The use of an Uninterrupted Power Supply (UPS) with any telephone system is strongly recommended. Even at sites that rarely lose electrical power, that power may occasionally have to be switched off for maintenance of other equipment. In addition, most UPSs also provide an element of power conditioning, reducing spikes and surges.

The capacity of UPS systems and the total equipment load the UPS is expected to support are usually quoted in VA. Where equipment load is quoted in Watts, multiply by 1.4 to get the VA load.

The calculation of how much UPS capacity is required depends on several choices.

What equipment to place on the UPS?
Remember to include server PCs such as the voicemail. It is recommended that the total load on a new UPS is never greater than 75% capacity, thus allowing for future equipment.

How many minutes of UPS support is required?
Actual UPS runtime is variable, it depends on what percentage of the UPS capacity the total equipment load represents. For example, a 1000VA capacity UPS may only support a 1000VA (100%) load for 5 minutes. This relationship is not linear, the same UPS may support a 500VA (50%) load for 16 minutes. Therefore, the lower the percentage of maximum capacity used, the increasingly longer the UPS runtime, for example up to 8 hours.

How frequent are the power loses?
You also need to include allowance for the UPS recharge time. For most UPS's the ratio of discharge to full recharge time is 1:10.

How many output sockets does the UPS provide?
Multiple UPS units may be required to ensure that every item of supported equipment has its own supply socket.


Example Values

The dominate factor in the power consumption of an IP Office system is the telephones attached to the control unit and any external expansion modules. This does not include IP telephones which require their own separate power supplies. If any server PCs are being used by the system, the requirements of those PCs should also be included in the assessment. Similarly support for adjunct systems such as DECT should be considered.

The following are worst case figures tested found using fully populated control units and external expansion modules:

IP500 V2A Control Unit: 115W.

IP500 Digital Station 16 External Expansion Module: 31W.

IP500 Digital Station 30 External Expansion Module: 56W.

IP500 DS16A Digital Station RJ21 External Expansion Module: 34W.

IP500 DS30A Digital Station RJ21 External Expansion Module: 60W.

IP500 Phone 16 External Expansion Module: 25W.

IP500 Phone 30 External Expansion Module: 45W.

IP500 Analog Trunk Module 16 External Expansion Module: 8.8W.