PoE dilemma: plugging in non PoE devices?

Does plugging a laptop or a computer into a PoE switch/RJ45 socket cause any damage?

I am doing some networking cable management and installed some RJ45 jack sockets where PoE devices wil be plugged in, like an Ubiquity AP or some security camras , VoIP phones.
But the workers here are clueless and careless, and I am prepraring for the worst, as always. My main fear is that they will plug in whatever device, without knowing any better.
Does the PoE injector have some sensing mechanism or the PoE switch auto negotiate if a device CAN or CAN’T be powered via ethernet cable?

If the port is using 802.11af (POE) or 802.11at (POE+) it will be fine. Power will not turn on that port unless the device needs it. If the port has passive POE (24V, or any other voltage) turned on it may damage the device if it doesn’t require power.


If the device is getting power from a POE brick I believe they are usually passive POE and ALWAYS provide power.

As @njongstra said, if it’s a POE switch then it should, according to the standard, perform a negotiation to decide how many volts and how much current it needs. So if it’s a decent brand then I wouldn’t worry. If it’s an off brand or a brick then maybe chop the end off a cable and drop a meter on it. As you are talking about phones, cameras and AP’s I hope you are on a switch not using a load of bricks.

If you are unsure I would leave the cabinet end unplugged until you connect a device. Once the device is connected then plug the brick / switch in.

If someone is then stupid enough to unplug a device to connect their laptop then they probably need a good slap. If you have to put a sticker on the port with DO NOT USE on it. I would also connect the cameras and APs using high level wiring or sockets in a false ceiling if possible to prevent people messing with them. Not so simple for phones.

I have a PoE switch with non-poe devices connected to it, didn’t experience any adverse issues.

If it is a POE switch you will not have any issues. PoE switches do not push power to the device the device pulls power from the switch.

Be careful with statements like that… Switches that supply passive POE definitely exist. Not all POE switches are Active POE (802.3af, at, bt)

True but PoE passive switches are rather old, and not commonly seen in the wild, and typically used for special purposes. Passive PoE injectors are much more common and I intentionally did not mention them, as it seemed out of the scope of the discussion.

When the premise of the original post is whether POE is safe (effectively asking about active vs passive) then I believe any answer that does not rely on knowing whether a device is using active or passive POE is too simplistic to be safe.

Need some clarification from @Anticupidon as to switch vs brick and af/at/bt vs passive. A model number for the switch would help

Thanks a lot for all answers.I am impressed.
Now, for the clarification.
The switch about to be bought is this: Netgear GS116LP
Now, I am waiting for the budget approval. If something changes, I will ask if needed.

Well I have several Netgear GS110TP switches with both PoE and non-PoE devices connected, I haven’t noticed any issues and there are no errors in the logs.

Keep in mind that switch looks like it’s unmanaged, if you want to bond between switches I suspect it won’t do LACP. Though as always read the manual to verify, sometimes it might change between versions and firmwares.

I also have the GS116Ev2, similar model type I suppose, it doesn’t have SNMP so not possible to monitor it via Zabbix.

LOL the more I think of it the less I would buy your switch :wink:

1 Like

I would add that Netgear (in the UK at least) have a fairly good warranty, if it’s dodgy they will send out a new replacement.

1 Like

What switch do you recommend, 16 PoE ports ?

Well I can only speak to the two Netgear PoE models I have (at home):

GS110TP - Has 8 PoE and 2 SFP ports, no fan, is Pro managed (LACP). SNMP. The costs for SFP modules are too high (in general) e.g 40% (ÂŁ50) of the cost of the unit (ÂŁ120) in my case. Absolutely could not get https to work.

GS516TP - Has 8 PoE and 8 non-PoE ports, is Pro managed (LACP). SNMP. In a home under the TV the fan is loud! though in an office I think it should be ok. https worked without effort from memory (it’s a backup in the box at the momment).

If you haven’t used a Netgear switch before prepare for a crappy UI, it works but most here prefer the snappy Unifi UI. These are cost effective switches so I’d say they do the job.

Though I would say I only power IP cameras and APs on them, you ought to check the power budgets meet the requirements for the devices you need.

Caveat Emptor.

My vote would be for a US-16-150W (providing 150w covers your usage (which is almost certainly will)). They are about (UK) ÂŁ225 so quite a bit more than the netgear one you were looking at but not totally out of the ball park.

I went off netgear products when I had to install a windows XP VM with IE5 in order to change the vlans on a switch because crap UI… (it was an old switch but even so…)

If you have or are getting ubiqiti AP’s then you will also have it all centrally managed which is nice.

Yeah some of the older firmware versions required IE I saw, however, the ones that are currently still supported will work in Firefox on Linux without any problems.

The UI is crappy but once you’ve set up the switch, you won’t need to look at it.

For my home Netgear works ok, if my job was to look at the UI all day I might have a different opinion.

Though I will say I think the prices and support have been pretty good from Netgear, their actual support is shitty but they will replace the unit.

I always disable POE on at least the ETH ports facing expensive equipment, like servers, or the firewall.
Yes POE has a standard that is supposed to auto negotiate if POE is required, or not. But I have seen at least a couple of times, an ETH interface on facing equipment…get cooked. And on various good brands, such as HP ProCurves. So as a “best practice”…I always disable POE on the ports facing expensive equipment on the other end. Firewall typically in port 1, servers and edgewater VoIP boxes typically on the last ports. Typically labeled ports that nobody should be monkeying with. Only takes a few seconds to put that safety measure in.

I recently killed my laptop’s Ethernet port with a PoE injector. I used a MikroTik PoE injector for a CAP AC access point, then wanted to check the connection directly. Once plugged into the laptop, smoke came out. Port was gone.

I’m sorry to hear that. There’s two lessons which it seems you’ve learned:
-Injectors like that are passive. Active (802.3af/at/bt) injectors do exist, but they are large bricks not a little wiring piece with scant electronics
-not all devices are designed with the proper isolation transformers which are called for in the ethernet specs - devices which have these are not affected by DC voltage being present.

That’s a good lesson learned ! Handy to ensure you buy an AP with two ethernet ports but must admit I would have accessed the AP via a switch.