GFCI testing

[Volta]

. . . The test resistor has to be designed so that at low line voltage the current will exceed at least the high spec limit of the GFCI. Looks like the resistance choice is good.

Also note there is an inverse time characteristic to the trip time vs current curve.

.

Ok. I have no trouble with that.

My initial post simply stated that AFAIK the only testing mechanism listed to test a GFCI device is the button on the front. Not an externally insertable resistance. The instructions I've seen included with the product don't seem to refer to any portable GFCI tester.

 

[gar]

100214-2150

Volta:

The reason for the official statement that the only way to test a GFCI is with the pushbutton on the GFCI is because it is too complex to describe to the average person or even some electricians how to do it externally and with validity.

Arc fault devices are a completely different story, and there is and can not be any simple test. Their complex algorithms apparently are not disclosed. Therefore one does not know how they work, if they work.

.

 

[Volta]

It shouldn't be that difficult to explain how to plug in a tester and press its button instead of the one on the device. :roll:

 

[gar]

100214-2205 EST

Volta:

The problem is that the outlet may not have an EGC or one that is good. Now you have explain to someone that thinks electricity is black magic that they need an adapter with the ground lead brought out and this has to be connected to a valid ground point. And further what if somehow the transformer center tap is not connect to ground. A whole host of problems are solved by saying the only way to test the device is with its pushbutton.

If you know what you are doing, then you can obviously externally test the device.

.

 

[mivey]

It shouldn't be that difficult to explain how to plug in a tester and press its button instead of the one on the device. :roll:

And if there is no ground?

Add: I'm too slow for gar.

 

[Teaspoon]

A bad splice.

I have also run across new conductors that just aren't complete between point A and point B.[/QUOTE
I have ran across new conductors that were bad. A couple of months back I ran into this problem.
This was on a new house the last receptacle on the circuit was dead.
Checked connections , Checked Receptacle,Checked resistance on
Neutral And hot.OL Checked black to black OL Checked white to whiteOL The ground was the only wire that had continunity.
The wire was ran thru drilled holes in stud wall. Had to run another wire under the floor up into stud wall.

 

[Volta]

. . .If you know what you are doing, then you can obviously externally test the device.

And if there is no ground?
. . .

Yeah, true.

 

[480sparky]

I have ran across new conductors that were bad. A couple of months back I ran into this problem.
This was on a new house the last receptacle on the circuit was dead.
Checked connections , Checked Receptacle,Checked resistance on
Neutral And hot.OL Checked black to black OL Checked white to whiteOL The ground was the only wire that had continunity.
The wire was ran thru drilled holes in stud wall. Had to run another wire under the floor up into stud wall.

Twice in my career have I found copper wires that have been somehow spliced end-to-end inside the insulation. It had to have been a factory connection as I found them stripping the insulation off. The two ends of the copper had distintively different colors, but they did not appear to be brazed or welded. Just looked like they had been cut square and SuperGlued together. Both times was early in my career, and was told by the foreman not to worry about them since it's a factory deal.

But if I ever see another one, I'm keeping it.

Makes me wonder how many of those factory butt-splices I have installed that I never saw.

 

[mivey]

makes me wonder how many of those factory butt-splices i have installed that i never saw.

27 .

 

[readydave8]

A bad splice.

I have also run across new conductors that just aren't complete between point A and point B.[/QUOTE
I have ran across new conductors that were bad. A couple of months back I ran into this problem.
This was on a new house the last receptacle on the circuit was dead.
Checked connections , Checked Receptacle,Checked resistance on
Neutral And hot.OL Checked black to black OL Checked white to whiteOL The ground was the only wire that had continunity.
The wire was ran thru drilled holes in stud wall. Had to run another wire under the floor up into stud wall.

We usually make up our grounds on rough-in but not hot and neutral, this reading would make me suspect a receptacle buried in sheetrock or an outside receptacle that got missed.

 

[Article 90.1]

Bad GFCI? I know you said the test button works, but we have come across a few faulty units out of the box over the years.

The more you think about it, we put a lot of faith in the safe operation of GFCI's, but then test them with a $5 tester that does not tell us anything, really. When I put my first GFI in 20 years ago, the boss had this cool tester that you could actually dial the milliamp range up as you held the test button to really test the device or breaker. I see ideal makes this, which is kind of cool: http://www.idealindustries.com/prodDetail.do?prodId=61-165

 

[TOOL_5150]

Bad GFCI? I know you said the test button works, but we have come across a few faulty units out of the box over the years.

The more you think about it, we put a lot of faith in the safe operation of GFCI's, but then test them with a $5 tester that does not tell us anything, really. When I put my first GFI in 20 years ago, the boss had this cool tester that you could actually dial the milliamp range up as you held the test button to really test the device or breaker. I see ideal makes this, which is kind of cool: http://www.idealindustries.com/prodDetail.do?prodId=61-165

I have that tester, I like it quite a bit. It has many more functions than I need on a daily basis, but its good to have.

~Matt

 

[gar]

100216-1329 EST

Article 90.1:

If you analyze a Leviton 7889 GFCI you find the following characteristics:

Pushing the TEST button sort of does a mechanical test. It mechanically unlatches the latch if the latch was latched. If you push TEST and the device trips open, then the latch mechanism has been proven to release.

The most important work is done when you press RESET. This starts reset of the mechanical mechanism, operates the 15,000 ohm test resistor to cause the electronics to function to momentarily active the unlatch mechanism which is really part of the relatch operation. If the trip solenoid does not operate the mechanism will not latch and the device remains off. Very ingenious, and a very good complete check. However, it can not provide protection against every possible failure mode.

As a redundant check an external 15,000 ohm resistor to ground is a good test.

.

 

[Article 90.1]

Thank you Gar!

 

[LarryFine]

As a redundant check an external 15,000 ohm resistor to ground is a good test.

Or a wiggy.

 

[bldgknow]

GFCI testing

I'm a home inspector ( not electrical inspector ) in Canada. I have had plug in GFCI testers that I thought were not working , only to find that I was not holding the test button long or hard enough. Some of them seem to be touchy.

The tester works differently than the GFCI device and will not work without the equipment ground.

I've sometimes wondered what can happen if you hold the test button for too long , for example on an exterior plug circuit that it turns out does not have GFCI protection.?
Some of the manufacturers ( of the plug in testers ) say hold for at least six seconds, and another brand I have says do not hold longer than six seconds. What is worst case from holding the button too long, and is their more risk if the polarity of the receptacle is reversed ?

 

[gar]

100301-2333 EST

bldgknow:

It is correct that an external tester works differently than the internal test button, but in terms of a valid test if wiring is correct and you have a good EGC at the outlet, then the resulting test is essentially the same.

Given that you have a good EGC connection, then the external tester is probably better because it would catch a reversed neutral and hot input to the GFCI.

The internal test resistor in units I have opened is 15,000 ohms. At 135 V the power dissipation in this resistor is approximately 1.25 W. If the test resistor is smaller than a 2 W unit, then holding the test button for a long time will burn out the resistor. Internal to a GFCI the test resistor looks to be 1/8 to 1/4 W. This wattage resistor would burn up quickly at 135 V if held in long. Even at 95 V it is about 0.6 W.

I do not know what wattage test resistor is used in an external GFCI tester.

At 95 V the test current is 95/15,000 = 6.3 MA. Still enough that it should trip a good GFCI, but the time could be into the 6 second range. At higher line voltages the trip time normally should be shorter than 6 seconds and is probably substantially shorter in time.

.

 

[bldgknow]

Thanks and my mistake

Thanks and my mistake

First I must apologize because I posted my previous reply after reading only page 1 of the thread, then to my surprise my post jumped to the end of page 4. So I have now learned, rookie that i am, to look at the number of pages and read all the postings before replying! That is why some of my comments were out of place.

So I have now read the whole thread, and thank you for the reply.

One angle of my questioning about risk of using or mis-using an external tester is whether or not anything that is plugged in on a 120 volt circuit could get damaged by an external GFCI tester ? For example cordless phones or other electronics?

 

[wptski]

100301-2333 EST
Given that you have a good EGC connection, then the external tester is probably better because it would catch a reversed neutral and hot input to the GFCI.

I might be wrong but as I recall the newer GFCI have some wiring diagnostics. They are packaged in the tripped position, if wired wrong, they won't RESET.

 

[macmikeman]

I have that tester as well. Love it, I treat it special. Leviton catalog # 6185
It only comes out on situations like the op has where the standard yellow gfi tester is acting funny. Then I use it to troubleshoot.