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The Long Lead (R2) Continuity Test for Periodic Inspections

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The Long Lead (R2) Continuity Test for Periodic Inspections

Post by terry gray on Wed Aug 22, 2012 5:31 pm

During the many conversations I have with electrical contractors in my region, a topic that often comes up is the recommended test procedures that should be performed when undertaking periodic inspections and testing. One of the little used methods is the Long Lead continuity test, mainly because contractors think that the long lead has to be run all the way back to the Main Earth Terminal (MET), thereby becoming a trip hazard. This is not actually the case, as for example in a domestic property any room will have central heating radiators connected to copper pipework, which will naturally have a very low resistance to the MET via the main protective bonding in the building and this metalwork can be used as a reference earth. This would also apply to structural steel-work in a commercial or industrial installations.

Even when this is not the case, a local socket-outlet earth pin could be utilized for this purpose once it has been established from a loop test that there is an effective earth fault loop path back to the supply transformer. Then comes the concern that the readings obtained would not be pure R2 values and what benchmark should the readings obtained be based against? My answer to this is it isn't terribly important what the test result values are, as long as they are very low - usually below 1 ohm - as in many cases it would be difficult to separate R2 from the parallel paths that may exist in an electrical installation.

The important thing is that all the points under test, particularly Class 1 equipment all have a low resistance earth fault return path, which can be quickly established when using this method and saves a lot of time and trouble doing the (R1+R2) method, although the results of two methods of continuity testing can be detailed together on the test schedule when completing an Electrical Installation Condition Report. Proprietary 'Long Leads' can be purchased from local wholesalers or NICEIC direct or simply made up from a reel of cable.

terry gray

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