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Posted By Topic: earth loop testing

May 25 2012 20:17

jst testing a new installation i have wired..what should my earth loop readings be under??

Brian H
May 25 2012 20:21

NOTES... on your Coc,Inspector has livened no doubt,so no need to supply that data unless challenged,correct?

May 25 2012 21:23

The EFLI readings should be NOT greater than the values shown in the Wiring Rules tables 8.1 or 8.2.

use table 8.1 when mains supply is available and a EFLI meter is used, or
use table 8.2 when the resistance of the conductors is being measured by a low ohm meter (use the one in your Megger).

The Wiring Rules section 8 tells you how to do the EFLI testing required.

Brian H
May 25 2012 21:34

Again without looking,please, I was wrong believing Earth loop impedance test could be done with an Multimeter not capable of producing min of 20amps@3volts?took me ages to buy a Megger,when .5ohms was good enough?

May 26 2012 16:55

On a side.
Can you measure PSSC between phases with a Fault Loop Meter if you have a 3 phase socket outlet.
Fluke 1653B Meter is the one we have at work.


Brian H
May 27 2012 09:44

PSSC. Prospective Short Circuit Current.Calculated to MEN Board,any cable calcs after that would include that a rule...any parameter that would reduce PScc would fly in the face of who-ever invented Electricity Safety.So my guess,use Megger @500v to test Insulation (1meg)I prefer infinity,use flying earth on low ohms(.5ohm)or use 1phase conductor temp to earth bar as your Fly Lead (.5ohm+/-)If all is good,and you have everthing else correctly installed,Liven.retest PPt etc for correct Voltage +/- 5%.check Earth again.Rotation Test.Make sure Plug in Lead has current Test Cert.Etc Etc.COC within 24Hrs.On the way out look at your feet.Otherwise you may have more paperwork Than you can handle.

Brian H
May 27 2012 10:19

Unless you going to tell us the Fluke can do that test.

May 27 2012 12:21

Brian H
For a small installation with only one switchboard (usually the Main switchboard) the taking of 1 EFLI measurement is OK.

But considerable savings can be made if you calculate the PSSC at each distribution switch as the building cabling will provide a reduction in PSSC level and you can then use a lower rated MCB on the distribution switchboard.

The sale price of 15 kA or 10kA MCBs is higher than 6kA MCBs, the alternative is to use high PSSC current rated HRC fuses and mounting in a fuse cabinet which are also expensive.

While the Wiring Rules will NOT tell you the above theory, your good trade training should have done so. From my observations in and around the trade, I\'m sure the above information will be something new to many.

May 27 2012 12:59

I remember reading somewhere, where as a guide they measure pssc L1-N, L2-N and L3-N and whatever the highest value is measured then multiply by 2 (as apposed to squareroot 3) to get the L-L PSSC.


Brian H
May 27 2012 17:19

Thanks Pluto and All.Kind of forgot PSSC was used to Choose Protection Devices that can operate safely and correctly in the event of Short Circuit.I struggle with the intricities through familarity.Please bring back Inspectors,Pain in the Butt,but they used to nail that oversight for me.Blow that,I like having to get things right,

May 28 2012 10:00

Pluto\'s suggestion \"use the one on your megger\" is no doubt because using an ordinary DMM to measure these values - either for EFLI or for PEC resistance - is a wasdte of time. The meter\'s error factor will be greater than the value you are trying to measure. Most Iins Res testers (\"meggers\" to most of us, even when wearing a different brand) have a low-ohgm range which has a suitably low error. For digital meters, anything that doesn\'t give readings in hundredths of an ohm will be useless.