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#54247 07/23/05 12:11 AM
Joined: Jun 2004
Posts: 176
Read This First

I went to an alternative power website, and they stated you can use a 250V/20A receptacle for 12VDC use... and the guy said that CODE allows this. I read my 2002 code, but didnt find anythign (unless it's hidden somewhere). I emailed he guy to quote me the code, and he said he didnt know what it was, but he was told by someone else.

Joined: Jul 2002
Posts: 8,443
Likes: 3
Personally I would not use like connectors because of the risk of cross-connection.

Joined: Jun 2004
Posts: 202
How common are the NEMA2-20 plugs & sockets?. These are the same configuration as the Australian made Clipsal 2 pin 'T'. (only drama is if the 2-20 plug fits a 5-20 or 6-20 socket...)

Joined: Sep 2003
Posts: 650
I don't recall seeing anything in the code that specifies the layout of plugs and receptacles. They need to be rated for the application, and different receptacles need to be used for different voltages.

My guess is that NEMA created and maintains the standardized plug and receptacle configurations used in North America. I know that they are called NEMA configurations...but perhaps a different organization now 'owns' the standard.

Using these configurations differently would not, IMHO, violate code. For example, if you had two _different_ 120/208V supplies (say one 400Hz and the other 60Hz) and wanted to make sure that equipment was not interchanged between these supplies, I would see no problem using the NEMA configuration specified for 277/480V for one of these supplies. Similarly, using the NEMA 240V receptacle configuration as the 12V configuration for your particular facility seems acceptable to me. For residential use, it would probably make sense to use an even less common receptacle, for example the 240V locking, or some suitable European receptacle that has a UL listing, but then you have to deal with cost issues.

I would be far more concerned with the use of a wiring device rated for _AC_ loads on _DC_ loads. One aspect of rating things like switches and receptacles is interruption capacity. A 20A DC load is much harder to interrupt (arcing and such) than a 20A AC load.


Joined: May 2005
Posts: 247
I suspect that we can blame Ma Bell for this practice of using NEMA 2-20 connectors for 12vdc.. That is the connector commonly used on service trucks for manhole blowers, drop lights, and similar. I suspect the practice dates back many years, probably long before the NEMA standard was introduced.

for the 120/208 60hz vs 400hz example, I will note that there are actually specific connectors for 400hz use.

All of these are 30A twistlock type.
FSL2 - 30A 120V 400HZ (similar to L5-30)
FSL3 - 30A 120V 3phase delta 400HZ (similar to L15-30) (yes, I know the voltage should probably be 250v, but that is how it is listed in my 1994 Bryant catalog)
FSL4 - 30A 120/208Y 400HZ (similar to L21-30)

Finally, there is a connector designated for
28V DC, designated FSL1, rated for 30A 28VDC,
also a twistlock.

In the entertainment industry, it is common practice to use L16-20 (480V 3phase delta w/ground) for powering chain hoists, and L14-20 (120/250V 1phase w/ground) for chain hoist control connections.
These are run in opposite directions, as a bundled pair of cables. Most of the time,
the motors being used are actually made to run on 208v, not 480, but the connector was apparently chosen to allow for the use of 480v hoists, while maintaining a common stock of cable within the industry.
Since chain hoists are used for overhead rigging, the industry tries to restrict access to the hoists to qualified personel.

I have also seen L14-20 connectors used for control pendants for scissor lifts, etc..

I have also seen various types of twistlock connectors being used for speaker systems,such as L14-20, L1-15, and L5-15, although the industry seems to be moving away from that practice for new equipment.

I do wish that NEMA had created a couple of special and control designations to allow for these uses, without interchanging with commonly used electrical types. Either that, or I wish that the manufacturers had picked connectors that would be highly unlikely to appear in an entertainment venue.

[This message has been edited by techie (edited 07-23-2005).]

Joined: Jun 2003
Posts: 1,143
We have the black plastic (Bakelite?) version of these on our ladder truck at the FD for 12vdc charging of the batteries, so it definitely got "adopted" somewhere...

Joined: Jan 2005
Posts: 5,445
Likes: 3
Cat Servant
As I have often stated, NEMA configurations aren't that old.

Prior to NEMA, (say pre-1970), there were a variety of plugs made. Not all of these patterns were adopted by NEMA- the three prong dryer plug, and the 30 amp, 125 volt RV plug among them.

The point is, many of these older styles carried dual ratings, for widely differing applications. It is very possible the plug this guy is describing had both a DC and differing AC rating.

The NEC does not require you to use NEMA configurations. There are still a multitude of non-NEMA patterns in use- just look at the back of your computer monitor!

Now for an editorial comment: Already I've had to "save the day" for folks who wanted 'alternative power,' but were given poor advice (and incompetent engineering) by the vendor. I have seen one licensed EC go bust, in part because such a job put him in way over his level of expertise.
Alternative power- be it solar cells, wind power, generators, or UPS systems, will become a larger part of our trade. Many times, you will have to sort out someone else's mess first. Start learning NOW, so you can 'save the day' yourself.

Joined: Aug 2001
Posts: 7,520
Over here it's become fairly common to see the old BS546 2-amp 3-pin plug and socket used for 12V connections in campers and trailers.

These connectors were originally designed for 240V lighting use, but are now rare even in house wiring. With the square-pin BS1363 plus now almost universal for 240V AC power, there's very little danger of cross connection.

Joined: Nov 2000
Posts: 246
Our fire department just got a new truck, and the chief called me to see if we could install power to each of 4 trucks, parker in bays. The purpose was to provide power for on-board battery chargers.

I sent my assistant, who came back with the following info. On 3 of the 4, it was going to be easy to drop down from the ceiling with 120v cords. But the newest truck needed to have 240v run to it.

I questioned this, so we went to the trucks to check it out. We found out that the newest truck did indeed have a 240v receptacle flange built onto the chassis, from the factory. We did an intensive exam on it, and found that the leads from the receptacle lead directly to the batteries! It was supposed to have a matching battery charger external to the truck.

My thought was this, what would have happened if my assistant (with 40 years experience) had went ahead and put 240v to that flange receptacle?????

Rick Miell

Joined: Feb 2005
Posts: 693
My prediction:


Larry Fine
Fine Electric Co.
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