Canadian Consulting Engineer

UPS — the advantages of clustering

January 1, 2000
By Canadian Consulting Engineer

POWER PROTECTIONWhen configuring power protection for computer networks, some designers use one Uninterruptible Power Supply (UPS) unit for every piece of equipment to be protected. However, in many a...


When configuring power protection for computer networks, some designers use one Uninterruptible Power Supply (UPS) unit for every piece of equipment to be protected. However, in many applications, particularly in medium to large-sized networks, “clustering” critical network equipment offers your client many advantages. The equipment cluster should be protected by a single UPS in order to achieve greater security, lower costs, and improved network performance and service quality.

Use of 3.5 kVA – 18 kVA on-line UPS’s is growing as an increased number of end users adopt a clustered network strategy. The opportunity for clustered protection is defined by the geography of the site. Targets are server “farms,” network rooms, equipment closets and multiple racks, as well as on-site wiring to distribute conditioned power or for plans to install power distribution systems.

Why does it make sense to support these clustered loads with one UPS?

higher reliability (on-line technology, fewer components, inclusion of internal and external bypass, power module control)

higher performing UPS’s (on-line units with voltage and frequency regulation)

easier management on the network

lower cost — fewer SNMP (single network management protocol) cards i.e. it supports multiple operating systems

lower future cost to maintain and support (one UPS, not multiple)

increased space use

orderly shutdown/monitoring of multiple operating systems

easier cleaning, installation, movement and maintenance (fewer units and batteries to test)

single battery issue, not multiple

UPS can be sized for future growth.

In general, in order to minimize risk, an on-line UPS with voltage and frequency regulation is in order. On-line technology draws power from an AC utility source and conditions it before sending it to a sensitive piece of electronic equipment. This conditioning assures that no matter what power surges, sags or brown-outs occur on the AC line, the power delivered to the device is pure and stable. At the same time the UPS continually recharges the battery, so if power is interrupted, back-up is immediately available. An inverter in the UPS converts the DC from the battery to the AC needed by the electronic system.

The following are points to look for regarding UPS devices when buying a cluster system:

A power management function which affords the user complete control of connected equipment, allowing for orderly shutdown or orderly start-up of network equipment. Connected loads can be switched on and off according to a user programmable schedule.

Upgrades — the kVA rating of the UPS can be increased on site, ensuring that the equipment will not outgrow the UPS. A 3.5 – 18 kVA size range allows the load to grow into the size of the UPS.

Quality — end users want continued up-time and do not want to worry that the system will fail. The UPS should be reliable, and since there is no switching involved with on-line technology, switch over time is not an issue.

Capacity — many networks change dramatically over a single year. Figure power protection requirements as far into the future as possible, and by identifying how power can be clustered onto larger, more full featured UPS’s, you may be able to reduce your total cost per VA, and at the same time reduce the need for expensive reconfigurations in the future.

A combination of clustered UPS’s and SNMP communications allows network administrators to assign priorities to protection, with a server or communications hub receiving the highest priority.

Large-scale advantage

Large-scale networks under a single roof require power systems designed expressly for mission-critical applications. This need is because a large network can create its own power problems, including:

harmonics that damage data and equipment

power sources that switch on and off continually, creating constantly shifting, unbalanced, non-linear loads

an accumulation of hundreds of lower power factor computers and peripherals that waste energy and money

power sags as equipment overloads available power sources.

A single UPS providing power to multiple loads provides a much higher degree of reliability than multiple UPS’s. Hence the educated client will accept a higher performance, on-line UPS rather than settle for the limitations inherent in a one-on-one approach.

Randy MacCleary, PE

Liebert Corporation


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