Calculator Inputs
Example Data Table
| Device | Qty | Watts | Duty % | Peak % | Cable m |
|---|---|---|---|---|---|
| IP Camera (fixed) | 16 | 12 | 100 | 10 | 60 |
| Wireless Access Point | 8 | 18 | 100 | 15 | 45 |
| VoIP Phone | 12 | 7 | 100 | 10 | 30 |
| Door Controller | 4 | 10 | 100 | 20 | 70 |
Formula Used
- Adjusted device power (W/device) = RatedW × (Duty%/100) × (1 + Peak%/100)
- Cable efficiency ≈ clamp(0.97 − 0.0004 × Length(m), 0.85, 0.97)
- PSE load (W) = Σ( Qty × AdjustedW / Efficiency )
- PSE with headroom = PSE load × (1 + Headroom%/100)
- Planned ports = ceil(PoweredPorts × (1 + SparePorts%/100))
- Switch count = ceil(PlannedPorts / (PortsPerSwitch × Utilization%/100)) ± redundancy rule
How to Use This Calculator
- Pick a PoE level that matches your highest-power endpoint.
- Set ports per switch and a utilization target.
- Enter each powered device type with quantity and watts.
- Adjust duty and peak for realistic design conditions.
- Enter average cable lengths to refine power budget.
- Submit to view ports, switches, and power requirements.
- Export CSV or PDF for review and procurement.
Power planning for connected jobsite systems
Construction sites increasingly depend on cameras, access points, phones, and controllers that draw power from the network. A sizing worksheet prevents underpowered switches, nuisance reboots, and last‑minute change orders. Start by listing every PoE endpoint, its quantity, and its rated watts from the datasheet. Include temporary cabins, perimeter zones, and future drops to avoid piecemeal upgrades.
Translating device ratings into usable switch budgets
Nameplate watts are not always continuous. Duty percentage models average draw, while peak allowance covers cold starts, IR illumination, heater elements, and radio bursts. The calculator converts each device into an adjusted watt value, then sums totals across the site. This creates a consistent basis to compare mixed device types and verify per‑port power limits for the selected PoE level.
Why cable length affects available power
Longer runs increase resistance, which raises loss between the power source and the device. Even when data works, voltage drop can reduce stability at high load. By entering typical cable lengths, the tool applies an efficiency factor and estimates the PSE power required at the switch. Use average lengths by zone, and be conservative for outdoor runs and patch‑panel paths.
Sizing ports, spares, and redundancy with intent
Port counts should reflect planned utilization, not the full label count. Reserving capacity supports moves, adds, and quick troubleshooting. Spare percentage increases planned ports, while utilization controls how densely each switch is loaded. For critical security and access control, apply a simple redundancy rule such as N+1 or a minimum stack, then verify uplinks and rack space.
Turning results into procurement and commissioning actions
Once the tool suggests switch quantity and PoE budget per switch, select models that meet or exceed the tiered budget and port plan. Confirm AC input, circuit loading, and heat management in the enclosure. During commissioning, measure real draw on representative ports and compare to assumptions, then update the CSV for as‑built documentation and handover. Always document labels, patching, and grounding before energizing.
FAQs
1) Should I size to device “maximum” or “typical” watts?
Use rated or maximum when safety is critical. If you have measured typical draw, model duty and peak to reflect reality, then keep headroom for growth and temperature effects.
2) What headroom percentage is practical for projects?
A common planning range is 15–25%. Use higher values when device mix is uncertain, outdoor heaters are present, or future additions are likely within the same switch cabinet.
3) Why does cable length change the required budget?
Long runs increase resistance and power loss. The switch must source more power to deliver the same load at the device, especially when several endpoints draw near their limits.
4) How do I handle mixed PoE levels on one switch?
Choose the highest required per‑port level for checking limits, then rely on the total budget calculation. If only a few high-power devices exist, consider placing them on dedicated ports or switches.
5) Is N+1 always necessary for redundancy?
Not always. Use N+1 for security, access control, and high-impact systems. For noncritical devices, spares and reasonable utilization may be enough, combined with clear labeling and spare patch leads.
6) What should I verify during commissioning?
Check actual per-port draw, switch PoE budget alarms, and AC circuit loading. Confirm cable lengths and terminations, then update the exported CSV to match the as‑built device list.