Hub safely shares power and data down the line
- By John Breeden II
- May 19, 2004
The 24-port PowerSense hub supplies electricity from an Ethernet to remote devices that can accept it'and safely detects which ones can't.
Henrik G. de Gyor
Not all power sources are equal for hooking up new remote devices to a network.
Ideally, webcams, wireless hubs and IP phones draw power from the Ethernet they're connected to. But even if they are power-over-IP-ready, you still have to connect them through a device that puts power into the data cable, or else default to a separate power plug.
That extra cord can spell trouble for network planners.
Category 5 cables snake about 100 feet through walls and ceilings to their destinations. But most power cords are only a couple of feet long.
So either the power source has to be close to the end device'which might require an uninterruptible power system with surge protection'or you have to run extension cords in addition to network cables.
Another solution is to place all power-over-IP devices together, and that can be inconvenient or produce a tangled mess of cables.
The 24-port PowerSense Modular MidSpan In-Line Power Hub meets all these power-over-Ethernet needs.
Power over Ethernet works because not all the wires in a Category 5 cable actually carry data. A Category 5, 5e or 6 cable has enough extra wiring inside to deliver power to remote devices without the need for an extra cord. This doesn't interfere with data transmission.
You plunk down the hub inside a wiring closet, or fit it into a standard 19-inch rack, and plug it in. Then you run the data cables through the hub and out to your remote devices. If a remote device can draw power from the Ethernet, you don't need to worry about powering it above and beyond hooking up the data cable.
We found another advantage to plugging all the devices into the hub: We could use a single UPS to protect all the remote devices on our network, some of them 50 feet away in different directions. In GCN Lab tests, we connected 18 power-over-Ethernet devices to the hub and then connected it to a UPS. All the devices worked fine.
That's a lot better than buying a UPS for every device.
When we pulled the plug on the UPS to simulate a power failure, the hub continued providing power. Caution: Make sure you have the right size UPS. Each port on the hub will supply 15.6 watts of power, which is the IEEE specification.
Setting up your network with a power-protected hub ensures that IP phones and wireless hubs will continue to work in a power outage.Easy does it
Setup was easy. We simply connected the hub to a UPS connected to AC power. Then we ran the data cables into the hub and ran separate cables back out of the hub to the remote devices.
There's even a safety measure, we found. No power will go down the wire to any device that cannot handle power over Ethernet. The hub first confirms the ability of a remote device to accept power before sending any, protecting the health of devices not designed to use it.
We tested this precaution, and it worked every time. Detection was very fast'a few seconds at most. That's no longer than the time for most devices to register themselves on a network.
As power over IP becomes increasingly popular, a network power hub makes a lot of sense and extends the usefulness of the Ethernet standard.
John Breeden II is a freelance technology writer for GCN.