GFCI *breaker* failure modes?

[Don Y]

Hi,

20A GFCI breaker (i.e., "GFCI with overload protection" -- NOT a
GFCI duplex receptacle!) seems to be tripping at low currents.
Doesn't appear to be a ground fault issue but, rather, as if the
"overload" was engaging too early (i.e., the breaker can be reset
and "hold" in the absence of a load).

For example, plugging 1HP electric drill into circuit
immediately trips the breaker (before the chuck even begins
to rotate). I should try some resistive loads to see how
the results differ (and, I can also get a better idea as to
*where* the trip point is -- one 100W lamp, two 100W lamps,
three 100W lamps, etc.)

This particular circuit sees heavy use (e.g., 100% rated
capacity) but only seasonally (e.g., holiday lighting).

All GFCI breakers are collocated in the same electric panel
(which is mounted outside the house). None of the other
circuits have *any* problems. E.g., 1000W hairdriers on
the bathroom circuit work without a hitch; electric frying
pans (two at once!) on the kitchen counter circuits have no
problem.

I could swap breakers (or, equivalently, loads) and verify the
problem is not related to wiring (e.g., moisture in one of the
outdoor receptacles? dead bugs?)

So, question is, how is the breaker failing? What is the likely
cause? Would the problem also have affected a *regular* circuit
breaker (given the same sort of loading)? Or, is there something
specific to GFCI breakers that makes them more temperamental?

And, how to prevent repeating this exercise, again? (GFCI breakers
are pretty pricey -- and, hard to find for 30+ year old panels!)

Thx,
--don

 

[Don Y]

On 19/09/13 08:22, Don Y wrote:

Probably a good idea to "megger" the circuit to check as you say, before
doing much else. Do the drill while you have the kit out.

Yeah though I suspect it's not a ground fault issue. Easy
enough to check, though.

Of course, I will now regret *not* "daisy chaining" the wiring
between receptacles as that would have made it easier to isolate
a problem *if* that proves to be the issue (i.e., drop the last
leg off the branch circuit and see what changes; then, move
upstream one step and repeat; etc.)

OTOH, *if* that's the problem, it is most likely *in* a receptacle
than in the actual wiring. So, I can still isolate individual
receptacles from the circuit by simply disconnecting their
respective pigtails...

<frown> Maybe I'll just swap the wires at the panel (different,
"known good" breaker) and see if the symptoms change. If so,
then I'll have the conductors "in my hands" to check out the
circuit.

 

[Phil Allison]

"Don Y"

For example, plugging 1HP electric drill into circuit
immediately trips the breaker (before the chuck even begins
to rotate).

** You are describing a faulty drill - dill.

Gotta eliminate that first.



.... Phil

 

[Charlie E.]

Probably a good idea to "megger" the circuit to check as you say, before
doing much else. Do the drill while you have the kit out.

If it is like my christmas light circuits, it has outdoor recepticals.
These seem to have a tendency to build up dirt and moisture that makes
them trip the breaker pretty easily...

 

[bud--]

Yeah though I suspect it's not a ground fault issue. Easy
enough to check, though.

Sounds like ground leakage in the circuit, or a defective GFCI.

Or ground leak in the drill. Does it trip on other loads?

Of course, I will now regret *not* "daisy chaining" the wiring
between receptacles as that would have made it easier to isolate
a problem *if* that proves to be the issue (i.e., drop the last
leg off the branch circuit and see what changes; then, move
upstream one step and repeat; etc.)

OTOH, *if* that's the problem, it is most likely *in* a receptacle
than in the actual wiring. So, I can still isolate individual
receptacles from the circuit by simply disconnecting their
respective pigtails...

<frown> Maybe I'll just swap the wires at the panel (different,
"known good" breaker) and see if the symptoms change. If so,
then I'll have the conductors "in my hands" to check out the
circuit.

Swapping to another GFCI breaker is an obvious test.

You can wire through a GFCI receptacle to protect the downstream
circuit. Cheaper than a GFCI breaker. A receptacle for this purpose
could be installed adjacent to the panel.

 

[Don Y]

Hi Bud,

Sounds like ground leakage in the circuit, or a defective GFCI.

I would have assumed that the GFCI would "trip" regardless of
load, if that were the case (??). As it is, it will handle
some *smaller* loads without a problem. Hence my thinking that
it was related to the "overload" portion of the breaker.

Or ground leak in the drill. Does it trip on other loads?

Yes, I first noticed it with a "lighting load". Thought I was
just pushing the circuit too hard. I've since noticed in
when trying to use various "hand tools" on that circuit
(drills, sabre saw, sawzall, radial arm saw, etc.). Of course,
all of these are reactive loads so I didn't know if that was
contributing to the problem.

Swapping to another GFCI breaker is an obvious test.

Agreed. Esp as I have others "available" and "within reach"
of the wires in the panel!

You can wire through a GFCI receptacle to protect the downstream
circuit. Cheaper than a GFCI breaker. A receptacle for this purpose
could be installed adjacent to the panel.

I've had bad experiences with GFCI receptacles outdoors. That's
what prompted me to spend the extra money for the GFCI breaker
(hoping it would be manufactured "better" than the "el cheapie"
receptacles).

 

[Don Y]

Why? Note the receptacles are "normal" (three wire) receptacles
(the GFCI function is in the breaker).

If this is the case, then I should (possibly) be able to find
some *other* receptacle on that branch circuit that doesn't
exhibit the problem? E.g., one of those on the (covered) porch?

OK, this (Charlie's comment) has to be at least part of the problem.

I went to one of the porch outlets (porch is shaded; other outlets
are out in the afternoon sun -- 2PM being the hotest time of day;
electrical panel similarly "exposed").

Plugged in a single 100W bulb in a fixture that is always used
indoors. Fine. Plugged in a second 100W bulb in another, similar
fixture. Also fine. Now have exhausted both receptacles in that
duplex outlet so introduce a short extension cord that terminates
in a 2G box (with a pair of duplex receptacles).

Transfer both fixtures to the that "extension". All is *still* OK.
(you would *expect* it to be, but... see below)

Figuring the 100W-at-a-time approach is going to quickly deplete me
of fixtures, I went looking for a larger load. Electric hair dryer!
Heck, it works fine on the indoor circuits so that should attest to
it's "quality" (as a load).

Adding this to the 200W load blew the breaker -- before the
hairdryer even got started.

[Hmmm... technically, there's a reactive component to this load
for the fan motor so it's not *purely* resistive]

Repeat with *just* the hair dryer. Works OK.

Add one 100W lamp. OK.

Add second 100W lamp. NFG.

Great! I now need to quantify the load represented by the hair
dryer and I know what the trip point is! (ASSUMING it is an
overload trip).

Hair dryer has four settings (not counting two fan speeds).
So, just switch among those settings and see at which point
the breaker trips (hair dryer had been on lowest heat setting
previously).

Low/cool -- OK.
Warm -- OK.
Hot -- OK.
VERY HOT -- OK!

WTF? Surely the difference between Low and VERY HOT is more than
the 200W incandescent load (that, when added to the Low setting,
had caused the breaker to trip!).

Repeat the previous exercise (with the lamps). Just to be sure
I didn't miss some important detail. Exactly the same results.

OK, stop "overlooking the obvious". SOMETHING is different in these
two tests. What is it?

Well, to plug in the three loads (two lamps plus hair dryer), I have
to resort to the receptacle multiplier represented by the "extension
cord". That particular cord is often outdoors. Just like most
of the duplex receptacles on that circuit!

So, while I can plug the hair dryer into the duplex receptacle ON THE
PORCH and have no problems, this isn't true if the load is fed from
the (three wire!) extension cord.

[I suspect if I tried plugging the hair dryer into one of the more
"troublesome" outlets, it wouldn't work on the VERY HOT setting,
either!]

And, this then appears NOT to be a case of overload but, rather,
ground fault/leakage! But, only manifesting at larger loads?
(or, perhaps only when certain outlets are utilized??)

So, what is it (?) about the receptacle's mechanical structure
that can cause this sort of failure ONLY WHEN IN USE?

I will test the hair dryer on the remaining receptacles (without
the "suspect" extension cord. And, possibly replace the
receptacles in this 2G extension cord Jbox to see if that "fixes"
the problem when using that extension cord. (This would then
lend credibility to the possible solution to the original
problem by simply replacing all the duplex receptacles on that
branch circuit!)

It also would be consistent with my observation that the GFCI
receptacles have high failure rates -- but, not because the
electronics in the receptacle are failing (from exposure) but,
rather, some inherent characteristic of "receptacles" themselves!

(which would reinforce my decision to opt for the GFCI breaker
with "traditional"/less expensive outlets instead of pricier
GFCI outlets!)

(sigh) What a PITA...

 

[Ecnerwal]

I've had bad experiences with GFCI receptacles outdoors. That's
what prompted me to spend the extra money for the GFCI breaker
(hoping it would be manufactured "better" than the "el cheapie"
receptacles).

We pragmatic/parsimonious folks manage both of these (I'm pretty sure
that's what bud-- is also describing.) First outlet on the circuit is a
GFCI located inside (as he said, can be right next to the CB panel -
perhaps not in your case if the CBP is outside), wired to protect the
rest of the circuit (line is fed from panel, load goes to remainder of
outlets.) The outside outlets are standard outlets, but they are
protected by the GFCI feeding them, which is a less-expensive, easily
replaced outlet-type GFCI, in a nice dry location. Label correctly so
you can find the tripped GFCI (ideally, so someone who is NOT you can
find the tripped GFCI...) when the attached outlets go dead.

Pragmatic observation - GFCIs do not last as long as breakers. So a GFCI
breaker is a problem waiting to happen, and in your case, it would
appear to be done waiting. Unless you are cursed with a code written by
the sleazeballs that make the things, a breaker and GFCI outlet is a
much better way to go, IME. Naturally, the sleazeballs do love to get
their crap into codes, and they spend quite a bit of money doing so,
while nobody (AFAIK) spends a lot of money keeping useless crap out of
the codes.

 

[Ecnerwal]

I'm assuming a "GFCI with overload protection" is the same as a device I
would call a RCBO, though I still see the occasional ELB (Earth Leakage
Breaker) (UK).

Is this a device that measures imbalance in the Live and Neutral
current,

Yes, that is what a (this side of the pond) Ground Fault Circuit
Interrupter is, and Don has the variant that is combined with a circuit
breaker. If line and neutral currents disagree by 5 mA (or more), the
GFCI part should trip.

 

[Ecnerwal]

30 years ago we had very few RCD devices and most protection was of the
ELB variety. Are you sure?

I am. They work on un-grounded (two prong - line and neutral, no
earth/safety ground connection) devices.

Over here the normal device trip currents are 30mA for personal shock
protection and 100mA for fire protection.

Well, the "magic numbers" I learned were that 10-100ma is the range of
current (through the heart) most likely to kill a person - below that
the heart does not go into fibrillation and above that the heart is
stopped (and will usually self-start when current is removed.) I can't
say I've independently tested the veracity of that, but it was what I
was taught from reasonably reliable/authoritative sources.

5mA sounds very low and we get enough nuisance trips at 30mA! I suspect
at 240V we are more likely to have more leakage.

5mA and 25mS is the North American standard (per the not stunningly
authoritative, but often correct anyway, wikipedia.) The 5mA part is
certainly consistent with what I had learned independently.

 

[Don Y]

We pragmatic/parsimonious folks manage both of these (I'm pretty sure
that's what bud-- is also describing.) First outlet on the circuit is a
GFCI located inside (as he said, can be right next to the CB panel -
perhaps not in your case if the CBP is outside), wired to protect the
rest of the circuit (line is fed from panel, load goes to remainder of
outlets.) The outside outlets are standard outlets, but they are
protected by the GFCI feeding them, which is a less-expensive, easily
replaced outlet-type GFCI, in a nice dry location. Label correctly so
you can find the tripped GFCI (ideally, so someone who is NOT you can
find the tripped GFCI...) when the attached outlets go dead.

We have 5 such branch circuits, here:
- garage
- two small appliance "countertops"
- bathrooms (share a single circuit)
- outside
I think that was all that Code required.

There's no place "outside" that would ever be "nice dry locations".
While we have practically *no* rainfall, when we *do* get some,
it is often very hard ("driven") and heavy. E.g., not uncommon
for rain to be traveling "sideways".

So, the "outside" circuit is always going to be an issue as far
as locating the GFCI aspect of the protection device.

The bathrooms are obviously indoors. And, *should* be "dry"
(unless you're splashing around in the sink!). You'd just
have to remember which bathroom had the GFCI receptacle
(I'm told putting two GFCI receptacles on a single branch
circuit is sometimes problematic?)

The kitchen circuits could have been handled by nominating
two outlets to be the "masters" and feeding the rest off of these.
But, I didn't like the idea of having an easy way of resetting a
tripped circuit there. I.e., it *shouldn't* trip and you
should really want to understand why it had tripped before just
reaching over and resetting it!

Curiously, none of these "indoor" circuits (breakers) have given
us any problems. And, they see far more use than the "outside"
circuit (though, as I stated, the outside circuit is run at ~100%
of rated load at times)

Pragmatic observation - GFCIs do not last as long as breakers. So a GFCI
breaker is a problem waiting to happen, and in your case, it would
appear to be done waiting. Unless you are cursed with a code written by
the sleazeballs that make the things, a breaker and GFCI outlet is a
much better way to go, IME. Naturally, the sleazeballs do love to get
their crap into codes, and they spend quite a bit of money doing so,
while nobody (AFAIK) spends a lot of money keeping useless crap out of
the codes.

See my followup post regarding today's testing. The GFCI breaker
does not appear to be the problem. Rather, certain (normal)
receptacles hanging off that circuit seem to irritate the condition.
I'm guessing moisture and/or insects/spiders may have infiltrated
these and, when in use, upset the GFCI?

I'll have to check isolation on these. Actually, I think I have
such a device (or HiPot) somewhere in my mess...

 

[Don Y]

Yes, that is what a (this side of the pond) Ground Fault Circuit
Interrupter is, and Don has the variant that is combined with a circuit
breaker. If line and neutral currents disagree by 5 mA (or more), the
GFCI part should trip.

Exactly. Though the "breaker" actually is a three terminal device
(having a pigtail that you run off to "earth/neutral" in the panel).
I suspect this is just to provide a reference that doesn't see the
currents flowing through the neutral bus bar in the panel (which
feeds all the other loads in the house). (?)

[I am always hesitant to dick with these things as the earthing point
for that pigtail is in "mains" side of the box, beside the actual
feed (before the main disconnect). Something about those big, fat
conductors always intimidates me -- even though the little ones
on the "breaker" side of the panel are just as deadly! Who cares
if the feed is fused at 500A instead of 15-20A... you're just
as dead if you slip!! :-/ ]

 

[Don Y]

I am. They work on un-grounded (two prong - line and neutral, no
earth/safety ground connection) devices.

E.g., the test button usually shunts current *across*/around the
current sense transformer -- no "earth" involved.

Well, the "magic numbers" I learned were that 10-100ma is the range of
current (through the heart) most likely to kill a person - below that
-----------^^^^^^^^^^^^^^^^^

the heart does not go into fibrillation and above that the heart is
stopped (and will usually self-start when current is removed.) I can't
say I've independently tested the veracity of that, but it was what I
was taught from reasonably reliable/authoritative sources.

While I'm sure there is *some* number that causes death if
the current does NOT go through the heart (, brain or other
critical organ), I've never seen a number for such a "safe"
(nonlethal) current. Aside from "burning tissue", if the
heart is "isolated" from the current path, is there such
a figure? Or, do you just worry about burnt flesh and
broken bones -- depending on the muscle groups affected?

 

[Phil Allison]

"Mike Perkins"

I don't understand why it is 3 terminal? Any device that measures current
imbalance has to be 4 terminal by definition.

ie 2 in and 2 out, and as you say a test button in series with a resistor
between neutral in and live out.

** Quite correct.

Active and neutral lines are both sensed, so it is four terminal.

Safety ground is not involved as "earth leakage" can use any path to actual
ground - eg plumbing, soil, wet concrete floors etc.

Plus and kinda obvious, is that the active circuit must open if the neutral
input is disconnected.

So it cannot be a spring loaded breaker with an electronic trip mechanism.


.... Phil

 

[Don Y]

Hi Mike,

I don't understand why it is 3 terminal? Any device that measures
current imbalance has to be 4 terminal by definition.

Sorry, I'm speaking "casually". Read "terminal" as "connections"
(that the installer has to make). The fourth "terminal" is typically
a contact on the back/bottom side of the breaker that engages a
portion of the bus bar behind it.

A "normal" breaker would be a "one terminal" device in this sense.
One load wire to connect to the breaker (the "other" being this contact
on the back side).

For a GFCI breaker, you have that "back side" contact plus the normal
"hot to load" screw terminal. Additionally, a "neutral to load" screw
terminal (not required on a regular breaker) and a *pigtail* that
runs off to the "grounding" block (where *it* sits under a screw)

 

[Phil Allison]

"Phil Allison"

Plus and kinda obvious, is that the active circuit must open if the
neutral input is disconnected.

So it cannot be a spring loaded breaker with an electronic trip mechanism.

** Ooops. That is not correct.

Loss of neutral to an RCD or GFCI means no trip is possible and you die.

I used to have a ( plug in) RCD with a normal relay inside, so with no
neutral it would not connect the active or neutral to the load side.

It's crap that most do not have this safety feature.



..... Phil

 

[ehsjr]

Why? Note the receptacles are "normal" (three wire) receptacles
(the GFCI function is in the breaker).

If this is the case, then I should (possibly) be able to find
some *other* receptacle on that branch circuit that doesn't
exhibit the problem? E.g., one of those on the (covered) porch?

OK, this (Charlie's comment) has to be at least part of the problem.

I went to one of the porch outlets (porch is shaded; other outlets
are out in the afternoon sun -- 2PM being the hotest time of day;
electrical panel similarly "exposed").

Plugged in a single 100W bulb in a fixture that is always used
indoors. Fine. Plugged in a second 100W bulb in another, similar
fixture. Also fine. Now have exhausted both receptacles in that
duplex outlet so introduce a short extension cord that terminates
in a 2G box (with a pair of duplex receptacles).

Transfer both fixtures to the that "extension". All is *still* OK.
(you would *expect* it to be, but... see below)

Figuring the 100W-at-a-time approach is going to quickly deplete me
of fixtures, I went looking for a larger load. Electric hair dryer!
Heck, it works fine on the indoor circuits so that should attest to
it's "quality" (as a load).

Adding this to the 200W load blew the breaker -- before the
hairdryer even got started.

[Hmmm... technically, there's a reactive component to this load
for the fan motor so it's not *purely* resistive]

Repeat with *just* the hair dryer. Works OK.

Add one 100W lamp. OK.

Add second 100W lamp. NFG.

Great! I now need to quantify the load represented by the hair
dryer and I know what the trip point is! (ASSUMING it is an
overload trip).

Hair dryer has four settings (not counting two fan speeds).
So, just switch among those settings and see at which point
the breaker trips (hair dryer had been on lowest heat setting
previously).

Low/cool -- OK.
Warm -- OK.
Hot -- OK.
VERY HOT -- OK!

WTF? Surely the difference between Low and VERY HOT is more than
the 200W incandescent load (that, when added to the Low setting,
had caused the breaker to trip!).

Repeat the previous exercise (with the lamps). Just to be sure
I didn't miss some important detail. Exactly the same results.

OK, stop "overlooking the obvious". SOMETHING is different in these
two tests. What is it?

Well, to plug in the three loads (two lamps plus hair dryer), I have
to resort to the receptacle multiplier represented by the "extension
cord". That particular cord is often outdoors. Just like most
of the duplex receptacles on that circuit!

So, while I can plug the hair dryer into the duplex receptacle ON THE
PORCH and have no problems, this isn't true if the load is fed from
the (three wire!) extension cord.

[I suspect if I tried plugging the hair dryer into one of the more
"troublesome" outlets, it wouldn't work on the VERY HOT setting,
either!]

And, this then appears NOT to be a case of overload but, rather,
ground fault/leakage! But, only manifesting at larger loads?
(or, perhaps only when certain outlets are utilized??)

So, what is it (?) about the receptacle's mechanical structure
that can cause this sort of failure ONLY WHEN IN USE?

Receptacle
hot -------------------+---| |----+
| o |
| |
+---| |----+
o |
|
neutral ----------------------------+
|
[R]
|
Gnd

R represents a partial short to ground via
spider web/crud/dirt/whatever.

With no load connected, there is no current in either hot
or neutral. Therefore, there is no imbalance between them,
and the GFI doesn't trip. But, when the receptacle is in use,
then there is current in both wires and current in the partial
short to ground. If the current through the partial short to
ground is ~5mA or more, the GFI trips.

If there was a partial short to ground on the hot wire,
then there would be current there without a load, and
the GFI would trip, provided the current was ~5mA or more.

That answers the "ONLY WHEN IN USE" portion of your question.
The failure is an environmental issue - crud getting in to
the junction box - not a receptacle mechanical structure
issue. The crud could just as easily have created a partial
short to ground on the hot side as the neutral side.

Ed

 

[[email protected]]

"The crud could just as easily have created a partial
short to ground on the hot side as the neutral side. "

Yes but in that case it would trip even without a load.

 

[Don Y]

Hi Ed,

On 9/19/2013 5:39 PM, Don Y wrote:

So, what is it (?) about the receptacle's mechanical structure
that can cause this sort of failure ONLY WHEN IN USE?

Receptacle
hot -------------------+---| |----+
| o |
| |
+---| |----+
o |
|
neutral ----------------------------+
|
[R]
|
Gnd

R represents a partial short to ground via
spider web/crud/dirt/whatever.

With no load connected, there is no current in either hot
or neutral. Therefore, there is no imbalance between them,
and the GFI doesn't trip. But, when the receptacle is in use,
then there is current in both wires and current in the partial
short to ground. If the current through the partial short to
ground is ~5mA or more, the GFI trips.

Note that this would require a high resistance neutral path
OR a significantly *low* resistance path to earth. E.g., if
you assume 100 ft of #12AWG as the neutral lead (to the panel),
that's ~0.2 ohms for the total run. If the circuit was not
tripping until seeing a full *20A* load (note mine was tripping
much before that), then you would expect 4V across the neutral.
For 5mA to flow through this, you'd need to be looking into
~1K ohms. That should stand out like a sore thumb -- with
even a crappy VOM!

If the circuit was tripping at 10A (or 5A) then you'd need an
even lower resistance short to shunt that much current away
from the neutral.

[OTOH, if there is a high-ohmic connection between the outlet
and the panel (e.g., a bad splice), then you would encounter a
higher "neutral potential" and a proportionately higher
resistance could cause the problem]

If the crud sat on the line side (to earth, not neutral), then
you're in the ~100K ballpark. But, the GFCI would trip *any*
time line voltage was present!

As I don't see anything (electrically) when probing the suspect
extension cord (easily isolated from the circuit in its entirety),
I suspect there is something more to the problem than just some
"static" partial short. E.g., something changing with the
mechanical introduction of the blades of the mating plug. Some
"gap" shrinking or the blades of the plug actually penetrating
further into the outlet than the blades of the receptacle, etc.

I know I've got a HiPot here, someplace. That's the ideal way
to check as I can then explore the "short" at various line
potentials (I think up to a few KV). Trick is figuring out
which box it's hiding in!! :-/ (Grrr... I *really* need
to downsize!)

 

[ehsjr]

short to ground on the hot side as the neutral side. "

Yes but in that case it would trip even without a load.

Right, as already stated in the post:
"If there was a partial short to ground on the hot wire,
then there would be current there without a load, and
the GFI would trip, provided the current was ~5mA or more. "

Ed