Whitepaper Rittal PDU international

Overview

PDUs come single- or three-phase with 16, 32 or 63 A; a 63 A three-phase PDU distributes a little over 43 kW, and nearly 90 kW with two redundant PDUs on separate paths. C14 inlets carry up to 10 A and C20 up to 16 A for large consumers such as blade PSUs. At 27 C inlet, servers exhaust 42-45 C air, so PDUs should be rated for ambient up to 45 C.

Relay design is examined: permanently energised mechanical relays can draw up to 50 W in a fully populated PDU, whereas bistable relays avoid this and keep their state on supply loss. Energy (kWh) is metered to +/-1 % and other values to +/-2 %; the cited PDU MTBF is 80,000 h and CMC III handles up to 32 external sensors or devices.

The power-factor section touches UPS sizing: UPSs are designed for +0.8 inductive PF while blade servers present -0.95 to -0.90 capacitive PF, so UPSs reach their limits sooner than planned. On security, SNMP v1/v2 send passwords in clear text, and SNMPv3 (RFC 3410-3419) with USM should be preferred. The paper rests on German rules (DIN VDE 0100-420) and reflects a manufacturer view.

Key points

1. PDUs come single- or three-phase at 16, 32 or 63 A; a 63 A three-phase unit distributes a little over 43 kW, nearly 90 kW with two redundant PDUs.
2. C14 inlets carry up to 10 A; C20 up to 16 A for large consumers.
3. At 27 C inlet servers exhaust 42-45 C air; PDUs should be rated for 45 C ambient.
4. Permanently energised mechanical relays can draw up to 50 W in a full PDU; bistable relays avoid this.
5. UPSs are designed for +0.8 inductive PF while blade servers show -0.95 to -0.90 capacitive PF.
6. kWh metered to +/-1 %, other values +/-2 %; PDU MTBF 80,000 h; CMC III handles up to 32 sensors/devices.
7. SNMP v1/v2 send passwords in clear text; SNMPv3 should be preferred.

Using it in design

• Keep PDU catalogue fields for phases, input A, max kW, outlet types, ambient rating, metering accuracy, relay type and management protocol (SNMPv3).
• Warn if a rear-mounted PDU rating is below the design exhaust temperature, and compute per-PDU kW from V x A x phases.
• In UPS sizing allow a (leading) load power-factor input and warn when IT PF is capacitive against the UPS rating.
• Flag SNMP v1/v2-only devices in the security check.

Who should read it

Electrical designers selecting rack PDUs and accounting for UPS power-factor effects, plus network security owners.

Related standards

• DIN VDE 0100-420
• EN 60950-1
• IEC 60320
• RFC 3410-3419 (SNMPv3)

Publication details

Authors

Rittal

Publisher

Rittal

Year

2014

Document number

5_2236

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation