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Ground fault switch aka residual-current device
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Carlos E.R.
Aug 6, 2023, 3:07:25 PM8/6/23
to
Hi,
You know this switches
https://en.wikipedia.org/wiki/Residual-current_device
In Spain, every house must have at least one protecting the entire
house. Typically 30 mA sensitivity.
Well, in some houses the thing seems to be temperamental and trigger
eventually for no apparent reason. Say once a month, twice a year...
So there are models that protect against harmonics (in Spain, they are
"class AC). Others are "immunized". Spanish Wikipedia says:
«Class AC residual current circuit breakers are the most commonly used,
although they are banned in many countries, such as Germany, due to
their ineffectiveness against harmonics and others. Semiconductors
generate leakage currents that are not detected by class AC circuit
breakers.1 It is symbolized by a rectangle showing a sine wave.»
«Class F residual current circuit breaker: they are used to protect
against alternating and pulsating leakage currents, as well as mixed
frequencies due to leakage in the electrical network. It is suitable for
earth leakage protection and to prevent untimely disconnections by
high-frequency drives; in case of tripping, it has a delayed effect. It
is also often referred to as a superimmunized residual current circuit
breaker.3 It is symbolized by a rectangle showing a sine wave overcoming
a second oscillation, plus a second rectangle with numerous sine waves.»
And there are other models that automatically reactivate after
triggering, with a motor.
Now, here goes the question.
Someone I know claims this automatic rearming is illegal in other
countries, like Germany, and that they are very dangerous. That the
devices are only sold in Spain. That spurious false triggerings do not
exist.
Is this true?
--
Cheers, Carlos.
You know this switches
https://en.wikipedia.org/wiki/Residual-current_device
In Spain, every house must have at least one protecting the entire
house. Typically 30 mA sensitivity.
Well, in some houses the thing seems to be temperamental and trigger
eventually for no apparent reason. Say once a month, twice a year...
So there are models that protect against harmonics (in Spain, they are
"class AC). Others are "immunized". Spanish Wikipedia says:
«Class AC residual current circuit breakers are the most commonly used,
although they are banned in many countries, such as Germany, due to
their ineffectiveness against harmonics and others. Semiconductors
generate leakage currents that are not detected by class AC circuit
breakers.1 It is symbolized by a rectangle showing a sine wave.»
«Class F residual current circuit breaker: they are used to protect
against alternating and pulsating leakage currents, as well as mixed
frequencies due to leakage in the electrical network. It is suitable for
earth leakage protection and to prevent untimely disconnections by
high-frequency drives; in case of tripping, it has a delayed effect. It
is also often referred to as a superimmunized residual current circuit
breaker.3 It is symbolized by a rectangle showing a sine wave overcoming
a second oscillation, plus a second rectangle with numerous sine waves.»
And there are other models that automatically reactivate after
triggering, with a motor.
Now, here goes the question.
Someone I know claims this automatic rearming is illegal in other
countries, like Germany, and that they are very dangerous. That the
devices are only sold in Spain. That spurious false triggerings do not
exist.
Is this true?
--
Cheers, Carlos.
legg
Aug 7, 2023, 9:04:34 AM8/7/23
to
It doesn't make sense that a safety protection circuit self-reset.
Thermal protection, no proplem.
Overload, no problem.
Stuck motion, no problem.
Tingle/fault current - how would the coroner know what killed you . .
. . or the next guy who wandered by?
RL
Peter W.
Aug 7, 2023, 9:08:59 AM8/7/23
to
Some basics from a US perspective:
Ground Fault Circuit Breakers are not what you linked to in your first post. A Ground Fault Circuit Breaker will trip either on an overload, or on a ground fault - that is leakage other than from Hot to Neutral. A ground fault Circuit Breaker must go through the OFF position before it can be reset. These are typically found in the main panel, not as part of a receptacle. What you pictured is a Ground Fault interrupter - that is, its primary purpose is to detect leakage, and break the circuit on that condition. These devices, typically, are not as sensitive to overload as a breaker, and although they may be "dead-front" devices, they do not kill the entire circuit, just what feeds from it. So:
A device such as you linked will 'look for' leakage in what is connected to it. A faulty device or similar. And, it will then trip. But, within the box, there is still power. So, these devices are not suitable for locations where they may be exposed to water or similar, because the circuit will still be "hot" to the box.
A panel-mounted ground-fault circuit breaker will kill the entire circuit, not just *that* location. Far safer. Example: Our hot-tubs are protected by a remote safety switch with a 50A, double-pole Ground Fault Circuit Breaker - so no part of the feed remains hot (electrified) if there is a trip.
Now, consider the situation of a self-resetting device in a residential situation. From what you are describing, that device 'protects' the entire residence, not just an individual circuit: "In Spain, every house must have at least one protecting the entire house. Typically 30 mA sensitivity."
There is a trip - you go ahead and try to diagnose why there is a trip. In the midst of this, power is re-applied without warning. Crispy Critters, perhaps? Keep in mind that even the very best device will not protect you if you insert yourself into the circuit - that is, if the current is going through you to the 'correct' neutral. Such a device would be madness. Consider such a device in a non-residential setting: Where I work, we purchase primary power (13,200 volts) and are dual-fed from two primary feeds into what is called a "tie-breaker" device. Both sides feed everything - but should there be a fault on one side, the tie-breaker automatically breaks the dual-feed, isolating the fault side. ALL OF THESE DEVICES MUST BE RESET MANUALLY. And when/if this happens, the person resetting wears a 'moon suit' - https://2313360.fs1.hubspotusercontent-na1.net/hubfs/2313360/Newsletter%20Images/Blog%20Article%20Images/The-Bulwark-Arc-Flash-Suit-A-Comprehensive-Review-image.png against an arc-flash.
Yeah, I would be unhappy if there were a self-resetting device of unknown behavior in my system.
Peter Wieck
Melrose Park, PA
Ground Fault Circuit Breakers are not what you linked to in your first post. A Ground Fault Circuit Breaker will trip either on an overload, or on a ground fault - that is leakage other than from Hot to Neutral. A ground fault Circuit Breaker must go through the OFF position before it can be reset. These are typically found in the main panel, not as part of a receptacle. What you pictured is a Ground Fault interrupter - that is, its primary purpose is to detect leakage, and break the circuit on that condition. These devices, typically, are not as sensitive to overload as a breaker, and although they may be "dead-front" devices, they do not kill the entire circuit, just what feeds from it. So:
A device such as you linked will 'look for' leakage in what is connected to it. A faulty device or similar. And, it will then trip. But, within the box, there is still power. So, these devices are not suitable for locations where they may be exposed to water or similar, because the circuit will still be "hot" to the box.
A panel-mounted ground-fault circuit breaker will kill the entire circuit, not just *that* location. Far safer. Example: Our hot-tubs are protected by a remote safety switch with a 50A, double-pole Ground Fault Circuit Breaker - so no part of the feed remains hot (electrified) if there is a trip.
Now, consider the situation of a self-resetting device in a residential situation. From what you are describing, that device 'protects' the entire residence, not just an individual circuit: "In Spain, every house must have at least one protecting the entire house. Typically 30 mA sensitivity."
There is a trip - you go ahead and try to diagnose why there is a trip. In the midst of this, power is re-applied without warning. Crispy Critters, perhaps? Keep in mind that even the very best device will not protect you if you insert yourself into the circuit - that is, if the current is going through you to the 'correct' neutral. Such a device would be madness. Consider such a device in a non-residential setting: Where I work, we purchase primary power (13,200 volts) and are dual-fed from two primary feeds into what is called a "tie-breaker" device. Both sides feed everything - but should there be a fault on one side, the tie-breaker automatically breaks the dual-feed, isolating the fault side. ALL OF THESE DEVICES MUST BE RESET MANUALLY. And when/if this happens, the person resetting wears a 'moon suit' - https://2313360.fs1.hubspotusercontent-na1.net/hubfs/2313360/Newsletter%20Images/Blog%20Article%20Images/The-Bulwark-Arc-Flash-Suit-A-Comprehensive-Review-image.png against an arc-flash.
Yeah, I would be unhappy if there were a self-resetting device of unknown behavior in my system.
Peter Wieck
Melrose Park, PA
Jeroni Paul
Aug 7, 2023, 11:12:28 AM8/7/23
to
Peter W. wrote:
> Ground Fault Circuit Breakers are not what you linked to in your first post.
Carlos refers to the device in the main breaker panel like this one:
> Ground Fault Circuit Breakers are not what you linked to in your first post.
https://en.wikipedia.org/wiki/Residual-current_device#/media/File:Residual_current_device_2pole.jpg
It is designed to trip if it detects a current leak and of course cuts both poles. But in general I consider a dangerous thing that it rearms automatically.
I know some people want them because if there is a false trip when you are away for some weeks then you have to throw away your frozen food and maybe the freezer if you can't remove the bad smell. Maybe there should be a special circuit for the fridge/freezer using a rearming GFCB and the rest a normal one.
I find these false triggers are more common with newer GFCB, maybe they react too fast to any transient or spike.
Peter W.
Aug 7, 2023, 2:44:07 PM8/7/23
to
> I find these false triggers are more common with newer GFCB, maybe they react too fast to any transient or spike.
Good point on the "pointer". A main-panel device is the only way to go for total-circuit safety.
Ground-fault devices seldom (very seldom, indeed) false-trip. Sure, they may be acutely sensitive to transient issues, which the typical end-user will perceive as a false-trip, but the reality is that *something* tripped it. And that *something* may be fatal if not understood and corrected. I have come across several conditions where an external receptacle got a salt-track from the hot to ground and presented apparent nuisance-trips - but, in fact, there was a problem. One had to look hard enough.
Rearming to save a freezer load of meat. Silly.
Carlos E.R.
Aug 7, 2023, 6:25:55 PM8/7/23
to
On 2023-08-07 17:12, Jeroni Paul wrote:
> Peter W. wrote:
>> Ground Fault Circuit Breakers are not what you linked to in your first post.
>
> Carlos refers to the device in the main breaker panel like this one:
> https://en.wikipedia.org/wiki/Residual-current_device#/media/File:Residual_current_device_2pole.jpg
>
> It is designed to trip if it detects a current leak and of course cuts both poles. But in general I consider a dangerous thing that it rearms automatically.
>
> I know some people want them because if there is a false trip when you are away for some weeks then you have to throw away your frozen food and maybe the freezer if you can't remove the bad smell. Maybe there should be a special circuit for the fridge/freezer using a rearming GFCB and the rest a normal one.
Yes, that is the case.
> Peter W. wrote:
>> Ground Fault Circuit Breakers are not what you linked to in your first post.
>
> Carlos refers to the device in the main breaker panel like this one:
> https://en.wikipedia.org/wiki/Residual-current_device#/media/File:Residual_current_device_2pole.jpg
>
> It is designed to trip if it detects a current leak and of course cuts both poles. But in general I consider a dangerous thing that it rearms automatically.
>
> I know some people want them because if there is a false trip when you are away for some weeks then you have to throw away your frozen food and maybe the freezer if you can't remove the bad smell. Maybe there should be a special circuit for the fridge/freezer using a rearming GFCB and the rest a normal one.
If I were inside the house, I would disable the auto arming. Of course,
if the fail condition remains active, it does not rearm. It is the same
strategy as a person does: the thing triggers, we go to the panel and
try to arm it, maybe several times.
Next step is to switch off circuits, then arm the RCD, till the
problematic circuit is found.
Then we go round the house removing whatever is connected to that circuit.
Finally, if the culprit is not found, call an electrician.
>
> I find these false triggers are more common with newer GFCB, maybe they react too fast to any transient or spike.
new.
There was a period, the first year, when they happened every day at a
precise time, 6:30 AM I think it was. Investigating, the electrician
found out that the substation switched the main transformer up or down a
notch at that time.
What he found then was that there was a lamp that was connected to one
current limiter on (L) and to another for the (N) line. That was
corrected and the regular triggers disappeared. There remained spurious
triggers, like once a year, which tend to happen when one is travelling
far (Murphy)
--
Cheers, Carlos.
Jeroni Paul
Aug 8, 2023, 5:48:46 AM8/8/23
to
Carlos E.R. wrote:
> If I were inside the house, I would disable the auto arming.
Sure one day you will forget to disable the rearming.
> If I were inside the house, I would disable the auto arming.
> Of course,
> if the fail condition remains active, it does not rearm. It is the same
> strategy as a person does: the thing triggers, we go to the panel and
> try to arm it, maybe several times.
> There was a period, the first year, when they happened every day at a
> precise time, 6:30 AM I think it was. Investigating, the electrician
> found out that the substation switched the main transformer up or down a
> notch at that time.
>
> What he found then was that there was a lamp that was connected to one
> current limiter on (L) and to another for the (N) line. That was
> corrected and the regular triggers disappeared. There remained spurious
> triggers, like once a year, which tend to happen when one is travelling
> far (Murphy)
Carlos E.R.
Aug 8, 2023, 6:32:28 AM8/8/23
to
On 2023-08-08 11:48, Jeroni Paul wrote:
> Carlos E.R. wrote:
>> If I were inside the house, I would disable the auto arming.
>
> Sure one day you will forget to disable the rearming.
>
>> Of course,
>> if the fail condition remains active, it does not rearm. It is the same
>> strategy as a person does: the thing triggers, we go to the panel and
>> try to arm it, maybe several times.
>
> The only way to know if the condition remains is to reapply power, so it should rearm and trip again. Not sure if it will be so fast tripping as it was the first time. If the leak was you on the bath this is not a good idea.
Nothing electric in the bath.
> Carlos E.R. wrote:
>> If I were inside the house, I would disable the auto arming.
>
> Sure one day you will forget to disable the rearming.
>
>> Of course,
>> if the fail condition remains active, it does not rearm. It is the same
>> strategy as a person does: the thing triggers, we go to the panel and
>> try to arm it, maybe several times.
>
> The only way to know if the condition remains is to reapply power, so it should rearm and trip again. Not sure if it will be so fast tripping as it was the first time. If the leak was you on the bath this is not a good idea.
Same problem as if I am in the bath, somebody else in the kitchen, the
RCD triggers, the other person resets it manually and immediately. It
will not hold.
>
>> There was a period, the first year, when they happened every day at a
>> precise time, 6:30 AM I think it was. Investigating, the electrician
>> found out that the substation switched the main transformer up or down a
>> notch at that time.
>>
>> What he found then was that there was a lamp that was connected to one
>> current limiter on (L) and to another for the (N) line. That was
>> corrected and the regular triggers disappeared. There remained spurious
>> triggers, like once a year, which tend to happen when one is travelling
>> far (Murphy)
>
> Asymetric wiring is a good way to trigger the newer super-fast protectors. I know of some cases of false-trigger, they are hard to diagnose because it happens once a year. There are various opinions on the cause.
L N
| |
| |
RCD
| |
| |
| |
| | protector
| +---/ o----------------------+---
| | . |
+-- | --/ o---- L |
| | |
| | 0 lamp
| | |
| | / switch
| | protector |
| +---/ o------ N |
| | . |
+-- | --/ o----------------------+--
| |
This is certainly bad wiring, but I fail to see why it would make the
RCD trigger every day at 6:30, when there was a voltage surge from the
transformer station. The electrician that found the problem was baffled.
--
Cheers, Carlos.
Jeroni Paul
Aug 8, 2023, 10:45:57 AM8/8/23
to
Carlos E.R. wrote:
> Same problem as if I am in the bath, somebody else in the kitchen, the
> RCD triggers, the other person resets it manually and immediately. It
> will not hold.
Bad idea. Water pipes and water heaters are earthed together with the rest of appliances, if any has a short to ground it will be dumping the full mains voltage to the water pipes. If all is well this will trip the protector fast enough to save your life assuming you was taking a bath. Think about it, you really want to keep trying to see if it keeps saving your life again and again?? Don't forget the protector could eventually fail as well.
> Same problem as if I am in the bath, somebody else in the kitchen, the
> RCD triggers, the other person resets it manually and immediately. It
> will not hold.
Also keep in mind that when "it will not hold", it is connecting the power back for some milliseconds. It has no other way to detect a leak than to apply power and check. I would not keep trying if someone is in the bath.
> This is certainly bad wiring, but I fail to see why it would make the
> RCD trigger every day at 6:30, when there was a voltage surge from the
> transformer station. The electrician that found the problem was baffled.
Peter W.
Aug 8, 2023, 12:29:37 PM8/8/23
to
Once more, an observation from a US perspective.
The basics: US residential systems are, typically 120/240 volt, single phase systems with two "Hots", a neutral and a ground. Hot-to-Hot is 240 volts @ 60 HZ ac. Hot-to-Neutral is 120 Volts AC. Ideally, Neutral and Ground are at the same potential, and, again, typically, are bonded together in the main panel. The main panel is also required to have a separate ground. The main service to the utility transformer is three-wire, typically. Just the hots and the neutral. However the Utility transformer is grounded as well. As our house has a copper water service to the street, the main panel is also tied to the water service, and the water meter is bonded (ground wire bridging the water meter) which grounds the copper plumbing throughout the house. We have an hydronic heating system (black iron) and a gas stove and dryer - also fed with black iron. Both those systems are bonded to the copper plumbing. Meaning pretty much all the piping in the house is grounded, but for a few peripheral odds and ends that are fed in PEX due to upgrades and/or repairs over the years.
The first thing I did when we moved in was "balance" the panel. This with a clamp-on ammeter. So, under most conditions, there is no asymmetrical loading. 240 Volt loads are always balanced. What this means is that if we get repeat trips on a ground-fault breaker, we know we have a problem to be checked and corrected before reapplying power. We also know that any 'leak' into the plumbing will go directly to ground.
Now, differential issues. One of the discovered weaknesses in US-code wiring early on was the multiple-devices issue. Say, there are eight receptacles on a single circuit, wired in parallel, of course. The last device in the chain is after multiple splices or connections. Each one adding some tiny amount of resistance. So, there is some potential between the ground of the first device and the last. If the original electrician was sloppy, that potential can be sufficient to trip a ground-fault device. And, the end-user will perceive this as a nuisance-trip, not a problem. For the record, it is a problem and should be corrected. Not sure how things are done in Europe, but if conditions are similar, look for this as well.
The basics: US residential systems are, typically 120/240 volt, single phase systems with two "Hots", a neutral and a ground. Hot-to-Hot is 240 volts @ 60 HZ ac. Hot-to-Neutral is 120 Volts AC. Ideally, Neutral and Ground are at the same potential, and, again, typically, are bonded together in the main panel. The main panel is also required to have a separate ground. The main service to the utility transformer is three-wire, typically. Just the hots and the neutral. However the Utility transformer is grounded as well. As our house has a copper water service to the street, the main panel is also tied to the water service, and the water meter is bonded (ground wire bridging the water meter) which grounds the copper plumbing throughout the house. We have an hydronic heating system (black iron) and a gas stove and dryer - also fed with black iron. Both those systems are bonded to the copper plumbing. Meaning pretty much all the piping in the house is grounded, but for a few peripheral odds and ends that are fed in PEX due to upgrades and/or repairs over the years.
The first thing I did when we moved in was "balance" the panel. This with a clamp-on ammeter. So, under most conditions, there is no asymmetrical loading. 240 Volt loads are always balanced. What this means is that if we get repeat trips on a ground-fault breaker, we know we have a problem to be checked and corrected before reapplying power. We also know that any 'leak' into the plumbing will go directly to ground.
Now, differential issues. One of the discovered weaknesses in US-code wiring early on was the multiple-devices issue. Say, there are eight receptacles on a single circuit, wired in parallel, of course. The last device in the chain is after multiple splices or connections. Each one adding some tiny amount of resistance. So, there is some potential between the ground of the first device and the last. If the original electrician was sloppy, that potential can be sufficient to trip a ground-fault device. And, the end-user will perceive this as a nuisance-trip, not a problem. For the record, it is a problem and should be corrected. Not sure how things are done in Europe, but if conditions are similar, look for this as well.
Jeroni Paul
Aug 8, 2023, 1:59:40 PM8/8/23
to
Peter W. wrote:
> Once more, an observation from a US perspective.
>
> The basics: US residential systems are, typically 120/240 volt, single phase systems with two "Hots", a neutral and a ground. Hot-to-Hot is 240 volts @ 60 HZ ac. Hot-to-Neutral is 120 Volts AC. Ideally, Neutral and Ground are at the same potential, and, again, typically, are bonded together in the main panel. The main panel is also required to have a separate ground. The main service to the utility transformer is three-wire, typically. Just the hots and the neutral.
Here in Spain most last mile distribution is 230/400V at 50Hz with four wires running through the streets, one neutral and three hots (triphasic). Hot-to-neutral is 230V and hot-to-hot 400V. Most homes are connected to only one hot and neutral (230V monophasic) and it is up to the electricity company to distribute homes through their three hots to balance their systems. Inside home there is nothing to balance. In residential areas triphasic is only used for older single or dual speed lift motors and heavy air conditioners.
> Once more, an observation from a US perspective.
>
> The basics: US residential systems are, typically 120/240 volt, single phase systems with two "Hots", a neutral and a ground. Hot-to-Hot is 240 volts @ 60 HZ ac. Hot-to-Neutral is 120 Volts AC. Ideally, Neutral and Ground are at the same potential, and, again, typically, are bonded together in the main panel. The main panel is also required to have a separate ground. The main service to the utility transformer is three-wire, typically. Just the hots and the neutral.
In older areas there are still some 115/230V networks, for example where I live. 115V was used maybe 50 years ago but it is very unlikely anyone is connected to that anymore, if someone keeps such vintage appliance there are plenity of 230-115 transformers available cheap second hand. In these areas two hots enter homes, the neutral is not even connected at the street wires (when it is, it was for 115V and currently unused).
>
> Now, differential issues. One of the discovered weaknesses in US-code wiring early on was the multiple-devices issue. Say, there are eight receptacles on a single circuit, wired in parallel, of course. The last device in the chain is after multiple splices or connections. Each one adding some tiny amount of resistance. So, there is some potential between the ground of the first device and the last. If the original electrician was sloppy, that potential can be sufficient to trip a ground-fault device. And, the end-user will perceive this as a nuisance-trip, not a problem. For the record, it is a problem and should be corrected. Not sure how things are done in Europe, but if conditions are similar, look for this as well.
Carlos E.R.
Aug 8, 2023, 5:43:56 PM8/8/23
to
On 2023-08-08 16:45, Jeroni Paul wrote:
> Carlos E.R. wrote:
>> Same problem as if I am in the bath, somebody else in the kitchen, the
>> RCD triggers, the other person resets it manually and immediately. It
>> will not hold.
>
> Bad idea. Water pipes and water heaters are earthed together with the rest of appliances,
Not here, no.
> Carlos E.R. wrote:
>> Same problem as if I am in the bath, somebody else in the kitchen, the
>> RCD triggers, the other person resets it manually and immediately. It
>> will not hold.
>
> Bad idea. Water pipes and water heaters are earthed together with the rest of appliances,
> if any has a short to ground it will be dumping the full mains voltage to the water pipes. If all is well this will trip the protector fast enough to save your life assuming you was taking a bath. Think about it, you really want to keep trying to see if it keeps saving your life again and again?? Don't forget the protector could eventually fail as well.
>
> Also keep in mind that when "it will not hold", it is connecting the power back for some milliseconds. It has no other way to detect a leak than to apply power and check. I would not keep trying if someone is in the bath.
>
>> This is certainly bad wiring, but I fail to see why it would make the
>> RCD trigger every day at 6:30, when there was a voltage surge from the
>> transformer station. The electrician that found the problem was baffled.
>
> My theory is that asymmetric wiring will behave like an antenna, a magnetic pulse for example from lighting, strong interference or heavy machinery nearby will induce a current in one wire different than the other. Also the opposite, all transients and spikes coming from mains will be radiated more from one wire than the other resulting in an imbalance. Not to mention different stray capacitance and inductance caracteristics from the different wiring paths affecting the response to fast transients.
Cheers, Carlos.
Peter W.
Aug 9, 2023, 9:47:50 AM8/9/23
to
> I don't understand how that small voltage drop in the cabling causes an imbalance in current. The earth in all appliances is supposed to be fully isolated from the hot/neutral isn't it?
A sensitive GF device will detect a difference between flow to the neutral and the ground, and perceive this as current going to ground.
The ground and neutral are bonded within the main panel, and there is a secondary ground feeding the main panel.
So, the full path of each circuit Neutral is from each device to the panel, where it is bonded to a local ground. From there to the Utility Transformer - which is also grounded in its location.
The full path of each circuit Ground is from each device to the panel, where it is bonded to the neutral and a local ground. It stops at the local ground.
In theory, the Neutral and the Ground should be at equal potential - thereby avoiding false trips - as that is what the GF device is looking for - current going to Ground (or somewhere), not Neutral. If the Ground and Neutral are not at equal potential - there may be something for the GF device to detect.
Jeroni Paul
Aug 9, 2023, 8:49:51 PM8/9/23
to
I seem to understand that the GF built in your wall plugs (we do not have them here) trips because the small voltage between neutral and ground. That does not look like the right thing it should trip on. Even if the installation has few interconnects if you plug a heavy load the drop will develop anyway.
Here in 230/400V areas there is no voltage between neutral and ground (they could also be joined at the panel) but if you short them in a plug the GFCB trips, this is because the small voltage drop developed in the cabling. Shorting them creates a parallel path and current will distribute proportionally, some current will flow through earth instead of neutral.
ehsjr
Aug 9, 2023, 9:42:47 PM8/9/23
to
On 8/9/2023 8:49 PM, Jeroni Paul wrote:
> Peter W. wrote:
>>> I don't understand how that small voltage drop in the cabling causes an imbalance in current. The earth in all appliances is supposed to be fully isolated from the hot/neutral isn't it?
>> A sensitive GF device will detect a difference between flow to the neutral and the ground, and perceive this as current going to ground.
>>
>> The ground and neutral are bonded within the main panel, and there is a secondary ground feeding the main panel.
>>
>> So, the full path of each circuit Neutral is from each device to the panel, where it is bonded to a local ground. From there to the Utility Transformer - which is also grounded in its location.
>>
>> The full path of each circuit Ground is from each device to the panel, where it is bonded to the neutral and a local ground. It stops at the local ground.
>>
>> In theory, the Neutral and the Ground should be at equal potential - thereby avoiding false trips - as that is what the GF device is looking for - current going to Ground (or somewhere), not Neutral. If the Ground and Neutral are not at equal potential - there may be something for the GF device to detect.
>> Peter Wieck
>> Melrose Park, PA
>
> Thanks for explaining.
> I seem to understand that the GF built in your wall plugs (we do not have them here) trips because the small voltage between neutral and ground.
..............................^^^^^^^....
> Peter W. wrote:
>>> I don't understand how that small voltage drop in the cabling causes an imbalance in current. The earth in all appliances is supposed to be fully isolated from the hot/neutral isn't it?
>> A sensitive GF device will detect a difference between flow to the neutral and the ground, and perceive this as current going to ground.
>>
>> The ground and neutral are bonded within the main panel, and there is a secondary ground feeding the main panel.
>>
>> So, the full path of each circuit Neutral is from each device to the panel, where it is bonded to a local ground. From there to the Utility Transformer - which is also grounded in its location.
>>
>> The full path of each circuit Ground is from each device to the panel, where it is bonded to the neutral and a local ground. It stops at the local ground.
>>
>> In theory, the Neutral and the Ground should be at equal potential - thereby avoiding false trips - as that is what the GF device is looking for - current going to Ground (or somewhere), not Neutral. If the Ground and Neutral are not at equal potential - there may be something for the GF device to detect.
>> Peter Wieck
>> Melrose Park, PA
>
> Thanks for explaining.
> I seem to understand that the GF built in your wall plugs (we do not have them here) trips because the small voltage between neutral and ground.
Not voltage. GFCI's trip on a difference in _current_ between
neutral and line.
Current normally goes through the GFCI like this:
Black--------GFCI-------->--load-+
White--------GFCI--------<-------+
Current goes through the GFCI from the black (hot) wire
through the load and returns through the GFCI to the
white (neutral) wire. The currents (out to the load and
back from the load) are compared in the GFCI and if they
are the same (within about 5ma) all is well and the GFCI
does not trip.
Now look at a problem where the neutral is shorted to ground
on the LOAD side of the GFCI:
Black--------GFCI-------->--load-+
White--------GFCI--------<-------+
Short to ground on LOAD side---<-+
Note the arrows < (and > ) - current passes through the
load and heads back toward the GFCI, but it also finds
a path through the short circuit. That causes the GFCI
to trip, because it detects a greater current from the
hot wire than it detects returning to the neutral wire.
GFCI's have a LINE (power input side) and a LOAD (power
output to the load) side, usually (always?) labelled
with capital letters LINE and LOAD. That's why I used
LOAD in some places.
Hope this helps.
Ed
Jeroni Paul
Aug 11, 2023, 7:02:40 AM8/11/23
to
ehsjr wrote:
> Not voltage. GFCI's trip on a difference in _current_ between
> neutral and line.
This is my view of that but Peter W apparently has another theory of GF tripping due to the wire+interconnects resistance.
> Not voltage. GFCI's trip on a difference in _current_ between
> neutral and line.
Peter W.
Aug 11, 2023, 9:13:58 AM8/11/23
to
>"....as that is what the GF device is looking for - *current* going to Ground (or somewhere), not Neutral. "<
Brian Gregory
Aug 11, 2023, 10:47:05 AM8/11/23
to
limit and a little bit of extra harmonic content pushed it over the edge?
--
Brian Gregory (in England).
Brian Gregory
Aug 11, 2023, 10:51:09 AM8/11/23
to
to feed to much stuff from it. Some leakage is normal for many devices.
Here we usually use several 30mA RCDs, maybe one for upstairs sockets,
one for downstairs sockets, one for lighting or something similar, but
making sure everything is still protected.
Carlos E.R.
Aug 11, 2023, 6:40:31 PM8/11/23
to
entire house, so that's the normal: one RCD at the house entry,
protecting all. Some houses may have two or more, if they are really big.
But the total maximum of the house was 5 or 6 KW at the time, and normal
usage was much lower. Fridge, hot water tank (1KW), washing up machine
(2KW), and a water pump (0.7 KW). TV and lights.
> Here we usually use several 30mA RCDs, maybe one for upstairs sockets,
> one for downstairs sockets, one for lighting or something similar, but
> making sure everything is still protected.
>
--
Carlos E.R.
Aug 11, 2023, 6:45:34 PM8/11/23
to
even one mA. There has to be something else.
At the time (1985), there were no electronic switched loads in the
network. Microwaves were barely just starting, no PC boom yet.
--
Cheers, Carlos.
Jerry Peters
Aug 14, 2023, 2:18:49 PM8/14/23
to
measures the difference in current between the 2 supply wires.
Look up a datasheet for the LM1851 IC, it will show sample circuits
for a GFCI, there's no connection to the ground wire at all. In fact
you can use a GFCI on an ungrounded circuit and it's still functional.
Brian Gregory
Aug 14, 2023, 3:46:17 PM8/14/23
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What do you mean by protector?
> At the time (1985), there were no electronic switched loads in the
> network. Microwaves were barely just starting, no PC boom yet.
>
--
Dave Platt
Aug 14, 2023, 7:02:24 PM8/14/23
to
In article <ubdr64$2duqe$1...@dont-email.me>,
When the system is in use (that is, when the Hot line is drawing
current), the Neutral and Ground wires are at the same potential
*ONLY* at points where they are actually bonded together - that is, at
the panel or sub-panel or transformer.
At other points (for example, at the outlet) they won't be at the same
potential. They can't be, because the neutral wire is carrying
current and has non-zero resistance, and thus has a significant
voltage drop between the outlet and the panel. The protective-ground
wire won't be carrying current, and thus has no voltage drop between
the outlet and the panel.
So, if a GFI considered "ground and neutral wires are not at equal
potential" to be a fault condition, it would trip every time somebody
turned on a light or appliance.
If you want to see this demonstrated, it's not difficult to do, if
you have an AC voltmeter with properly-shrouded insulated test leads.
Using one half of a standard outlet, measure the voltage between the
neutral and ground contacts. If nothing on that circuit is drawing
current, it should read 0 volts, or within noise-factor of that.
Then, plug a 15-amp space heater into the other half of that outlet,
and turn it on. You'll almost certainly see a significant voltage
develop between ground and neutral, caused by the current flowing
from the outlet back to the panel through the neutral wire. I'd
expect something on the order of a volt or so to show up on
the meter.
If you don't see a voltage drop between ground and neutral under
these conditions, it may very well mean that your outlet is
mis-wired, and has ground and neutral connected together at
the outlet... which is a definite no-no.
Jerry Peters <je...@example.invalid> wrote:
> In theory, the Neutral and the Ground should be at equal potential -
>thereby avoiding false trips - as that is what the GF device is looking
>for - current going to Ground (or somewhere), not Neutral. If the Ground
>and Neutral are not at equal potential - there may be something for the
>GF device to detect.
That's almost exactly backwards, in practice.
> In theory, the Neutral and the Ground should be at equal potential -
>thereby avoiding false trips - as that is what the GF device is looking
>for - current going to Ground (or somewhere), not Neutral. If the Ground
>and Neutral are not at equal potential - there may be something for the
>GF device to detect.
When the system is in use (that is, when the Hot line is drawing
current), the Neutral and Ground wires are at the same potential
*ONLY* at points where they are actually bonded together - that is, at
the panel or sub-panel or transformer.
At other points (for example, at the outlet) they won't be at the same
potential. They can't be, because the neutral wire is carrying
current and has non-zero resistance, and thus has a significant
voltage drop between the outlet and the panel. The protective-ground
wire won't be carrying current, and thus has no voltage drop between
the outlet and the panel.
So, if a GFI considered "ground and neutral wires are not at equal
potential" to be a fault condition, it would trip every time somebody
turned on a light or appliance.
If you want to see this demonstrated, it's not difficult to do, if
you have an AC voltmeter with properly-shrouded insulated test leads.
Using one half of a standard outlet, measure the voltage between the
neutral and ground contacts. If nothing on that circuit is drawing
current, it should read 0 volts, or within noise-factor of that.
Then, plug a 15-amp space heater into the other half of that outlet,
and turn it on. You'll almost certainly see a significant voltage
develop between ground and neutral, caused by the current flowing
from the outlet back to the panel through the neutral wire. I'd
expect something on the order of a volt or so to show up on
the meter.
If you don't see a voltage drop between ground and neutral under
these conditions, it may very well mean that your outlet is
mis-wired, and has ground and neutral connected together at
the outlet... which is a definite no-no.
Jerry Peters
Aug 26, 2023, 1:21:35 PM8/26/23
to
You've misquoted me, that's from Peter W. This is what I wrote:
This make no sense, the GFCI doesn't care about the ground wire, it
measures the difference in current between the 2 supply wires.
Look up a datasheet for the LM1851 IC, it will show sample circuits
for a GFCI, there's no connection to the ground wire at all. In fact
you can use a GFCI on an ungrounded circuit and it's still functional.
In other words I agree if the ground & neutral being at differing
This make no sense, the GFCI doesn't care about the ground wire, it
measures the difference in current between the 2 supply wires.
Look up a datasheet for the LM1851 IC, it will show sample circuits
for a GFCI, there's no connection to the ground wire at all. In fact
you can use a GFCI on an ungrounded circuit and it's still functional.
potentials matters then there's some sort of leakage and the GFCI
should trip.
Jerry
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