What is it, and why is it of interest? People are regularly put in danger by unsafe electrical devices, including hi-fi equipment. Originally just out of interest, we now carry out these electrical tests on all equipment brought to us for repair, and on customers' equipment, brought here just to be tested.


Why do we test, why would you want it? Possibly as much as one in four units brought here for testing are potentially unsafe - quite an alarming figure. Whilst most defects are minor, occasionally equipment can be very dangerous, so by avoiding our customers being injured, we retain happy satisfied customers for longer!


Another reason for testing, is for use in public places, like rented halls for public performances, and for use in hospitals, retirement homes etc. Here a different requirement of greater strictness applies, as such venues will often refuse to allow the use of untested electrical items. Whilst we cannot always be sure our safety labels will be sufficient, (some on site electricians have odd views!), they are generally accepted.


So - what is involved?


Test for light electrical and electronic equipment


Before carrying out an electrical test with a PAT test meter, we check the following:-

1) Visually check that the equipment appears in good order, with no damage to casing that appears dangerous.

2) Visually check power lead appears undamaged.

3) For a captive lead, tug wire at the point of entry into the equipment, to check that it is secure.

4) Check that the plug is safe, correctly wired, and fitted with a suitable fuse.


What we test


We carry out a safety check using a test and measurement unit that carries out a test which is more stringent than the visual checks, (above).


The test device is regularly checked with a 'minimum pass' test load, (a simple device that mimics the minimum acceptable pass indicated below). This is to ensure that the test device operates correctly. It is a bit of a nuisance, but safety checks cannot be allowed to fail - the test must be accurate every time.


1) If the equipment is earthed, we will test the earth connection to the equipment by measuring its resistance at approximately 1 amp current. The pass level will depend on the nature of the equipment, but will always be less than half an ohm. Further tests will be applied if appropriate. The earth security test is to ensure that the earth provision is in good condition and safe.


2) All equipment with exposed metal will be checked for insulation resistance from mains power at not less than 500 volts dc, (a figure considerably in excess of mains, to ensure that the case is not live, even, with earthed equipment, if the earth comes disconnected). The normal pass level will be 2 million ohms, which at mains voltage is considered quite safe, (at mains voltage, the current leakage therefore is less than one eighth of a milli-amp, which is very low). This is considered a conservative safe level - the lowest tolerable level is five hundred thousand ohms, but London Sound will not accept below two million ohms, to ensure an acceptably high level of safety. If requested, we can test to greater than twenty million ohms.


REMEMBER - our electrical safety checks only look at the condition that is evident at the time of testing; faults can appear later. Passing the electrical safety check does not confirm that the equipment works in any particular fashion, or at all, only that it is electrically safe at the time of testing.




For further information, please contact London Sound