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#150016 - 07/27/04 01:46 AM Fault Current Testing?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Just an off-the-cuff question.
How many of you guys that work with large current supplies, actually bother to do, or even have the test gear to do a true Fault-Current Assessment at the Mains Entry point, like at a Main Panel and the like?.
Your fusing and other protection equipment is based upon this figure.
And it is measured not in Amps, but Kilo-Amps.
This roughly will also give you the size of explosion that you can expect, should you Short circuit a Phase to Ground or from Phase to Phase.
There is a lot of test gear around these days that will do this for you automatically.
Fault currents are the single biggest killer, as in terms of serious burns recieved, next to direct contact with a live Phase.
Please, let's try and minimise the risk out there, guys!.
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#150017 - 07/27/04 08:33 AM Re: Fault Current Testing?
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Mike, that is an excellent question, and I believe you may be referring to “Prospective Short-Circuit Current” testing. As far as I know, it has never “caught on” in North America. Fault duties are done by calculation {as far as I can tell} with no attempt to do actual circuit impedance tests on a completed system, such as looks like can be done with a “Robin(?) Loop Tester.” That may change with the new NFPA 70E requirements.



{Image from www.themeterguy.com/photogallery}




[This message has been edited by Bjarney (edited 07-27-2004).]

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#150018 - 07/30/04 01:41 AM Re: Fault Current Testing?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Bjarney,
It was PSCC testing that I was referring to.
We do this over here, as the PoCo, investigates areas, where PSCC is of a very high value, versus the poor protection provided by local EC's here.
Regardless of what the Type of Protection that you use for your Circuit, it ain't nothin' if the Category Of Duty of that device, isn't at least over the PSCC, by a certain margin, measured in kA.
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#150019 - 07/30/04 06:55 AM Re: Fault Current Testing?
sabrown Offline
Member

Registered: 12/12/02
Posts: 297
Loc: Ogden, Utah, USA
I will do calculations often on the low voltage (120/208 and up) amperage systems over 400 amps. On our lower amperage systems I protect at the 22,000 level knowing that in the rural settings that I deal with that this is overkill that does not really cost me anything more. I may be wrong in doing this but after so many times of not approaching the need for greater protection, I made it my rule of thumb for the low voltages. If I am wrong in doing so, I would like to know as I would rather do 100 calculations than have just one person get killed.

Bjarney,
I would be interested in learning more about the ? loop tester.

Thanks,
Shane

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#150020 - 07/30/04 02:48 PM Re: Fault Current Testing?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Shane,
A loop-tester (or Ground Loop Impedance tester, to give it it's correct name) is a test instrument that is connected to a point on an electrical circuit, say a light switch or receptacle.
The tester then measures the total impedance of the circuit, from the point of test, through all the circuit wiring, through the fusing, the Mains wiring and back to the supply Transformer Secondary winding.
The beauty of these testers, is everything on the circuit gets tested in one foul swoop, the Ground wiring, all Neutral wiring and Phase wiring and also all the connections have thier integrity tested at the same time.
Another advantage of using this tester (and something I use my one for quite regularly) is testing sockets to see that the Earth (ground) contact is making good contact with any plug that may be inserted into it.
It's a really handy tester to have and I use mine like water comes out of the faucet!.
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#150021 - 08/19/04 06:01 AM Re: Fault Current Testing?
GamecockEE Offline
Member

Registered: 07/28/04
Posts: 49
Loc: Georgetown, SC 29440
Trumpy,
Have you had opportunity to compare your readings with calculated values. do the calculated values appear conservative?
Also would this test instrument be useful where there is a number of motor loads that add to the fault current in the first few cycles?
Do you have a link to the manufacturer who sells this product?

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#150022 - 08/24/04 07:49 PM Re: Fault Current Testing?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
GC,
Sorry I haven't got back to you sooner on your questions above.
The comparisons that I've done using calculation and then measurement of Earth Loop resistance, have at times shown wide variations between the two values, the measured value being the lowest, 99% of the time.
While I agree that motors do add to Fault current levels, the Loop test is only used to verify that the installed wiring and it's connections, back to the point of supply (ie: Transformer), are of high electrical integrity (ie: Low Impedance).

Here is a link to the Kyoritsu 6015 Multi-tester, that I use at work for the majority of my testing:

http://www.kew-ltd.co.jp/en/products/multifunction/6015.html
This thing cost an absolute fortune (NZ$3500), but it was well worth the money spent, considering all the features it has, all the seperate test instruments, would cost a lot more than this, if bought seperately.
Finally, here is a link to a loop tester I found made for the US market:

http://www.megger.com/us/products/ProductDetails.php?ID=141&Description=


{Message edited to space out links}

[This message has been edited by Trumpy (edited 08-24-2004).]
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#150023 - 08/24/04 09:03 PM Re: Fault Current Testing?
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
It sounds like potentially a very valuable tool. I found something like that described the other day, by Fluke/Robin UK.
www.fluke.co.uk/comx/show_product.aspx?pid=117&product=INS&type=2&locale=uken

“PFC, PSC Tests” look like very interesting capabilities. About 20 years ago, not knowing they were being developed elsewhere, I wanted to build a “fault-current tester” that operated as a very simple extrapolation of Ohm’s Law. A person in the business that I greatly respected told me that it was a complete waste of time and money.

Later, I was loaned a prototype briefcase-sized Prospective Short-Circuit Current tester by an outfit in the UK— BICC Dorman Smith. Its {mid 1980’s} readings are still penciled on my house-meter box: 2,566 amperes at 0.866PF—from a 15kVA trasformer and around 70 feet of ~1/0AWG aerial triplex.




[This message has been edited by Bjarney (edited 08-25-2004).]

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#150024 - 08/25/04 10:38 AM Re: Fault Current Testing?
aland Offline
Member

Registered: 05/20/04
Posts: 187
Loc: United Kingdom
Mike. Here in the UK BS7671 requires that prospective short circuit and earth loop be recorded at each sub distribution board. Installation certificates do have a dedicated box for the value to be recorded in.
I personnaly use a Chauvin Arnoux 6115 test meter it has all the same features as your Koyoritsu about £800 sterling, do not know how that fairs with your NZ$3500. Only problem I find with it its a three wire tool and you need to be related to an octopuss in some situations to handle all probes at once. Also have a Megger MFT 1500 two wire this does the same job but does not perform quite as many functions (does not store results either) Not that I ever risk using that facility. like a pencil amd paper for that. Do any of you folks use the store facility on meters? Sorry guys I dont know how you do links to webb sits so it will have to be a search if you need more info.

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#150025 - 08/31/04 04:25 AM Re: Fault Current Testing?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Bjarney,
Just regarding that above pic.
Where did the explosion actually happen behind that panel?.
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Let's face it, these days if you're not young, you're old - Red Green grin

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