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In my science classroom all outlets on the lab benches are gfci protected--that's great. I plug in multiple computers into some of these outlets and use power strips to do this, but it seems there might be a problem occasionally with this.

It seems that there might be a negative interaction between the surge-protected power strips and the gfci e.g. excessive tripping of gfci or even wearing out of the gfci. The electrician told our head custodian that it wasn't good to use surge-protected strips with gfci and I'm wondering if this is the problem and if so is there some way to mitigate it. But, maybe it's just a bad strip, maybe these old computers' power supply?

Edit: Before posting this question I spent ~30 minutes searching E-SE site for any information on possible interaction between these two components, to no avail. These 2 components are commonly used in residential and commercial electrical power distribution systems, yes? Ideally, the answer will provide specific technical knowledge on the design/functioning of these 2 components and explanatory/theoretical knowledge explaining why they might interact negatively.

HOWEVER, my question assumed 'generic' designs of surge protection circuits in inexpensive power strips and also generic designs of gfci. Perhaps this is a bad assumption?

migrated from electronics.stackexchange.com Aug 11 '16 at 18:42

This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

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    please explain why down-voted, how is one to learn otherwise? – David G Aug 11 '16 at 15:29
  • This seems like a logical question to me. I wished I had an answer. But typical SE behavior. I see no reason for the down-vote. So a +1 from me....I'd actually like to know the answer. – cbmeeks Aug 11 '16 at 15:32
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    Of the first two votes to close, 1 is for not being about electronic design, theory etc. and one is for not being clear what the question is. Use and troubleshooting of consumer products is often voted for closure, particularly when there is no clear answer likely, but only various speculations on possibilities. Down votes and votes to close are not necessarily for the same reasons. – Charles Cowie Aug 11 '16 at 15:39
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    @cbmeeks: maybe read the hover text of the downvote button. This question is merely a call to speculation about a fuzzy situation with no details at all given to suggest anything about what is going on. Even the implied question is maybe "why does the gfci trigger so often" or maybe the real question this wants us to answer is something else? Besides that, downvotes do not need to be explained, and demanding explanation is nonsense, imagine how much time people would then need to spend that use their daily downvote quota up... – PlasmaHH Aug 11 '16 at 15:40
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    @Tut I re-edited the question as per your and other comments, thanks. As one new to this community, I'm still learning about this site's norms and yours and cbmeeks' comments both educate and help a newbie feel welcome. – David G Aug 11 '16 at 16:20
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If either the power strips or connected equipment have capacitors between the power conductors and ground, there would be some current to ground through the capacitors. If there are MOVs between power and ground, there could also be some leakage through those. Deterioration of insulation can also result in small intermittent leakage currents to ground before the insulation actually fails and trips the GFI or breaker every time the faulty device is plugged in.

  • Would it be typical of a surge-protected power strip to have a capacitor located as you say? And "MOVs", sorry, what are these? Also, this school year I can do some trouble-shooting about devices/insulation issues, thanks @Charles-Cowie – David G Aug 11 '16 at 15:41
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    I believe capacitors and MOVs are sometimes connected form line to ground, but I don't know if it is typical. MOVs are metal oxide varistors. They are common surge protection devices. You can find a complete explanation on the internet. – Charles Cowie Aug 11 '16 at 15:52
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Surge protectors typically have three MOVs -- from hot to safety ground, from neutral to ground, and between hot and neutral. The connections to safety ground, if they leak any current, would indeed be the kind of unbalanced flow that the GFCI is designed to detect and cut off.

A properly designed surge suppressor shouldn't leak enough current to be a problem, under normal circumstances. However:

1) Any surge being shunted aside might cause the GFCI to pop. That's a case of everything working as designed, even if leaving the equipment unprotected by a surge suppressor would not blow the GFCI (but might blow the equipment).

2) MOVs do eventually take enough surges to start to fail. I'm not sure what the failure modes are, but if one of them starts leaking more than its spec calls for that too could trigger the GFCI. Again, though, that's the GFCI working as designed and telling you that the surge suppressor is no longer trustworthy.

So I don't see any reason not to try this combination. If it works, it will continue working modulo surges.

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It can be an accumulation of multiple devices.

Not enough from a single device but given you are using power boards, it is the sum of many small leakage currents on one circuit.

Should be possible to fault find, try substituting out the power boards for new or non surge protected model.

Also try using less computers and devices on one circuit. It may be an accumulation from multiple devices or one in particular may be causing issues.

Narrow your problem down.

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Actually residential surge protectors have 2 metal oxide varistors, 1 from hot to ground and 1 from neutral to ground. MOV's work by dumping excess voltage to ground. After taking several hits some MOV's start conducting to ground at lower voltages until they fail. MOV's in power strips are after the ground fault protective devices (GFCI's) so if they do there job during a spike or after they are damaged from doing their job they can trip a GFCI. The way to eliminate false trips and still protect sensitive equipment is to install a "whole house" or main panel surge suppressor in the main with a dedicated standard inverse time double pole circuit breaker as required by the manufacturer. This will dump spikes on the line and from other branch circuits that may generate spikes but will not protect fully if a motor load is on the same branch circuit. If motor loads are on the same circuit a plug in or power strip surge suppressor may be the only way to protect the equipment but once they start tripping the GFCI protective device they will need to be replaced.

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