Earth pin missing

Probably done in a misguided attempt to remove "hum" aka an earth loop.


However, removing the mains earth is NEVER the correct way out of this problem. 


The correct way is:


    a). Use equipment which uses a 'balanced line' for the interconnections or


   b). Use audio isolation transformers to break the loop.


Whoever did this is either an amateur who does not understand what he is doing, or, if doing it for a living, is clearly NOT a professional!


I've had to solve this & similar issues in a live & time pressured environment - this is not the way to sort this issue, even in an "oh ***" moment

seconded, but note that on double insulated kit the earth pin is only there as a location feature, indeed it is sometimes plastic, so it may not matter. However, it is a very bad idea. If you need to have an earth free supply sockets fed by isolation transformer is a better way, but normally just looking a the layout of the mains wiring and the screens on audio cables allows you to see where the one turn transformer is, and to re-lay it to have zero area, these days mains frequency hum is as likley to be an RF pick up problem from and SPMPS or dimmer bank generating fast edged pules at a high frequency that is modulated at 50 or 100 Hz. In whcih case proper filtering is the solution.

Looks to me as though these where plastic earth pins.

Possibly accidently broken of.

Possibly deliberately removed in a misguided effort to remove mains hum.

Whilst a missing PLASTIC earth pin is obviously not directly electrically dangerous, I would still be inclined to condemn such items in  a work place, they wont fit the common types of 13 amp socket outlet that relies on the earth pin to open the shutters. Increases the risk of dangerous bodges or improvisations to fit the damaged plug in to a standard outlet.

How likely is it the earth pin actually provided an earth connection?


Would it have provided any function other than opening the shutters for the live and neutral pins?


Andy b.

This afternoon I found myself peering at a Polish travel adapter being used to plug a kettle into a UK 13-amp socket built into a cooker switch, probably beyond the scope of a landlords EICR.

Hum loops can be an audio problem. It is similar to diverted neutral currents in PME systems, and can be very difficult to deal with under certain circumstances. However, the problem here is that the PAT testing is again not being carried out correctly. The (portable?) equipment is not each item making up the system, but the system as a whole. It has been assembled from often a very large number of items, and if these are all disconnected by an unskilled person, they are unlikely to reassemble the whole correctly and this is often very expensive to correct. Usually, such systems are assembled in metal cabinets or racks, and that is the earth reference to test, not some random radio mic (usually class 2) or similar. The whole system will have a single supply source, and that is the point to test Earth continuity, insulation etc. A single reference in the record for the whole system as being satisfactory, and a single sticker if you wish is the result. I have had to deal with this kind of mess too many times, why anyone thinks that one piece can fail and the whole system can then pass is completely beyond me, but them PAT is the lowest level electrical job available, although it should not be as the inspection is the important part, not some magic "automatic" result from a machine.


Earth continuity of such equipment may not be via the mains socket, but it is there all the same as anything else will be heard as a very loud hum immediately. The equipment does not need an isolating transformer, numerous audio transformers or to be designed as entirely balanced. Such suggestions are the result of completely inadequate knowledge of this imagined problem. A missing plastic pin just makes it impossible to plug into a BS1363 socket. It is NOT an electrical failure, and the PSU has actually failed "safe", hasn't it? Just to make it clear too, balanced systems can still have earth loop difficulties, the common-mode rejection of balanced systems is not infinite, and any hum at all above the inherent noise level should be completely unacceptable.

"A missing plastic pin just makes it impossible to plug into a BS1363 socket."


Not if the sawn off pin is left in the socket ?