Chapter 9: Calculator

Interactive Engineering Calculators for Lightning Protection and Network System Design

This chapter provides five interactive engineering calculators to support lightning protection and network system design decisions. Each calculator is directly linked to a specific design choice — from sizing fiber uplinks to selecting SPD cascade levels — ensuring that infrastructure sizing decisions are made with full awareness of their surge exposure implications. All calculations update in real time as inputs are adjusted.

Network Bandwidth Calculator

Estimate required uplink bandwidth to determine where fiber boundaries and media converters should be placed. Fiber uplinks at zone transitions eliminate copper surge paths — this calculator helps justify the fiber-first decision with real numbers.

Inputs

200
1.5
4.0
1.20
30%
65%

Results

Peak Aggregate Traffic 1,200Mbps
Required Effective Throughput 1,872Mbps
Recommended Link Capacity 2,880Mbps
Suggested Port Class 10G
Utilization at Peak65%
Fiber uplinks recommended at zone transitions. At this bandwidth, 10G fiber eliminates copper surge paths and provides sufficient headroom for storm-related rerouting.
Formulas
T_peak = N × T_avg × K_peak
T_eff = T_peak × K_oh × (1 + H)
C_link = T_eff / U_max

Storage Capacity Calculator

Estimate storage required for logs, monitoring data, and critical records. After a lightning event, UPS logs, SPD alarms, and network telemetry are essential for root-cause analysis. Insufficient storage causes log loss at the worst possible time.

Inputs

200
30
0.60
2
1.25
1.30

Results

Raw Retained Data 6,000GB
After Compression 3,600GB
Total Required Capacity 11.7TB
Raw Data
6,000 GB
Compressed
3,600 GB
With Replication
7,200 GB
Final Required
11.7 TB
Size storage systems with SPD-protected power feeds and rack bonding. Storage arrays must be included in the earthing and bonding schedule.
Formulas
S_raw = D_day × R
S_comp = S_raw × K_comp
S_req = S_comp × K_rep × M × G

PoE Power Budget Calculator

Determine PoE switch and UPS sizing, and identify whether outdoor PoE copper runs should be converted to fiber with local power. PoE copper is a primary surge entry path — this calculator helps quantify the power budget and identify high-risk segments.

Inputs

24
15.4
0.70
0.90
80
15
0.90

Results

Total PoE Delivered Power 258W
Switch Input Power (PoE) 287W
Total Switch Power 367W
UPS Energy Required 102Wh
PoE Load vs Switch Rating72%
For outdoor PoE devices: consider fiber + local power injection to eliminate copper surge paths. Install PoE-rated SPDs at both switch and device ends for any remaining outdoor copper runs.
Formulas
W_poe = P × W_dev × K_div
W_poe_in = W_poe / K_eff
W_total = W_poe_in + W_sw
E_ups = (W_total × t/60) / K_ups

SPD Coordination Calculator

Verify that your SPD cascade provides adequate protection voltage (Up) at each stage and that the residual voltage at the equipment is within the equipment's withstand level (Uw). Also checks minimum separation distance between SPD stages for coordination without additional decoupling inductance.

Inputs

2.5
1.2
0.80
1.5
0.50
5.0

SPD Cascade Visualization

Type 1
2.5
kV Up
→
Type 2
1.2
kV Up
→
Type 3
0.8
kV Up
→
Equipment
1.5
kV Uw
Residual Voltage at Equipment 0.80kV
Protection Margin (Uw - Up3) 0.70kV
Lead Inductance Penalty ~1.0µH
Protection Margin47%
Cascade coordination is adequate. Ensure Type 1 and Type 2 are separated by ≥10 m or use a decoupling inductance ≥1.5 µH if closer.
Key Rules
Up1 > Up2 > Up3 (cascade)
Up3 < Uw (equipment protected)
Lead inductance ≈ 1 µH/m × lead length
Separation ≥ 10 m or add decoupling

Earth Resistance Estimator

Estimate the earth resistance of a vertical rod electrode system based on soil resistivity and electrode geometry. Use this to determine how many rods are needed to achieve the design target, and to assess whether the existing earthing system is adequate for the site's lightning protection requirements.

Inputs

100
2.4
16
4
3.0
10

Results

Single Rod Resistance 27.4Ω
Spacing Factor η 0.66
Estimated System Resistance 4.5Ω
Rods Needed for Target 3rods
Resistance vs Target45%
Estimated resistance is within the design target. Verify with actual measurement using the fall-of-potential method after installation.
Single Rod
27.4 Ω
System (4 rods)
4.5 Ω
Design Target
10 Ω
Dwight Formula (single rod)
R = (ρ / 2πL) × [ln(4L/d) − 1]
R_system ≈ R_single × η / n
η = spacing factor (0.5–0.9 typical)