ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2]  All   Go Down

Author Topic: Galvanic isolation of all three pins in XLR vs ground lift  (Read 1109 times)

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3228
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #10 on: August 28, 2018, 12:05:38 am »

sure... mike probably has pictures of melted stuff over in the power forum from rogue ground currents.

JR
Like this one?
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16115
  • Hickory, Mississippi, USA
    • Resotune
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #11 on: August 28, 2018, 09:29:00 am »

Like this one?
exactly...

I'm probably repeating myself but UL performs a ground bonding test on any external product connection labelled as ground, to carry something like 50A fault current with single digit voltage rise. That wire melting is obviously a failure, but that audio jack may not have been labelled "ground". The intent is to protect humans irrespective of where the fault occured, and trip the breaker.

JR   
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Pete Erskine

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1209
    • Best Audio
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #12 on: August 28, 2018, 09:46:08 am »

exactly...

I'm probably repeating myself but UL performs a ground bonding test on any external product connection labelled as ground, to carry something like 50A fault current with single digit voltage rise. That wire melting is obviously a failure, but that audio jack may not have been labelled "ground". The intent is to protect humans irrespective of where the fault occured, and trip the breaker.


50 mA
« Last Edit: August 28, 2018, 10:37:51 am by Pete Erskine »
Logged
Pete Erskine
917-750-1134
www.bestaudio.com
peter@bestaudio.com

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16115
  • Hickory, Mississippi, USA
    • Resotune
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #13 on: August 28, 2018, 10:04:39 am »

50 mA

??

Not sure what you are saying...

I had to redesign a PCB inside a small install mixer/amp product when the UL ground bond test completely evaporated a PCB trace off the circuit board. I had the option of relabelling the audio termination 0V instead of "ground", but did the right thing and passed the test with a new fatter ground trace on the PCB.

JR
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Pete Erskine

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1209
    • Best Audio
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #14 on: August 28, 2018, 10:39:14 am »

??

Not sure what you are saying...

I had to redesign a PCB inside a small install mixer/amp product when the UL ground bond test completely evaporated a PCB trace off the circuit board. I had the option of relabelling the audio termination 0V instead of "ground", but did the right thing and passed the test with a new fatter ground trace on the PCB.

JR

the UL standard is 50 mA not 50A for a dangerous current
Logged
Pete Erskine
917-750-1134
www.bestaudio.com
peter@bestaudio.com

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16115
  • Hickory, Mississippi, USA
    • Resotune
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #15 on: August 28, 2018, 11:22:01 am »

the UL standard is 50 mA not 50A for a dangerous current
50mA will not trip any fuse or circuit breaker I ever saw.

Ground bond test has to pass several tens of amps with low single digit voltage drop.

The first commercial ground bond tester I found on google provides 10A to 30A test current.

Quote from: ESTGUIDE.P65
Ground Bond
A ground bond test verifies integrity of the
ground path by applying a high current, low
voltage source to the ground path circuit,
typically a 25 or 30 A current.
This test is similar to the ground continuity
test with the additional benefit of verifying
how a product will perform under actual fault
conditions.
When a ground fault occurs, current starts
to flow through the ground circuit. If the
current-carrying capacity is high enough
and the circuit resistance low enough, the
system operates properly and the user is
protected from shock.
If, however, the ground circuit cannot carry
enough current or has too high an electrical
resistance, the circuit breaker may not trip
or the fuse may not blow. If this occurs,
voltage can build up to a point where current
will flow through the userís body instead
of the ground circuit.

I try not to be too pedantic but ground safety is important.

JR
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3228
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #16 on: August 28, 2018, 09:01:37 pm »

50mA will not trip any fuse or circuit breaker I ever saw.

Ground bond test has to pass several tens of amps with low single digit voltage drop.

The first commercial ground bond tester I found on google provides 10A to 30A test current.

I try not to be too pedantic but ground safety is important.

JR

I'm with JR on this one. Remember, this isn't continuous current, but it needs to be long enough in duration to trip a circuit breaker. That's the primary job of the EGC (Equipment Grounding Conductor). The NEC could care less about reducing hum in your sound system. They just don't want anything to have a elevated voltage due to a line-to-chassis short.
« Last Edit: August 28, 2018, 09:39:46 pm by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org
Pages: 1 [2]  All   Go Up
 


Page created in 0.071 seconds with 22 queries.