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GFCI Tripping Levels

mather 462 41 December 4, 2015 at 08:42 AM
Anyone know what was the tripping level for residential Class A GFCIs prior to the current 6 mA?

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Quote from mather View Post :
Anyone know what was the tripping level for residential Class A GFCIs prior to the current 6 mA?
It isn't easy to find a definitive answer.

This is in komondor's link above:
Quote :
If the system voltage is less than 150 V and the equipment is neither grounded nor double insulated, a Class A GFCI with 4 to 6 mA trip current is required to provide both let-go protection and protection against fibrillation.

If the system voltage is less than 150 V and the equipment is either grounded or double-insulated, a Class C GFCI, with 20 mA trip level, is allowed, as it needs only to provide protection against fibrillation, with let-go protection optional.
I thought it used to be 10 or 15ma, but I'm really not sure there are good reasons to keep it below 10ma. I think some of the earliest GFCI's may have been less precise. Equipment protection allows up to 30ma.

GFCI's were first required in 1971 I think, possibly a little sooner in pools. Here's some general history on GFCI's: http://www.necconnect.org/resources/gfcis/

http://www.nema.org/Products/Docu...tation.pdf
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Thanks, I saw a couple of the links before. I couldn't find a definitive answer such as the code changed from "xx to 6 mA", etc. Thought it may be a pretty easy answer but so far it hasn't.
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Quote from mather View Post :
Thanks, I saw a couple of the links before. I couldn't find a definitive answer such as the code changed from "xx to 6 mA", etc. Thought it may be a pretty easy answer but so far it hasn't.
The wikipedia article on GFCI's talks about some of the earliest GFCI's which tripped at 250mA and a few years later 12-17mA. It talks about the first transistor based GFCI and GFCI requirements, but makes not mention on the sensitivity of these devices. Early on, some of the codes and standards may not have spelled out the exact tripping requirements.

The first 'transistorized' GFCI was patented in 1965 and had a sensitivity of 20-30mA or 17ma depending on the design variant:
https://www.google.com/patents/US3213321
Most breakers (including gfci's) had something of a trip curve. They trip faster at high current and slower at low current. I think as the technology of the time allowed, the trip threshold was lowered. Patents that followed for circuits and devices made by companies that made breakers and other electrical equipment vary widely, one was as low as 3.5mA in 1968 while another was 100mA.

Earliest versions of electrical codes and UL and other standards relating to GFCI's may not have even specified the trip current, but that certainly isn't easy to find. I suspect that by some time in the early 80's if not sooner the current 6ma standard was enacted.
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You're right, perhaps the specs weren't as detailed as currently. I'm not too sure the 6 mA standard went back to the 80's though. I thought it was a more current change, as in recently within the last year to five years.
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Quote from mather View Post :
You're right, perhaps the specs weren't as detailed as currently. I'm not too sure the 6 mA standard went back to the 80's though. I thought it was a more current change, as in recently within the last year to five years.
The more recent changes (as in the last 20 years) involve standardizing the trip curve (without changing the trip level from what I could tell), shutting off if it's wired wrong, shutting off when it's damaged and can't trip, etc

I didn't find anything recent about a change in the trip level.
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Quote from mather View Post :
You're right, perhaps the specs weren't as detailed as currently. I'm not too sure the 6 mA standard went back to the 80's though. I thought it was a more current change, as in recently within the last year to five years.
The 6 mA limit has been in existence since at least the 1970s, and here's the datasheet for an ancient National Semiconductor LM1851 GFI controller chip that I've seen in some old GFCIs (another popular chip back then was from General Instruments): http://www.ti.com/lit/ds/snis158/snis158.pdf Notice the graph on page 4 that shows tripping current versus duration of ground fault, both for this chip and the old UL943 standard. For about 250 mA the GFCI must shut off current in about 30 milliseconds or less, while a 5 mA fault is allowed to last for up to 7 seconds. The test button for GFCIs is set for about 8 mA because it uses a 16,000 ohm resistor to produce a ground fault.
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Thanks all. I may have solved my initial problem which started me search on this topic.
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