A rack PDU is the least glamorous thing in the rack and the one that takes everything down when it's wrong. Here's how to pick one in the right order: the circuit first, then the outlets, then the intelligence.
1. Start at the wall, not the rack
What matters first is the circuit feeding the rack: its voltage, its amperage, and the shape of the receptacle. Look at the outlet and the breaker, not at the equipment.
- 120V 15A, a standard wall outlet (NEMA 5-15R). Common in small closets.
- 120V 20A, a 5-20R with a sideways slot, or a twist-lock L5-20R.
- 120V 30A, almost always twist-lock (L5-30R). Dedicated circuits in server rooms.
- 208V 20A or 30A, twist-lock L6-20R or L6-30R, in data centers and larger rooms.
Buy the PDU whose plug matches. Adapters that change plug shape are a red flag: they let you connect a PDU to a circuit it was never designed for.
2. Work out how much of that circuit you can actually use
Electrical code treats equipment that runs all day as a continuous load, which means planning to no more than 80% of the breaker's rating.
| Circuit | Usable current | Usable watts |
|---|---|---|
| 120V 15A | 12A | about 1,440W |
| 120V 20A | 16A | about 1,920W |
| 120V 30A | 24A | about 2,880W |
| 208V 30A | 24A | about 4,990W |
Add up the real draw of what's going in the rack: switches with PoE budgets, a UPS charging its batteries, a couple of servers, a recorder. If the total lands near the usable figure, move up a circuit size or split the load across two.
This is also the argument for 208V in bigger rooms. The same equipment draws roughly half the current at 208V that it does at 120V, so one 30A circuit carries far more gear.
3. Match the outlets to the cords you actually have
Count the plugs going into the rack and check their shape.
- NEMA 5-15R takes ordinary three-prong cords: most switches, injectors, recorders and small appliances.
- NEMA 5-20R has a T-shaped slot and accepts both 5-15P and 5-20P plugs, so it's the more flexible choice on a 20A circuit.
- IEC C13 takes the kettle-style cord on servers, larger switches and most UPS units.
- IEC C19 is the bigger one, for blade chassis, large UPS units and high-draw servers.
Buy a few more outlets than you need today. Nobody has ever regretted spare outlets, and our basic PDUs come in counts from 6 to 24. If you're unsure which connector you're looking at, the plug chart shows them side by side.
4. Pick the shape: 0U vertical or 1U horizontal
0U vertical strips mount down the side of the rack and use no rack spaces at all. Ideal in a full rack, and they put outlets near the gear so cords stay short. They need a rack deep enough to take them.
1U or 2U horizontal units mount in a rack space like any other device. They're the practical choice in shallow wall-mount cabinets, in two-post racks, and anywhere access matters more than density.
5. Decide how much intelligence you need
This is where the price moves, so match it to the site rather than buying features by reflex.
- Basic: power distribution, nothing else. The right answer for a closet you visit anyway.
- Metered: a display showing the load, so you know what's left before adding gear.
- Switched: reboot an outlet from a browser. Pays for itself the first time it saves a drive.
- Transfer switch: two power feeds, with automatic failover for single-cord equipment. We don't have one listed right now, so email us for a quote.
Our guide on metered versus switched works through the cases in more detail.
6. Check cord length and mounting before you order
Measure from the rack to the receptacle and add slack for cable management. Cords run from about 6 to 15 feet, and a PDU that can't reach the wall is a PDU coming back. Check that the mounting hardware suits your rack, especially on two-post and open-frame installs.
Where to start in our range
- Small closet on a standard 15A outlet: the Middle Atlantic PDX-915R, 1U horizontal, 5-15P plug, nine 5-15R outlets.
- 120V 20A circuit: the APC AP9563, 1U horizontal, 5-20P plug, ten 5-20R outlets.
- Twist-lock 20A circuit: the Middle Atlantic PDT-2020TL-NS, a vertical strip with an L5-20P plug and twenty 5-15R outlets.
- 208V 30A server rack: the APC AP7541, 0U vertical, L6-30P plug, 20 C13 and 4 C19 outlets.
Still deciding?
Email support@rackit.com with the receptacle type and a list of what's going in the rack, and we'll tell you which unit fits, usually within one business day. If you buy regularly, a trade account gets you project pricing on multi-unit orders. Browse everything in rack PDUs.