If you can't see your rack's power load, you won't know it's overloaded until a breaker trips. A rack's real limit is its power feed and its PDU's rating, not the number of empty sockets. Basic PDUs show nothing, so load creeps up as servers, switches and storage are added. The trip usually comes at the worst moment: when one of two redundant feeds fails and the other has to carry everything. A metered PDU shows the load. A switched PDU adds remote control of each outlet. For most racks, the fix is a metered PDU, an alert threshold, and keeping each feed loaded lightly enough to carry the whole rack on its own.
What do the different types of rack PDU show you?
| PDU type | What you can see | What you can control | Example (SourceIT price) |
|---|---|---|---|
| Basic | Nothing | Nothing | APC Basic 1U 16A, 12× C13 (S$278.75) |
| Metered (input) | Total current on a local display, and over the network on some models | Nothing | Eaton FlexPDU G2 Metered Input 1U (S$386.40); APC NetShelter Metered AP8858 (S$777.50) |
| Monitored / upgradeable | Remote input metering | Nothing (upgradeable) | Vertiv Geist Monitored 32A 0U (S$828) |
| Per-outlet metered and switched | Load on each outlet | Switch each outlet on or off | Eaton FlexPDU G2 Managed 0U (S$913.20) |
| Switched | Metering | Remote reboot, power-on sequencing | APC NetShelter Switched AP7920B (S$956.25); Vertiv Geist Switched 32A 0U (S$1,872) |
Source: SourceIT listings (listed 8 Nov 2026); PDU type names follow common industry use and the vendors' product titles. Exact features vary by model, so check each datasheet. Prices change; ask for a current quotation.
Why do racks get overloaded without anyone noticing?
Because nothing in a basic setup tells you. A basic PDU is just a set of outlets with a breaker. You can plug in another server as long as there's a free socket, and the PDU gives no warning until the current exceeds its breaker or the feed's breaker. Racks grow by small additions: another switch, a NAS, a second firewall, a GPU server. Each one looks harmless. Together they can push a 16A feed close to its limit.
Messy cabling makes it worse. When nobody knows which cable goes where, nobody knows which feed each device is on. We cover the wider cost of that in our post on messy network cabinets.
Why does a rack trip when one power feed fails?
Many servers have two power supplies, connected to two PDUs on separate A and B feeds. In normal operation the load is shared, so each feed carries roughly half. If feed A fails, or someone switches off its UPS for maintenance, feed B suddenly carries everything. If each feed was running at 60% of its rating, B is now at 120%, and its breaker trips. The redundancy you paid for takes the rack down instead of keeping it up.
The rule that follows: each feed must be able to carry the whole rack alone. A common practice is also to keep continuous load at or below 80% of a circuit's rating. That figure comes from the US electrical code and is widely used as good practice; check Singapore requirements with a licensed electrician. Combining the two gives a planning limit for normal operation:
- 16A feed at 230 V: about 3.7 kVA capacity. At 80%, 2.9 kVA for the whole rack, so each feed should normally carry no more than about 1.5 kVA (CALC).
- 32A feed at 230 V: about 7.4 kVA. At 80%, 5.9 kVA total, so about 2.9 kVA per feed in normal operation (CALC).
- 32A three-phase at 400 V: about 22 kVA capacity (CALC: √3 × 400 × 32).
The same 80% guidance applies to the UPS behind the PDU: APC recommends not exceeding 80% of a UPS's rated capacity. Our line-interactive vs online UPS guide covers choosing the UPS for a rack.
Each power feed must be able to carry the whole rack by itself. If both sides together are near the limit, your redundancy is an outage waiting to happen.
Why is this getting more urgent?
Rack power density is rising fast at the high end. NVIDIA's reference architecture for four DGX B300 systems works out to about 56 kW per rack, and OEM figures for a GB300 NVL72 rack are about 132–142 kW. Few offices will host those, but the same trend reaches smaller rooms: a single GPU server or a four-GPU workstation can draw more than an entire rack of older servers. If AI hardware is coming into your server room, plan its circuit before it arrives. See also our DGX Station power and heat guide.
Heat rises with power. ASHRAE's 2021 thermal guidelines recommend inlet air of 18–27 °C for data-centre equipment. Singapore's 2025 annual mean outdoor temperature was 28.1 °C, according to the Meteorological Service, so a small server room depends entirely on its cooling. Temperature sensors on the PDU or network card catch a failing air-conditioner before the servers do.
What should you monitor, and who should get the alert?
- Total current per feed. Set a warning well below the breaker rating, and a critical alert at your planning limit.
- Load on each outlet, if the PDU supports it. This shows which device is drawing the most and makes it easier to balance A and B.
- Temperature and humidity at the front of the rack, where equipment draws in air.
- UPS status: on battery, battery fault, load percentage.
Monitoring only helps if someone acts on it. Send alerts by email or SNMP to a person or a monitoring system that is watched out of hours, and review the readings whenever you add equipment. A switched PDU adds one more benefit: you can remotely power-cycle a hung device instead of sending someone to the server room.
A small rack may not need a switched PDU. For a single 1–2 kW cabinet on a 16A feed, a metered PDU plus the UPS's own load display is often enough. The point is to see the number. If your rack still runs on household power strips, read power strips vs rack PDUs first.
Buying in Singapore
SourceIT lists rack PDUs from APC, Eaton and Vertiv (listed 8 Nov 2026). For visibility on a budget, the Eaton FlexPDU G2 Metered Input 1U is S$386.40 and the APC NetShelter Metered AP8858 is S$777.50. For 32A racks, the APC Metered 2U 32A (AP7822B) is S$1,407.50 and the Vertiv Geist Monitored 32A 0U is S$828. For per-outlet control, see the Eaton FlexPDU G2 Managed 0U at S$913.20 or the APC NetShelter Switched AP7920B at S$956.25. Add the APC temperature and humidity sensor (S$240) to an APC network card for environmental alerts. More in our Eaton rack PDU collection. Tell us your feed rating and equipment list and we'll suggest a layout. Prices change; ask for a current quotation. Use Request for Quotation on the product page, call (65) 6978 3502, email Sales@sourceit.com.sg or use our contact page.
Frequently asked questions
What is the difference between a metered and a switched PDU? A metered PDU shows the current load, locally or over the network. A switched PDU also lets you turn individual outlets on and off remotely, for reboots and power-on sequencing.
How much can a 16A rack PDU carry? About 3.7 kVA at 230 V. Planning at 80% gives about 2.9 kVA, and with A and B feeds each side should normally carry about half of that.
Why did my rack trip when only one UPS failed? The remaining feed had to carry the whole load. If both feeds together were above one feed's limit, the second breaker trips too. Keep each feed light enough to carry everything alone.
Do I need a switched PDU for a small office rack? Not always. A metered PDU and the UPS load display are often enough for a 1–2 kW cabinet. Switched PDUs pay off when remote reboots save a site visit.
What temperature should a server rack be? ASHRAE's 2021 guidelines recommend inlet air of 18–27 °C. Put sensors at the front of the rack, where equipment draws in air, and alert someone who can act.
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