Understanding UPS's and Extension Cords

[Galant]

Hi guys!

Thought I'd throw this one out here to see what input you might have on a subject that seems to draw a wide variety of responses.

One arm of the company I work for is a retail shop selling home electronics and related kit including home UPS devices - the typical types you see for PC setups with APC brand and others.

Every now and again the sales staff/shop will reach out to those of us on the service/solutions team for some input and recently there have been a few queries concerning using UPS units with power extensions cords/splitters.

I'm not an electrician in any way, shape or form. I have nothing but a rudimentary understanding of things, but I'm aware that there are risks when it comes to plugging UPS units into extension cords, especially with surge protectors built in, and also when plugging them into the output side of a UPS.

One consideration is that surge protectors will mask the supply in some way causing the UPS to function incorrectly and possibly go to battery when it doesn't need to, or on the outlet side will keep the UPS from correctly judging the load placed upon it.

More seriously, I believe there are also risks when it comes to resistance and heat build up due to all that extra cabling (not to mention possible low quality cabling).

UPS companies all warn against the use of extension cords and their usage will void warranties. Lots of online sites vary between saying, "High risk, don't do it!", and "If you use high gauge cables you should be okay," or "use power strips but not with surge protectors built in" etc.

I'd like to be able to lay this to rest once for all, if possible, so I was hoping some of you might be able to clarify the risks and reality of using UPS units with extension cords/surge protectors.

Anyone have any insight?

Cheers!

[Zak33]

Real world example - I have only one and it has nothing to do with quality cables and more about keeping the UPS charged and it working at all.

When I worked on a PC plugged into a UPS, which is turn was plugged into a surge protector, the UPS kept running flat. It seemed that the surge protector was "protecting" the things plugged into it, (UPS included), and in doing so the UPS kept kicking into battery backup (as it's supposed too with power drop)because it thought there was a current shortage

It was empty in a few hours.

So... plugged it straight into the wall and it was happy as can be, charged up and worked

So my only real life lesson was... use one or the other for your PC. Not both. Lets face it.. for the UPS tro work it HAS a circuit monitoring power.. you don't need both if you have a UPS

By all means use the surge protector on monitors, power bricks for speakers, external drives etc.. but plug the PC into a UPS that's pluged into the wall directly.

[Ferral]

I would say looking at this from an electrical side of things (Currently training to be an electrician and we have briefly looked at cabling requirements and back up generators etc) if you plugged an extension cord with surge protection into the output of the UPS potentially it would feed back into the UPS which is a battery and could cause the battery to explode.

As for plugging the UPS into a multi extension cord (4 or 6 sockets) could be down to power draw so usual rules would apply with Amps/Current flowing at any given time. To many Amps/Current flowing the cables heat up and could cause an electrical fire

[Galant]

Pardon my ignorance, but if we can dumb this down even further - how would the surge protected extension feed back into the UPS?

[Ferral]

So you have a fault current (surge or whatever you want to call it) which then if connected to a wall socket feeds back to the earth and will cause the RCD (Residual Current Device - or the switches in your electrical box on the wall) to trip shutting the supply down to stop damage to the circuits that are connected. Circuits there being your home/work wiring basically, a general misconception is the RCD is there to stop people from getting a shock but they aren't!

So say the extension feeds back to earth as the current has to go somewhere, it can stop it hitting devices (TV's and the likes for ease here) and causing damage. Now if these UPS don't have correct earthing then where is it going to go - most likely back into the battery. TNS (Terra Neutral Separate) earth systems use the neutral/blue wire to return the current where it goes down to earth but the earth is clamped onto the incoming supply. So if anything gets pushed back into the neutral on the UPS and the internal switch is connected to the battery it is going to cause problems

[Galant]

Excellent. Thanks.

What about power strips with no surge protection on them - either in or out?

[Ferral]

Same principle

See the internal circuit of the UPS is done with a switch and batteries, so while the power is on the UPS charges up and the power bypasses the battery using an internal switch, if the power goes off then the switch will be in the position to allow the battery to flow through the inverter (batteries are DC so the inverter changes it back to AC). Without a proper earth system in the UPS then it will send any overcurrent back through neutral if there isn't an earth available which will cause your RCD to trip but it will be pushing the overcurrent back through the inverter and then into the battery and possibly a bang

[Dashers]

Plus your UPS directly into the mains where possible - they have their own electronics to manage surges etc (it is after all, their rasion d'etre), they'll do it better than a surge protected extension lead.

As for extension leads in general, the same rules always apply when dealing with them - do not overload things as that can cause fires.

Powering a UPS from an extension lead (a simple non-surge protected variety) is unlikely to be a problem as unless you're looking at industrial UPS's, then they're not going to be drawing anywhere near 13 amps.

On the other side of the UPS, be mindful of the maximum rating of the UPS. An IEC connection, which most use, are rated to 10 amps - not something you're going to hit running your average home-hardware.

There are risks though, you stick an extension lead on the output side and somebody sees it and plugs the vacuum cleaner in - that might cause you problems.

I had an extension on my previous UPS so I could drive my NAS/server and router. It had a bunch of sticky labels warning not to use it for anything else.

[Galant]

Alright, so this is an example of what I mean about varying opinions. Some say just be careful about load, others says there's a risk of damaged/exploding batteries etc.

[Dashers]

Varying opinions and varying products. As with everything, there isn't one size fits all.

But, electrical safety is an important thing with standards. You can damage your UPS if you overload it - using an extension lead can lead to a higher likelyhood of overloading it. There should be protections in the UPS (e.g. a fuse) to protect against overload.

Good practice is not to rely on those protections kicking in.

If you buy a high-quality branded product, e.g. APC, you're not going to get it to blow up by overloading it. You buy a white-label Chinese device then who knows.

[DanceswithUnix]

Excellent. Thanks.

What about power strips with no surge protection on them - either in or out?

We have a UPS at work which is plugged into the power for a small 19 inch rack, so that is effectively a power strip. That's fine, if there are no special protection/filter components in the way then the UPS can't really tell whether it is directly on the ring main or on a spur (and electrically a simple power strip is basically a portable spur).

We were also considering adapting a simple extension cord for the output side, simply because we have things that we want on the ups that *cannot* take the IEC leads like the broadband router that has a switch mode plug on it. What we should probably do is buy/make an IEC to single socket cable to adapt one device per output to keep things slap-in-the-face obvious what is going where.

But in line with what Dashers said, the location of that UPS is such that no-one can plug a heavy load like a kettle or an inductive load like a vacuum cleaner. That is the big danger, you should be actively choosing what you plug in and not leave room for errors, and a 4 way is error wiggle room you can drive a bus down.