Weird electric shocks from iMac and studio gear

[Infensus]

So here's a weird one. I've been getting little electric shocks, both from my audio interface and from the metal shell of my desktop iMac. I just got a nasty zap just now when I went to switch my mac on, button at the back. I have my mac set up in a home music studio, audio interface is connected via USB, various instruments connected to audio interface - synth, piano etc. 

 

Whenever the audio interface is switched on AND an instrument, like my piano, is connected to it via MIDI the shell gives little  shocks. The iMac shell also gives off electric shocks, but only when the audio interface is switched on and connected to the USB port.

 

Is there some weird static build up going on here and any suggestions to mitigate it? I think it's a bit more than just carpet static

[KarathKasun]

Your studio does not have a proper earth ground.

 

Electrically Earth and neutral are tied together in the electrical distribution box where they both go to earth ground.  Some lazy people will take this to mean that you can just use neutral as a ground at the outlet, except this will allow a person or other equipment to become the shortest path to ground when power is applied.

 

Thankfully, the loop back to the distribution box has a lower resistance/impedance, you only get a tingle instead of a full force shock.  HOWEVER, if you happen to directly touch the case and something grounded, you can receive a fatal shock.

[Infensus]

17 minutes ago, KarathKasun said:

Your studio does not have a proper earth ground.

I imagined something like that would be happening, how do I go about resolving that?

[KarathKasun]

1 minute ago, Infensus said:

I imagined something like that would be happening, how do I go about resolving that?

I updated my post wit a bit more information.

 

For utmost safety, remember to de-energize any circuit you are inspecting and test for live wires before putting your hand near any bare contacts or bus bars.  If you have a service disconnect that is independent of the distribution panel, de-energize the whole distribution box.  If you can not de-energize your distribution box, seek the help of a licensed electrician.

 

First, make sure you have three conductor wires (bundle containing black and white plastic sheathed wires and a bare wire) and that the wiring in the socket is correct (earth ground to bare wire, live to black, neutral to white).  If you have three conductor wire and its correctly wired, check for a loose ground connection in the distribution box. Lastly, make sure you have a ground rod (outside building where power connects to building) has a good connection.  You can also try "watering" the ground rod if everything else seems correct.

[Infensus]

30 minutes ago, KarathKasun said:

I updated my post wit a bit more information.

 

For utmost safety, remember to de-energize any circuit you are inspecting and test for live wires before putting your hand near any bare contacts or bus bars.  If you have a service disconnect that is independent of the distribution panel, de-energize the whole distribution box.  If you can not de-energize your distribution box, seek the help of a licensed electrician.

 

First, make sure you have three conductor wires (bundle containing black and white plastic sheathed wires and a bare wire) and that the wiring in the socket is correct (earth ground to bare wire, live to black, neutral to white).  If you have three conductor wire and its correctly wired, check for a loose ground connection in the distribution box. Lastly, make sure you have a ground rod (outside building where power connects to building) has a good connection.  You can also try "watering" the ground rod if everything else seems correct.

So I live in the UK (three pronged plugs) brown live, earth yellow and green, and blue neutral. Got lost a bit there. Anyway yeah I can see from the setup I have that not everything has a path to earth, because the interface is powered by the mac USB, it doesn't have it's own power source and everything is sat on wooden tables, no path to earth (I know nothing about electronics can you tell?) I will try moving some things around, and hopefully not get more zapped in the process. I assumed it was a fault with the gear, not the room... I'll report back if I manage to fix it

[KarathKasun]

5 minutes ago, Infensus said:

So I live in the UK (three pronged plugs) brown live, earth yellow and green, and blue neutral. Got lost a bit there. Anyway yeah I can see from the setup I have that not everything has a path to earth, because the interface is powered by the mac USB, it doesn't have it's own power source and everything is sat on wooden tables, no path to earth (I know nothing about electronics can you tell?) I will try moving some things around, and hopefully not get more zapped in the process. I assumed it was a fault with the gear, not the room... I'll report back if I manage to fix it

Yeah, building codes are different in different countries.

 

The Mac will be the source of the problem then, or anything else connected to the cluster of wires that is also connected to the wall.  Thats the thing, case ground on pretty much every wire (USB, Audio, Video) traces back to earth ground when connecting anything to the wall.

[Infensus]

3 minutes ago, KarathKasun said:

Yeah, building codes are different in different countries.

 

The Mac will be the source of the problem then, or anything else connected to the cluster of wires that is also connected to the wall.  Thats the thing, case ground on pretty much every wire (USB, Audio, Video) traces back to earth ground when connecting anything to the wall.

I think I identified one of my several instruments connected to the interface as the source... my very old electric piano, perhaps unsurprising, disconnected that and now everything seems fine. Perhaps that was just causing a loop without route to ground... who knows, thanks for the help. There's so many wires in here it's hard to tell haha

[KarathKasun]

8 minutes ago, Infensus said:

I think I identified one of my several instruments connected to the interface as the source... my very old electric piano, perhaps unsurprising, disconnected that and now everything seems fine. Perhaps that was just causing a loop without route to ground... who knows, thanks for the help. There's so many wires in here it's hard to tell haha

You could manually ground that instrument to earth ground, and that would fix the issue (connect the ground of the audio/midi interface to earth ground).  Finding ground faults is a daunting task on any room sized installation of gear, patching them up can be even more of a pain.