How do you safely measure large AC currents using a multimeter without a current clamp?

Question

I would like to measure the RMS current draw of several house appliances, in addition to the primary and secondary side current of a step-down transformer.

Simply placing my multimeter in series with the load through its leads will cause sparking due to the small cross-sectional area of my multimeter's lead tips (only speculating what would happen, I haven't actually tried it nor should anyone else). In addition, I would rather not have to repeatedly place my hands close to exposed live wires and sparks.

I have contemplated other alternatives, such as directly placing both sides of the wire I wish to measure the current through into the multimeter sockets after removing its leads. This is not an optimal solution since higher-gauge wires, such as 16 AWG (1.5 mm²), might slip or spark. Alligator wires rated for high currents and power shunts (though the latter may be less accurate if it were not designed for AC current measurements due to the skin effect) are an attractive option for this, however, I would like to know if there are other options available to me and what the usual procedure is for doing this kind of thing?

Note: The multimeter I have can measure RMS currents of up to 10 A (true RMS); I do not understand why it did not come with specialized alligator leads.

Answer 1

You suggest the possibility of placing the power leads in the meter sockets.

• DON'T!

There are too many possibilities for unintended consequences.

If you have two wire ends, as you mention, a good alternative would be to connect the power leads and meter probe ends via suitably rated screw down connector blocks. Using probes in this manner is a "non standard" application - done sensibly with due attention to shock hazards it could be done in an electrically safe manner.

I may update this image with an improved one but for now, this shows how connection could be made.
The probe is the "wire" on one side and the mains lead is the wire on the other. The simple screw type connectors would be adeqyate if properly sized.
Power must be disonnected while connections are made or broken.

Images from here
Ledt hand image is copied by them from Wikimedia.

Answer 2

Most people would buy a plug in power monitor for ordinary household appliances. Electricians might use a test lead, with the three cores separated, and a clamp meter.

If you're going to do this regularly, you could make up an adaptor, using the plug and socket from an extension lead, and insulated 4mm plugs to fit the multimeter. That way, you could set up the multimeter connections, then simply plug the appliance in.

The leads supplied with multimeters are mostly for probing around electrical or electronic appliances. The probe handles are designed to keep your hands away from the bare metal while you are holding them.