Mueller's new Patent Pending BU-21AEZ, clips are now in stock and will be shipping to distributors soon.

This New clip takes only 1/4 of the force to open compared to a standard BU-21 series clip. If you or your workers are struggling to use a standard center spring alligator clip, then give the "EZ" a try. Everyone who has tried it, loves it!

If your favorite Mueller distributor doesn't have it yet, then just ask them. We ship to most of our distributors everyday so your estimated lead time will be two weeks or less.

To learn more about different types of clips, check out our clip guide.

Banana plug sizes and types

Banana Plugs (male) and Banana Jacks (female) have been used in the testing applications for almost 100 years.  They come in three common diameters 4mm, 3mm, and 2mm.  Manufactures have different tolerances, but the table below shows typical dimensions for the three sizes.  Plugs are measured at the largest OD of the banana section.  Jacks are measured at the ID of the connection

The 4mm version accounts for more than 94% of the total usage.  In fact, when someone uses the term “banana plug” or “banana jack”, they are almost certainly referring to the 4mm version.   The 3mm and 2mm variations are both called “mini-bananas”, but they cannot be used interchangeably.

Banana plugs and jacks also come in different safety variations.  The first banana plugs were un-shrouded, (1) in the photo below.  These are the easiest to manufacture and are still very popular in many low voltage applications.  Fully shrouded banana plugs, (3) in the photo below, were introduced for protection at high voltages, but they require a banana jack that will accept them.  A cross between shrouded and un-shrouded is the retractable shroud banana plug, (2) in the photo below.  These, as the name implies, have a spring loaded shroud that gets pushed/retracted into the housing when the plug is inserted into a jack.  Although retractable banana plugs offer a practical safety level, they do not meet the requirements of approval agencies for high voltage applications.

          (1)                   (2)                            (3)

For more information about banana plugs, check out our guide here.

The simple answer is they do not have sufficient, if any, insulation for human protection.  Most alligator or crocodile clips are rated for current (amperage) and not voltage.  Even clips equipped with slip-on insulators do not meet agency requirements for a voltage ratings because the insulator can be moved (without tools) which would expose potentially hazardous bare metal. 

Technically speaking...Most slip-on alligator clip insulators are designed to prevent the clips from shorting against other conductive items.  They are not intended for human protection!  The photos below show a typical alligator clip and slip-on insulator. Clips like this, even with the insulator installed, cannot carry a voltage rating and they should only be used in either low voltage (less than 42V) or “hands free” applications.

A "hands-free" application is one where the clips are attached or unattached only when the circuit is not energized or when the electrical potential is less than 42 volts.  If the clips are being used in a "hands-free" environment, the insulators will typically protect against shorting up to 3kV or higher.  Be aware that the voltage rating on the wire used may not be rated this high and thus, may be the limiting test voltage.

Agency Requirements for hand held testing devices: IEC61010-031

To meet IEC61010-031 requirements:

• The insulators need to be permanently installed and can't be slipped on or off, or moved out of the way; and
• There must be a guard placed at a specified distance to prevent accidental contact with exposed conductive metal parts; and
• A finger probe applied at any angle is not allowed to touch any current-carrying exposed metal; and
• Clearance and creepage distances must be maintained.
• The junction between the clip and the wire it is attached to must also meet all of the requirements above. Because of this, the clip must have an insulated connector (most commonly a shrouded banana jack) to attach it to a wire. Alligator clips with screw, crimp or solder connections do not meet these requirements.

There are clips with insulators and connectors that meet IEC61010-031 requirements, but not many.  These clips also require the use of test leads equipped with shrouded banana plugs.  They cannot be connected to bare wires

Voltage Rated Clips...   Mueller Electric offers a limited line of fully-insulated alligator clips with voltage ratings as well as test leads with shrouded banana plugs.  For more information & specifications on these products, please click on the appropriate photo below:

To learn more about different types of clips, check out our clip guide.