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How To Tell If A Wire Is Live Without A Tester

Safety Warning: You should never test wires unless you are a qualified electrician. Also, do not work on a live wire unless the power supply is switched off from the consumer unit. 

For testing any electrical wires, a tester is a first and obvious choice. However, in some cases, you might not have a tester at the ready. So is it possible to tell if a wire is live or not without a tester?

Yes, it is possible.  

Note: There are several types of electrical testers. We will assume that you do not have non-contact or inductance testers and the tester screwdriver for this post. 

Let’s begin. 

Use a multimeter

Using a digital multimeter is the easiest way to tell if a wire is live without a tester. It is also the safest way to test a live wire, especially if it is exposed. 

Set up the multimeter by rotating the dials to the V spot on the device. In domestic household settings, it should be under the A/C setting. In most digital multimeters, you will also find a ~ next to the V.

Now, you need to select the voltage range on the multimeter. Power outlets in the UK have a voltage of 230V, so you need to set the range above this number on the multimeter. 

If you do not see many numbers on the multimeter, it probably has an auto-ranging function. In this case, you just need to set the dial to V~, and it will automatically kick in when it picks up the voltage.

When it comes to the probes, the black one goes into the common socket, COM. On the other hand, the red probe goes into the VΩ socket. This may be on the left or right, depending on the model of your multimeter.

Testing exposed live wire with a multimeter

Working with exposed wires always warrants extra attention, so you should take note of it. Wearing a pair of insulated gloves is still essential. You should also consider standing on an insulated or rubber mat to prevent electrical shocks. 

Here is a pair of high-voltage safety gloves that we like. It has the right combination of safety and price. 

Hold one test lead to any metal surface to act as the ground reference. It can be a screw, metal pipe, or even an appliance. 

Next, hold the other test lead and touch it the each of the wires. Ideally, two out of the three wires should show a reading of zero to near zero. These are your earth and neutral wires. On the other hand, the other wire should give a reading of about 230V, which is your live wire. 

Testing a live wire in the switch

Another instance where you might need to test for a live wire is in the switch. In this case, you need to unscrew the switches so you can access the terminal. 

Hold one of the test leads to the ground terminal and the other to the live wire. When you check the reading, it should be near about 230V, give or take. 

Testing a live wire in the socket

Note: If you have a receptacle tester, you can also use it to test for voltage before proceeding. It is effortless to use and is relatively cheap too. Check out this receptacle tester from Klein tools. 

Testing wires in the socket is easy and safe. Nevertheless, you should always follow the necessary safety procedures, including wearing an insulated glove.

The black probe goes into the slot on the left. The left slot is usually where the neutral wire is connected. Then, you can proceed to insert the red probe into the right slot. If the reading registers about 230V to 250V, you have a live wire working with the right amount of voltage. 

Testing live wire behind a wall

In some instances, you might need to test wires behind a wall. The best option is to use Ultra-wideband or UWB in such cases. These radar-like devices allow you to test whether a wire is live or not without tearing down the wall. 

Ultra-wideband devices are professional quality and can be very pricey. Also, these advanced wire detectors are not user friendly and require some level of training. This is why you will only see qualified electricians using them. Bosch has a good selection of Ultra-wideband in their inventory. This live wire detector, in particular, is a favourite of our team due to its efficiency of price and performance. 

Tips for testing a live wire safely

  • Use clips on the test leads while working with wires. This way, you use only one hand to test the cables. We love using this multimeter test clip set. It comes in a wide range of colours that makes it easy to identify which wires you are working on. Besides, the price is unbeatable.
  • If you come across a wire and cannot determine it by the colour code, trace it to the consumer unit. Only if you can identify it as part of an appliance or a device should you test it with a multimeter.
  • In instances where you dig up an unknown cable, or you find it laying around, don’t attempt to test the wire yourself. Clear the area immediately and call a qualified electrician. 
  • Working with live wires is extremely dangerous. If you doubt your ability to test a wire or use a multimeter, call an electrician to take care of the job. 

Conclusion

Testing live wires can be effortless or dangerous depending on who and how you approach it. For a qualified electrician, it is among his most straightforward works. However, without the right experience and tools, it can cause serious harm. 

Hiring an electrician is no doubt among the more expensive works in any household. However, it is far less costly than sustaining an injury or something worse. And since working with live wires requires more precaution, don’t hesitate to enlist an electrician’s services.  

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