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Author Topic: Test your grounds regularly!  (Read 26294 times)

Ray Aberle

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Re: Test your grounds regularly!
« Reply #20 on: November 23, 2014, 10:38:54 PM »

BTW……how does a thread go from testing grounds regularly to food and drink references???
It is one of the reasons I love this forum…..

My Bad. I was going on the whole "TLA that then has a word after that's also one of the letters in the TLA." thing, and mentioned Tuna Fish. Tuna... is a fish.... duhh....
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Jonathan Johnson

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Re: Test your grounds regularly!
« Reply #21 on: November 23, 2014, 10:58:45 PM »

Tuna... is a fish.... duhh....

Or a Tuna Boat. (But that's used for catching Tuna... fish.)

You can tuna fish, but you can't teach it to sing.
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Stop confusing the issue with facts and logic!

Mike Sokol

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Re: Test your grounds regularly!
« Reply #22 on: November 24, 2014, 01:00:32 AM »

The only question the GFCI asks is: Are the Hot & Neutral currents identical and opposite in phase (±5mA).  The unit does not ask 'why is there a current difference?'.

Yes, it's a common misconception that the GFCI considers the ground wire current. As you note, it's only looking for equal current in the Hot and Neutral wires. Now, if some of the Hot current is diverted to the Ground (EGC) wire, that will cause the GFCI to trip. But it's not tripping because of the current in the EGC Ground, it's tripping because of the H-N current imbalance caused by this diversion. You need to keep this in mind when troubleshooting GFCI tripping. Here's a link to a GFCI primer and graphic on how this works. http://www.noshockzone.org/rv-electrical-safety-part-viii-gfci/
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Lyle Williams

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Re: Test your grounds regularly!
« Reply #23 on: November 24, 2014, 02:50:48 AM »

I never thought GFCI/RCD considered ground current.  I thought that the simplest way to implement the test button and create a active/neutral imbalance was to shunt current to ground, but that isn't the way it is done these days.
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Steve M Smith

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Re: Test your grounds regularly!
« Reply #24 on: November 24, 2014, 03:05:04 AM »

I never thought GFCI/RCD considered ground current.  I thought that the simplest way to implement the test button and create a active/neutral imbalance was to shunt current to ground, but that isn't the way it is done these days.
If all you have is live, neutral and ground, how else can you do it?


Steve.
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Steve Bradbury

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Re: Test your grounds regularly!
« Reply #25 on: November 24, 2014, 07:32:23 AM »

The device doesn’t care what causes the imbalance in current. If you connect a resistor from the input supply to the load a current will bypass the device and, depending on the resistance value, trip the device. Testing in this manner means that the device can be checked without relying on an external earth.

Regarding the PATest, the current (sorry) standards specify that the stickers should not have a next test date on them simply the date of the latest test.

This is to clarify that there is no specified test period and because testing companies were taking advantage of the confusion and over testing equipment. I recently (6 months ago) went on a general health and safety course run by my local authority and the guy running the course got this wrong. It made me wonder what other errors he made, but it got me a certificate that says I have core H&S knowledge.  I digress…

The test period should be risk assessed. A computer sitting in a server room which is never turned off is not subject to the same abuse as an amplifier that is dry hired to a different customer every day. The test periods should reflect the type of use and abuse that the equipment is subject to. With the latter prior to every hire would be sensible.

Someone mentioned tests not straining equipment to the same level as actual faults. With some PAT equipment (generally mains powered) the earth bond test can be set up to 25A although IT or business equipment is tested at 100mA. Most testers also hold the test for a short preset period of time. Standard insulation tests were usually done at 500V but increasingly, due to concern about damaging electronic equipment, 250V can be selected.

Interestingly most literature I read suggests that most faults are picked up on by the visual check.

Disclaimer: I did electrical engineering at university a long time ago but as I approach senility I consider myself more as an informed enthusiast. Several years ago I attended a PAT training course run by Seaward.  The level of electrical knowledge required to pass was minimal.
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Lyle Williams

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Re: Test your grounds regularly!
« Reply #26 on: November 24, 2014, 11:49:41 AM »

If all you have is live, neutral and ground, how else can you do it?


Steve.

The test button and resistor either sits diagonally across the current imbalance sensor, from live on the load side to neutral on the supply side allowing some current to bypass the sensor,
  or
The test button and resistor are connected to an additional winding in the current imbalance sensor.
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Lyle Williams

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Re: Test your grounds regularly!
« Reply #27 on: November 24, 2014, 12:03:10 PM »

The Australian PAT standards do specify durations, but they are somewhat risk based.  Equipment in a residential environment might be allowed five yearly testing, while hire gear needs monthly visual and three-monthly electrical tests.

The standards also have a few options for earth continuity testing within an appliance, including a high current test.  The high current test methodology isn't mandatory, so is rarely done in practice.

All of that assumes that there is an earth available from the wall socket.
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John Roberts {JR}

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Re: Test your grounds regularly!
« Reply #28 on: November 24, 2014, 12:52:00 PM »

If all you have is live, neutral and ground, how else can you do it?


Steve.
The value of GFCI/RCD is that they work independently of ground. I installed GFCI in my bathroom and kitchen precisely because my house wiring does not have solid safety grounds.

An external test would logically have to divert current elsewhere, and internal test button can imbalance the internal detection mechanism.

JR
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Steve M Smith

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Re: Test your grounds regularly!
« Reply #29 on: November 24, 2014, 01:44:14 PM »

I think I have it now.  The test switch must place a load diagonally. i.e. from one conductor at the input to the other one at the output so its current only appears in one half of the sense circuit causing the imbalance.


Steve.
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ProSoundWeb Community

Re: Test your grounds regularly!
« Reply #29 on: November 24, 2014, 01:44:14 PM »


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