Ethernet Cable for VoIP: PoE First, Bandwidth Second
Quick answer / TL;DR: Short answer: Cat5e is enough for a VoIP phone; Cat6 adds margin and is the better choice for new runs. The phone needs PoE from the switch, typically class 2 or 3, so confirm the switch budget and the cable's current capacity. Configure QoS so voice traffic is prioritised over file transfers.
Three PoE adapters: injector adds power, splitter removes it, midspan sits in the run.A VoIP call uses well under 1 Mbps. The cable requirement is therefore about power and reliability, not bandwidth.
PoE class and switch configuration decide whether the phone works at all.
Power Classes
| Standard | Class | Power at port |
|---|
| 802.3af | 0 to 3 | Up to 15.4 W |
| 802.3at | 4 | Up to 30 W |
| 802.3bt | 5 to 8 | Up to 90 W |
A desk phone typically draws under 10 W, which sits comfortably inside 802.3af.
Practical Configuration
- Enable PoE on the port, not globally
- Set QoS trust for voice VLAN
- Provide a PC pass-through port if needed
- Label ports by extension
- Test power budget per switch
The pass-through port is often overlooked: a phone with a PC port doubles the port count per desk.
Real-World Applications
A 30-desk office with PoE phones uses Cat6 to each desk and a switch with a measured power budget above the sum of phone draw. A warehouse with long runs uses the same cable but checks voltage drop, because the run may be close to 90 m.
Standards and Verification
| Reference | Relevance |
|---|
| IEEE 802.3af and 802.3at | PoE |
| TIA-568.2-D | Cabling |
| IETF RFC 3550 | Real-time transport |
Power draw for a specific phone model is not provided in the knowledge base. Check the datasheet.
References
- IEEE 802.3af, Power over Ethernet
- IEEE 802.3at, PoE Plus
- IETF RFC 3550, RTP
Practical Notes
Measure the switch power budget before adding phones. It is the number that limits deployment.
Related reading: ethernet cable — blogs/news/ethernet-cable
Related reading: white ethernet cable — blogs/news/white-ethernet-cable
Related reading: weatherproof ethernet cable — blogs/news/weatherproof-ethernet-cable
Frequently Asked Questions
How much bandwidth does VoIP need?
Under 1 Mbps per call.
Do I need Cat6?
Cat5e works; Cat6 gives margin.
Why does a phone reboot?
Insufficient PoE budget.
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