Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[D Edgcumbe]

Thanks for the link Cailen

Frank, I'll look at the surgeX.  For adding circuits it will probably all be AC90 (BX), other than if an existing conduit gets used from existing panel.  That was also kind of where I was going with isolated ground - didn't know if having the ground bonded to everything was good thing.... although that means the equipment itself would need to be isolated from the building (for most part it would I guess). 

I also like your conduits and spare wires, just the way I think but have trouble convincing others (Im usually the one that has to solve NOT having it...)  Although it is a drop ceiling and accessible anyway, I would like to do something like a cable tray.  There happens to be cat5e run to everywhere (upwards of 100 - none of which were labelled) including over 20 in the area shown in my diagram, although not as much as I would like to see concentrated in the auditorium area.

Mike, Ive learned in my time I should never assume anything and start from scratch, although I haven't learned how to consistently remember that fact, thanks

[D Edgcumbe]

Steve, a reason it seemed natural to go on the heating was there is a "lighting" panel on it next to unused (I wasn't correct in saying unused), we're essentially relocating the one circuit still in use and "moving" (actually replacing with more circuits) the panel.  But you're right I need to double check that two, I think I remember seeing a neutral that looked new in the splitter.
Which also reminds me in all the runaround with the electrician, He's (intending) to have a stove added to a heating panel - and I don't think there's a neutral there - not sure how I missed catching that (at least forget to look), thanks.

Mike, yes the electrical ground is going to be "bonded" everywhere, it's all armoured or conduit, strapped or lying on metal (mostly) trusses, and yes steel studs, with standard receptacles.  I also think the conduit is used for the safety ground, I don't recall seeing any bond conductor in conduit...or even the old armoured now that I think.  Which as I say is why I wondered isolated receptacles?  Unfortunately I don't think I can pull off the everything from one panel...all the lighting and existing receptacles around the outside are on the existing panel (obviously) and can't add all the new to that, and switching everything over to the new (then undersized) panel won't fly.

[Stephen Swaffer]

Sight unseen, with your description, I would expect to not have a neutral in any of the heating panels-but I could very well be wrong.  It would be possible to run a 120 VAC circuit off a panel like that by running the neutral to the ground bar (actually the could be the same bar as a neutral in another panel of the same design-its use and connection determines whether it is a ground or neutral and would take some examination to discern.).  Possible but NOT correct-but this is also the kind of thing I would expect from someone that "knows how to wire."  I would not assume that lighting circuit is right.  Best to verify the neutral from the service on in-not by loads attached.  I feel like we are "piling on" with the neutral/grounding stuff-but as Mike teaches that is where a lot of headaches with AV start.  Better to address it at this stage then try to chase ground loops later.

If you run BX and want an isolated ground, you might ask your AHJ.  I was allowed to run 12-3 with ground a remark one of the phase conductors as an ISO ground.  You can buy the "right" stuff, but as it is not used as often it is pricey and hard to find-might save some $$ and headaches-just be extra diligent when marking and mark at every box.

[D Edgcumbe]

I don't expect to see a bond conductor in the heating either.
I can see what I'll be looking at next time...
And sounds like I should be looking at ISO ground somehow.

[Mike Sokol]

Mike, yes the electrical ground is going to be "bonded" everywhere, it's all armoured or conduit, strapped or lying on metal (mostly) trusses, and yes steel studs, with standard receptacles.  I also think the conduit is used for the safety ground, I don't recall seeing any bond conductor in conduit...or even the old armoured now that I think.  Which as I say is why I wondered isolated receptacles?  Unfortunately I don't think I can pull off the everything from one panel...all the lighting and existing receptacles around the outside are on the existing panel (obviously) and can't add all the new to that, and switching everything over to the new (then undersized) panel won't fly.

My general attitude is that if you can't get a properly isolated grounding system, then you need to isolate the ground loop current paths to prevent hum and buzz. One way to do this is by providing pin-1 lifts in appropriate XLR paths. Another way is to install audio isolation transformers in the XLR connections between things plugged into different outlets. For instance, if your mixing console is plugged into power in the back of the room, and you're driving a bunch of active Mackie floor wedges for monitors up on the stage, you'll find that they hum with only 100 mA of ground loop current, which equates to only about 1/10th of a volt ground loop differential potential. Whirlwind makes an ISO-8 transformer isolation box which I placed in the drive rack for my analog system. However, I've been using digital snakes for the last few years, and since the digital stage box is located on the stage and connected to the same outlets (grounds) as the active wedges, there's no ground loop differential voltage, and thus no ground loop current or induced hum.

In many of the churches I'm called in to troubleshoot hums, it's far cheaper to spend $500 on audio isolation transformers rather than spending $5,000 on rewiring the entire electrical system. I had one church last year that spent $15,000 on a technical ground subpanel, but then forgot to install isolated ground receptacles on the stage and mixing positions. Hum was everywhere...

[Stephen Swaffer]

Mike,  (for my own learning, too!)

Given the size of this building/auditorium my thought was just to put the AV circuits (as was suggested 2 stage, 2 FOH, 1 projector) on the best available panel, perhaps using ISO ground receptacles for all AV gear.  Existing lights/receptacles could be left as is-yes one would need to be careful to isolate all gear from building grounds and utilize only ISO receptacles.

Since we are already talking new dedicated circuits, running 5 new circuits of BX out of a panel should be reasonably cost effective?   

Would that not effectively eliminate ground loops?  Perhaps the biggest challenge might be the projector mount, since that need to be attached to structural steel?

[Scott Holtzman]

Mike,  (for my own learning, too!)

Given the size of this building/auditorium my thought was just to put the AV circuits (as was suggested 2 stage, 2 FOH, 1 projector) on the best available panel, perhaps using ISO ground receptacles for all AV gear.  Existing lights/receptacles could be left as is-yes one would need to be careful to isolate all gear from building grounds and utilize only ISO receptacles.

Since we are already talking new dedicated circuits, running 5 new circuits of BX out of a panel should be reasonably cost effective?   

Would that not effectively eliminate ground loops?  Perhaps the biggest challenge might be the projector mount, since that need to be attached to structural steel?

If you do go that route there is sleeved hardware just for that purpose.  It's most common application is in securing racks.  There are even isolated drop anchors for concrete.

[Mike Sokol]

Mike,  (for my own learning, too!)

Given the size of this building/auditorium my thought was just to put the AV circuits (as was suggested 2 stage, 2 FOH, 1 projector) on the best available panel, perhaps using ISO ground receptacles for all AV gear.  Existing lights/receptacles could be left as is-yes one would need to be careful to isolate all gear from building grounds and utilize only ISO receptacles.

Since we are already talking new dedicated circuits, running 5 new circuits of BX out of a panel should be reasonably cost effective?   

Would that not effectively eliminate ground loops?  Perhaps the biggest challenge might be the projector mount, since that need to be attached to structural steel?

Yes I think that's an affordable plan. However, all sound techs need to be aware that any sound and video gear must be plugged into the isolated "A-V" receptacles. Also, remember that to comply with code a double ground wire may need to be run. But that really depends on if metal J-Boxes are required or you can get by with plastic. If it's a plastic box, then the receptacle mounting ears are isolated from building steel and a single EGC can remain in isolation. However, most modern commercial buildings in the US require metal j-boxes that are bonded to metal studs in the wall. So an isolated receptacle with a single green wire acting as the EGC won't effectively ground the metal j-box itself, even if there's armored BX cable run to it. In fact, you can get insulators to isolate the j-box from the armored cable, effectively floating the j-box from your EGC.

In one recent Texas church I was in there was rigid conduit run to every box that served as the EGC, no green ground wire at all. That's allowed by code there, so they just needed to fish a new green/yellow tech-ground wire through the conduit, put in all iso-ground receptacles, and bond the new tech-ground wiring back to a common point on the ground bus in the sub panel. Voila, the system was then ground loop hum free. And it only cost a few hundred dollars for a spool of green/yellow-stripe wire and a dozen iso-ground receptacles. One of the church staff was a licensed electrician so he was able to confirm local code compliance and do the labor himself.  I think this is a reasonable way to rewire a building to be hum free, as long as someone will look closely at how the panels and boxes are bonded/grounded.

I had another hum situation where all sub-panels were bolted to building steel and all G-N bonding screws in every sub-panel had been installed. The local inspector claimed this would make a better ground (hah), but it contaminated all audio grounds terribly, and there was a ton of hum. After the church's journeyman electrician convinced the inspector to let him remove the bonding screws on all the sub-panels, the audio hum went away. Of course they argued with me for a month before they did it, but in the end it took perhaps an hour of labor to do what should have been done during install. Yes, the church was a new build less than 6 months old, and they had done this on purpose. Yikes...

[Steve M Smith]

I've seen tons of mid-century (that's what they call the 60's now) electrical boxes with common neutrals and grounds here in the states.

I don't think I have ever seen that here.  No one would even think about doing it.




Steve.

[Mike Sokol]

I don't think I have ever seen that here.  No one would even think about doing it.

Steve.

The USA has a lot of grandfathered electrical power. In fact, you'll find K&T (Knob & Tube) wiring in many pre-WWII buildings here. That's really dangerous since in lots of cases all the wiring was black, and they often switched the neutral wires for overhead lights and such. It's the wild west for electrical power in the states which is why we need to be so careful when running any new lines.

Also, while I see High-Leg Delta power pretty often in old industrial buildings here, I wonder if that ever even existed in GB. Can you clarify that, Steve?

For newbies here, check out http://en.wikipedia.org/wiki/High-leg_delta

[ProSoundWeb Community]