Way to check earth connection to metal fittings without removing them?

[xd400]

Hi All,

Have various metal light fittings, mains sockets and light switches in property. I wanted to check if the earth wire has been connected to the metal fitting itself. Is there a way to test this without having to open all of them up?

Thanks

 

[plugwash]

Connect a long wire to the main earth and then measure continuity between that long wire and each fitting.

 

[bernardgreen]

Connect a long wire to the main earth and then measure continuity between that long wire and each fitting

Turn all the power off at the Consumer unit main switch before doing any continuity checking.

If there is a wiring fault that has made the metal of a fitting Live then a normal economy priced multi-meter will suffer damage if connected between the Live metal and Earth while set to Ohms or Continuity. Some times the damage can be spectacular and painful to the hand holding the meter or it's leads,

Before the continuity check it is best to always do a voltage check to make sure there is no voltage on an un-earthed lamp even if the main witch is OFF

 

[OwainDIYer]

I wanted to check if the earth wire has been connected to the metal fitting itself. Is there a way to test this without having to open all of them up?

No.
You can test for continuity to earth with a tester and a long lead, but in most cases with flush metal boxes you will have an adequate earth contact through the fixing screws, especially if there is one fixed and one adjustable lug on the back box - and at least adequate enough for a continuity test with a multimeter.

You really need a proper continuity tester which will use a high enough current for testing to break down a dodgy connection.

 

[plugwash]

It seems that most installation testers use 200mA or so. That is much higher than a multimeter but still quite low in the grand scheme of things and still very low compared to typical fault currents. I belive higher current tests used to be done in some circumstances but fell out of favor due to the fire risk.

Ultimately the only way to prove there is a wired connection is to inspect it, a tight fixing screw into a fixed lug will easilly take any reasonable test current.

 

[ericmark]

612.2.1 Continuity of protective conductors,
including main and supplementary equipotential bonding.
A continuity test shall be made. It is recommended that the test be carried out with a supply having a no-load voltage between 4 V and 24 V, d.c. or a.c., and a short-circuit current of not less than 200 mA.

With a PAT testing machine 25 amp was common, but this could damage bearing so often there is a lower current option of 200 mA.
With live testing so as not to trip an RCD often 9 mA is used.

So main tools are the low ohm ohmmeter, which uses 200 mA in the main, or the loop impedance tester, the latter can cause danger as if the earth is not sound it can raise the item being tested to mains voltage.

The problem is a small whisker of wire is enough to show an earth, but a fault could well result in that whisker being destroyed, hence the traditional 25 amp with PAT tester. However that too is a problem as it could melt a printed circuit track.

So the inspector has to use his skill to decide how to test without causing danger or damage. City and Guilds 2377 and 2391 are normally preceded by some course, where the dangers to personal and equipment are explained. This included parallel paths etc.