How to size a PoE switch and the UPS behind it

Know which PoE standard each device needs.

Power over Ethernet sends power and data over one cable, so an access point, camera or desk phone doesn't need an outlet where it's mounted.

Check each device's spec sheet for the PoE standard it needs and its maximum draw. Many access points and cameras need PoE+. Pan-tilt-zoom cameras, cameras with heaters and some Wi-Fi 7 access points can need 802.3bt.

Each standard sets a limit at the switch port and a lower one at the device. The difference is what the cable loses on the way.

• 802.3af (PoE): 15.4 W at the port, 12.95 W at the device
• 802.3at (PoE+): 30 W at the port, 25.5 W at the device
• 802.3bt Type 3: 60 W at the port, 51 W at the device
• 802.3bt Type 4: 90 W at the port, 71.3 W at the device

Add up the watts, then leave room.

A PoE switch has a total power budget, and it's separate from the port count. A 24-port switch with a budget of a few hundred watts can't run 24 devices at full PoE+ power. Add up the maximum draw of every device you'll plug in and compare the total to the budget.

Use the maximum figure from each spec sheet, not the typical one. Cameras draw more at night when their infrared lights come on. Outdoor cameras with heaters draw the most on the coldest nights.

Some switches reserve a port's full class limit as soon as a device connects, whatever it actually draws. That uses up the budget faster than the real load does. Check how your switch allocates power before you plan to the last watt.

As a rule of thumb, keep about 20 percent of the budget spare, for growth and for devices that draw more than expected.

Count ports for today and the next few years.

List every wired device: access points, cameras, phones, card terminals, printers, the recorder, the gateway and any desktop computers. Then add spare ports. A common rule of thumb is about 20 percent spare, more if you expect to add cameras.

Look at the uplink ports too. SFP and SFP+ ports take fiber modules for runs longer than 100 meters or a link to another closet, and 10G uplinks keep a busy switch from becoming the bottleneck. If you're installing Wi-Fi 7 access points, multi-gig (2.5G) ports let them run faster than 1 Gbps.

Decide between managed and unmanaged.

An unmanaged switch is plug and play. It has no settings, which is fine for a few devices on one simple network, such as a desk or a small camera setup.

A smart or web-managed switch adds VLANs and basic monitoring at a lower price than fully managed. A fully managed or cloud-managed switch adds per-port power control, alerts and remote management. Power-cycling a port from the management console restarts a frozen camera or access point without a ladder.

If one switch will carry card terminals, cameras and guest Wi-Fi, buy a managed one. You'll need VLANs.

Use VLANs to keep cameras, card terminals and guests apart.

A VLAN splits one physical network into separate ones. Typical small-business VLANs are staff, guest Wi-Fi, cameras, card terminals and phones.

Cameras get their own because many are hard to secure, and most only need to reach the recorder. Card terminals get their own because separating payment systems limits how much of the network falls under PCI DSS, the card industry's security standard. Guest Wi-Fi gets its own so a customer's phone can't see your computers.

The switch carries the VLANs, and the gateway or firewall decides what can reach what, so plan both together. Access points map each Wi-Fi network name to a VLAN, so they need to support VLAN tagging as well.

PoE switches are at /shop/switches. Gateways and firewalls that route between VLANs are at /shop/routers-gateways and /shop/firewalls.

Size the UPS for the closet.

A PoE switch powers the cameras, access points and phones plugged into it. If the switch loses power, all of them go down with it. Put the switch, the gateway, the modem or fiber box (ONT) and the recorder on a UPS.

Add up the watts. For the switch, use the maximum power consumption with full PoE load from its spec sheet. A UPS has a VA rating and a watt rating, and the watt rating is the one to size against. A common rule of thumb is to keep the load under about 75 percent of it.

Runtime comes from the manufacturer's runtime chart at your load, and it drops quickly as the load rises. Decide what the UPS is for: riding through flickers and short outages, shutting equipment down cleanly, or keeping cameras and phones up through a longer outage. The last one may need a model that takes extra battery packs.

For a network closet, a line-interactive UPS with sine wave output is the usual choice. On a site with a generator or unsteady utility power, an online (double-conversion) UPS handles the transfer better. A network card or USB connection lets the UPS send alerts and shut equipment down. Plan on replacing the batteries every three to five years.

Rack and tower UPS models are at /shop/ups-power.

Before you order.

To have the switch, gateway and UPS sized together, send your device list through /rfq?department=network-hardware.

• Every PoE device, the standard it needs and its maximum draw
• Total watts against the switch's PoE budget, with spare
• Port count with spare, plus the uplinks you need
• The VLANs you need and the gateway or firewall that will route them
• The UPS watt rating, your runtime target, and rack or tower