120V plug in surge protectors.

[GG]

Hello, I went on a call today where the HO had a 3 prong 120V surge protector plugged into a 3-2 prong plug adapter which was plugged into a 2 prong receptacle that was not grounded. The HO has already lost a computer that was plugged into this SP and plans on plugging her new one right back into the same SP. I have a couple of questions : (1) Will a plug in surge protector even work properly without a ground? (2) How likely is it that the computer was destroyed by the absence of a ground wire at the outlet? (3) The HO has a plasma TV plugged into a 2 prong non grounded outlet and how risky is this given whats already happened to the computer? (4) Would it be wise to drop a grounded circuit to each room that has expensive electronics in it? The service panel does have a ground rod and a CWG.

 

[Rampage_Rick]

1) Doubtful. Most consumer surge protectors only have MOVs between hot and ground. Better-quality units have protection between hot-neutral, hot-ground, and neutral-ground, so those ones MIGHT be able to divert surges to neutral. Every single suppressor I have for ethernet, RS-232, or twisted pair has a nice #12 ground lead.
2) The computer wasn't destroyed by the lack of ground per se, but had there been a functioning ground it's likely that the surge protector may have had some effect to reduce the harm.
3) Well considering you've already blown up some electronics, clearly there's a power quality issue at play. Then again, since you don't mention a surge protector on the TV, it's doubtful that ground/no ground would make a difference in the event of a surge. Buy a good power bar that also protects the coax. What would concern me more is the chassis of the TV becoming energized without a ground path. At the very least you could run into some RF interference problems. Same goes for computers too I guess.
4) Well it would be wise to replace all ungrounded receptacles, but of course budget comes into play. I'd do as much as you can. Might I also recommend a whole-house TVSS in the panel?


When the increase lasts three nanoseconds (billionths of a second) or more, it's called a surge. When it only lasts for one or two nanoseconds, it's called a spike.

"Many UL-listed products are also of inferior quality, of course, but you're at least guaranteed that they have some surge protection capabilities and meet a marginal safety standard. Be sure that the product is listed as a transient voltage surge suppressor. This means that it meets the criteria for UL 1449, UL's minimum performance standard for surge suppressors. There are a lot of power strips listed by UL that have no surge protection components at all. They are listed only for their performance as extension cords."

 

[GG]

Rick, thank you for the very imformative reply. It was very helpful.

 

[petersonra]

These kind of surge protectors can only absorb a relatively small amount of energy, often less than the equipment it is supposedly protecting can absorb w/o damage itself.

I have not heard about surge suppressors with only L-G MOVs. Everyone I have ever used seems to have L-N, N-G, and L-G MOVs.

If they did have only L-G MOVs and the circuit was not grounded. It is unlikely they could work at all. but in all reality, it is not likely that would matter all that much.

<added>
There is a lot of 2 wire equipment out there. It is no more susceptible to spikes and surges than 3 wire circuits.

As for changing the 2 wire outlets to three wire outlets, how is that going to help a 2 wire circuit?

Best advice is IF there actually are some power problems as you seem to suspect, get a whole house suppressor and install it at the main panel board.

 

[GG]

As for changing the 2 wire outlets to three wire outlets, how is that going to help a 2 wire circuit?

Simple, so the HO can throw away the 3-2 wire plug adapters they are using and ground all of the electronics that have 3 wire plugs on them.

 

[ELA]

I would definitely run a ground to the computer circuit.
One thing people overlook is the fact that most commercial computers incorporate an integral EMI filter. Many of the these filters have capacitors from line-PE and neutral-PE. If the PE lead from the computer is left floating this means that the computer case(metal portions) can float up to 60V!

Whenever a computer, microwave etc is involved a ground lead is mandatory. This in addition to the fact that surge protection (common mode) will not work properly without a ground lead connection.

As a side note:

EMI filters are designed to help attenuate electric fast transients or high frequency noise (& continuous wave RF).



Transients or spikes typically have fast rise times in the area of 5 nanoseconds.

MOV surge protectors do a poor job of protecting against this type of noise. They are designed to protect against "surges". The standards they are tested to are 1.2/50 (rise/fall time)microseconds or 8/20 microsecond times. The fastest test time they are required to suppress is the 500 nanosecond rise time "ringwave test.

Better quality plug strips incorporate both EMI filters and MOV surge protection. Both of these are reliant on the ground connection to work properly. (excluding series mode protection)