Testing live

[SgtTrojan]

I've passed it in July 2007. It was a question in that paper that I am seeking clarification on.

What would you say the answer is Risteard?

 

[Risteard]

I've passed it in July 2007. It was a question in that paper that I am seeking clarification on.

What would you say the answer is Risteard?

Oh right! Belated congratulations then!

But my answer would be:

Live Polarity
External earth fault loop impedance / earth electrode resistance
PFC

 

[Taylortwocities]

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.

Read 612.8. Specifically

Polarity. It says that polarity shall be verified. There is nothing that states this is done with the installation energised. When it is done live then it is a functional test and outside the boundaries of this question (the FIRST three). So I am right.

PFC, PSCC 612.11 states that BOTH shall be measured. That means tested. The question does not ask what should you record in your test results.
You say

PFC is the highest of PEFC and PSCC

but you cannot determine which is higher unless you test BOTH. So I am right.
By the way. You cannot have a highest when there are only two items. It is the comparative tense so it is higher, not highest.
(See, I can be picky too).

RE RCD tests. Read the book. 612.8.1
For TT and TN systems the RCD test to check it complies with BS (using a calibrated RCD tester) is done before you get to functional testing. The only functional test on an RCD is to check the test button operates (612.13.1). So I am right.

This is an exam question based on BS7671. If you dont answer correctly then YOU ARE WRONG!

 

[Risteard]

Polarity. It says that polarity shall be verified. There is nothing that states this is done with the installation energised. When it is done live then it is a functional test and outside the boundaries of this question (the FIRST three). So I am right.

No, because Polarity of the Incoming Supply needs to be confirmed which can only be a live test. Think of CRIPPLER. Polarity is both a dead and a live test - not just a dead test.

And it does not say that:

"PFC, PSCC 612.11 states that BOTH shall be measured."

It is that PEFC and PSCC shall be measured. The highest is PFC. You do not appear to understand the difference between PFC and PEFC.

PEFC is Prospective Earth Fault Current. PSCC is Prospective Short-Circuit Current.

Prospective Fault Current (PFC) is the highest of the PEFC and the PSCC.

"RE RCD tests. Read the book. 612.8.1
For TT and TN systems the RCD test to check it complies with BS (using a calibrated RCD tester) is done before you get to functional testing. The only functional test on an RCD is to check the test button operates (612.13.1). So I am right."

Wrong. RCD testing forms part of the functional tests.

I suggest you digest IEE Guidance Note 3, "Inspection and Testing".

 

[LiamPope]

Can you not get hold of 2007 paper answers from your college? That'll settle this! Or create a new argument about how the examination board is also wrong...

 

[Taylortwocities]

BS7671 says

and I will quote

"The prospective short-circuit current and prospective earth fault current shall be measured....."

it does not say OR, it says AND.

Please also remember the difference in wording between GUIDANCE and REGULATION.

 

[Risteard]

"The prospective short-circuit current and prospective earth fault current shall be measured....."

I never said that they shouldn't.

I said that Prospective Fault Current should be tested. Prospective Fault Current is the highest of the two so obviously involves measuring the two. Clearly you don't understand the difference between PFC and PEFC.

 

[SgtTrojan]

There is nothing like a good debate to come to the correct answer. Taylor whilst I do not doubt your knowledge of Part 6 of BS7671 I think that what you have stated above is not 100% correct. The OSG lists the tests in sequence "with the supply connected". I posted it above.

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

The dilemma was really about whether or not the earth fault loop impedance is classed as the third test or whether it is the PFC test. As the 2nd test does stand as the result for the third test...
"A loop impedance tester is connected between the line conductor at the source of the TT installation and the earth electrode, and a test performed. The impedance reading taken is treated as the electrode resistance" GN3 p48
...then I can only agree with Risteard's answer.

But my answer would be:

Live Polarity
External earth fault loop impedance / earth electrode resistance
PFC

The live polarity test, it seems, only needs confirming at the source of the supply (once it is connected).

 

[SgtTrojan]

Ahh missed your two last posts while I was posting.

"Regulation 612.11 requires that the prospective fault current (PFC), under both short circuit and earth fault conditions, be measured...at the origin" GN3 p52

and

"Regulation 434.5.1 states....The term prospective fault current includes the prospective short-circuit current and the prospective earth fault current. It is the greater of these....which shall be compared with the breaking capacity of the device" GN3 p52

and then later

"Whichever is greater of the prospective short-circuit current and the prospective earth fault current obtained shall be recorded on the schedule of test results" GN3 p53