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[Nitin Sidhu]

Hello!

GLD112 + Stage Racks.

Gig in an auditorium. We setup sound for live performances outside of the glass window control room. Control room has Projector and video, so video crew sets up there. The video crew give us Laptop audio out (via laptop audio out). Laptop VGA out is connected to a video switcher, video switcher is connected to high power (I think 10/13Kl) projectors.

We are sourcing power from a single phase house receptacle available back stage feeding our amps/foh. We are well measured and all is in order. We are seeing a higher voltage of 245v, but assured will be down as soon as the AC kicks in.
Control room has an Online 3ph UPS supplying power to all gear in Control Room. This is not measured.

As soon as we plug the laptop EP cable to our local inputs on the console, our RCBO trips. Console is also on a UPS, so remains powered. Console then no longer outputs any audio, anywhere, local or to stage rack. Nothing on headphones but a buzz either. A&H local tech tells me we have fried a 15v rail (if that is correct terminology) . We have a Qu as backup and up and running without much fuss. No tie in to control room now.

Inspection then reveals that all power stringers used by the video crew (Suppose only for laptop and switcher) were 2 core power cables, so no ground. Live and Neutral on the same were reversed. And my crew connected to an alien audio source without galvanic isolation. Additionally, the laptops sound has also stopped working. Almost as though the soundcard chip on the mb is fried.

I am not educated in the field. And only try my best to follow good practices. So I am seeking advice on how to prevent such scenarios. This is not the first time I have seen consoles go down as soon as they are tied into any feed coming from the Video vendors.

Thank you all for your time.
Sidhu

[Tim McCulloch]

Hello!

GLD112 + Stage Racks.

Gig in an auditorium. We setup sound for live performances outside of the glass window control room. Control room has Projector and video, so video crew sets up there. The video crew give us Laptop audio out (via laptop audio out). Laptop VGA out is connected to a video switcher, video switcher is connected to high power (I think 10/13Kl) projectors.

We are sourcing power from a single phase house receptacle available back stage feeding our amps/foh. We are well measured and all is in order. We are seeing a higher voltage of 245v, but assured will be down as soon as the AC kicks in.
Control room has an Online 3ph UPS supplying power to all gear in Control Room. This is not measured.

As soon as we plug the laptop EP cable to our local inputs on the console, our RCBO trips. Console is also on a UPS, so remains powered. Console then no longer outputs any audio, anywhere, local or to stage rack. Nothing on headphones but a buzz either. A&H local tech tells me we have fried a 15v rail (if that is correct terminology) . We have a Qu as backup and up and running without much fuss. No tie in to control room now.

Inspection then reveals that all power stringers used by the video crew (Suppose only for laptop and switcher) were 2 core power cables, so no ground. Live and Neutral on the same were reversed. And my crew connected to an alien audio source without galvanic isolation. Additionally, the laptops sound has also stopped working. Almost as though the soundcard chip on the mb is fried.

I am not educated in the field. And only try my best to follow good practices. So I am seeking advice on how to prevent such scenarios. This is not the first time I have seen consoles go down as soon as they are tied into any feed coming from the Video vendors.

Thank you all for your time.
Sidhu

Galvanic isolation is your only protection from this level of silliness.

Transformer isolation from and to *anything and everything* that you do not have 100% control over.  We learned this from Clair - as a matter of corporate policy and field practice they supply iso transformers for any input or output connection that is not part of their touring package.

As a point of clarification, the *console* didn't go down because of this connection, the mains AC was interrupted by the RCBO/RCPD/GFCI device.  Presuming your gear and electrical stuff is 100% correct, these interruption devices did the job they were supposed to do - prevent a hot chassis.  You should beat the offending video suppliers and burn their cables.  This is the kind of shit that kills people and you should note that I didn't use a "smiley" emoticon.  I'm very serious.

I realize India is very much a 'whatever works, works' place and that if you take a moral high road you may forfeit some work.  Use the transformers on all 'outside' audio sources and destinations and don't look back.  Demand that your crew fully understand WHY you're requiring this - it's not just to prevent nuisance AC interruption, it's to prevent injury to death to your crew, client or client's presenters/bands/employees.

[Nitin Sidhu]

Thank you Tim!

I take electrical safety very very seriously. Hence wee have RCBO's across all our distros, do not work if we do not get proper ground. Refuse to plug in gear which comes with Suko type plugs (which is not the indian D-type, so no ground) etc. Fortunately, crew is also trained to understand and have standing orders not to compromise.

While I was upset with them for plugging in the laptop without using the available DBT, I can understand why they thought it was a non issue, they were not aware of the video in the loop, and even if they were, they probably would've overlooked it. One lives and learns.

You say the console did not go down because of the connection. Why would it be damaged then ? I understand the RCBO did its job, which is satisfying. But my impression is that the audio cable coming from the laptop was Hot. Hence.

Thank you again.
Sidhu

[Tim McCulloch]

Thank you Tim!

I take electrical safety very very seriously. Hence wee have RCBO's across all our distros, do not work if we do not get proper ground. Refuse to plug in gear which comes with Suko type plugs (which is not the indian D-type, so no ground) etc. Fortunately, crew is also trained to understand and have standing orders not to compromise.

While I was upset with them for plugging in the laptop without using the available DBT, I can understand why they thought it was a non issue, they were not aware of the video in the loop, and even if they were, they probably would've overlooked it. One lives and learns.

You say the console did not go down because of the connection. Why would it be damaged then ? I understand the RCBO did its job, which is satisfying. But my impression is that the audio cable coming from the laptop was Hot. Hence.

Thank you again.
Sidhu

Sorry, Sidhu, I somehow overlooked the blown 15v rail part of your report.  I have a pretty good guess as to the electrical failure mode but I think Mike Sokol will have a much better explanation of it...

[Ed Hall]

Galvanic isolation is your only protection from this level of silliness.

Transformer isolation from and to *anything and everything* that you do not have 100% control over.  We learned this from Clair - as a matter of corporate policy and field practice they supply iso transformers for any input or output connection that is not part of their touring package.

Tim,

Would a Radial ProAV2 provide the isolation you're talking about here?  I always use this or similar passive whenever someone connects to my system. I just want to make sure I'm getting the protection I think I am.

Ed

[Keith Broughton]

Tim,

Would a Radial ProAV2 provide the isolation you're talking about here?  I always use this or similar passive whenever someone connects to my system. I just want to make sure I'm getting the protection I think I am.

Ed

Yes.
They have transformers on the outputs and you get complete isolation with the ground switch in the lift or off position.

[Ed Hall]

Yes.
They have transformers on the outputs and you get complete isolation with the ground switch in the lift or off position.

Thanks Keith.  BTW It was nice to meet and chat with you the other day.

[Mike Sokol]

Sorry, Sidhu, I somehow overlooked the blown 15v rail part of your report.  I have a pretty good guess as to the electrical failure mode but I think Mike Sokol will have a much better explanation of it...

I find that it often helps to sketch out all the connection paths including audio, video, line, neutral and grounds. Then you can more easily trace the potential current paths and predict possible failure modes. Sidhu, can you draw up a simple diagram of how this was all hooked up? Doesn't have to be fancy, it could just be a picture of a pencil drawing on paper. That would allow a more educational discussion by everyone on the forum. This is a really important topic that we should pursue. In fact I was doing a banquet production last night when this thread popped up, and I had a discussion about audio transformer isolation with one of my A-V techs. We were able to trace out all the copper paths of the gear around us, and note potential failure modes if this A-V system spanned to a secondary room or even another building. Many of our church gigs request audio sends to overflow rooms that can be in a different building on a separate service panel. That's when it gets really dangerous. 

[Nitin Sidhu]

I have a pretty good guess as to the electrical failure mode but I think Mike Sokol will have a much better explanation of it...

thank you Tim!
I await Mike's revert and i do hope he stumbles in here, I have learnt so much from his generous advise! But do take the time to share your impressions.

Also, what sort of isolation would you be using in the shop ? We use the DBT+ http://www.laaudio.co.uk/product_dbt_1339.aspx by LA Audio.

Thank you
Sidhu

[Nitin Sidhu]

I find that it often helps to sketch out all the connection paths including audio, video, line, neutral and grounds. Then you can more easily trace the potential current paths and predict possible failure modes. Sidhu, can you draw up a simple diagram of how this was all hooked up? Doesn't have to be fancy, it could just be a picture of a pencil drawing on paper. That would allow a more educational discussion by everyone on the forum. This is a really important topic that we should pursue.

Mike, Thank you for dropping by! I wish I had the width to do a thorough inspection myself, but I was a bit tied up firefighting the situation, and asked my crew to measure all coming in from the Control room. Im on the road now, but I will ASAP speak to as many ppl possible and get you your drawing.

Thank you again!
Sidhu

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