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[Gary Christenot]

1.  The AC service needs a back-box over the exposed terminals and connections (the boots are not sufficient by themselves), and this box must be of non-combustible material; next you cannot mix different *services* in the same box.  The AC PowerCons need to be on one plate/same back box and the audio on the other plate, which does not require a back box but I'd recommend a separate box anyway, for protection of the terminations.

2.  With a bigger back box, you can install a GFCI outlet and use a power strip (without surge protection) for the items in the cart.

3.  The metal plate with the now-colocated PowerCons (see #1) must be bonded to the Equipment Grounding Conductor.  If your back box is plastic, it will not/cannot be bonded.  If it's metal it must be bonded to the EGC.

4 & 5.  I've not used or handled any similar case that has the metal trim grounded separately.  If you use a metal back box it should not touch any other metal object; obviously not a problem for plastic boxes.  If you use a GFCI (#2) any fault with a device plugged into the power strip should trip the GFCI and de-energize the entire assembly.  Also from the picture it looks like the rack rails and equipment do not touch the trim, so a failure that would energize the rails prior to the GFCI trip would not energize the case trim.

Thanks Tim.  Excellent inputs.  I just got in from a 10 hour drive from Orlando and am a little wiped.  But wanted to acknowledge your insights and beg your indulgence to come back tomorrow with a couple of follow-up questions.

[Gary Christenot]

One rule of thumb I always try to adhere to is to separate high voltage and low voltage in separate enclosures -so if my eyes are seeing the picture properly I wouldn't put XLR's in the same dish as power.

When I was building cases I ended up by installing a foot-square (or bigger) flush door/hatch in the side or back of the case that when you opened revealed all of your connections on a recessed panel inside.  In that panel I would mount old-work metal boxes for the high voltage stuff which either would internally be connected to surface boxes with raised cover mounted receptacles using emt, m-c, or chase nipples.  All the low-voltage stuff would just be banded looms with exposed connections to XLR's speakons or whatever. 

I ended up going this route because inspectors like seeing things they know -and properly installed nema generic parts always yielded the best responses compared to the arguments we would get with "mysterious" stuff like powercons mounted on stamped jack dishes and soldered to looms behind.  (I still shy-away from powercons due to past experiences with that (-and the electrician in me still likes my Hubbell twistlocks!)

There would be no specific grounding of the case metal trim as most of my cases were of the plywood type with either rat-fur or case-over type shock racks

There is a hatch door in the back so access is no problem.  Unfortunately the case design on this build is already locked in for the Neutrik D-ring form factor so Powercon it is.  He's thinking through some potential mods for a future build and will discuss with him.

Thanks!

Gary

[Gary Christenot]

1.  The AC service needs a back-box over the exposed terminals and connections (the boots are not sufficient by themselves), and this box must be of non-combustible material; next you cannot mix different *services* in the same box.  The AC PowerCons need to be on one plate/same back box and the audio on the other plate, which does not require a back box but I'd recommend a separate box anyway, for protection of the terminations.

2.  With a bigger back box, you can install a GFCI outlet and use a power strip (without surge protection) for the items in the cart.

3.  The metal plate with the now-colocated PowerCons (see #1) must be bonded to the Equipment Grounding Conductor.  If your back box is plastic, it will not/cannot be bonded.  If it's metal it must be bonded to the EGC.

4 & 5.  I've not used or handled any similar case that has the metal trim grounded separately.  If you use a metal back box it should not touch any other metal object; obviously not a problem for plastic boxes.  If you use a GFCI (#2) any fault with a device plugged into the power strip should trip the GFCI and de-energize the entire assembly.  Also from the picture it looks like the rack rails and equipment do not touch the trim, so a failure that would energize the rails prior to the GFCI trip would not energize the case trim.

Once again thanks for you insights Tim. 

At this point I'm not sure how a metal or plastic back box can be integrated in to the unit. See the photo for what the back of each pass through plate looks like.  We'll of course be taking the XLR out and putting the other Powercon in to that position.  The case sides are 3/8" plywood so there's not much to screw in to there for any kind of surface mount application.  Also having trouble seeing how anything bought off the shelf - which it have to be at this point - doesn't leave some of the wood of the side panel exposed inside the box.  It gets even a little dicier on the other end of the cabinet because the interior of that side is completely lined with foam over the plywood.

I've been thinking about some kind of surface mount box like the one shown in the attached photo.  Create a cutout in the back of it to match the plate shape and size, 4 small holes to accommodate the rivets, and then surface mount to the side wall over the plate.  Work inside the box could be accomplished by removing the cover.  To mount would ould probably have to go all the way through the wall with a nut and bolt rather than just screw to the interior of the wall due to the wall thinness.  Then wire out through knockouts to a separately mounted box with the GFCI per your suggestion.  The bottom of the case is standing on a 3/4" plywood deck so I could mount a separate single gang box for the GFCI to the floor of the interior.

I guess as a last resort we could always make completely new cutouts somewhere in the case sides for some old work plastic boxes just for the power in and out but I sure would hate to start cutting in to this thing.  It would really damage the aesthetics.  I know in the end that is a secondary consideration but still something to be thought of. 

Any other suggestions?

The right hand rack rail passes right over the back side of the latches that secure the front cover, with hardly a hair's breadth of clearance.  Too close for comfort.  I've checked with a meter and verified that all of the case edge trim and latches are electrically continuous around the entire perimeter - i.e. if I probe a steel corner on the left side of the case and a corner or latch on the right side of the case, I get a 0 ohm reading.  Likewise going around and checking multiple points around the case.  The edge rails themselves must be coated with something non-conductive because if I just probe 2 places on a rail I get no continuity.  But if I probe 2 items riveted to any of the rails - 2 corners, a corner and a latch, etc, then I get a 0 ohm reading.  So everything appears to be tying together via the rivets and body material of the trim.  So given the proximity of the rack rail to the latches, it would seem prudent to tie the case frame to ground as well.  You're thoughts?

I'm still somewhat stuck on how to hook up the outgoing power for the speakers.  We need to get AC from the rack mount power supply to the power out Powercon.  I'm thinking to come directly out of whatever back box arrangement we devise with 12/3 SOOW cable, fitted with a male 3-prong plug, and plug plugged directly in to the power supply.  Again any thoughts or suggestions are appreciated.

So if the Powercons and the back of the plate they are in are buried in a plastic box, you don't see any need to tie any of the other stuff outside the plastic box (the case frame excluded) to ground - like the plate hosting the audio/XLR jacks, the carrying handles, etc?  Yes, seems like an infinitesimally small chance that any of those could get energized but considering it will be high school kids rolling this thing around and using it, seems like an abundance of caution might be in order.  Would there be any harm in doing so?

Thanks for letting me bend your ear.

Gary

[Geoff Doane]

At this point I'm not sure how a metal or plastic back box can be integrated in to the unit. See the photo for what the back of each pass through plate looks like.  We'll of course be taking the XLR out and putting the other Powercon in to that position.

I think you're on the right track with both inlet and outlet Powercons on the same panel.  For a backbox, one of these should do the trick (Iberville part no. BC1110R).  Stack two if you need more depth, and put a blank cover plate on it once it's wired.  You could simply wire some short tails of SO and caps/connectors to interface with the rack mount power supply.  Use the proper clamps in the extension box and you should be fine.

I'm not sure if that image will show up, so here's a link:

http://www.tnb.ca/en/web-catalogue/?co=CA&lang=en&a=nav&N=4372+4374&Ntt=

GTD

[Lyle Williams]

If you are just looking for an extra bit of safety assurance, power the rack through a GFCI/RCD.

[Stephen Kirby]

If you are using some sort of 1U rack power strip, why not put the PowerCons into that?  That's what the "Poor Man's Distro" in my amp rack is made from.  I got a power strip from a place that sells computer surplus parts that didn't have any other nonsense in it like filters or surge suppressors (although you could take a simple Juice Goose or Rack Rider strip to do this).  It was fairly cheap and already had 20A Edisons on the back.  I punched holes in the front to mount several PowerCons and wired it up inside.  The object is if anything goes wrong, any sparks or burning insulation is contained in the non-flammable metal box. 
In my case I have the Edison outlets on the back divided into 3 separate circuits with a PowerCon in and 2 outs for each on the front and two Edison on the back.  Everything is bonded together internally making up the "Poor Man's Distro".  The DSP and sub amp are on one circuit so when I'm using my regular distro, I can just run one PowerCon cable to it.  I also have a couple of short jumpers to daisy chain circuits together in cases where I don't have multiple services but want to use my stage stringers which have PowerCon for use with the regular distro.

Then make up a separate I/O panel for the XLRs to feed signal in and out.  In my case of powered tops and passive subs, I have the XLRs and SpeakOns for the subs along with the XLR in to the DSP and XLR out for the tops on one panel.

[Eric Vogel]

2.  How to make the transition from the Powercon connectors to a useable physical interface for the rack mounted power supply and speaker out power?  Wire to a receptical in a box?  Pigtail to a 3-prong plug?  With of course female fixtures for incoming power and male for outgoing.

Buy one of these (see link below) and mount in place of the blue powercon inlet.  Remove the inlet (blue) and mount thru box on rear of dish connector plate... reassemble with the inlet mounted on front of plate - you now have a back box that is finger proof with no way of accidently pulling the faston tabs loose.  Whack the 15amp edison male off of your rack PDU and replace with a grey cable mount powercon.

Do the reverse for the power out panels, and build some short 15 amp edison to blue power cables to plug from your PDU to the power out panels.

If you can, using crimp ring terminals, tie your PDU chassis to the dish plates via connector screws.


http://www.neutrik.us/en-us/accessories/nac3mm-1

[Gary Christenot]

Buy one of these (see link below) and mount in place of the blue powercon inlet.  Remove the inlet (blue) and mount thru box on rear of dish connector plate... reassemble with the inlet mounted on front of plate - you now have a back box that is finger proof with no way of accidently pulling the faston tabs loose.  Whack the 15amp edison male off of your rack PDU and replace with a grey cable mount powercon.

Do the reverse for the power out panels, and build some short 15 amp edison to blue power cables to plug from your PDU to the power out panels.

If you can, using crimp ring terminals, tie your PDU chassis to the dish plates via connector screws.


http://www.neutrik.us/en-us/accessories/nac3mm-1

Excellent!  Thanks so much.  I'm assuming when I disassemble that I will find the wiring between the blue and grey end to be removable so I can thread it all back through the hole and reconnect the wires?

The only change I would consider to that approach is altering the cord on the power supply.  It is county school board equipment and we don't want to be responsible for any modifications.  I'll look at creating a pig tale with a Powercon plug on one end and a female edison on the other.  Do the reverse for the outgoing direction.

Also don't think its possible to tie on to the power supply chasis for ground.  What I'm thinking about doing is putting a receptical box after the Powercon inbound connectors with a GFCI outlet.  Power supply plugs in to that and I'll ground the case elements there as well.

[Gary Christenot]

If you are using some sort of 1U rack power strip, why not put the PowerCons into that?  That's what the "Poor Man's Distro" in my amp rack is made from.  I got a power strip from a place that sells computer surplus parts that didn't have any other nonsense in it like filters or surge suppressors (although you could take a simple Juice Goose or Rack Rider strip to do this).  It was fairly cheap and already had 20A Edisons on the back.  I punched holes in the front to mount several PowerCons and wired it up inside.  The object is if anything goes wrong, any sparks or burning insulation is contained in the non-flammable metal box. 
In my case I have the Edison outlets on the back divided into 3 separate circuits with a PowerCon in and 2 outs for each on the front and two Edison on the back.  Everything is bonded together internally making up the "Poor Man's Distro".  The DSP and sub amp are on one circuit so when I'm using my regular distro, I can just run one PowerCon cable to it.  I also have a couple of short jumpers to daisy chain circuits together in cases where I don't have multiple services but want to use my stage stringers which have PowerCon for use with the regular distro.

Then make up a separate I/O panel for the XLRs to feed signal in and out.  In my case of powered tops and passive subs, I have the XLRs and SpeakOns for the subs along with the XLR in to the DSP and XLR out for the tops on one panel.

Thanks Stephen but that is way over board for what we can do.  First the equipment is school board property so no way could we legitimately open it up and start making mods.  It needs to stay in off-the-shelf condition.  But even if we wanted to, it's a fairly sophisticated power unit with several front panel controls and displays so doing what suggest wouldn't be possible anyway.

Regards,

Gary

[Stephen Kirby]

The Powercon connector is rated at 20 amps.  However the rack mounted power supply is only rated at 15 amps.  According to the specs, power consumption on the speakers is 2 amps each and there are 3 of them - 2 speakers plus a sub woofer.  They QSC K12 speakers and QSC Ksub woofer.  So a total of 6 amps for the speakers.  Not much else in the system of consequence.  The mixer is a Behlinger - 60 watts consumption I think.  The fans are negligible.  The keyboard is powered off USB from the laptop so not much draw there.  I expect the small monitor speaker facing the player is also low consumption.

Gary

I was recommending using a simple low end rack mount power strip.  If you look around here you'll find that fancy "power supplies" aren't in great favor.  They rarely add anything of value and often create more problems when the "surge suppressors" go bad.  But if you're not comfortable with messing around with the wiring inside a $50 box, or messing around with AC wiring in any event, then I would definitely stick with complete off the shelf solutions.  AC is not something to mess with if you aren't sure.

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