PoE, PoE+, PoE++ Explained: 802.3af vs 802.3at vs 802.3bt
Power over Ethernet sends DC power and data down the same RJ45 cable, but "PoE", "PoE+" and "PoE++" hide four different IEEE power tiers. This VOOHU Electronics guide lays out the standards, the power each delivers, 2-pair vs 4-pair delivery, and what they demand from the cable and connector.
The PoE standards at a glance
| Name | IEEE standard | Type | Power at switch (PSE) | Power at device (PD) | Pairs used |
|---|---|---|---|---|---|
| PoE | 802.3af (2003) | Type 1 | 15.4 W | ~12.95 W | 2 pairs |
| PoE+ | 802.3at (2009) | Type 2 | 30 W | ~25.5 W | 2 pairs |
| PoE++ (4PPoE) | 802.3bt (2018) | Type 3 | 60 W | ~51 W | 4 pairs |
| PoE++ (4PPoE) | 802.3bt (2018) | Type 4 | ~90–100 W | ~71.3 W | 4 pairs |
What the differences actually mean
PoE (802.3af, Type 1)
The original standard: up to 15.4 W from the switch, about 12.95 W usable at the device over two pairs. Enough for VoIP phones, basic Wi-Fi access points and simple IP cameras.
PoE+ (802.3at, Type 2)
Doubles source power to 30 W (~25.5 W at the device), still over two pairs. Powers PTZ cameras, dual-radio access points and thin clients.
PoE++ (802.3bt, Type 3 & 4)
802.3bt introduced 4-pair power delivery (4PPoE). Type 3 supplies 60 W (~51 W at the device); Type 4 supplies up to ~90–100 W (~71.3 W at the device). This runs Wi-Fi 6/7 APs, video conferencing units, LED lighting, building access systems and even some laptops and displays.
2-pair vs 4-pair delivery
802.3af/at deliver power on two of the four pairs (Mode A puts power on the data pairs; Mode B on the spare pairs). 802.3bt uses all four pairs, which halves the current per pair for a given power and is what enables the higher Type 3/4 wattage. Spreading current across four pairs also reduces heating and voltage drop.
Cabling and connector requirements
Higher PoE power means higher current, and current means heat and contact stress:
- Cable grade: Cat5e carries PoE electrically, but Cat6/Cat6A is recommended for 802.3bt Type 3/4 to manage temperature rise — particularly in large, tightly packed bundles where derating applies.
- Connector current rating: the RJ45 contacts must handle the per-pin current without overheating. For 4PPoE this is a real selection criterion, not a formality.
- Plating and arc resistance: disconnecting a connector under load can arc and erode the contact. Quality gold plating over proper nickel resists fretting and arcing — see our materials & plating guide.
- Integrated magnetics: PoE designs often use integrated-magnetics jacks (PoE MagJacks) rated for the bias current; see our CMC placement guide for the magnetics side.
How to choose
- Match the type to the load: phone/basic AP → PoE (af); PTZ camera/dual-radio AP → PoE+ (at); Wi-Fi 6/7 AP, lighting, displays → PoE++ (bt Type 3/4).
- Budget at the switch: confirm the PSE's total PoE power budget covers all ports at their class, not just one port's maximum.
- Specify cable and connector for the power tier, including bundle derating for 4PPoE.
Need PoE-rated RJ45 connectors?
VOOHU Electronics manufactures PoE and PoE++ (802.3bt) rated RJ45 connectors and integrated-magnetics MagJacks, with plating and contacts engineered for high-current delivery. Request datasheets or samples to validate your PoE design.
Visit www.voohuele.com · Email olivia@voohuele.com · WhatsApp +86 133 5804 1040
Frequently asked questions
- What is the difference between PoE, PoE+ and PoE++?
- PoE (802.3af, Type 1): 15.4 W source / ~12.95 W device, 2 pairs. PoE+ (802.3at, Type 2): 30 W / ~25.5 W, 2 pairs. PoE++ (802.3bt): Type 3 = 60 W / ~51 W and Type 4 = ~90–100 W / ~71.3 W, both 4 pairs.
- Does PoE++ (802.3bt) need special cabling?
- It uses all four pairs and higher current, so heat rises. Cat5e works electrically, but Cat6/Cat6A is recommended for Type 3/4, and connectors must be rated for the per-contact current. Apply bundle derating.
- How many pairs does each PoE type use?
- 802.3af/at use 2 pairs (Mode A or B). 802.3bt Type 3/4 use all 4 pairs (4PPoE), lowering per-pair current and enabling higher power.
- What voltage does PoE use?
- Nominal 48 V DC; the PSE typically outputs about 44–57 V, with negotiation and classification handled automatically by the standard.