GFCI vs RCD trip threshold-why?

[iwire]

UL only makes back reference to NEC for class-A only, not sure why UL even mentions NEC. class-C can be used where some class-A is currently used, but NEC has chosen to not allow class-C within its code.

Which means we cannot use class C for personal protection so stop saying that we can.

 

[FionaZuppa]

Which means we cannot use class C for personal protection so stop saying that we can.

i didnt say we can !! i said NEC should allow it, and i gave examples. my comment was that according to UL class-C is ok for some places we use class-A because NEC only allows class-A, etc.

... and what about the other Q i had, "grounded 60HZ only" ??

 

[FionaZuppa]

Quote what I said, I am not going to comment based on your paraphrasing.

A GFCI is required to be connected to a grounded source such as a wye supply or corner grounded delta. You cannot use a GFCI on an ungrounded source. That is what the quote you posted is saying.

GROUND-FAULT CIRCUIT
INTERRUPTERS (KCXS)
GENERAL
This category covers ground-fault circuit interrupters (GFCI) for use in
accordance with ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC).
A GFCI is a device whose function is to interrupt the electric circuit to the
load when a fault current to ground exceeds some predetermined value that
is less than that required to operate the overcurrent protective device of the
circuit.

GFCIs are intended to be used only in circuits where one of the conductors
is solidly grounded.

UL does say this in the General section, but what the heck does that mean? how exactly would a 2-pole GFCI be compliant? line side it would have neutral tail for the electronics, but there is technically no grounded ckt CCC on a 2-pole GFCI. does that statement mean "GFCI's only work if the GFCI has a 120v reference" ?

and from vendor docs, 2-pole GFCI still trip w/o N wire, but N is there for the test button to work, it needs a way to allow mA to bypass one of the CCC's, so you need a N line side (a grounded path).

if that verbiage is there to allow test button to work, makes good sense.

 

[jim dungar]

UL does say this in the General section, but what the heck does that mean? how exactly would a 2-pole GFCI be compliant? line side it would have neutral tail for the electronics, but there is technically no grounded ckt CCC on a 2-pole GFCI. does that statement mean "GFCI's only work if the GFCI has a 120v reference" ?

The system is effectively the service or the 'output' of an SDS. Pertinent NEC sections include 250.20(B), 250.24(A), and 250.28
You appear to be discussing circuit conductors and their EGC. These are covered in 250.110, 250.114, 250.130(C), and 406.4.

 

[FionaZuppa]

The system is effectively the service or the 'output' of an SDS. Pertinent NEC sections include 250.20(B), 250.24(A), and 250.28
You appear to be discussing circuit conductors and their EGC. These are covered in 250.110, 250.114, 250.130(C), and 406.4.

i am not sure these NEC sections answer anything. they are NEC requirements for service and ckt side.
the UL verbiage means what exactly? if there is CT xfrmer and the CT is not "grounded" the GFCI still works a designed. isnt this the truck mounted generator example that was given? i simply do not understand why UL has added that verbiage. i do see rare change that the non-grounded CT becomes something other than earth but this would could possibly render the test button useless. someone will need to explain that UL verbiage with clarity, i obviously dont understand the reasoning behind it.

 

[Ingenieur]

It's stating fibrillation @ 30ma and up.....

~RJ~

The one chart says 50, regardless
contingent upon duration
easily survivable with no effect if trip < 6 Hz

ac 4.1 5% chance
50 mA for 2 sec
if it trips in 0.2 sec no lasting effect

the current class is allowed because you are going to have an egc
in a 120 ckt you may not if cord connected

also shock effect proportional to body mass
i = body wt / sqrt time

a child is likely to encounter 120
unlikely in a 480 industrial environment

 

[Ingenieur]

So one must ask... what happens when you can't let go but arent going to fliberate?

the cb trips

there are 2 scenarios
the person is the series fault path
the person is a parallel path with the egc

the second current divides
if it trips at 50 mA and the egc is 4 ohm to X0 and the person is 500 what does the person see?

 

[GoldDigger]

UL does say this in the General section, but what the heck does that mean? how exactly would a 2-pole GFCI be compliant? line side it would have neutral tail for the electronics, but there is technically no grounded ckt CCC on a 2-pole GFCI. does that statement mean "GFCI's only work if the GFCI has a 120v reference" ?

and from vendor docs, 2-pole GFCI still trip w/o N wire, but N is there for the test button to work, it needs a way to allow mA to bypass one of the CCC's, so you need a N line side (a grounded path).

if that verbiage is there to allow test button to work, makes good sense.

For the test button to work, there needs to be a return conductor, not necessarily a neutral, so a 120V two wire ungrounded circuit would allow a GFCI to work.
But when you go to two pole the designer has a choice of three ways to bypass the test current around the CT.
of those three choices only one (bypassing L1 to L2) will work without a neutral connection, grounded or not.
You can make the assertion about any particular design two pole GFCI but you cannot generalize to all possible implementations.

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[Ingenieur]

Which means we cannot use class C for personal protection so stop saying that we can.

You can and we do
for 240 up w/egc

not 120 2 W w/o egc

the equipment protection is moot
30 mA?
why not just use a 15 A ngr with warning but no trip?

we use 15 A for personnel protection
we ground monitor the egc <4 ohm, if > 4 trip cb
if phase contacts frame it rises to 4 x 15 or 60 volts
a 1000 ohm person sees 60 mA
ngr ct sees the rest ~ 15 A and trips in <6 Hz
easily survivable

I'd rather have a 50 mA gfp that trips in 6 Hz than nothing

 

[GoldDigger]

Exactly how long is "6 cycles per second"?
You cannot blindly substitute Hz for cycle.

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[Ingenieur]

Exactly how long is "6 cycles per second"?
You cannot blindly substitute Hz for cycle.

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60 Hz basis afaik for the US power grid

your lack of understanding does not render ME blind lol

 

[GoldDigger]

60 Hz basis afaik for the US power grid

In which case the time would be 100ms, or six *cycles*. Not 6 Hz.
A lot like treating the light-year as a time rather than a distance!

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[Ingenieur]

CLOSE​

The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

 

[Ingenieur]

In which case the time would be 100ms, or six *cycles*. Not 6 Hz.
A lot like treating the light-year as a time rather than a distance!

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Incorrect
1 Hz = 1 cycle/sec

 

[wwhitney]

trips in <6 Hz

What does trips in less than a frequency mean? You mean it trips if the AC frequency is below 6 Hz, but doesn't trip when the AC frequency is above 6 Hz?

If you are trying to specify a period of time, you can't use the unit Hz.

Cheers, Wayne

 

[Ingenieur]

What does trips in less than a frequency mean? You mean it trips if the AC frequency is below 6 Hz, but doesn't trip when the AC frequency is above 6 Hz?

If you are trying to specify a period of time, you can't use the unit Hz.

Cheers, Wayne

6 Hz on a 60 Hz basis = 0.1 sec

 

[GoldDigger]

Incorrect
1 Hz = 1 cycle/sec

So tripping within 6 Hz must mean tripping on any voltage system between 54Hz and 66Hz?

6Hz equals six cycles *per second*, which is not a unit of time. The GFCI is characterized by either the time or the number of cycles till trip.

The transition from cycles to Hz was complicated by the fact that people carelessly called our normal power system 60 cycle instead of 60 cycles per second.

To move this to a more familiar context, would you be OK with a maximum stopping *distance* specified in feet per second?

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[GoldDigger]

6 Hz on a 60 Hz basis = 0.1 sec

6 cycles per second on a 60 cycle per second basis is .1 not .1 seconds.
Dimensional consistency is more important than consistency in grammar or spelling, so I think the distinction is worth commenting on.


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[jim dungar]

i am not sure these NEC sections answer anything. they are NEC requirements for service and ckt side.
the UL verbiage means what exactly? if there is CT xfrmer and the CT is not "grounded" the GFCI still works a designed. isnt this the truck mounted generator example that was given? i simply do not understand why UL has added that verbiage. i do see rare change that the non-grounded CT becomes something other than earth but this would could possibly render the test button useless. someone will need to explain that UL verbiage with clarity, i obviously dont understand the reasoning behind it.

Earth has nothing to do with the function of the test button.
Earth has nothing to do with how the difference in current is sensed by the device.
In the US, 'ground' and 'reference plane' are common synonyms.

Have you asked UL to clarify their language?

 

[wwhitney]

6 Hz on a 60 Hz basis = 0.1 sec

That is very wrong. Your units don't agree.

6 cycles / 60 Hz = 0.1 seconds. Now units agree.

Cheers, Wayne