-phase

Nominal Voltage (V):

Run Length (ft):

Current (A):

Load Power Factor (PF):

Wire Size	Vd (V)	% Vd

Pull/Handhole Box Sizing (Large)

Select Pull Type:

Incoming Raceways (in inches):

Outgoing Raceways (in inches):

Results

Box Length:

Horizontal Dimension:

Vertical Dimension:

Minimum Distance:

Small Junction Box Sizing

Select Configuration Type:

Incoming Raceway Sizes (in inches):

Outgoing Raceway Sizes (in inches):

Results

Box Length:

Horizontal Dimension:

Vertical Dimension:

Minimum Distance:

Conductor Sizing/Ampacity Calculator

Required Ampacity (A):

Material:

Insulation Temperature Rating:

Installation Type:

Number of Current-Carrying Conductors (Optional):

Recommended Conductor Size:

Internal Conductor Sizing

Standard Sizing Reference

Amp Range	Phase Conductor	Equip Ground	Conduit
15-20A	#12	#12	3/4"
30-40A	#10	#10	3/4"
50A	#8	#10	1"
60-70A	#6	#8	1"
80-90A	#4	#8	1.25"
100A	#3	#8	1.25"
110-125A	#2	#6	1.5"
150A	#1	#6	1.5"
175A	#1/0	#6	2"
200A	#2/0	#6	2"
225A	#3/0	#4	2"
250A	#4/0	#4	2.5"
300A	250 kcmil	#4	2.5"
350A	350 kcmil	#3	3"
400A	400 kcmil	#2	3"
500A	600 kcmil	#1	3.5"

Values are based on standard NEC guidelines. Always verify with current electrical codes.