Power surge via LAN cable

[TooNice]

So, at present I am in a country with fairly frequent power outage. And while the place I stay now has a power generator, it takes a couple of minutes to kick in, during which my PC will go down. So I bought an entry level UPS (with the generator kicking in seconds I didn't want to get anything huge).

The UPS also acts as a puny power surge (under 300 joules), which I nevertheless welcome given as I question the quality of the infrastructure here. But I also mistook the modem port on the UPS for an ethernet port, which means that my ethernet line is unprotected. Bummer.

Still, given that my setup is router -> power line transmitter -> power line receiver -> Cat5 cable -> PC, is the PC likely to be harmed before the router / power line device get fried? I am not concerned with thunderstorms and the likes as I doubt power surge protector would be of any help there in those instances and I should just unplug, but I am concerned with minor surge that might occurs on a daily basis from, say the AC being switched on, or entire building suddenly getting powered on by the generator, etc.

And while I am at it, how much energy does it take to fry a computer, and how much energy is found in every day surges? I see dedicated power surges rated in thousands of joules, dwarfing my UPS's 300<, but just how much is really necessary (again excluding mother nature induced surges). My equipments have survived, for long period of time without any surge protection in the UK and Japan, so I wonder just how much protection is really necessary.

[peterb]

My personal view is very little protection is required. There is a risk from over voltage surges, but other than nature induced, they are rare. The risk is greatest if if you are on a long spur from the main distribution system.

In terms of energy, the mains system is a low impedance source - meaning it will supply an infinite amount of power until a protection device (fuse or cct breaker) operates.

Do you notice lights briefly dimming or brightening when high current devices (air conditioners, heaters etc) are switched on or off? If not, you are probably OK - even if you do there is probably not much to worry about unless it is really severe. Your UPS will act (to some degree) as a smoothing device and will take some of those voltage fluctuations out.

[watercooled]

Ethernet ports should have galvanic isolation from the rest of the system through a type of isolation transformer unless something like PoE is being used. Surge protection is more relevant for a modem port as power is supplied over phone lines, hence why corded phones don't need their own power supply.

A decent computer power supply will already include some form of basic surge suppression in the form of MOVs (basically all you find in most 'surge protectors' anyway), as well as APFC which can absorb brief changes in voltage.

Depending on the type of UPS you have, if the voltage changes substantially for more than a moment, it might either change a transformer tap to bring the voltage back within tolerance (e.g. a line interactive UPS) or just disconnect mains and run from battery power until it comes down again.

For something to fry a computer besides just the mains side of the power supply, you'd need a surge energetic enough to cross the usually substantial electrical separation of the isolation transformer.

I'd hesitate to offer any specific advice about your situation, not knowing what sort of risks are present, but you can get standalone Ethernet surge protectors if you're really concerned. What sort of surges are you expecting through the Ethernet cable - just what arrives through the power line adapter?

[philehidiot]

In order to remove spikes, there will be a metal oxide varistor in your PSU and UPS. It will very much depend on the individual model as to how capable this is (higher voltage than specified = low conductivity and below = high conductivity). Often there will be a resettable polyfuse which will reset itself rather than burn out. There will also be capacitors after these two chappies which smooth the power out further (primary and secondary caps). There may well be chokes to limit the inrush current as well so you should have decent protection from voltage and current spikes just there. 300J is a decent amount. That'll happily send yer heart into some very unfortunate rhythms and so you can imagine any delivery system which is allowing surges at that level is intrinsically dangerous. The specifications of these components and what they can take will vary depending on the quality of kit you get. There will probably also be a standard fuse in there somewhere.

With both a UPS and a PSU with this kind of protection, I'd not expect surges to do anything other than potentially fry the UPS at worst. I have seen power surges which have tripped breakers, leading us to emergency generator power fry a UPS before but this was one of several UPSes in use on multiple systems and so I suspect it was faulty (it was old and abused). When the UPS was bypassed, the PC itself was just fine.

I strongly suspect your current set up is fine as per above replies and I would expect the UPS to be sacrificial, protecting the computer in any extreme setting.

As for your ethernet port, I'm afraid I can't help.

[OilSheikh]

Which country have you gone to, TooNice ?
Sounds like an Asian country called Bangladesh. They have something called a stabilizer to deal with voltage fluctutions , which can blow up capacitors.

[DanceswithUnix]

Is this a desktop or laptop you are talking about? If it is a desktop, I would get a cheap ethernet card and use that. Chances of damage are pretty slim, but for peace of mind either a £10 pcie sacrificial ethernet card that you can just discard if it dies or an ethernet protector seems cheap if it reduces worry and lets you sleep better. I suspect if a surge gets further than an ethernet card, nothing was ever going to stop it.

https://www.laptopsdirect.co.uk/apc-...gb/version.asp

[philehidiot]

Or there's this.

[peterb]

I'm not convinced of the use of these - I put them just above the snake oil level of value. MoVs do degrade over time.

Power surges caused by indirect lightening strikes tend to affect mains power supplies rather than induced voltages in ethernet cables, unless it is very close - in which case you probably have other things to worry about.

A simple way to protect against incoming power surges on signal cables iare to use a couple of media converters and a length of fibre - but of the media converters are run of the same mains supply and that has a surge - same problem.

But as TooNice said in the OP, he isn't really concerned about natural events - more switching surges caused by high current devices on poorly regulated mains supplies. (Such as off a long spur from the main distribution transformer where I^2R losses become significant.)

[DanceswithUnix]

But as TooNice said in the OP, he isn't really concerned about natural events - more switching surges caused by high current devices on poorly regulated mains supplies. (Such as off a long spur from the main distribution transformer where I^2R losses become significant.)

When a power cut ends you can get funny voltage spikes.

Thinking about it though, stick an ethernet switch on the UPS output and that will be the device taking any abuse. They can be pretty cheap, and a spare switch is always handy to have around.

[TooNice]

Thanks for all the replies

I should mention that I am on a laptop, but since my (second) battery is dead, so the laptop dies as soon as the power cuts off. And since I am planning to get a new laptop within the next 6 months, and it is unlikely that I can get a spare for such an old laptop here anyway, I decided to go for the UPS route (besides, I might get a desktop if I stay here long).

I haven't paid too much attention until I read some of the comments here, but while I haven't noticed the lights flicker from switching an electric appliance, I have noticed something that, from my Googling, seem to correspond to a voltage sag (light very briefly dimmed and AC almost powered down for a very brief instant). I am guessing that those things could cause a surge too.

What sort of surges are you expecting through the Ethernet cable - just what arrives through the power line adapter

I am actually not sure what sort of surge can come through the ethernet cable: the internet connection comes from a cable broadband service via simple router with a built in modem. I hooked an ethernet cable from the router to a power line transmitter, plugged in a receiver in my room and hooked an ethernet cable from that to my PC. I would imagine that an major external surge could fry the router, my laptop and everything in between unless the router/everything in between fries before the current can go any further. But again, I am more concerned with power fluctuation within the building than anything else. TBH, I am not entirely sure how things get transmitted down a power line and how that is affected by power surges.

An ethernet surge protector would give me complete peace of mind (along side the UPS and built in surge protector), but I am a bit doubtful that I will find one here.. but running the ethernet cable to a switch (which I know can be obtained) connected via the UPS though sounds like a brilliant idea. Later on, even if I get a new laptop/desktop, I could use the switch to keep everything wired (which I kinda prefer).