Years ago I touched a guitar that was plugged into an amp against a radiator, and it blew the amp and melted the guitar string. DC ground loops I used to have my phone plugged into USB power via cigaratte lighter adapter in my car to charge — not always, no problem when not plugged in , plus the phone connected via 3. Understanding them will doubtless save you money and hassle. The actual cause may even be a poor connection to ground i.
You are likely to touch your scope during operation and unless it is fully insulated and all external bits isolated you have a potentially leathal piece of test gear. Read about twisted pair, and understand why it exists https: You do have an earth leakage switch on the gear under test right? This can be heard, usually as a low-level hum or buzz.
The focus is on audio, but I think it extrapolates. If the scope is plugged in and referenced to the same earth ground as the primary side of the circuit under test, should that not be the reference to connect the scope ground clip?
For safety any phase imbalance is returned via the multiple earth neutral.
This does break the loop, obviously, so any related hum will disappear. Imagine for example someone kicks the power cord of your equipment off the wall.
With a multimeter. The motors run on a wall wart no third prong. Not sure why installation guides everywhere say otherwise. If the two bits of equipment are plugged into the same mains socket, their chassis safety earths are effectively tied together at the same potential, and so there is unlikely to be any circulating ground current, despite the apparent ground loop.
Perhaps he was being a bit satirical as in practice the realities are very different. Ideally, the solution is to make sure that everything is earthed at one central point, so that everything shares the same common earth reference point. Makes it much more difficult to touch a circuit and your scope at the same time. Unfortunately, the metal was painted, and each ground pin either poorly connected, or not at all.
Move plugs around so that they are plugged into the same outlet, making your loop as small as possible. This site uses Akismet to reduce spam. I see lots of stuff about proper neutral bonding, but nothing stating it is illegal. Inside the equipment, the audio screen earth is often linked directly to the chassis earth, hence the possibility of a loop.
Technical Editor Hugh Robjohns replies: Safety is the 1 reason. Ground and hot were on the top of the cable.