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.