test-talk-banner

Question:

Why does my PAT tester keep failing long extension leads?

Answer:

The IET Code of Practice states that a cord set (extension lead) should have an Earth Continuity of <0.1Ω+R.

The “R” is the resistance of the lead itself.

This can be calculated by obtaining the milliohm per metre for the cable size and multiplying it by the lead length. (See page 134 of IET Code of Practice for a useful table).

All PAT testers have a preset fail limit on an Earth Continuity test. If the Extension lead that is being tested is particularly long, then the increased resistance may be enough to be higher than the fail limit of the tester and would therefore indicate a “Fail”.

This would then require a calculation of the “R” in order to determine if the reading obtained is less than the maximum permissible, and if the reading is lower than the maximum permissible than the item has passed, even if the tester is indicating a “Fail”.