My outlets are not grounded, will using a UPS and surge protector be OK?
February 22, 2010 9:37 AM   Subscribe

My outlets are not grounded, will using a UPS and surge protector be OK?

On the third floor of my house none of the outlets are grounded. I have my computer upstairs, the connection is as follows: Outlet -> UPS -> Surge protector -> Computer.

The UPS is a 350W model by APC. The surge protector is mainly for protection and the extra outlets it offers. If there is a surge or a brownout will my computer and electronics be OK?
posted by abbat to Technology (14 answers total) 2 users marked this as a favorite
I asked pretty much this same question a while back.
posted by nitsuj at 9:40 AM on February 22, 2010

Having looked at the innards of a few UPSes, and the schematics for a few more, and done the "yank the plug out of the socket" test with many more, they all seem to work fine, as UPSes, without a ground. You might get a "site wiring fault" indication, but the inverter still kicks in and supplies backup power when it should.

The surge protection function becomes less useful in the absence of a ground, though. It should still stop rapid spikes (which are blocked by inductors in series with the line and neutral conductors, no ground connection there) and surges between line and neutral (a MOV is connected between L and N with no ground there either).

What would worry me is the MOVs between line and ground, and between neutral and ground, to protect against common mode surges and surges on the neutral. Not only do these NOT function without a ground connection, but I can't see what stops them from coupling dangerous voltages onto the ungrounded "ground" conductor in the event of that type of surge.

I would be concerned about touching any metal parts of protected equipment which could become momentarily electrified when connected to this type of surge protector when a surge occurs, and the ground isn't really grounded.
posted by FishBike at 10:05 AM on February 22, 2010

There are several things to consider:

1. The computer case acts as a ground and is tied to the ground wire. This has two effects - the first is safety. If the computer develops a short for some reason, then the case could be become a potential. If you are touching the ground when you touch the case, you become the path to ground. The second is to allow the case to act as a Faraday cage for the computer and offer some protection against random EMF - although, this is admittedly a small concern.

2. Surge protectors work in a variety of ways, and some not as well as others. If it is dumping excess voltage into the ground which is tied to your computer case.... Well, things can get VERY exciting.

3. There are UPSes that filter the incoming signal and clean it up (I think the 350 is one of them). This isn't as useful as it sounds since any good power supply will deal with a variable signal anyway - the rectifiers should fix it - but this also implies that there will be some period of time between power going low/out and the battery providing backup. This will produce some ringing and other funny behavior that may or may not be problematic when the UPS kicks in. Back to point 2, if the voltage goes high for a bit and gets dumped to ground by the surge strip, things can get exciting. Better UPSes run the computer off of the batter full time, and work to keep the battery charged, so this is less of a concern.

To sum up - You'll probably be OK. But there is a risk involved, and it could result in injury or death. In your shoes, I would find a way to get that outlet grounded.
posted by Pogo_Fuzzybutt at 10:15 AM on February 22, 2010

you'll be fine 99% of the time. the lightning strike, or transformer blowing down the street, though, will likely kill at least one piece of gear. i know of no surge protectors which are effective when ungrounded.
posted by kimyo at 10:32 AM on February 22, 2010

How would I get my outlets grounded?
posted by abbat at 10:51 AM on February 22, 2010

If you own the place, hire an electrician. If you rent, see if the owner will.

The installation runs from the very simple to really complex, depending on what all will need to be done.
posted by Pogo_Fuzzybutt at 11:44 AM on February 22, 2010

> How would I get my outlets grounded?
I'm guessing you might meant that your outlets lack a ground plug, so they're only 2 prong. These outlets are still grounded (ie. the metal outlet box inside the wall is grounded), but you can't get to it through the plug.

You can use a 2-to-3 prong adapter, which includes a little screw hole tab. You screw this into the middle screw of the outlet - the one that normally holds the faceplate on. This is because that screw contacts the outlet housing, which is grounded. It's a temporary (and fragile) solution, but it's a bit more "safe" than having no grounding outlet.

The better solution is to replace the 2-prong outlet with a 3-prong outlet. These can be had cheap (about $1 or so at homedepot?), and are relatively easy to install. HOWEVER, you have to do this safely, and there's a lot that goes into that. I'd ask someone with experience, or a licensed electrician to do this for you (or at least look over your shoulder while you learn). Don't want to zap yourself, it hurts.

If you truly have an ungrounded outlet (even the housing is not grounded), I'd look into rewiring the house. I'd be more worried about the house burning down then the PC burning up.

Side note - the grounding plug is like a lightning rod for shorts - if a short happens, the ground plug sucks all the volts away so it doesn't reach you. So instead of 110v on the case of your PC that you touch & get zapped, the grounding plug pulls the volts away from the case so you don't get shocked. It'll still cause trouble, but it's safer than using yourself as a grounding plug.

So having a UPS there will prevent spikes, etc, but probably wont protect against shorts. It might shut off in the event of a short, but it doesn't seem like it could provide a route for the shorted volts to escape through. So for that brief period, you could still get zapped, which is the point of having a grounding plug in the first place.

I'm not an electrician - all this could be completely wrong. But that's what I understand of it so far.
posted by jumpfroggy at 12:24 PM on February 22, 2010

Those 2 to 3-prong adapters will only provide a grounded outlet if they're properly installed and if the electrical box itself, inside the wall, is grounded. This is not always the case.

You could install an adapter (using the screw) and then plug in an outlet tester. It'll tell you if it's working right. If not, you'll have to call an electrician.
posted by echo target at 12:36 PM on February 22, 2010

Yeah, having a good ground is important. But the UPS and the surge protector is better than nothing (unless the surge protector is crappy or failing or failed, in which case it can make things worse. check out dansdata, I think he did something on it.)

The other thing is that you need to be sort of careful installing three prong outlets in place of two prong outlets. You can test for "ground" if you get continuity between the neutral and the proposed ground path, or that path and a good ground somewhere else. But I am almost sure that this doesn't guarantee that the ground path will actually work properly in the event it needs to pass any appreciable current.

(Beanplating: in the event of a nearby lightning event, the ground can actually act as a reverse path for the lightning to get into the machine. Because voltage (and the damage caused by it) isn't a static (ha!) number. It is the difference between two potentials. If you have a computer power supply, and you measure one wire to ground and get 5volts, and another wire to ground and get 12 volts, if you measure those two wires, you will have 7 volts. The power supply might not like powering anything that way, but the voltage is there. Alright. So, lightning strikes nearby and for that instant, the ground near you is charged at buh-zillity volts. If your grounded equipment happens to be in just the right spot, that charge may find that going back up through your computer and sparking out against something will be one of the paths of least resistance. I've seen it happen. Completely protected building, all machines on the same protection circuitry. Yet after a storm, one of them ends up with a smoldering hole in it where something shorted to ground. Or, as I theorize, from ground. Anyway.)
posted by gjc at 2:45 PM on February 22, 2010

I am confused as to why you have a UPS *and* a surge protector... I thought that UPSes have surge protection built in and also line conditioning. If I'm wrong, then why not place the surge protector between the UPS and the wall, and protect the UPS too? UPSes are expensive. Someone please hit me with the clue stick.
posted by IndigoRain at 12:38 AM on February 23, 2010

@ IndigoRain

My UPS has only 6 outlets, my surge protector as 12. I have 3 LCDs, my computer, printer, router, phone chargers, dsl modem, etc. So the surge protector comes after the UPS.
posted by abbat at 10:18 AM on February 23, 2010

Ohh, I see.
posted by IndigoRain at 12:16 PM on February 23, 2010

Sometimes when I touch my computer case I feel a slight tingling sensation. I now attached a wire from the case to the metal legs of my desk, will it help?
posted by abbat at 4:29 PM on February 24, 2010

Sometimes when I touch my computer case I feel a slight tingling sensation. I now attached a wire from the case to the metal legs of my desk, will it help?

It might, but a desk leg is generally a very poor grounding system, so you may just start getting shocks off the desk leg too. In the event of something going seriously wrong in the power supply inside your computer (a short to ground), you've also set up a way for your desk to become electrified.

I would take this as a sign to get proper grounding sorted out for your computer stuff. In the vernacular of Ask MetaFilter: "See an electrician."
posted by FishBike at 10:26 AM on February 25, 2010

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