Dangerous male to male power adapters

Every so often, one sees an inherently dangerous male to male power adapter recommended.


QST 2012

Fig 1:

The latest instance is the device shown in FIg1 published by (Sant Andrea 2012) in QST magazine. The device is an adapter for measuring line current in a piggyback mains power adapter, and it extends the active conductor to an ordinary bare male banana plug. The US National Electric Code specifically prohibits two male attachment plugs Attachment plugs shall be installed so that their prongs, blades or pins are not energized unless inserted into an energized receptacle. Whilst this is not an attachment plug, it is dangerous for the same reasons and should not be done.

More insidious than the plainly un-insulated male plug parts is the metal screw in the side of the insulated body. It is almost certainly connected to the male pin and accessible even when the plug is inserted into a matching socket.

The need to connect instruments to energised circuits is not new, and the older un-insulated male plugs for the instrument end of the adapter are no longer acceptable, safer insulated plugs with fixed or retractable shrouds are used on most quality multimeters and similar instruments.

Fig 2:

Fig 2 shows two types of safety 4mm banana plugs. The upper plug has an insulated tip and retractable sleeve and will engage ordinary banana sockets. The lower plug has a fixed shroud and requires a socket designed to accommodate the shroud.

eHam / Cuthbert (WX7G) 2010

(Cuthbert 2010) offered the following.

 Take an extension cord and cut off the female connector. Install a male connector and you have a male-to-male extension cord. Plug the cord into another room (on another circuit breaker) and plug this into the same wall socket the ALS-1300 is plugged into. If the other room uses the other side of the 230 VAC drop it will trip a breaker but do no damage. Plugged into a room on the same side of the 230 VAC drop you now have a pseudo-30 amp circuit. If either room exceeds 15 amps average that breaker will trip and then the breaker for the other room will trip. No damage done.

Dangerous, and in direct violation of NEC's Attachment plugs shall be installed so that their prongs, blades or pins are not energized unless inserted into an energized receptacle.


Think of the consequences of energised exposed / un-insulated male pins. They may create a risk of:

Some apparently handy techniques or devices might not be innovative, but just the result of unintelligent and dangerous application.

If you could not safely sell an adapter of a particular design, think about whether you should make one at all.

Think about potential danger from components that should not be left lying around for kids to play with, eg mains plugs with the cover removed, or mains cordsets with a plug on one end and the other end stripped for use.

Use mains power connectors ONLY for their intended purpose. I recall seeing an old (antique?) telephone set on a table at a jumble sale, and it was wired with an ordinary 240V 3 pin plug. Very dangerous if you took it home and the kids played with it! One used often see car trailers with the lights wired to two three pin power plugs. What a dangerous thing if the kids plug one of them into a mains extension cord.

Safety is not rocket science, but it does require thinking about the unintended consequences of actions.



Version Date Description
1.01 15/10/2011 Initial.

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