If anyone has read my recent posts, you know that I have been replacing ungrounded receptacles in a residence with grounding type. Also, so far this particular residence has no ground available in the device boxes. I'm running a seperate ground wire.
This has me wondering if those surge protection devices that plug into a grounding receptacle REQUIRE a ground to work properly. I noticed that the homeowner has a computer plugged into one of these and the receptacle has an open ground. Someone had improperly replaced an ungrounded receptacle with a grounding type. I have only grounded a few of their receptacles so far but I would like to advocate bringing some of these illegal ones up to code. In addition to making them code-compliant, I'd like to have a technical argument concerning the operation of the surge protection devices i.e. do they need a ground?
Don

Why don't you use GFI outlets to protect the circuit and then use 3 wire outlets on the load side of the GFI

IF you're looking at a good surge arrestor, it provides protection from line to neutral, line to ground and neutral to ground. Without an equipment ground, you've given up 2/3 of the protection.

There is no substitute for a proper equipment ground, especially when dealing with electronics. tsolanto's advice is fine in most cases, but you wouldn't see me betting my computer or TV on a circuit that does not contain an equipment ground.

Tom

Some surge protectors I have taken apart have MOV's in them. There is almost no protection if there is no ground. The MOV's "wear out" if they are constantly hit with spikes and such. Try telling someone to replace these every year or so and they look at you funny.

UPS manufacturers state that the circuit must have a ground for them to work.

I had a client that used to fry his computer equipment 3 times a year till I told him to hire an electrician to rewire his outlet. (had a ground outlet in an ungrounded 2 wire cloth romex circuit)
Static electricity is murderous to computer equipment in an ungrounded circuit.

Yep, without a ground you'll lose all common-mode surge protection and only get differential protection, i.e. high voltages between hot & neutral.

If you connect up a lot of equipment with filters on the AC line there will also be appreciable capacitance from hot & neutral to your "floating ground." The casings will likely sit at about 60V to true ground.