Using computer on open ground electrical receptacles

2011-08-21 00:04:42

I have an older home that still contains knob and tube in a few rooms. It was recently home inspected and the electrical was evaluated by a qualified electrician. All electrical outlets that are connected to knob and tube were replaced by the electrician with GFCIs, however the electrical receptacle plug tester indicates they are open ground.

Could I risk damaging my computer if I plugged it into those GFCIs that read "open ground"?

Using computer on open ground electrical receptacles

Reply #1 – 2011-08-22 04:52:45

Yes and No.  Yes, you risk damaging your computer, but your computer was likely damaged already for this to be a problem.

Now I'll preface by saying that I am NOT a certified/qualified/insured electrician.  Just an electrical engineer who spends most of his time on low voltage and low power dc circuits.  And as such, I may have missed something.

Basically, the chassis is connected to that ground (or supposed to be).  That way, if the wiring ever got messed up and the "hot" wire touched the chassis, it would create a short circuit that should blow the fuse or circuit breaker in your house.  More importantly, that current is NOT going through you.

Now however, your chassis is ungrounded.  So if the wiring got messed up, your computer case could be "live".  Fortunately, your GFCI will protect you from allowing the current to run out you.  But now you'd have a "live" case which presents a short circuit danger for anything else in your computer.

Using computer on open ground electrical receptacles

Reply #2 – 2011-08-22 15:56:40

Thanks for the reply. That coincides with everything else I've read on the topic. It seems my only options are not to use a computer on open ground receptacles, or get an electrician to ground at least one receptacle upstairs.

Using computer on open ground electrical receptacles

Reply #3 – 2011-08-30 06:23:09

Sorry for not following up.

Yes those are your options, but to be honest, you start becoming rather paranoid by doing so.  Why?  Because it's not the outlet's job to prevent the computer from f***ing itself up.  Grounding can help, but in one of the smaller possible ways: i.e. your case will never be allowed to go "live".  It'll automatically pop that GFCI, if you had ground.  Without it, the case could be 120v, which won't hurt you much with that outlet, but it'll be a little tingly and/or feel like a static shock depending on how well YOU were grounded.  That static shock can actually be enough to kill the GFCI outlet: essentially the same as pulling the plug on your computer.  Literally.

The kicker is that there are only 2 ways your computer could go live.  One is a bizarre PSU fault, and the other more common one is.... a miswired outlet.  And you've eliminated one of them already.

In summary, your PSU has to mess up (and early on in the circuit at that!) for grounding to make a difference.  And what's the equivalent damage that could happen?  Well, the same as if you had lost power.