mm2 ampacity restrictions

Your views on Stateside electrical testing seems to be held by another American Electrician on the forum, ''Gnuuser'' from NW Pa who has recently purchased his own Earth Loop Tester. Though i've never seen a loop tester come with earth spikes, so it must be a Chinese multi function bit of kit.

Check out the forum test meter sponsor (test-meter.co.uk) to check out the typical loop testers that are commonly used in the UK and EU....

gnuuser said:

got the earth loop tester i ordered
it arrived a full week ahead of schedule
the thing is a bit of a beast! came in a handsome case with heavy short and long leads (with rather stout clips on them)
2 earth spikes and manual(chinese manual, but manufacturer included a link to download it in english)
Ill post pics as soon as i can.
taking the time to read the manual right now

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shanky887614 said:

efli is bassically checking the resistance L-E at the supply through the supply transformer to its star point then through the return earth path to make sure it complies to the max values in the iee wiring regs.

each mcb/fuse etc has a max zs, if it doesnt comply then a different type or a bigger cable is required

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How does the tester perform the earth loop test? Does it short circuit the line for 1/50 of a cycle and look for the magnitude of the current pulse or does it send a DC current through the line and look for a fall of potential?

My understanding is that during a phase to earth fault, earth loop impedance testing guarantees that the fault current under a bolted fault (no impedance in the short/fault itself) causes a current flow that is equal to or greater than the breakers instantaneous magnetic trip?

Engineer54 said:

Earth fault loop impedance testing is basically to confirm or otherwise that a sufficient low impedance exists to cause the operation of the protective device, within the required time anywhere on the circuit under test. eg Zs

Earth Loop testing at the origin of the supply ''Ze'' will confirm if any earthing exists and will give a value for that earth. An earth loop tester will also give the PEFC and PSCC at the origin of the installation....

I'm sure others here will give you a more in-depth explanation... lol!!

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By earth you mean the conductor that goes back to the star point? Unless RCDs are present like in a TT system, the earth (soil) itself should never, ever be a ground fault path since the soil is always a much higher resistance than copper wire. In TN-S and TN-C the fault should always be cleared via a wire rather than a grounding electrode like a earth rod or plate. In fact, if one took 230 volts to a ground rod or plate, the current that would flow would only be a few amps.

Ze means Impedance earth? My take and I may be wrong, is that earth fault loop is the total impedance from one phase, through the conductors, through the fault, to the earth wires all the way back to the transformer star point? The total Impedance will yield a current. That current must be very high. If a breaker has a magnetic trip rating of 10x the handle rating, (20amps x 10=200) the impedance should yield a current over 200amps? Thus, during a fault, if the current is 2000amps, a 20 amp breaker like above will trip immediately?

Engineer54 said:

Your views on Stateside electrical testing seems to be held by another American Electrician on the forum, ''Gnuuser'' from NW Pa who has recently purchased his own Earth Loop Tester. Though i've never seen a loop tester come with earth spikes, so it must be a Chinese multi function bit of kit.

Check out the forum test meter sponsor (test-meter.co.uk) to check out the typical loop testers that are commonly used in the UK and EU....

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He did the right thing! Tell him he is steps ahead already. A megger would also compliment is earth loop tester very well.

I will check the link out

He did the right thing! Tell him he is steps ahead already. A megger would also compliment is earth loop tester very well.

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Tell him yourself, he is a member here just like yourself!! lol!!

As for your take on ELI testers, and the principles of how they work are to be honest a little flawed, but i'm sure someone here will explain them for you, (or you can wait until i have enough time to do so). Right now, i'm trying to do too many things, plus getting ready for the students i tutor coming to site tomorrow morning. ...Bang goes my Saturday off this weekend!!

Engineer54 said:

Tell him yourself, he is a member here just like yourself!! lol!!

As for your take on ELI testers, and the principles of how they work are to be honest a little flawed, but i'm sure someone here will explain them for you, (or you can wait until i have enough time to do so). Right now, i'm trying to do too many things, plus getting ready for the students i tutor coming to site tomorrow morning. ...Bang goes my Saturday off this weekend!!

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I will tell him!

An EFLI tester measures the volt drop occasioned by the Tx secondary, line conductor and protective conductor resistances when the supply is connected across a low (approx 10Ω) resistance; a high current flows through the fault path and from the volt drop measured the resistance of the earth fault path can be calculated.
The tester can often also calculate the prospective fault current from this resistance and the supply voltage.

The description of the fault path you have given is correct and I have attached labelled diagrams of the TNCS, TNS and TT systems earth fault paths for reference.

Posts like the one by Richard above are the reason that this forum is still worth using. Daz

My understanding, is that for a trailer, the system must be TN_S?

It depends what supply is available where they are parked up. No problem with having a TT earthing system, providing adequate protection is provided. TNC-S isn't recommended if the trailer has an overall outer metal skin as part of it's construction...

Any chance of posting a few photo's of these trailers your company produces?? What sort of function do they fulfil, (eg, temporary site offices/workshop, residential)

Engineer54 said:

It depends what supply is available where they are parked up. No problem with having a TT earthing system, providing adequate protection is provided. TNC-S isn't recommended if the trailer has an overall outer metal skin as part of it's construction...

Any chance of posting a few photo's of these trailers your company produces?? What sort of function do they fulfil, (eg, temporary site offices/workshop, residential)

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These are primarily work trailers. Id have to ask if its ok to post any pics.

My understanding is that if TT is used (Correct me if I am wrong) its not involved with pin and sleeve connections. In any cases, a TT network would need a local earth electrode. The main breaker is recommended that it be a 100ma delayed RCD, while the branch breakers are RCBOs 30ma. The dual RCD in series in the event one fails another can back this up?

Gardner said:

These are primarily work trailers. Id have to ask if its ok to post any pics.

My understanding is that if TT is used (Correct me if I am wrong) its not involved with pin and sleeve connections. In any cases, a TT network would need a local earth electrode. The main breaker is recommended that it be a 100ma delayed RCD, while the branch breakers are RCBOs 30ma. The dual RCD in series in the event one fails another can back this up?

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I would think that most trailer/caravan/small port-a-cabins are connected to a power supply via plug and socket, most if not all caravan sites in UK/EU certainly are. The provision of a back-up 100mA S type RCD is prudent recommendation rather than an actual requirement.

Being a trailer, denotes to me that it's a mobile workshop, rather than being normally set up in a permanent position. A suitably sized plug IP rated & socket will generally be fine for such trailers...

Thanks!

In fact, when AFCIs (Arc Fault Circuit Interrupters) were required for general use residential circuits a few years back, the ones that had 30ma differential protection caught a lot of wiring errors. Complaints were and are still common of them tripping on new home construction. Turns out electricians were making tons accidental neutral to ground and crossing neutrals between circuits... all code violations that testing would have caught. Without a doubt older installations before the AFCI requirements have boat loads neutral to earth faults. I have seen it first hand.

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Unless something has radically changed with these AFCI's it was proved over and over again by some prominent US Electrical Engineers they just didn't work as claimed. This was proven many times by independent test labs, none ever managed to get any of these breakers to trip when subjected to a series arc fault or a full on sustained arch fault. You i think mentioned Mike Holt, who also undertook to test these breakers, and again couldn't get any of the breakers to perform as claimed by the manufacturers... There still isn't (to my knowledge) a commercially available means to test these breakers (eg, ...AFCI test kit/meter) the only way to get these breakers to trip, is pressing the blue test button on the breaker !!

So what's your take on these breakers whether including a GFCI element or not??

As far as i'm aware, these AFCI breakers are not requirement in the UK/EU, to be honest i'm not even sure they are available/stocked this side of the big pond. Personally i've only seen mentions of these devices in manufactures catalogues, but without showing the usual data and specifications....

Unless something has radically changed with these AFCI's it was proved over and over again by some prominent US Electrical Engineers they just didn't work as claimed. This was proven many times by independent test labs, none ever managed to get any of these breakers to trip when subjected to a series arc fault or a full on sustained arch fault. You i think mentioned Mike Holt, who also undertook to test these breakers, and again couldn't get any of the breakers to perform as claimed by the manufacturers... There still isn't (to my knowledge) a commercially available means to test these breakers (eg, ...AFCI test kit/meter) the only way to get these breakers to trip, is pressing the blue test button on the breaker !!

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You are correct AFCIs do not work as claimed or advertised. The AFCI logic in them is total baloney. They are nothing but pure fraud. There is absolutely no way you can accurately differentiate between real arcs and a normal one with the primitive logic circuit boards inside of them. In fact since they came out there has been mountains of nuisance tripping caused by new UL listed vacuum cleaners, televisions, treadmills, fans, electronics, ect only because AFCIs can not accurately differentiate waveforms from these appliances and a real arc. In response manufacturers came out with new and improved designs... they are the same thing just way less sensitive. Correct they are far less likely to blow on your new vacuum cleaner, but try and trip them with a real arc from a loose connection and there is far less chance it will trip here to, if at all. Trust me, I have done bench top experiments in my workshop with new 'improved' AFCIs, you can light paper with the arcs but they will not trip.


For what its worth, I have seen real AFCI logic used in protective relays controlling Feeder breakers and automatic circuit reclosers for medium voltage (2.4kv to 35kv) distribution lines and HV transmission lines. It is light years ahead. The wave form is run through high bit oscilliogarphy and then run through a triage of different mathematical wavelet analysis programs. The micro processors even take line impedance, inductance/reactance, phase sequence elements ect of the line into consideration. The computing power is impressive and yes they are very expensive, but will also differentiate between customer loads and a real arc flawlessly, in addition to telling you exactly how far down the line it took place and what caused it!

In order for a residential AFCI to detect faults accurately the computing power needed would at least be that of a lap top or a late addition I phone.



AFCIs only got into the code because Eaton Cutler Hammer, a prominent American manufacturer bribed the CMP into accepting them into the code. Why? Because every AFCI breaker is around 35 to 45 us dollars where a standard breaker is only 2 to 5 dollars. Each and Every new home constructed or panel change now brings in 20 times more profit than before. Not even an economic renaissance could bring in that amount of money for circuit breaker manufacturers.

So what's your take on these breakers whether including a GFCI element or not??

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The only part that is both real and doing good in them is 30ma GFCI logic. It has caught a lot of wiring errors. Sadly only 80% of AFCIs have 30ma GFCI logic. A few versions do not (in particular newer General Electric models) so they can be used on Multi wire branch circuits. A MWBC is just a special term for a shared neutral circuit. Basically instead of running two 3 conductor cables only one 4 conductor cable can be run. Because 120 and 240 exist in a US electrical panel, 2 hots can share a neutral provided those two hots have 240 volts between them giving two 120 volt circuits hot to neutral. Great way of saving copper, but wont work with single pole AFCIs that have 30ma protection. You would think a double pole version would come out and fix that... so far the few double pole version available costs over 100 dollars... so we just use 2 single poles that don't have the 30ma in them Crazy.

As far as i'm aware, these AFCI breakers are not requirement in the UK/EU, to be honest i'm not even sure they are available/stocked this side of the big pond. Personally i've only seen mentions of these devices in manufactures catalogues, but without showing the usual data and specifications...

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I hope they never become mandatory. So far in the US they have proven to be a fraud. The 30ma RCD part is the only thing that will trip on a fault. Its funny though, because its claimed they will stop fires, yet I can think of a million other NEC code changes that will do the same without huge cost. Trust me when I say the NEC is becoming a marketing catalog.


FWIW this video will be a kick. Mid way through AFCIs trip from a ham radio!!!!

Video from thread: http://forums.mikeholt.com/showthread.php?t=162009


https://www.youtube.com/watch?v=JsILD0Fce1s