Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > AC Power and Grounding

Venue with NEMA 10-50R side stage

<< < (3/6) > >>

Erik Jerde:

--- Quote from: Douglas Cyr on January 10, 2022, 07:46:18 AM ---
Interesting, and is there such a thing as +phase and - phase? Does it matter which phase goes to which terminal and is there a way to test that with a multimeter?

Also in this image:

What is going on what that ground wire running to the receptacle? What would that be connected to?

--- End quote ---

I haven’t seen phases labeled +/-.  I’d avoid that because of the connotations to DC power.  Usually in my experience it’s legs 1-3 or by color. 

For wiring on a system with equal phases (no wild leg etc) it doesn’t matter which leg hits which line terminal on your wiring device.  The point is the voltage differential created between the two legs and/or between line and neutral.

Stephen Swaffer:

--- Quote from: Tim McCulloch on January 10, 2022, 01:49:58 AM ---
Second, Douglas, your question of a separate ground shows you payed attention to what each wire does.  Code says all wiring must be enclosed so Code says no.  I have seen what you are asking, done in locales where permitting and inspections are lax.  That should not be considered an endorsement, but an observation.

--- End quote ---

Actually, 250.138 Requires cord and plug equipment to have it's frame mounted by one of two paragraphs-the second paragraph (B) says By means of a separate flexible wire or strapBy means of a separate flexible wire or strap, insulated or bare, connected to an equipment grounding conductor and protected as well as practicable against physical damage where part of the equipment..

In existing locations, generally ground wires are allowed to be run to any exposed point on the grounding electrode system without regard to running with the the conductors.  Of course, local jurisdictions might be more strict.

The best method (and by far the safest)-especially given the close proximity of the panel indicating an easy solution would be to update to a grounding receptacle.  If there is objection because of other users, code would allow adding a second grounding receptacle in parallel.  I'd have to think about whether or not I as an electrician would want to touch that "upgrade" though and enable others to continue unsafe practices.

This is getting good.  One of the reason's I replied, to get tagged to the thread.  Having residential and light commercial electrical experience and stage experience I'm not sure I fully understand all that's been discussed thus far.

Scott, not picking at your post.  Where does one find H-N-G (Hot Neutral Ground) with 240VAC potential?  That would almost have to be a 480V system.

COMMENT:  Any of today's amplifiers with multi-voltage capability i.e. 125V-250V should not require a neutral.

That being stated, it appears the manufacturers are left in a quandry.  The multi-voltage connectors I'm familiar with are all 4-wire L1 L2 Neutral Ground.

As Scott pointed out on the Powersoft amp the input connector for the AC line calls for a neutral.

I have Crown's with 20A 125V pigtails for power that can run on 240.  Haven't wired the racks yet, but will wire 'em up for 240V operation to get full power from multiple amps and keep wire gauge down.

So, what NEC do we violate to power up an amp with 208/240V?

For the OP Doug, what Tim said:  "Finally, if none of your equipment requires 240V to operate the whole 208V from 3 phase is kind of a moot issue, other than being aware of it.  The primary issue here is the connector and wiring lacks the equipment safety ground.  It should be changed to a NEMA 5-50.  The venue and other users will resist because they have "Kludge Kords" built and changing all that is where the expenses really are."

Jonathan Johnson:
The electrical requirements for the K20 DSP state thus:
Power Supply:Universal, regulated switch mode with PFC (Power Factor Correction)Nominal power requirement:100-240 V ±10%, 50-60 HzOperating voltage:90 V – 264 V
I'm assuming that, like most switch-mode power supplies, it's technically agnostic about which is "hot" and which is "neutral". (Some may reference between the line conductors and ground, but I have no idea why that would be necessary. Stinger caps haven't been a thing for decades.)

Given that, then it's physically possible and *should* be safe to connect the line conductors of the amp to the two "hot" legs of the 10-50R, thereby feeding 208V to the power supply of the amp, and the ground lead to the center "neutral" conductor of the 10-50R, rendering it a ground rather than a neutral. Two legs of three-phase is single phase.

Since the receptacle is actually listed for the "neutral" to provide a "bootleg" ground (or is it a "bootleg" neutral? -- though typically only for residential ranges), and the National Electrical Code permits it (though not for new installations), I don't see why an inspector would disapprove of the use as you propose.

Where you'd get into trouble is if you split it off to also power 120V equipment, thereby using the center pin of the 10-50R as both ground and neutral (even though that's still a "listed" application).

I do agree that having the venue install a 14-50R is the best way to resolve it. But I don't see a problem -- either from a safety perspective or a regulatory perspective -- of using a 10-50R receptacle in this manner, since the listings and codes seem to allow it.

The only quibble would be if the amp requires a genuine "neutral" on one of the legs, but I doubt it. It could *if* the power switch only broke one leg of the circuit, but if it breaks both legs of the circuit, then the choice of which wire is "neutral" is entirely arbitrary. If you're really concerned about it, contact Powersoft.

Bottom line: my understanding of the codes is that the NEMA 10-50R is listed to provide two hots and a ground, which would be sufficient to supply the Powersoft K20 DSP. Bear in mind that overcurrent protection must be sized accordingly.

DISCLAIMER: I am not an electrician, inspector, or engineer. I'm just a random guy on the Internet giving his unqualified opinion.

Steve Crump:
So, what NEC do we violate to power up an amp with 208/240V? As far as have seen, most of the IEC inlets are 250volt rated, so I guess it just takes finding a rated cord assembly. Most cords are rated 300volt, it is the plugs that cause the rating to go to 125volt. So it would be a matter of finding the correct cord assembly for the voltage/amperage. Example LINKY


[0] Message Index

[#] Next page

[*] Previous page

Go to full version