GFCI Timer Delay

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mbrooke

mbrooke

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Do modern GFCIs have a time delay? I'v heard that older GFCIs would trip on refrigerators starting and this was mitigated by an internal time delay inside the GFCI. Is there any truth to this?
 
mbrooke said:
Do modern GFCIs have a time delay? I've heard that older GFCIs would trip on refrigerators starting and this was mitigated by an internal time delay inside the GFCI. Is there any truth to this?
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There is an inverse-time curve that defines the maximum allowable time delay before tripping vs. fault current. UL 943 specifies this maximum time as (20 / IF) 1.43 in seconds where the fault current IF is in milliamps, for relatively low levels of fault current. And so at 20 milliamps the maximum time to trip would be one second.


Apparently many manufacturers do not implement this particular inverse time characteristic because of the extra cost it would require. Like you I've also heard that more recent GFCIs are less likely to trip than older ones, and so perhaps manufacturers have taken advantage of the extra time allowed, particularly at lower levels of fault current.
 
synchro said:
There is an inverse-time curve that defines the maximum allowable time delay before tripping vs. fault current. UL 943 specifies this maximum time as (20 / IF) 1.43 in seconds where the fault current IF is in milliamps, for relatively low levels of fault current. And so at 20 milliamps the maximum time to trip would be one second.


Apparently many manufacturers do not implement this particular inverse time characteristic because of the extra cost it would require. Like you I've also heard that more recent GFCIs are less likely to trip than older ones, and so perhaps manufacturers have taken advantage of the extra time allowed, particularly at lower levels of fault current.
Click to expand...


Thanks.

IMO I think they might have considering how newer GFCIs tend to "hold" better.
 
mbrooke said:
You've seen those where the defrost heater terminals were apparently getting moist and corroded?
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Dust, holding moisture, then eventually tracking to ground. Nobody reads the instruction manuals for their fridge telling them to clean it once in a while.

As to "delaying" a GFCI:

The GFCI function has a defined maximum inverse trip time formula in UL943;
T = (20/I)1.43 where T is Seconds, I is current in milliamps

You really can't play around with that aspect. But that said, in reality if you plot that out, a GFCI trip current of 6mA comes out to almost 4 seconds, whereas most GFCIs on the market will trip in 100msec or less because they want to be OVER protective rather than under. So technically you COULD make one that still meets the UL requirement but was more tolerant than others who just decide to err on the side of conservative. I don't know of anyone actually doing that on purpose, but it is possible.
 
Jraef said:
Dust, holding moisture, then eventually tracking to ground. Nobody reads the instruction manuals for their fridge telling them to clean it once in a while.

As to "delaying" a GFCI:

The GFCI function has a defined maximum inverse trip time formula in UL943;
T = (20/I)1.43 where T is Seconds, I is current in milliamps

You really can't play around with that aspect. But that said, in reality if you plot that out, a GFCI trip current of 6mA comes out to almost 4 seconds, whereas most GFCIs on the market will trip in 100msec or less because they want to be OVER protective rather than under. So technically you COULD make one that still meets the UL requirement but was more tolerant than others who just decide to err on the side of conservative. I don't know of anyone actually doing that on purpose, but it is possible.
Click to expand...


Is the 100msec still delayed or is it just instantaneous?
 
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