How to wire a male 28V DC plug?
 

A Hubbell HBL7485 Twist-Lock to be specific. I need to know,

a/ where to connect the + wire ( at X or Y?) and
b/ what is the center terminal doing?

Please?

A Hubbell HBL7485 Twist-Lockis a NEMA ML-3P 125/250 Vac ungrounded 15 Amp plug. Its use in 28Vdc systems is non standard. It may be electrically possible to use this for such an application, but having a load equiped with such a connector that could mate with an incorrect supply is dangrous and possibly a code violation (Depending on the code applicable in your area, of course).

The center terminal (in its 125/250 Vac application) is the neutral connection. The two outside blades being 125 V each to the neutral (180 degrees out of phase), for 250 V between them.

AC ? I ordered plugs for connection to an aircraft 28 V DC outlet !?!#¤%#"

From whom?

Its a non-standard use. Here in the USA, it could get you into some trouble (plugging into the wrong supply). That use might be permitted elsewhere, but due to the international nature of aircraft, one of those plugs is bound to show up in the wrong place. Not something I'd expect a competent aircraft manufacturer to let slip by.

Its possible that someone at an electrical supply house figured the 'AC' stood for 'aircraft' and pulled the wrong part off the shelf. Just guessing here.

The plug was ordered via my operators tec dept. Where they got it from I have no clue.
The intended use is to power a printer which does not like 115 V AC / 400 Hz.
As it is ground-only it is hardly any more dangerous than the cleaning staff using the 115 V outlets, or??
Come Monday I'll have a chat with the techies again. Thanks!

Well, it turns out that Mr. Boeing actually did use a female Twist-Lock receptable which fit the Hubbell HBL748.

And while he was at it, he drew a wiring diagram showing the small terminal as positive and the remaining as grounded.

28 V DC Ground Handling Bus.

Enjoy the remaining week-end!

The danger isn't to the aircraft. That plug/socket combo will work just fine there.

The danger is that this 28 Vdc piece of equipment will find its way somewhere that has a twist lock 125/250 Vac receptacle.

Not to worry: according to our technicians there is only one such receptable outside E&E compartment (on our birds).

I hope your insurance will cover the situation if someone "helpfully" loans the printer to another organisation, or you take on some work from another operator with a different setup, or someone finds a use for a printer in the E&E bay on a turnaround, or it gets sold second hand, or .... :uhoh:

The main problem is that Boeing uses the same female outlet for its 115V/400Hz AC outlets and its 28V DC outlets, at least on the 737 flight deck. If someone wants to run DC powered equipment directly on the 28V outlet you have to use the same male adapter as for the AC one, strange but sadly true.

Denti, that sounds like trouble by design!

Fortunately we have an other design on the AC outlets of our 76s.

I'll specify in writing not to assume it will work on other than our a/c's.:= Until they are sold... :rolleyes:

Thanks for your input, gents!