How to find a wire in a wall with a detector and folk methods

Recommendation points

• The importance of mapping the SCS
• Typical laying routes
• Detectors and locators
• Homemade devices
• Searching with the radio

In the event of a break in the power line hidden in the wall, you have to resort to dismantling the finishing coatings. Ripping the entire wall entirely is a simple matter, but it would be much more correct to find out the exact location of the cable. What methods and devices are used for this – read our review.

The importance of mapping the SCS

In professional electrical installation, it is considered mandatory to transfer to the customer a three-dimensional sketch, which displays data on the structure of the cable network (SCS). And this is not a rule of good taste: the power supply of the facility is carried out at the first stages of construction. In all subsequent work, it is required to coordinate technological processes with the placement of engineering communications and wiring is no exception..

The SCS card can appear as part of the power supply project, or as a separate document if there is none. The description of the structure of the cable network includes a visual display of the route of laying – a sweep of surfaces with an indication of the distance to the conductors from the control points and the depth of laying. Additional annotations are the brand of cable products, section and purpose of each line..

The need to search for hidden wiring arises primarily in the absence of a description of the structure of cable lines. Without it, it is impossible to guarantee the safety of the cable when attached to walls and ceilings of various kinds of building substructures, finishes, furniture and decorative elements. Also, troubleshooting is significantly complicated in case of damage to conductors walled up inside the walls. We are obliged to point out the critical need for mapping during electrical installation before proceeding with the description of the available methods for finding hidden wiring..

Typical laying routes

One of the easiest ways to find wall wiring is to visually assess the surface. Also, a good help in this matter will be knowledge of a number of rules, both non-written and established by the standards of electrical installation. Electricians use these rules when choosing a laying route, so it is possible that a separately taken electrical network will be mounted on them..

Purely empirically, the direction of cable laying can be determined by the traces of the termination. As a rule, the sealing of the wire with wires is carried out much later than the plastering work, which is why the filling composition has obvious differences in color and structure. Naturally, this detection method is acceptable only if the decorative trim is removed..

Sometimes visual methods of locating the cable route cannot be used, for example, if the wiring is hidden under a general layer of plaster or finishes that cannot be dismantled. In such cases, knowledge of typical laying routes is useful. Cable lines are predominantly located either in a strictly vertical or strictly horizontal direction. Not a single electrician, being of sound mind, will fasten the cable diagonally, and even more so along a curve.

The starting point for determining the route of installation is always the installation box of the outlet, switch or group of connections. It remains to understand: in which direction the conductor goes from the box, that is, left, right, down or up. In the overwhelming majority of cases, this can be judged by the side from which the ends of the conductor are brought into the box. In the future, you need to be guided by the wiring diagram to determine the end point of the laying route. So, the wires from the switches are almost always directed to the junction box, from the sockets – either also to the box, or to a neighboring outlet. It is good if the ends of the cable cores were previously matched with a continuity.

It should also be remembered that usually from connection points located below 1.8 m from the floor, the cable is first directed vertically up to a mark of 20-30 cm from the ceiling, then the direction of laying is changed to horizontal towards the corresponding junction box. Also with the ceiling plane: from the point of exit of the wires for connecting the lighting fixtures, the cable is directed to the wall on which the junction box is located along the nearest route, that is, along the perpendicular. Sometimes ceiling wiring is hidden inside the voids of floor slabs.

Detectors and locators

The above methods for locating wiring in the wall are simple, but the search can take a lot of time. In professional activities, it is unreasonable to use this approach, so qualified electricians use hidden wiring detectors. Unlike universal detectors of inhomogeneities, the class of devices we are considering reacts either to metal objects or to an electromagnetic field generated when an alternating current passes through a conductor or when an electric potential is induced. It is this nuance that allows you to accurately determine the hidden cable route even in reinforced concrete walls or in a layer of reinforced plaster.

Bosch D-tect 150

Discontinuity detectors are suitable for finding wiring, provided that the device has the appropriate mode. This group includes a wide range of devices, from the budget Skill DT or Topex94W, to the more expensive Bosch GMS and Bosch PMD, the Bosch D-tect group of devices is considered the most advanced. The main disadvantage of such detectors is a large number of false alarms and the impossibility of detecting wiring located close to shielding materials such as plaster mesh or foil-clad insulation. The advantage of devices of this type is the versatility of use and high flexibility in setting the operating modes, which allows you to accurately determine the location and depth of the wire, even without voltage and load. Universal detectors with wiring locator require pre-calibration before each use.

Zircon MultiScanner Pro SL

Signaling devices of hidden wiring, reacting to disturbance of the electromagnetic field, are based on the induction principle of operation. Such devices include the familiar to many E121 “Woodpecker”, “Poisk-4”, TS-75, MAG-2 and the like. In essence, these devices are short-range metal detectors, their only advantage is their low price, while the probability of a false alarm is one of the highest. The Zircon Pro SL is rightfully considered the most accurate of this kind of detectors, but its price is appropriate.

Mastech Cable Tracker MS6812

Special devices for detecting hidden wiring are called locators. Such devices consist of two blocks: a generator that sends pulses of a certain frequency along the conductor, and a sensor that registers interference from these pulses. Since the device was initially calibrated exactly to the frequency of the generator, it does not work either on fittings or on other cables. As examples of locators, one can cite both the cheapest Mastech MS6812, FWT-11 or “LIS-M” kits, and professional ones – CEM LA-1012, NF-8601, or NF-300. The main difference between devices of the highest price category can be called the ability to detect conductors at a very significant depth, as well as a number of additional functions: search for a break, short circuit, measuring the length of the route. Locators are best used to find not only power cables, but also signal wires, including coaxial.

Homemade devices

There is no particular difficulty in making a simple wiring detector on your own, and a homemade device will have a fairly high sensitivity. The first way of manufacturing is the use of a low-power N-channel field-effect transistor with an opening current from 100 μA to 1 mA, for example, K1109. The circuit of the detector is outrageously simple: the transistor controls the power supply of the LED connected to the battery according to the polarity. To protect against overcurrent in the circuit, it is desirable to include a current-limiting resistor of 50–100 Ohm. The transistor gate is controlled by an antenna – a piece of copper wire 50–70 mm long, which takes over the induction of the electromagnetic field. To change the sensitivity, a 200 Ohm – 2 kOhm trimmer potentiometer can be connected in series to the antenna circuit.

The second manufacturing method is based on the NE555 universal timer. This microcircuit is connected according to the standard piping scheme for supplying serial pulses to a low-power LED, set on the 3rd pin and minus the power supply. The essence of the detector’s operation is to change the operating frequency of the built-in comparator when voltage is applied to the 5th output through a field-effect transistor, the gate of which is controlled by induction to the antenna. Thus, even the slightest change in voltage will significantly change the frequency of the timer, which will immediately affect the character of the LED blinking. The advantage of such a scheme is the high flexibility of setting, the ability to unambiguously determine the operability of the device at idle and connect, in addition to the light indication, also an audio one, that is, a piezo emitter.

Searching with the radio

If you are not sophisticated in electronics and are not ready to spend even a modest amount to buy a detector, you can use the old proven method. To do this, you will need an ordinary pocket radio receiver into which a fresh battery is inserted..

First, you need to tune the receiver to a low frequency that is a multiple of 50 Hz, that is, resonant with the oscillations of the mains: 5, 10, 15, 20 kHz. In this mode, the radio is extremely sensitive to fluctuations in the current in the circuit, while “white noise” from the speaker is replaced by crackling and abrupt whistling. To be sure, you can try and configure the device by bringing its antenna to the extension cord, turning the load on and off.

To make it easier to find the wiring in the power circuit, you can include an improvised breaker. As such, any household appliance with a collector motor will fit – an electric shaver, a coffee grinder, or an ordinary doorbell with an electromagnetic relay. The disadvantage of this method is obvious: in this way it will not be possible to find a wire through which an electric current does not flow. But in the presence of a load, the wire can be found even at a depth of 50-60 mm, although the accuracy of this detection method leaves much to be desired.