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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Rich Grisier on April 29, 2014, 10:23:29 AM

Title: NEMA 14-50R & 14-30R
Post by: Rich Grisier on April 29, 2014, 10:23:29 AM
Most places we play have a NEMA 14-50R near the stage for band use.  For this reason I have my distro (ADC-100) equipped with a power cable terminating  with a 14-50P.  Occasionally I run into a place that has a 14-30R.  I've yet to find a commercial adapter with a 14-30P to 14-50R configuration.  What do you guys do when you encounter a 14-30R when your distro takes a 14-50?

For reference:

(http://electric.carstations.com/wp-content/uploads/nema-14.jpg)
                                           14-30R                                                                                          14-50R

Title: Re: NEMA 14-50R & 14-30R
Post by: Jim Turner on April 29, 2014, 10:41:23 AM
  What do you guys do when you encounter a 14-30R when your distro takes a 14-50

I bought a 3 foot dryer(14-30) pig tail and a range(14-50) receptacle and box at home depot and built an adapter.
Not the most elegant solution but it works for the odd show.
Title: Re: NEMA 14-50R & 14-30R
Post by: Geoff Doane on April 29, 2014, 10:50:50 AM
I bought a 3 foot dryer(14-30) pig tail and a range(14-50) receptacle and box at home depot and built an adapter.


Same thing here.  Try to find a dryer cordset that has a full size neutral if you can.  Most of them go one size down (12 ga. instead of 10), since in a dryer the only things using the neutral are the timer and motor.  I've had luck with older ones removed from junked dryers.

BTW, those drawings in the original post are reversed (30A receptacle should have the L-shaped pin), but we knew what you meant.  :)

GTD
Title: Re: NEMA 14-50R & 14-30R
Post by: TJ (Tom) Cornish on April 29, 2014, 11:17:20 AM
Same thing here.  Try to find a dryer cordset that has a full size neutral if you can.  Most of them go one size down (12 ga. instead of 10), since in a dryer the only things using the neutral are the timer and motor.  I've had luck with older ones removed from junked dryers.

BTW, those drawings in the original post are reversed (30A receptacle should have the L-shaped pin), but we knew what you meant.  :)

GTD
Yep.  For those reading along at home, this is safe because by code the 14-30R receptacle must be protected by a 30A breaker in the building wiring.  If the user exceeds this current, the wall breaker will trip, protecting the 30A infrastructure.  The distro will only have 30A per leg available instead of the usual 50A, but there isn't a safety hazard, as the 50A distro is limited to 30A by the wall breaker.

The reverse is not necessarily true.  If you have a 30A distro and you are trying to plug into a 14-50R receptacle, there is the potential for 50A of supply current going to your distro intended for a 30A service.  If your 30A distro has a 30A main breaker, you are protected, however if you have something like a MotionLabs rack pack with no main breaker: http://www.motionlabs.com/c-78-l14-30-in-thru.aspx you can't just make a 14-50P -> L14-30R adapter, otherwise you may overload your 14-30 system.
Title: Re: NEMA 14-50R & 14-30R
Post by: Chris Hindle on April 29, 2014, 12:09:27 PM
I bought a 3 foot dryer(14-30) pig tail and a range(14-50) receptacle and box at home depot and built an adapter.
Not the most elegant solution but it works for the odd show.
Me 3.
Title: Re: NEMA 14-50R & 14-30R
Post by: Craig Hamilton on April 29, 2014, 12:10:42 PM
It's also not a huge deal if the neutral is undersized. It is better if it's full sized so you can load only one leg full current and have the neutral handle the return current but under normal use you would be loading both legs with current simultaneously which will not load the neutral. Even if you had a 20a difference from one leg to the other, the undersized neutral would easily handle that. I also have an adaptor made up just like the others.
Title: Re: NEMA 14-50R & 14-30R
Post by: Rob Spence on April 29, 2014, 12:19:54 PM
It's also not a huge deal if the neutral is undersized. It is better if it's full sized so you can load only one leg full current and have the neutral handle the return current but under normal use you would be loading both legs with current simultaneously which will not load the neutral. Even if you had a 20a difference from one leg to the other, the undersized neutral would easily handle that. I also have an adaptor made up just like the others.

True except most of our loads are not constant. Audio has varying loads which WILL result in neutral current.


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Title: Re: NEMA 14-50R & 14-30R
Post by: Geoff Doane on April 29, 2014, 12:24:24 PM
It's also not a huge deal if the neutral is undersized. It is better if it's full sized so you can load only one leg full current and have the neutral handle the return current but under normal use you would be loading both legs with current simultaneously which will not load the neutral. Even if you had a 20a difference from one leg to the other, the undersized neutral would easily handle that. I also have an adaptor made up just like the others.

Only if you have a single phase source.

If you happen to be in a building with 3 phase power (most commercial buildings), the two loads do not cancel any longer.  If you draw 30 amps on each phase, the neutral will have 30A in it as well.  You need to draw equally from all 3 phases to have the returns all cancel in the neutral.

It's true that for most practical situations, it probably won't matter, especially because of the transient nature of an audio load, but it's good practice to plan for the worst case scenario.

GTD
Title: Re: NEMA 14-50R & 14-30R
Post by: Rich Grisier on April 29, 2014, 02:53:36 PM
Anyone care to post a pic of the adapters they've made?
Title: Re: NEMA 14-50R & 14-30R
Post by: Tim McCulloch on April 29, 2014, 03:09:37 PM
Anyone care to post a pic of the adapters they've made?

For use as evidence, or illustrating poor advice?

Note that clothes dryer cord sets are not listed for this use (feeders).

Also, go back and re-read TJ's reply, esp the 2nd paragraph.  He forgot to mention that using #10 (typical on a 30 amp circuit) with a 14-50 plug isn't permitted, as the 14-50R is presumably protected with a 50 amp breaker, higher than allowed for #10.  Having a master breaker in your rack pack or distro doesn't matter.

The UPSTREAM breaker protects the wires in the wall, the outlet, and YOUR feeder that plugs into the outlet.  The breakers in your distro or rack pack protect the individual outlets on your distro.
Title: Re: NEMA 14-50R & 14-30R
Post by: eric lenasbunt on April 29, 2014, 03:16:52 PM
I actually just installed a Leviton plug today with a 14-50r, but the plug can be easily changed by switching the pin for the neutral. The plug end was $20 or so at Home Depot. I am saving the pin in my distro rack for this reason.
  Adapter would be faster, but this is cheap and I rarely run into the 30amp version. Every place hear tends to be 50r or CS.
Title: Re: NEMA 14-50R & 14-30R
Post by: Rich Grisier on April 29, 2014, 05:54:51 PM
... using #10 (typical on a 30 amp circuit) with a 14-50 plug isn't permitted, as the 14-50R is presumably protected with a 50 amp breaker, higher than allowed for #10. ...

True, The recommendation from the manual for the ACD-100 when wired to a 240 system is #6/4 AWG.

They also mention that the neutral conductor can be #10, but doesn't have to be.  Most cable has the same wire size for all wires, so in this case they would all be a minimum of #6.