One system that is often overlooked in the development of Voice over IP (VoIP) phone systems is the uninterruptible power supply (UPS) in access level cabinets. This is due to the transition from a traditional PBX telephone system, where everything is powered by a central PBX. To a distributed system of VoIP phones connected to network switches. If a UPS Online UPS is not installed to provide clean power to the network switches that supply Power over Ethernet (PoE) to the IP phones. There is a good chance that the system will detect strange activity on the phones. This is due to the nature of AC and DC power and how the power is transmitted over the data network to the handsets.
A necessary starting point for the discussion is agreeing that VoIP should provide better performance. And reliability than the traditional phone system it replaces, which means no trade-offs. In the event of a power outage in a building, a traditional phone system will still power the phones for at least a few minutes. And if a good-sized UPS is connected to the phone system in the phone room, even longer. This means that IP phones should not be powered from a wall outlet.
But from an Ethernet cable that also connects them to the network. That the LAN switches that power the phones have large enough UPSs of the right type to power all the connected phones. PoE switches are also used to power phones, security cameras, wireless access points, and security systems. Making it even more important to plan the power supply properly! Visit also: UPS Systems for Industry
Traditional LAN switches that do not support PoE consume about 50W of power. PoE switches with 24 and 48 ports can consume between 400 and 1200 W. Depending on the model and the devices connected to the ports. Most IP phones consume about 8 W of power, so a 48-port PoE switch typically consumes about 400 W. When video cameras and monitors are added to the IP phones. The power consumption increases to about 16 W per phone. If less than half of the switch’s 48 ports are used to power the devices, a 400 W switch is sufficient. But if the deployment is dense, more powerful switches should be used.
LAN switches are typically powered by 120 volts AC from conventional outlets. This AC power is converted to DC power in the switch as efficiently as possible. That is usually divided into 3, 5, 12, and 48-volt busses. 48 volts DC is used to power VoIP phones. Since an Ethernet network can extend up to 100 meters. The PoE specification requires that there be enough power at the end of the Ethernet line to power the device.
DC power is safer, but not as efficient as AC. Voltage and power losses occur on a long, thin cable. For example, if a switch is powered by 48 VDC. The voltage drops to about 41 VDC at the end of 100 meters of Cat 5e cable. The IEEE 802.3af specification requires a minimum voltage of 44 volts at the output of the switch. This means that a device using PoE DC power expects at least 37 VDC. If the LAN switch were powered by 120 V AC, there would be no problem. But that is not always the case.
A building’s electrical power supply can vary widely. There are three main types of UPS: standalone, line-interactive, and online. Both use different technologies to provide power to connected equipment in different ways. The problem with some technologies is that when the voltage at the LAN switch drops below a certain level. Such as 110 VAC, the DC voltage delivered via PoE to the phones at the end of the long Ethernet cabling drops below 37 VDC. And the phones either reboot or simply don’t work.
– Stand-alone UPSs conduct the mains voltage directly from the input to the output until the mains voltage drops below a certain value, e.g. 107 VAC. At this point, the internal switch is switched and the output power is provided by the battery and inverter. This works well in the event of a power outage, although the drop in power causes remote phones to reboot just when they are needed most.
– Line-interactive UPSs compensate for fluctuations in line voltage by varying the AC voltage with a transformer. For example, if the mains voltage drops to 113 VAC, the UPS converts the AC voltage to 123 VAC. It can do this until the mains voltage is too low to provide enough current for rated power. And then switches to battery operation, just like a standalone UPS.
– Online UPSs are designed differently because they do not use a switch to switch to a battery. Instead, the AC current is converted to DC, and then the DC current is converted back to AC. Full double-conversion requires more expensive components but has several significant advantages. First, the output voltage is always 120 VAC at a constant frequency of 60 Hz. The second advantage is that additional batteries can easily be inserted into the DC bus, allowing the UPS to provide several hours of emergency power at rated load.
An online UPS is the right type of UPS to use when LAN switches with PoE are used to power phones and other devices connected to the network because they provide reliable power at the right voltage and frequency. And because the dual-conversion system operates continuously, the UPS is not subjected to additional stress in the event of a power failure and continues to function reliably. Standalone and line-interactive UPSs use the other system precisely when it is needed most, and there is a chance that the internal switching and battery system will fail in the event of a sudden load.
UPSs are not expensive compared to the rest of the VoIP system, but if they are not provided for at the planning stage, they are often overlooked. When planning UPSs for access cabinets, it’s also important to make sure there’s enough power for the cabinets. A typical dedicated 20-amp 120-volt AC circuit can provide about 2,400 watts of power, which sounds like a lot of the circuit is really just for the cabinet. However, if you plan to install more than five 400-watt switches in the cabinet, there is a good chance that the cabinet power supply will have to be upgraded as well.
A single UPS can typically provide power for 5-15 minutes at full load. If the disaster recovery plan requires PoE-powered equipment to last longer, battery packs should be added to the UPS.
After all, UPS batteries wear out and need to be replaced every 3-5 years. If your disaster preparedness plan does not include manually checking every closed circuit breaker on UPS units that have failed battery warning lights, it is wise to plug the UPS units into the network and monitor them with power monitoring software.
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