Don't you love to see unexpected sparks between chassis and USB B plug? - Page 1
Forum section: electronics / general

author: Zucca
author_rank: Unknown
timestamp: February 13, 2019, 11:03:02 pm
content: I was moving some USB cables behind my Marantz PM-80mkII, noticed I had light muscle contractions on my arm when touching the amply chassis.Guess what, it sparks...The Fluke 87V says156 VAC!

author: amyk
author_rank: Super Contributor
timestamp: February 14, 2019, 02:07:54 am
content: Y capacitors in power supply... how much current can you draw? If it's below the safe limit (300uA comes to mind, although I'm not completely sure --- check IEC 60950 for details) there shouldn't be a problem, although it can be a little surprising.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 14, 2019, 05:48:47 pm
content: Yep, It's because of the filter capacitors in the power supply.The solution is to put the plug of your PC in a properly grounded socket.I once spent half a day putting the extra Earth wire in the wall because I do not like tingling fingers and my Oscilloscope & low voltage electronics stuff doesn't like that either.After that I still had similar problems with a 10m audio cable between my PC and my stereo.The stereo may be on another phase, but it does'n have a GND connection, I found it a bit weird.But because there already was the audio cable, I just ran an extension cord from the same socket as my PC to my stereo set.Also:Some electricians Multimeters have a low impedance mode to prevent these "ghost" voltages from appearing on the display.High Impedance DMM's can also give false readings because of capacitive couplings between wires in the same cable, especially when one of the wires is not connected at all.

author: Zucca
author_rank: Unknown
timestamp: February 15, 2019, 08:42:38 am
content: Quote from: Doctorandus_P on February 14, 2019, 05:48:47 pmIt's an old apartment, I don't know if it has a proper PE. will check.

author: Gary350z
author_rank: Regular Contributor
timestamp: February 15, 2019, 01:45:10 pm
content: Quote from: zucca on February 13, 2019, 11:03:02 pmI had this same problem with an old stereo receiver (about 1970). I opened it up and found a ceramic disc capacitor connected from the live mains wire to the chassis. This caused the chassis to be at 110 VAC through whatever the impedance of the capacitor was, resulting in sparks and mild shocks from the chassis to ground. The receiver came from the factory like this. I don't understand the reason for this capacitor.Nice pictures of the sparks! How did you take these pictures? Record a video and then capture the frame with the spark?

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 15, 2019, 02:34:18 pm
content: Quote from: zucca on February 15, 2019, 08:42:38 amGet a surge protector with coax protection and connect it to the cable TV outlet.

author: Zucca
author_rank: Unknown
timestamp: March 17, 2019, 11:09:53 am
content: Ok, time to investigate more....I think I found the reason for that.My old german flat is connected to the main grid by 4 wires:1.Blue2.Brown3.Black4.Yellow/Greenif I measure them I got 1-2-3 are the three 380VAC phases and the 4 is the neutral. So for example 1-2=V380VAC and 1-4 is 220VAC.So it turns out that I no have a proper PE at all.The apartment neutral and the apartment PE are connected together to the cable 4.Quote from: NiHaoMike on February 15, 2019, 02:34:18 pmSo basically taking the PE from the coax TX outlet? I don't have an antenna on the roof (TV cable is coming from the ground), so I don´t know if it´s a proper solution.My ideaconnecting something like this:and then connecting the apartment PE to the plumbing metal pipes. Of course separate/disconnet the cable 4 from the apartment PE.What would you do?Quote from: Gary350z on February 15, 2019, 01:45:10 pmSort of, I was taking a continuous shot with the phone and then I sorted them out.PS: Am I the only one who gets nervous when a yellow/green cable it connected to the neutral connection?

author: Gyro
author_rank: Super Contributor
timestamp: March 17, 2019, 11:21:36 am
content: https://en.wikipedia.org/wiki/Earthing_system

author: Zucca
author_rank: Unknown
timestamp: March 17, 2019, 11:24:41 am
content: Thanks, now I know I have a TN-C-S earthing system.

author: WildMOSFET
author_rank: Contributor
timestamp: March 17, 2019, 11:41:18 am
content: I thought the same thing.The sparks are given by the emi filter capacitors, without earth connection.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: March 17, 2019, 12:36:14 pm
content: Quote from: zucca on February 15, 2019, 08:42:38 amConnecting the chassis of the PC and the Amplifier, in fact everything together with a ground strap would also help.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 17, 2019, 01:34:04 pm
content: Quote from: zucca on March 17, 2019, 11:09:53 amThat's exactly what you're trying to do.

author: magic
author_rank: Super Contributor
timestamp: March 17, 2019, 02:37:31 pm
content: There is no reason to mess with your mains installation.Your problem is that the ground of one device is connected to Earth while the other device injects some tiny charge from mains into its ground. The charge jumps from one device's ground to the other and then to Earth.Identify which device lacks Earth connection and why. If something is wrong with it or its individual mains outlet, fix it. If the device doesn't have PE on its mains plug at all, leave it alone or earth it by other means. Beware that the latter may sometimes cause hum in audio gear.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 17, 2019, 08:44:56 pm
content: I've often read here and elswhere people blaming this on the Y capacitors in the mains filter.In a normal usage case, if there are Y capacitors there is an earth pin on the plug and if the household electrics are up to standard you should get near to no stray voltage.Most power supplies with an earthed plug will have the secondary side linked to earth at one point.The problem is the parasitic capacitance between transformer's primary and secondary windings and the capacitor added across these windings to minimise ringing.As an example C301 here: