General Inspection & Testing Questions

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7 Jun 2005
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United Kingdom
Hi I am currently revising for my City & Guilds 2391 Inspection & Testing Exam, and I am wondering if anybody can help me on some questions. I would be very grateful as I am a bit stuck as to the explanations:

1. Why do certain E14 & E27 edison screw lampholders need not be checked for polarity?
2. From which points in an installation are a distribution circuit and a final circuit connected?
3. A test result sheet indicates that the total ZS of a circuit is lower than the sum of ZE + (R1+R2). State three possible reasons for this?
4. What is the maximum required test operating time of a 100mA RCD?
5. Identify the BS7671 definition for the current flowing:
a)Normally in a CPC
b)In a circuit where the fault occurs between live conducters
c)Under normal full load conditions
6. With reference to instrument test leads, state the:
a)Voltage above which GS38 generally applies when conducting voltage measurements
b)Requirements of GS38 regarding the test probe tips used at or above voltage in a)above.
c)Action to be taken before testing CPC continuity
7. Which instrument should be used to test\\\"live\\\" circuit polarity?
8. Why is it unneceesary to check polarity on a standard BC lampholder?
9. An earth fault loop impedance value is measured at the extremity of a radial circuit, which is supplied via a TN-S system. The reading obtained was higher than the expected BS7671 maximum value. State:
a)Two possible reasons for this high value
b)One practical solution if no faults found
10. The earth fault loop impedance of an immersion heater circuit is to be measured. State:
a)What type of lead is to be used
11. What is the maximum test current and disconnection time of a 20mA RCD used for supplementry protection against direct contact?

Your help would be really appreciated.

Many thanks


please note 1a your 5 other posts (same question) have been removed. I would also point out this is a diy forum. Ask your tutor

I have now locked this post
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afaict he posted through the tutorials linked to the forum

a setup which is always causing situations that are horrible for the forums themselves.
The answers lie in a book called BS 7671 2001(2004). This answers all of your questions in one

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