Testing live

[SgtTrojan]

Hi Chaps,

What are the FIRST three live tests carried out on a new installation when the system is a TT system?

Is it:

1. Test Method 2 for testing the earth electrode (with an earth fault loop impedance tester)
2. Earth fault loop impedance Zs
3. Earth fault loop impedance Ze

???

 

[Risteard]

What about live polarity?

 

[SgtTrojan]

Hmmm

After connection of the supply, polarity should be confirmed using an approved voltage indicator

So it could be yes.

1. Polarity with approved voltage indicator
2. Test Method 2 for testing the earth electrode (with an earth fault loop impedance tester)
3. Earth fault loop impedance Zs

 

[Risteard]

Also Prospective Fault Current.

 

[1john]

Polarity
Ze
PSC

your Zs readings will more than likely exceed the max permitted values hence the need for an RCD to provide adequete disconnection times.

 

[SgtTrojan]

THere was a question in a 2391 paper and it asked for the first 3carried out.

 

[SgtTrojan]

Final answer? ^^


1. Polarity (using the loop tester as an approved voltage indicator)
2. Ze (testing earth electrode with loop impedance tester)
3. PSCC (at source of supply)

 

[Taylortwocities]

Gareth, why the question. The answer is laid out for you in the On-site Guide. See 9.3.1. It is conveniently titled "Testing Checklist".

All you need to do is to go down the list and decide which are live and which are unenergised tests.
One item is even specifically marked "TT systems".

 

[1john]

Polarity
Ze
PSC

your Zs readings will more than likely exceed the max permitted values hence the need for an RCD to provide adequete disconnection times.

 

[Risteard]

3. PSCC

PFC, not PSCC. Your PFC is the highest of your PEFC and PSCC. For a three phase system it will be your PSCC between phases.

 

[Taylortwocities]

3. PSCC

PFC, not PSCC. Your PFC is the highest of your PEFC and PSCC. For a three phase system it will be your PSCC between phases.

Why don't you read the red book ?

For TT systems the three live tests are

Electrode resistance (612.8.1 (1))
Effectiveness of RCD (612.8.1 (2))
Earth fault loop impedance (612.9)

I would maintain that polarity is a dead test and is determined when carrying our R1 + R2


NOTE: the regulations state that both PSCC and PFC shall be measured. That woul;d be test number 4 in live testing on a TT.

Do have read of 612. Its easier than guessing.

 

[Risteard]

Why don't you read the red book ?

For TT systems the three live tests are

Electrode resistance (612.8.1 (1))
Effectiveness of RCD (612.8.1 (2))
Earth fault loop impedance (612.9)

I would maintain that polarity is a dead test and is determined when carrying our R1 + R2


NOTE: the regulations state that both PSCC and PFC shall be measured. That woul;d be test number 4 in live testing on a TT.

PFC is the highest of PEFC and PSCC so you are wrong.

Polarity is both a dead and a live test so you are wrong.

Earth electrode resistance tests are used for generator sets etc. otherwise an earth fault loop impedance test is likely on a TT system protected by RCD.

RCD testing comes under functional tests so would NOT be one of the first three live tests.

 

[SgtTrojan]

I am after the definitive answer as required by the 2391 examiners.

The testing checklist on OSGp75 does not explicitly specify the live polarity test but GN3 clearly states on p46

After connection of the supply, polarity should be confirmed using an approved voltage indicator

So if we assume the polarity test is Test 1,
Test 2 is the live earth electrode test using a loop impedance tester (which is regarded as the external earth loop impedance), that would make
Test 3 the PFC (Thank you Risteard) test


But 10.2.2 states, that with the supply connected

1. Check polarity with supply connected, using an approved voltage indicator
2. Earth electrode resistance using a loop impedance tester
3. Earth fault loop impedance

Are 2 and 3 not regarded as the same test?

All of those can be done with one test. That is where I am getting confused.

 

[Risteard]

Earth fault loop impedance in that instance refers to Zs.

But obviously Ze (or Ra for TT) comes first.

 

[Risteard]

If you don't mind me asking, when are you sitting the written paper?