GFCI Tripping on Inrush

[iwire]

How do you figure? Do some of the electrons get lost on the long trip?

Yes, sort of.

 

[andinator]

A construction electrician which is mostly if not all thats here won't see the problems a industrial electrician who are becoming more electronics technicians will see like nuisance tripping.

Not that I'm buying what you're selling, but I did flip to the "about the author " section of this textbook. Sure enough, "teacher of and an industrial electrician for many years".

 

[winnie]

I would define as nuisance tripping any activation of the protective device for reasons other than an actual electrical fault.

For example, current transformers are never perfectly accurate, and can have different errors depending upon the position of the conductors under test in the window. GFCIs work by measuring the net current on two (or more) conductors going through a current transformer window. Because these conductors _must_ of necessity be in different locations, there will be different coupling between the various conductors and the CT coil. The net result is that a small difference current may be measured, even if the actual current flow is perfectly balanced. A GFCI tripping on a _mismeasured_ current difference is IMHO a nuisance trip.

If you think about it, it is _very_ impressive that a GFCI will reliably trip on difference currents of 4-6mA, even as currents 1000x greater are flowing in the conductors.

I agree, however, that most of what is call nuisance tripping is really tripping on otherwise un-noticed fault current. 10mA (or even 100mA) of leakage through a well bonded EGC will not show up as a shock or other sort of equipment problem, but it _will_ trip a GFCI. It is my opinion that such current flow represents a fault that should be fixed, but I could understand just wanting to 'live with it'. 100mA on the EGC is not a problem until the EGC is interrupted and the frame energized!

I believe that it would be reasonable to relax the trip sensitivity requirements for fault current flowing through the EGC of an appliance, however such a change would require different GFCI equipment, and such equipment would be of benefit only where the equipment being served is already broken. One could imagine a GFCI which measures both the supply circuit difference current _and_ also uses a different CT to monitor the current including the EGC. Then have different sensitivity levels on the different CTs, for example: trip if the supply current difference exceeds 50mA, _or_ trip if the supply current plus EGC has a net current in excess of 5mA. In this way any current flowing from the device via a non-controlled path would be detected and interrupted at normal GFCI levels, but there would be relaxed protection if the fault current flows along a well identified path (the EGC)

-Jon

 

[iwire]

Bill

You may think that there is no such thing as nuisance tripping because your field is too limited or your not opened minded enough.

A construction electrician which is mostly if not all thats here won't see the problems a industrial electrician who are becoming more electronics technicians will see like nuisance tripping.

You did not really mean that did you?

I think you may need to step off that pedestal before you fall. :roll:

All you have to do is Google "nuisance tripping" and read up.

Actually I did just that, a couple of times I found nothing I would call definitive and nothing proving harmonics have any thing to do with GFCIs tripping.

Have you had time to think about Larry's great question?

Bill, what condition would you consider legitimate nuisance tripping, i.e., tripping of a GFCI device (or any other, if you like) that is not indicative of a genuine electrical concern?

 

[wptski]

Bill






You did not really mean that did you?

I think you may need to step off that pedestal before you fall. :roll:



Actually I did just that, a couple of times I found nothing I would call definitive and nothing proving harmonics have any thing to do with GFCIs tripping.

Have you had time to think about Larry's great question?

Even if you had the proper credentials, my employer would send to core skills for testing, 80% walk as soon as they gather what's coming. It's no match for a construction electrician. It's where our "all" apprentices from every trade are sent at different times during the program. I'm not a electrician but a machine repairman and a x military electronics tech. I've seen the trade change from simple relay logic to what it is today. I've seen many electricians come from construction before we tested, try the work and quit.

I wish you guys would reread my posts, I never said anything about harmonics tripping GFCI at all. It's all about "nuisance tripping", fact or fiction.

Any circuit breaker tripping, fuse blowing should be a concern but "if" the source can't be found or none appears, it becomes a "nuisance".

 

[Dennis Alwon]

a GFCI operates by looking for a current imbalance on the circuit conductors, any inrush current will be equal on each of the circuit conductors.

I am way out of my league here but I have a nagging question. I know that lightning can trip a Gfci and not cause damage to the unit. I am thinking that this must be inrush current. If this is the case how can we say that inrush current will not trip a breaker. Please correct me if I am misunderstanding ( I know you will). Just be nice about it---

 

[jim dungar]

I am way out of my league here but I have a nagging question. I know that lightning can trip a Gfci and not cause damage to the unit. I am thinking that this must be inrush current. If this is the case how can we say that inrush current will not trip a breaker. Please correct me if I am misunderstanding ( I know you will). Just be nice about it---

A GFCI works by looking at the amount of current that goes out versus the amount of current that comes back. Too much current coming back (i.e. like what might be induced by a lightning strike) will cause the GFCI to trip the same as too little current.

 

[winnie]

I am way out of my league here but I have a nagging question. I know that lightning can trip a Gfci and not cause damage to the unit.

Try thinking about it this way:

A GFCI looks at the _net_ current flowing on a set of conductors. The normal description of the GFCI comparing each conductor for balanced current flow derives from this; if the current flow is balanced then the net current will be zero. However _any_ situation that causes a net current flow greater than 4-6mA will cause the GFCI to trip.

The measurement of net current flow is via a current transformer. So anything that induces current in the transformer secondary will cause the measurement of a net current, and cause the GFCI to trip.

Lightning could trip the GFCI if it pushes current through the conductors, causing a real net current. It could also trip the GFCI if a changing magnetic field somehow coupled with the current transformer, causing a net current reading without real net current. Finally lightning could somehow activate the sense circuitry that responds to current flow from the CT.

-Jon

 

[haskindm]

Any circuit breaker tripping, fuse blowing should be a concern but "if" the source can't be found or none appears, it becomes a "nuisance".

Bill, you have exactly stated my concern. The breaker or GFCI is tripping. We do not have the skill, tools, or time (you pick) to diagnose the cause so we use the term "nuisance tripping" as an excuse to do nothing, install a higher amperage breaker, or eliminate the GFCI protection. This can and does lead to dangerous situations. Electrical manufacturers do not want to admit that they have defective products, equipment manufacturers do not want to admit that their equipment has voltage leakage or other defects, and electricians do not want to admit that their wiring may be defective or inadequate. And nobody wants to admit that they do not have the skill or tools to properly diagnose a problem. So we have come up with the phrase "nuisance tripping" to allow us to do nothing or even violate the NEC. The actual phrase that should be used is "unexplained tripping" or "undiagnosed tripping". That would indicate that everything appears to be OK, but the device still trips and we don't know why. That is more honest than "nuisance tripping". I maintain that given the right expertice the cause for ANY nuisance tripping could be determined and remedial action taken.

 

[wptski]

haskindm:

I agree! Well, where I work they could get a piece of test equipment easier than I can get a somewhat special wrench! Things get out of cycle all the time, they just power down, reboot it, manually valve things in position and away you go again! Some of it is just poor engineering though.

BTW- There is thread in Safety about nuisance tripping of AFCI that's been revived from June this year.

 

[masterelect1]

A construction electrician which is mostly if not all thats here won't see the problems a industrial electrician who are becoming more electronics technicians will see like nuisance tripping.

All you have to do is Google "nuisance tripping" and read up.

Not really:
Industrial - copper refinery - 3 yrs.
" " - Chemical plant - 5 yrs.
" " - Food manufacturing - 15 yrs.

You still haven't been able to cite an example of nuisance tripping.
Hint: next time you encounter this "problem", switch circuit breaker with another of same size or circuit with another and see if the problem follows or stays.
Either way, this will eliminate your confusion.

 

[wptski]

Not really:
Industrial - copper refinery - 3 yrs.
" " - Chemical plant - 5 yrs.
" " - Food manufacturing - 15 yrs.

You still haven't been able to cite an example of nuisance tripping.
Hint: next time you encounter this "problem", switch circuit breaker with another of same size or circuit with another and see if the problem follows or stays.
Either way, this will eliminate your confusion.

No need to site a example of nuisance tripping since it's definition should be good enough for all except those trying to be a, what you'd define as a nuisance.

Several other threads here on AFCI nuisance tripping too! Must be becoming fairly common or unless you want to ignore them or think that there is no such thing.

Here's the thread on AFCI nuisance tripping: http://forums.mikeholt.com/showthread.php?t=87850

 

[andinator]

The "nuisance tripping" I experienced with AFCI breakers occured on what would become "RECALLED FROM THE MANUFACTURER" breakers.:grin: Since that little fiasco was cleared up I've yet to have an AFCI trip without cause.

 

[haskindm]

Andinator,
I maintain that what you experienced was not "nuisance tripping", it was a defective breaker. There is always a reason that a breaker trips, whether it is a standard breaker, GFCI, or AFCI. It is either performing the function for which it was designed, or it is defective and tripping for no reason. There is no such thing as nuisance tripping and the term nuisance tripping should not be used as an excuse to either do nothing or violate the NEC.

 

[TOOL_5150]

I have been told quite a few times by an inspector that I did not need a GFCI on a dedicated circuit if: I used a single recep AND the appliance covered the recep, or if the recep was above 6' on the wall. Each time the inspection was on a detatched building at a residence.

He was wrong in both instances right? In a detached building [tool shed] GFCI protection is required, as it is in garages etc...

~Matt

 

[andinator]

Andinator,
I maintain that what you experienced was not "nuisance tripping", it was a defective breaker. There is always a reason that a breaker trips, whether it is a standard breaker, GFCI, or AFCI. It is either performing the function for which it was designed, or it is defective and tripping for no reason. There is no such thing as nuisance tripping and the term nuisance tripping should not be used as an excuse to either do nothing or violate the NEC.

You are preaching to the choir, bro. I am of the school that equates "nuisance tripping" to stumped or lazy electrician.

 

[JohnJ0906]

I have been told quite a few times by an inspector that I did not need a GFCI on a dedicated circuit if: I used a single recep AND the appliance covered the recep, or if the recep was above 6' on the wall. Each time the inspection was on a detatched building at a residence.

He was wrong in both instances right? In a detached building [tool shed] GFCI protection is required, as it is in garages etc...

~Matt

Depends. Read 210.8(A) all the way through, especially the exceptions.

Sometimes it's legal, sometimes not. Of course, you may have local amendments.

In the '08 NEC, I think many of the exceptions will go away.

 

[wptski]

You are preaching to the choir, bro. I am of the school that equates "nuisance tripping" to stumped or lazy electrician.

Or your field of work limits the chances of you ever seeing genuine "nuisance tripping".

 

[haskindm]

WPTSKI,
Please give us an example in which a known non-defective breaker with no overload, no ground-fault, with no defective wire, no defective equipment, trips. That would be a nuisance trip. In other words there is absolutely no reason for the breaker to trip, but it trips anyway = nuisance tripping. I maintain that such a situation does not exist. If the breaker trips, and is not defective, it has acted as designed. The fact that it has tripped may cause a nuisance, but it is not a nuisance trip. The reason for the tripping can should be discovered and corrected. Unfortunately, it is often blamed on "nuisance tripping" and this is used as an excuse to eliminate some level of protection. It is the same mind set that leads a homeowner to put a penny under a fuse, or replace a cartridge fuse with a piece of copper pipe to eliminate the "nuisance" of a overloaded fuse blowing. A professional electrician should be above such actions.

 

[ELA]

Andinator,
I maintain that what you experienced was not "nuisance tripping", it was a defective breaker. There is always a reason that a breaker trips, whether it is a standard breaker, GFCI, or AFCI. It is either performing the function for which it was designed, or it is defective and tripping for no reason. There is no such thing as nuisance tripping and the term nuisance tripping should not be used as an excuse to either do nothing or violate the NEC.

While I agree that you should not use nuisance tripping as an excuse to do nothing or violate the NEC - Nuisance tripping does exist and there is nothing wrong with using the term.

I have worked in the Industrial environment for over 25 years and have experienced many such nuisance trips first hand. GFCI's often trip due to electrical noise and I consider that a nuisance trip. Especially if the source of the noise is not continuous. Many on this forum do not believe this. If you do a search on the internet you will find that manufacturers are aware of these issues.

For ref: http://www.bayneselectric.com/html/pressgfci.html (see note #4)

The better manufacturers design and test their GFCIs for electrical immunity.
If they are good they will state the level of noise immunity in their specifications.

So in the case where the breaker trips due to noise it is not considered defective but instead not immune enough for the level of noise it is exposed to.

As one example I had a 3 phase GFI tripping intermittently. It was replaced twice with the same manufacturers brand and continued to trip. We then replaced it with a different model that had specifically been tested for noise immunity and it held fine.
In another case an automation servo drive caused a GFI to trip when the controller was in regeneration mode as the motor decelerated. In this case the breaker was also not defective but still nuisance tripped.

It is well known that any circuit that incorporates integrated circuits can fail if exposed to a certain level of electrical noise or RF fields. GFCIs included.