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I live in an apartment that has essentially no 3-prong electrical outlets. I need to plug in a modest amount of computer equipment (which has a mix of 2- and 3-prong plugs), and I want to plug this equipment into surge protectors. Physically, I can accomplish this using cheap 3- to 2-prong adapters, but is that safe?

In part, my question is, what happens when a surge protector does its thing? One plausible scenario is that it dumps the excess energy into the ground conductor, which seems like it could pose a much worse problem than damaged equipment if that ground is poor or nonexistent.

This is in Colorado if that matters.

These questions seem related but don't directly answer the surge protector safety question:

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Have you checked to see if the electrical box is grounded? If so, you can likely replace the receptacle with a three pronged self-grounding one. –  Edwin Dec 21 '13 at 18:35
When I lived in a rental house with only ungrounded outlets, I used a 2 prong adapter and an "online" UPS to protect some expensive computer equipment (I had over $5K of equipment). An online (or double conversion) UPS converts AC to DC then back to AC to power the equipment, so any surge should be absorbed by the UPS rather than the computers. This protected the equipment, but not me since there was no ground. Ungrounded outlets were within code when the house was built, so the landlord had no responsibility to provided grounded outlets under our local laws. –  Johnny Dec 21 '13 at 21:14
A gfci pigtail plugged into your 3 prong adapter then plug the surge arrestor into the gfci should give you the same protection as if a gfci receptacle were to be in the wall for that outlet. –  user24125 Sep 23 at 19:03

3 Answers 3

up vote 3 down vote accepted

According to howstuffworks.com the most common type of surge protectors contain a metal oxide varistor or a gas discharge arrestor that utilizes the grounding wire to divert extra current.

However, as others have commented, the neutral wire is usually also used in conjunction with the ground, and therefore, you should get some, but not full protection when bypassing the 3rd prong.

That said, it's never considered safe to use bypass the 3rd prong (even with 2 to 3 prong adapters) and it is likely your insurance / the manufactures insurance will not cover damages caused as a result of such use.

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The use of a MOV for over voltage spikes is traditionally done from ungrounded to grounded (hot to neutral). Purposely shunting to the safety (equipment ground) is not correct. I agree that adapters have dubious use with 3 wire devices. –  HerrBag Dec 21 '13 at 22:47
@HerrBag: I was quite concerned by the howstuff works article, as I've always felt a little uncertain that the 3rd prong is really truly grounded, and was a bit unsettled to see that surge protection was working that way. Can you find an alternate source or even a picture of the circuitry that show neutral being used instead? –  virtualxtc Dec 21 '13 at 22:59
Mind you, you may not know what sort you have - but most better surge protectors conduct on overvoltage between any two of the three lines (ie, they use 3 MOVs or SOVs in a triangle configuration) not a "hot to ground" only configuration. I've gone to whole house protection with an SOV lightning arrestor plus a surge capacitor at the main panel. –  Ecnerwal Dec 21 '13 at 23:10
@virtualxtc From Tripp Lite: "Includes full normal mode (H-N) and common mode (N-G / H-G) line surge suppression" from their tripplite.com/en/products/model.cfm?txtModelID=97. As Ecnerwal mentions, all three modes are protected. You would have some protection from a 2 wire connection, but warranty and ultimately, safety would argue for 3 wire. –  HerrBag Dec 22 '13 at 0:14

You could, of course, actually connect the ground pigtail or tab on the 2-3 prong adapter and then plug in an outlet tester to see if you have ground.

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For background: there was a narrow period of time where grounded wire was used, but outlets were still 3 prong. In some cases it was two wire cable with bare copper ground wire strung through the same holes. –  Bryce Sep 23 at 4:53

A good option is a "whole house" surge protector, which is very easy to install (See a guide I wrote at http://guides.obviously.com/Whole-House-Surge-Protectors/1482 ).

It won't add a third prong to your plugs, but at modest cost for your landlord will protect his house (e.g. protect his sump pump, dishwasher, light bulbs, etc.). That's what you tell him. And it will protect your computers.

As for the point of use strips: it's true most will have three protection devices arranged in a triangle. But keep in mind neutral and ground are connected together at the panel anyway. From a surge point of view the 2-prong is not all that bad.

But point of use protection is not enough anyway, not in areas that actually have lightning. An "online" UPS can be a good substitute. But the best protection is to have both a whole house unit and point of use protection.

Note: you have very little to worry about with computer equipment and the third prong ground: I rip the 3rd prong off most laptop supplies for example, as I know it goes essentially nowhere.

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