Are there any voltage dependencies of typical circuit breakers normally used for 120/240 volt systems in the US, especially the GFCI and AFCI breaker designs? What if I run the breakers on half voltage? Or less? Would they still work or would the internal circuits not function? It will still be 60 Hz AC at the lower voltage.
For those interested in why I would do that, I will post that at a later time if it turns out to be practical to do with existing products.
They are designed for operation at "normal" line voltage, plus or minus a reasonable tolerance. I have tested a few, and they quit working below around 80 volts. The electronics continuously energize the solenoid with a loud buzzing, and it no longer trips. I suspect that component failures would be imminent at this condition.
Ben Miller
I should have mentioned that this refers to GFCIs.
Ben Miller
|> For those interested in why I would do that, I will post that at a later |> time if it turns out to be practical to do with existing products. |>
| | They are designed for operation at "normal" line voltage, plus or minus a | reasonable tolerance. I have tested a few, and they quit working below | around 80 volts. The electronics continuously energize the solenoid with a | loud buzzing, and it no longer trips. I suspect that component failures | would be imminent at this condition.
That's similar to the behaviour I have found with GFCIs when subject to an RF field of sufficient strength at the right frequency (for example my 2m ham radio transmitter triggered it within 2 meters at 1 watts, 222 Mhz did not trigger it at all, and 70cm took 5 watts at 1 meter to trigger it). It actually did trip, but the buzzing indicated to me it continued to try to trip.
This suggests to me a design flaw in the GFCIs, unrelated to its inability to work at low voltages. After tripping and opening, normally there would be no more fault current. But false triggers, of which RF is only one possibility, can still cause this. Maybe the solenoid needs to be powered from the load side of the contacts so it ceases when it opens them.
I wonder what dangers could be present from these situations. Are the component failures you suspect are imminent in the GFCI itself? Could the solenoid burn up under this condition, either at lower voltage or at full voltage? Could that start a fire? Likely it wasn't designed for continuous tripping duty.
In addition to the RF field trigger source, I see a couple other scenarios where this can happen:
Utility distribution single phasing at the delta primary side of a substation or intertie transformer can result in half voltage on 2/3 of the single phase services downstream of it. I've seen this happen at least 3 times, with the worst case covering half of a town that wasn't cleared for over 3 hours. If a GFCI gets triggered in this situation (or worse, falsely triggers because of the low voltage), could it withstand 3 hours of punishment like that?
Because balanced power systems, where each load takes power from two hot lines at 180 degrees (such as 240 volts loads connected via NEMA 6-20) have much lower common noise introduction into the power lines, this can be the preferred wiring method in special applications like recording studios. But to get the best benefit you have to do it for every (all noise sources). And given most things run on 120 volts in the US, that means a modified system where the center tap is 60 volts into a 120 volt secondary, and it wired like the 240/120 volt system, but at 120/60 volts. Putting that in a circuit breaker panel would mean 2-pole breakers for everything, and the half-voltage scenario for GFCI breakers.
GFCI receptacles, depending on how they are wired with respect to the neutral and grounding wire, may work fine, or be worse.
AFCI would likely have problems similar to GFCI.
The solenoid is powered through an SCR. I'll bet the RF is triggering the SCR into conduction!
It is!
The SCR & solenoid are designed for momentary duty. Normally, it is a very short pulse that trips the mechanism and then deenergizes the circuitry. They will overheat if continuously energized.
Ben Miller
I was wrong. I just checked a schematic and it is on the line side. That is the reason it can trigger with the GFCI tripped.
There have been cases of mobile/cell phone use nearby triggering them, although I haven't heard of this for some time now.
On Fri, 16 Apr 2004 18:52:27 GMT Ben Miller wrote: |> That's similar to the behaviour I have found with GFCIs when subject to an |> RF field of sufficient strength at the right frequency (for example my 2m |> ham radio transmitter triggered it within 2 meters at 1 watts, 222 Mhz did |> not trigger it at all, and 70cm took 5 watts at 1 meter to trigger it). | It |> actually did trip, but the buzzing indicated to me it continued to try to |> trip. | | The solenoid is powered through an SCR. I'll bet the RF is triggering the | SCR into conduction! | |> possibility, can still cause this. Maybe the solenoid needs to be powered |> from the load side of the contacts so it ceases when it opens them. | | It is!
Then how is it that the RF can trigger the solenoid to conduct if it has already opened the circuit and it's connected on the load side?
|> I wonder what dangers could be present from these situations. Are the |> component failures you suspect are imminent in the GFCI itself? Could the |> solenoid burn up under this condition, either at lower voltage or at full |> voltage? Could that start a fire? Likely it wasn't designed for | continuous |> tripping duty. | | The SCR & solenoid are designed for momentary duty. Normally, it is a very | short pulse that trips the mechanism and then deenergizes the circuitry. | They will overheat if continuously energized.
That's my fear. That's why I think that it should be designed so that once it opens the circuit, it can't get any more power because the power's path to the solenoid is via the open contacts.
On 16 Apr 2004 19:37:36 GMT Andrew Gabriel wrote: | In article , | snipped-for-privacy@ipal.net writes: |> |> That's similar to the behaviour I have found with GFCIs when subject to an |> RF field of sufficient strength at the right frequency (for example my 2m |> ham radio transmitter triggered it within 2 meters at 1 watts, 222 Mhz did |> not trigger it at all, and 70cm took 5 watts at 1 meter to trigger it). It |> actually did trip, but the buzzing indicated to me it continued to try to |> trip. | | There have been cases of mobile/cell phone use nearby triggering them, | although I haven't heard of this for some time now.
I'm sure the length of wires attached affect the frequencies that will cause the problem.
|> It is! |>
| | I was wrong. I just checked a schematic and it is on the line side. That is | the reason it can trigger with the GFCI tripped.
OK. Then that is what I think needs to be changed.
What about the possibility of wiring it backwards (one that does NOT have any built-in receptacles because that would obviously energize them direct and not via the openable contacts).
No! You would be interrupting the circuit that provides the power to trip the solenoid. The possibility is that the solenoid would oscillate, never tripping fully. The contacts would arc, and could weld such that the thing could not trip. Not only would that leave the fault condition (that started the sequence in the first place), it would place continuous drive on the solenoid, resulting in a fire.
There could be a re-design of the GFCI to do what you want, but installing one with no design changes backwards is inviting trouble.
U/L recently changed the GFCI listing spec so what we "know" may not still be true. They were addressing the problems of wiring to the "load side" and improving the test function.
|> |> It is! |> |>
|> | |> | I was wrong. I just checked a schematic and it is on the line side. That is |> | the reason it can trigger with the GFCI tripped. |> |> OK. Then that is what I think needs to be changed. |> |> What about the possibility of wiring it backwards (one that does NOT have |> any built-in receptacles because that would obviously energize them direct |> and not via the openable contacts). |> |> -- | | No! You would be interrupting the circuit that provides | the power to trip the solenoid. The possibility is that | the solenoid would oscillate, never tripping fully. The | contacts would arc, and could weld such that the thing | could not trip. Not only would that leave the fault | condition (that started the sequence in the first place), | it would place continuous drive on the solenoid, resulting | in a fire.
The existing design allows the oscillation. The solenoid needs to be of a design that allows it to complete the tripping, or else you need some kind of lockout mechanism to prevent the oscillation.
| There could be a re-design of the GFCI to do what you | want, but installing one with no design changes | backwards is inviting trouble.
If the solenoid design is not good enough to complete the tripping, then of course a simple backwards connection would be a problem.
| U/L recently changed the GFCI listing spec so what we "know" may not still be | true. | They were addressing the problems of wiring to the "load side" and improving | the test function.
Those GFCI devices that are part of permanent fixture wiring should be under the authority of the NFPA/NEC, in particular due to the fire hazard they present. While U/L would have standards that rate specific products, NEC should be where a specification is that requires a specific level to be installed (or not installed, as the case may be). The NEC should specify that it's requirements may only be met through the use of GFCI devices that cannot be falsely tripped, and will function correctly, when certain conditions exist. These are conditions that do not happen frequently, but certainly can and do happen many times. These conditions include strong radio frequency fields (possibly correctable with RF filtering), and half voltage as a result of single phasing. GFCI devices should be required to function correctly with voltages deviating from nominal between 40% and 125%. AFCI devices should have similar requirements. They should also function correctly under RF fields induced on the wiring, or received directly, at a level equivalent to a 10 watt half wave radiator within a distance of 1 meter, at all frequencies from 100 kHz to 10 GHz. Shielding and RF filtering is one way to do this. Alternatively a lockout method is also acceptable (while the device would falsely trip, it would not oscillate and thus present no hazard).
The new standard requires that a GFCI can not reset if wired backwards, reversed polarity, or N-G downstream connection. It also must tolerate much greater transient energy without damage to its circuitry/function. It looks like the manufacturers are finally moving the MOVs away from the other circuit components, and isolating them so that when they burn up there is no other damage.
Ben Miller
That's certainly an improvement. But IMHO, it's not enough, yet. There needs to be something in the design to prevent it from oscillating.
UL943 requires single pole GFCI devices to work down to 85% of rated voltage.
Get a clue. 20a breaker trips above 20a! Even at a few millivolts.
For those interested in why I would do that, I will post that at a later time if it turns out to be practical to do with existing products.
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----------------------------------------------------------------------------- | Phil Howard KA9WGN |
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| Get a clue. 20a breaker trips above 20a! Even at a few millivolts.
Modern circuit breakers have more "features" in them which can, and often do, require specific voltages. There are breakers rated for a wide range of voltages, and it may well be that those work fine even on millivolts. But lots of breakers may not. And it has been established that GFCI and AFCI breakers WILL NOT. Other features in special breakers could also have similar risks. It has become apparent that when considering the use of a breaker on an unusual voltage, to verify carefully that the breaker is rated and tested for safe use at that voltage.
And just where do you buy your breakers? What brands and model numbers are you specifically talking about?
| Get a clue. 20a breaker trips above 20a! Even at a few millivolts.
Modern circuit breakers have more "features" in them which can, and often do, require specific voltages. There are breakers rated for a wide range of voltages, and it may well be that those work fine even on millivolts. But lots of breakers may not. And it has been established that GFCI and AFCI breakers WILL NOT. Other features in special breakers could also have similar risks. It has become apparent that when considering the use of a breaker on an unusual voltage, to verify carefully that the breaker is rated and tested for safe use at that voltage.
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----------------------------------------------------------------------------- | Phil Howard KA9WGN |
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