Earth Fault Loop Impedance Ze test at origin

[Tony_spark]

Hi,

I have a my am2 practical testing exam next week and I'm confused about the earth loop impedance test.
The centre use a three lead instrument, I just want to know if this is right.

Connect the third lead to the neutral bar, and connect one lead to the earth bar
Then measure over the three phases L1 L2 L3 and record the highest reading

Cheers

 

[bugsy]

If your testing Ze disconnect tncs / pme connection and test ( not at DB)

 

[IQ Electrical]

Hi,

I have a my am2 practical testing exam next week and I'm confused about the earth loop impedance test.
The centre use a three lead instrument, I just want to know if this is right.

Connect the third lead to the neutral bar, and connect one lead to the earth bar
Then measure over the three phases L1 L2 L3 and record the highest reading

Cheers

At the origin, you do as you've already said but you need to connect directly to the earthing conductor, removed from the main earth terminal to eliminate any parallel paths.

For PFC, you need to measure worst case scenario so you leave all parallel paths connected, thereby causing a higher PFC.

 

[Izzy's Dad]

My tester has the 3 lead cofig (it's a Metrel Easitest) When doing Ze, IR or continuity tests you plug the neutral lead into the top of the earth lead.

 

[Tony_spark]

Thanks Guys,

So to carry out the test, using a 3 wire test instrument.

1.Disconnect the main earthing conductor
2.Connect one lead to the neutral bar
3.Connect the earth lead to the disconnected main earth conductor
4.Test over L1 L2 L3 record highest reading

 

[Sparky Ninja]

Are you going to be carrying out PFC/PSC tests as well?

 

[Tony_spark]

Yea, I'm ok with that, just never used a three lead instrument before thats why I'm a little unsure

 

[telectrix]

Thanks Guys,

So to carry out the test, using a 3 wire test instrument.

1.Disconnect the main earthing conductor
2.Connect one lead to the neutral bar
3.Connect the earth lead to the disconnected main earth conductor
4.Test over L1 L2 L3 record highest reading

Spot on there.

 

[Sparky Ninja]

Yea, I'm ok with that, just never used a three lead instrument before thats why I'm a little unsure

Well in my experience students often find using a 3 prong lead fairly simple, but sometimes get a little stumped when going from measuring the PFC to the PSC or vice versa.

 

[pushrod]

Thanks Guys,

So to carry out the test, using a 3 wire test instrument.

1.Disconnect the main earthing conductor
2.Connect one lead to the neutral bar
3.Connect the earth lead to the disconnected main earth conductor
4.Test over L1 L2 L3 record highest reading

strictly speaking, in case they want to be awkward, you should also firstly switch off installation as well, as the rest of the installation is potentially not safe with the main earth disconnected.

 

[Tony_spark]

Yea, I'd have the main switch at the D/B switched off.

Is there two ways of doing the test with a 3 wire instrument

1. Put the Green and Black leads together and connect them to the main disconnected CPC
2. Red lead,test over L1 L2 L3 record highest reading.

Or do I connect the third test lead to the Neautral bar?

Are both methods acceptable?

cheers

 

[pushrod]

Yea, I'd have the main switch at the D/B switched off.

Is there two ways of doing the test with a 3 wire instrument

1. Put the Green and Black leads together and connect them to the main disconnected CPC
2. Red lead,test over L1 L2 L3 record highest reading.

Or do I connect the third test lead to the Neautral bar?

Are both methods acceptable?

cheers

The board you are testing will probs be backed with an rcd so you will probs have to do the "no trip" version which is with all three leads to separate points ie line , neutral and earth.

edit: or at least that is how it is with my tester

 

[Tony_spark]

The Tester I'm using is going to be a Megger MFT1552. (I think thats what they have at the centre)
I think you need to use 3 wires to carry out EFLP & PFC tests.

 

[pushrod]

The Tester I'm using is going to be a Megger MFT1552. (I think thats what they have at the centre)
I think you need to use 3 wires to carry out EFLP & PFC tests.

that is what i have - it will do a 2 lead test but that will trip out if there is an rcd at the DB supplying the rig. So best be familiar with the 3 lead test
you set the meter dial to "no-trip".

 

[Sparky Ninja]

The Tester I'm using is going to be a Megger MFT1552. (I think thats what they have at the centre)
I think you need to use 3 wires to carry out EFLP & PFC tests.

Yes, and it's depending on wether you can carry out the test on the high loop setting that will depend on your polarity. If it is high loop, and you have three leads.. I scanned this out of one of my books..

 

[pushrod]

go on you tube and search "megger 1552" (not the one where someone reverses over it lol) there are 2 clips showing all the lead connections for all the various tests.

edit: it is on "part 1" the first clip that comes up - part 2 shows rcd testing - use auto for that , much easier than manual.

 

[Tony_spark]

Thanks alot guys for all your help.

really appreciated

 

[pushrod]

When you are doing the live tests with a probe, which you will probs want for the red to line (can probs use the crocs on neutral and earth) make sure you have ( or ask for) the little plastic shroud that fits over the metal tip and leaves just 2mm sticking out. All depends on how strict awkward they want to be but without the shrouds the test leads don't conform to gs38. good luck with it.

 

[Tony_spark]

Thanks alot for all your help.

1.Set the Dial to no trip.
2.crocodile clip the Green to the Earth bar, Black to the Neutral bar
3.Test over L1 L2 L3 with the red lead with plastic shroud on. Record the highest

Thanks again for all your help, I've really been worrying about this test.

 

[pushrod]

Thanks alot for all your help.

1.Set the Dial to no trip.
2.crocodile clip the Green to the Earth bar, Black to the Neutral bar
3.Test over L1 L2 L3 with the red lead with plastic shroud on. Record the highest

Thanks again for all your help, I've really been worrying about this test.

spot on and for pfc just reconnect the earth and advance the dial one more space to "pfc" and press test button. The guys checking you will probs be friendly, they were with me, but you do hear one or two horror stories so you are right to be prepared.

 

[Sparky Ninja]

spot on and for pfc just reconnect the earth and advance the dial one more space to "pfc" and press test button. The guys checking you will probs be friendly, they were with me, but you do hear one or two horror stories so you are right to be prepared.

Then take into account what to do with your reading, being that there are 3 lines. Also, if you are measuring the PFC you will be expected to carry out the PSC. This may be understood already, but I wouldn't want someone else picking up this advice without this little bit added in.

 

[pushrod]

Then take into account what to do with your reading, being that there are 3 lines. Also, if you are measuring the PFC you will be expected to carry out the PSC. This may be understood already, but I wouldn't want someone else picking up this advice without this little bit added in.

Think Tony said earlier that he was ok with pfc it was just the instruments that he was unfamiliar with, but good point for anyone else reading the thread.