Page 672 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

Incorrect method of connecting leads Continuity of protective conductors
–ve The purpose of testing earth continuity is to verify that the protective
+ve bonding in the house is not broken. Note that safe isolation is essential
and must be carried out before the test. To measure the continuity of
Current flow has to travel across the hinges protective conductors, a low-resistance ohmmeter is required, typically in
the range of 0.2–2 ohms. Note that general-purpose multimeters are not
Correct method of connecting leads
suitable or capable of carrying out this test.
–ve +ve
Method

1 Select the correct meter (low-resistance ohmmeter).
Current flow is straight from clip to clip 2 Select the correct scale (depends on meter/manufacturer).
p Figure 11.29 Incorrect vs correct 3 Check the meter/leads for damage.
method of connecting leads 4 Insert the leads in the correct location (follow the manufacturer’s
instructions).
5 Correctly connect the leads – as shown in the diagram.
6 ‘Zero’ or ‘null’ the meter leads so meter says 0.00 Ω.
7 Test between all earthed points. Test results between conductive parts
should be in the order of 0.05 Ω or less. Further details on specific results is
given in BS 7671 or consult a qualified electrician.
In a room containing a bath or shower, tests are carried out with a low-
resistance ohmmeter to prove bonding between, for example, hot and cold
water, central heating, a heated towel rail, lighting circuit and shower.

Supplementary
bonding
conductor

Low-resistance ohmmeter

p Figure 11.30 Testing for continuity

Polarity

The purpose of testing for polarity is to ensure that line is line and neutral is
neutral. All single pole switches must be in the line conductor. All light fittings
and sockets must be connected the correct way round. Failure to check this can
lead to electric shock.

660

9781510416482.indb 660 29/03/19 9:09 PM