| Endpoint | Qty | Watts (each) | Cable length (m) | Notes |
|---|---|---|---|---|
| Fixed IP Camera | 12 | 7 | 60 | Basic analytics, IR off |
| Wi‑Fi Access Point | 6 | 18 | 45 | Dual‑radio, moderate client load |
| Door Controller | 8 | 10 | 35 | Reader + controller, no lock power |
| VoIP Phone | 20 | 6 | 25 | Backlight and speaker use varies |
| Digital Signage Player | 2 | 55 | 30 | High draw; verify per‑port limits |
- Per device current: I = P / V, where P is device watts and V is supply voltage.
- Cable loop resistance: Rloop = Rper‑m × L, where L is cable length.
- Cable loss: Ploss = I² × Rloop.
- Source power per device: Psrc = P + Ploss.
- Usable switch budget: Budget × (1 − derate) × (1 − headroom).
- Utilization: Total Psrc ÷ Usable budget × 100%.
- Enter the switch’s total PoE budget and the number of usable PoE ports.
- Select the PoE standard to set a practical per‑port cap.
- Choose a loss model and cable type for long‑run estimation.
- Add devices with quantity, typical watts, and average cable length.
- Click Calculate and review status, remaining watts, and port usage.
- Use headroom and derating to build safe capacity for expansions.
- Download CSV or PDF to attach to submittals or commissioning reports.
PoE Standards and Port Limits
Construction networks often mix cameras, access control, and Wi‑Fi. Standards such as 802.3af, 802.3at, and 802.3bt set realistic per‑port ceilings that help prevent over‑subscription and nuisance reboots. Use the per‑port limit as a design guardrail, then verify each endpoint’s maximum draw from the datasheet and the injector or switch specification.
Budgeting for Mixed Endpoint Loads
A switch PoE budget is a shared pool, so total demand depends on both device count and device wattage. This calculator adds device power plus estimated cable loss to produce “source watts,” which is what the switch must deliver. When utilization approaches the high‑80% range, plan for growth, firmware updates, and cold‑start inrush that can momentarily increase draw.
Cable Length and Loss Planning
Long runs raise loop resistance and increase I²R losses. The impact is usually small for low‑watt endpoints, but it can matter for higher‑power signage, PTZ cameras, or multi‑radio access points. Selecting lower‑loss cabling, shortening pathways, or relocating IDFs can reduce losses and keep ports within their negotiated class limits.
Headroom, Derating, and Diversity
Headroom reserves capacity for future moves, adds, and changes. Derating reflects temperature, aging power supplies, and installation realities. The simultaneous‑load factor models diversity when not all endpoints peak together. For conservative commissioning, set diversity near 100% and include headroom so the system remains stable during power cycling and cutover events.
Example Data for a Typical Floor
With a 370 W switch budget, 15% headroom, 54 V supply, and basic loss enabled, one planning set is shown below.
| Endpoint | Qty | Watts (each) | Length (m) | PD Total (W) |
|---|---|---|---|---|
| Fixed IP Camera | 12 | 7 | 60 | 84 |
| Wi‑Fi Access Point | 6 | 18 | 45 | 108 |
| Door Controller | 8 | 10 | 35 | 80 |
| Subtotal | 272 |
Usable budget is approximately 314.5 W (after 15% headroom), leaving margin for small losses, endpoint variance, and future additions.
1) Why does the calculator add “cable loss” to device watts?
The switch must supply both the device load and resistive losses in the cable. Adding estimated loss gives a closer view of the switch’s delivered power and per‑port stress.
2) What should I enter for device wattage?
Use the datasheet’s typical or maximum PoE draw for planning. If the device has heaters, IR, or radios, model the worst expected operating mode for reliable commissioning.
3) How do I choose a PoE standard in the form?
Pick the standard supported by your switch and endpoints. It sets a practical per‑port cap so high‑draw devices are flagged before procurement or installation.
4) When should I increase headroom?
Increase headroom for phased rollouts, tenant fit‑outs, unknown future loads, or high availability needs. Many projects target 15–25% to avoid re‑cabling or switch replacement.
5) What does “simultaneous load” mean?
It is a diversity factor that reduces modeled watts if not all endpoints peak together. For cutovers and acceptance testing, keep it near 100% for a conservative check.
6) My per‑port limit is exceeded. What can I do?
Reduce cable length, move the endpoint to a higher‑class port, use a midspan/injector rated for the load, or choose a switch that supports a higher PoE standard.
7) Is this report suitable for handover documentation?
Yes. Export CSV or PDF after calculation to document assumptions, device counts, and remaining capacity. Attach it to network submittals, commissioning packs, or O&M manuals.