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BOOKS AND ARTICLES
6. Probes
Directory / Electrician in the house They are divided into two groups. The first includes those probes that serve to check the integrity of a de-energized electrical circuit when repairing wall lamps, table lamps, electric stoves, etc. Each of these probes consists of conductors, a current source, and a current signaling device. In the simplest of the probes of the first group, the current source is a battery from a flashlight, the signaling device is a 1,5 V light bulb. The light bulb socket is made by winding a wire rod of a suitable diameter. If the wire is too elastic, then it is annealed. It is clear that the diameter of the wire in the spiral must allow the light bulb to be screwed in. All elements of the probe can be placed in a box by making holes in it for wires and light bulbs. Plastic, wood, cardboard are the preferred materials for the box. Any wires for the probe are suitable. The key is to keep them isolated. o Multi-core wire is more durable than single-core wire, which will break if the probe is used frequently. No special probes are required for this probe. It is enough to clear the free ends of the wires by 2 ... 4 mm. A light bulb is an optional element of the circuit of this probe. It will be successfully replaced by a handset, headphones or radio. At the moment the probes are applied to the area being checked, a characteristic crack is heard, unless, of course, the electrical circuit of the device is intact. Instead of a light bulb, they successfully use one of the measuring instruments with a resistor, which is installed to limit the electric current flowing through the device. Moreover, these devices must be of the magnetoelectric type of direct current. In a milliammeter, sensitivity is increased by removing the shunt. And in a voltmeter, the additional resistor is eliminated by soldering a conductor to the contacts. If you have a choice, then for the probe it is better to take a milliammeter with a scale diameter of 65...80 mm and a maximum scale reading of 100 µA...1 mA. Before removing the shunt, check the deviation of the instrument pointer on the scale. Sometimes you will have to select another shunt that would eliminate the impact of the needle on the scale stops. Our probe with a measuring device is actually an ohmmeter, because it can determine not only the location of the break in the circuit being tested, but also the approximate resistance of this circuit. By the way, heads that measure the recording level in tape recorders are also suitable as measuring probes. The resistance of resistors to limit the current is calculated as the ratio of the voltage of the battery to the current of the total deflection of the instrument needle. For example, for an element of 1,5 V and with a full-scale needle deflection current of 1 mA, the resistor should have a resistance of 1,5 kOhm. After assembling the ohmmeter, the resistor can be selected more accurately by connecting another one in parallel to the calculated resistor. The resistance of this resistor is taken to be several times greater when the instrument needle does not reach the end of the scale. But if the arrow goes off scale, then the resistance of the resistor is reduced several tens of times. In some cases, despite the presence of divisions on the scale, it has to be re-calibrated. The need for this will be indicated by control measurements of resistances of 100 Ohm, 1 kOhm, etc. The gaps between the marked positions of the arrow are divided along the circumference into an equal number of parts. The more resistances for control checks and the smaller the gaps without marks, the more accurate the graduation of the scale. Current sources for probes of the first group are no less diverse than signaling devices. When there are no batteries for a flashlight, batteries, radio and lighting networks are used. But then compliance with safety regulations is mandatory in order to avoid death !!! For a probe with a power source from a lighting network with a voltage of 127 or 220 V, all elements are taken from materials intended for this network: electric lamp, socket, wire, plug. It is more convenient to mount the probe in a box made of non-conductive material. This, in particular, will eliminate the danger of the flask exploding when the probe is operating. If all elements of the probe are open, then the electric lamp is hidden in a plastic cup or at least the cardboard tetrahedron in which it is sold is put on it. At the same time, do not point the open part of the package on the side of the flask at either yourself or another person. To reduce the size of the probe, you can use a socket and a light bulb from a refrigerator or sewing machine. The following brands are used for cords and wires for probes from the lighting network: ShVP-1, ShPS, PVS, ShVVP, etc. Since these wires and cords are quite difficult to purchase in a store, they use the remaining irons, electric stoves, etc. that have become unusable. It is not necessary to attach probes to the ends of the conductors. The conductors can protrude 1...2 mm from under the conductor insulation. The very insulation of conductors from bare ends over a length of 100 ... 150 mm is covered in several layers with rubberized electrical insulating tape. But when probes are designed to penetrate to points not located on the surface, they are designed a little differently. For the first option, you can use collet pencils. They take out the insides. A piece of copper wire with a diameter equal to the diameter of the lead is passed through the collet. The length of the cut should be such that after soldering the conductor core, the soldering point “hides” inside the plastic case. The piece may protrude several millimeters from the collet. The disadvantage of this option is that the collets can be wrapped around with your fingers and the current will "move" through the body. Probes with a power source from a lighting network with a voltage of 17 or 220 V can only be used inside dry rooms away from grounded devices (water pipes, pipes and radiators, etc.). The person must stand on a rubber mat. Another version of the probes resembles the probes of a voltage indicator or a test lamp. Two tubes with flanges are machined out of plastic. A brass or copper rod with a diameter of up to 3,5 mm is inserted and fixed into each of the tubes, to which the conductor core is soldered. The junction itself is located inside a plastic tube. Tube rods can protrude to the desired amount, say up to 180 mm. When working inside the device, this will not cause accidental contacts because PVC or rubber tubes are put on the rods. The rods protrude from these tubes by only 2...3 mm. Using a tester with a power source from the lighting network, you can check electrical circuits that are also designed for this voltage, that is, sconces, chandeliers, irons, vacuum cleaners, etc. But this tester cannot be used to verify the installation of a telephone or radio point, because their parts are designed for a voltage of only 30 V. On radios, televisions, and tape recorders, a similar tester verifies the integrity of only two supply wires and when they can be separated thanks to a special connector from the named ones devices. Failure to comply with these recommendations will lead to combustion of the elements of the tested section of the electrical circuit. Probes with audible alarms are less economical than the ones previously listed. Therefore, during long breaks in operation, the power source should be turned off. The parts of one of these probes are mounted on an insulating strip in a metal case in the form of a wristwatch, to which a metal bracelet is connected. The second group includes probes for determining the presence of voltage in conductors, for finding a phase wire when connecting switches, cartridges, etc. These probes, in turn, are divided into single- and double-pole. The first ones are made according to the type of a fountain pen and are used mainly in household electrical installations, calling indicators-screwdrivers. The action of the indicator-screwdriver is based on the glow of a neon (gas-discharge) lamp when a capacitive current flows through it. To limit the current flowing to the lamp, a 1 mΩ resistor is mounted in front of it. This resistor prevents the glow discharge in the lamp gas from turning into a breakdown one. For the IN-91 indicator, use the IN-3 lamp. For use, the handle indicator is inserted between the index and middle fingers of the hand. Press the handle cap with your thumb. The human body begins to act as a grounding conductor when a screwdriver touches the surface through which the electric current flows. Even with a voltage in the conductor up to 380 V, a current of too little strength flows through the indicator, and then the human body, to damage it. This is both a plus and a minus. The plus, as noted, is human safety, and the minus is that the neon bulb glows approximately the same both at a voltage of 100 V and at 220 V. That is, when looking for an open circuit, it is impossible to determine the actual voltage in the electrical circuit without a voltmeter or a control lamp or, as one of the manuals says, "the disadvantage of such indicators is that they cannot be used to distinguish the neutral from the phase wire that has a break, or to determine whether the wires belong to the same or different phases." The screwdriver indicator, I emphasize again, saved many lives during the initial determination of the presence of electric current on parts of electrical installations, when the control lamp was powerless. The indicator screwdriver, of course, is used only as the end of the probe. And so that this probe, which in some types of indicators reaches a length of 50 mm, does not make a short circuit, a tube of insulating material is pulled onto the screwdriver rod so that the metal protrudes only 2...3 mm. You can make a screwdriver indicator yourself from a used fountain pen and a starter for fluorescent lamps. To do this, the petals are bent and the aluminum glass of the starter is removed, the two conductors of the neon lamp are disconnected from the contact legs and removed, leaving the capacitor on the panel. Next, a resistor with a resistance of 100 ... 200 kOhm is soldered to one of the ends of the conductor. The greater the resistance, the less will be the glow of the lamp, which, together with the resistor, is inserted into the body of the pen. At this point, a hole should be made in the housing against the location of the lamp. Instead of the feather and its support, a metal rod well selected in diameter is inserted. It is clear that the piston mechanism or pipette is removed from the body in advance. The free end of the lamp and the metal rod are connected by soldering or threading, the second end of the resistor is connected to the metal cap of the pen body. The homemade indicator operates in the range of 50...220 V AC voltage. For car and motorcycle enthusiasts, we can offer a sampler of approximately the same design. With its help, faults are found in the electrical circuit of lighting, generator, relay regulator, etc. The difference between this probe and the previous one is that it uses not a gas-discharge lamp, but a regular lamp for the required voltage in the range of 12... XNUMX V. One wire from the lamp is connected to the probe, the other (long) is equipped with an alligator clip. To check the required electrical circuit, use a crocodile to grab a cleaned area of the housing. The probe is then applied to the investigated wire of the circuit. If the light flashes, the circuit is good. The predominant number of professional electricians use pilot lamps when repairing the electrical network in domestic premises. Although this is strictly prohibited by safety regulations. It is allowed to use only voltage indicators, other special devices. But what is allowed is usually absent, and it is not always convenient for them to detect the presence of an electric current. Can a person with little electrical knowledge use a test lamp? I think that it is safer to use it than to climb into the water without knowing the ford: In order to put this safety into practice, a number of conditions must be met. 1. Start up the control lamp only up to the electric meter. 2. The “controller” must put on dielectric gloves on his hands, pulling their bell over the sleeves of his clothing. In a dry room, these gloves will to some extent replace household rubber gloves. 3. The "controller" is allowed to stand only on a dry dielectric rug or a dry dielectric track. It is permissible to replace them with a household rubber mat, which must be folded in half and placed on a dry wooden board. There is no need for a board when there is a dry wooden floor or a floor covered with linoleum under the rubber mat. 4. The test lamp should be placed in a box made of insulating material with a slot for the light signal. A mesh metal case protects the lamp from shock, but if the lamp bulb explodes, small fragments can hit the eyes, skin... 5. Two conductors to the lamp socket must be inserted into the box through different holes. This will prevent short circuits between the conductors when their insulation is rubbed by the edges of the holes. Therefore, it would be good to insert and secure plastic bushings with rounded edges into the holes for the conductors. The length of the conductors from each hole is made at least 1 m. When checking for voltage, the box with the lamp should hang on the conductors. If this check is carried out near the floor, then the box with the lamp is moved away from you as far as possible. The cords and wires for the conductors themselves are chosen of the type described above, i.e. ShVP-1, ShPS, etc. 6. The conductor probe holders are made of plastic as described earlier. The flanges on the probes will prevent fingers from getting on the current-carrying parts of the installations, and even on the bare ends of the metal probes inserted into these holders. 7. The control lamp is equipped with an electric lamp with a voltage of 220 V. It happens, and at this voltage, the bulb of the lamp explodes after passing through it. Therefore, you should always turn away from any lamp when you turn it on. Well, if you apply, for example, 380 V to the lamp, the bulb will immediately fly apart. Hence the recommendation: it is forbidden to use a control lamp outside the mains, "served" by an electric meter !!! So, on a floor electrical panel, where the wiring from the apartment to the electric meter in modern multi-storey buildings goes, an inept tenant will “catch” 380 V with the probes of the control lamp. The same can happen on electric inputs to a one-story rural house. Back (Defects of hidden electrical wiring) Forward (Knives fitter for electricians)
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