Terminal Block - a device for switching electrical circuits for various purposes, representing a line of pairwise connected terminals, insulated or uninsulated, under a wire of a fixed cross section. Products optionally contain part of larger diameter sockets. Often we will see similar designs, assorting distributive guards. Terminal strips are mounted on DIN rails.
General information, characteristics
The distribution box has no phase pad. It is too dangerous to leave bare metal carrying tension. Blocks unite chains of a neutral, grounding.
Conclusions pads produce threaded and bezrezbovye. Metal screws are used with which the core is tightened in place. Masters know: the compound is suitable for immobilized areas. Most modern pads have a completely different fastening system. Own patented developments have been released by dozens of companies. The name of the label determines the manufacturer.
The diameter of the core wire
Terminal blocks described GOST 30011.7.1, sets the rules for the manufacture, use of products. A document describing low-voltage equipment. Regulates the release of units with threaded and non-threaded clamps, with a cross-section of laid wires of 0.2 - 300 square millimeters. Since the standard is international, American caliber 24-300 kcmil is being given in parallel. Foreigners operate in thousandths of an inch, commonly referred to as miles. Since the speech touched the area, the derivative of the mentioned value is used. Circular mil. For Russian-speaking society, the value is unusual.
24 kcmil is equivalent to 0.2 square millimeters. You can understand by studying the text of the standard. Circular mil - wire section with a diameter of a thousandth of an inch, is 5.076 / 10000 square millimeter. The value is purposefully used to mark the wires, the diameter is simply calculated, it is supposed to resort to using the number Pi, converting units. To find the linear size of the specified area is calculated square root. The result is the diameter of the core in thousandths of an inch.
NEC standards prescribe using mil AWG gauges larger than 0000. It is appropriate here to make a digression to describe the production of wire. Through special machines, the sample is pulled repeatedly, obtaining the required diameter. A template is fixed on the frame, each hole is smaller than the previous one. These are calibers. The said 0000 is considered the largest, corresponding to 11.684 mm, equivalent to an area of 212 kcmil. The root of this value will be the number 460.43.Easy to check: it is the same when calculating the fractions of an inch with the above millimeters of diameter.
In the AWG system, 40 is considered one of the smallest calibers, the standard only goes down to 6. Thinner conductors are sealed with terminal blocks, the requirements for which are regulated by a different regulatory act. It makes no sense to provide a complete list of documents, since the nomenclature will be continuously updated with new products. NEC Standards The core area is adjusted to 2000 kcmil. More than the AWG 0000 caliber. Instead of the physical unit kcmil, the abbreviation MCM is sometimes used. The numbers are indicated by the technical information of the terminal block.
The AWG system has been in use since 1857, apparently becoming the first historically. In the United States, it is strongly associated with Brown & Sharpe of HexagonMetrology. A relatively small joint stock company with an annual turnover of about 3 billion euros. Brown started the company in 1841, in 1853 took the case of Sharpe. The company specialized in the production of tools of various auxiliary means. At the time of 2016, the company's engineers are taking the AICON three-dimensional optical measurement method.
It remains to add that the sections are selected from the series specified by the standard. The numbers correspond to the real brands of wires and cables.
The electrical strength of the pads determines the specifics of operation. The following figures correspond to the products of GOST 30011.7.1:
- Voltage below 1 kV AC, 1.5 kV DC.
- Frequency up to 1 kHz.
Terminal blocks are applicable for industrial networks 230, 380 volts. It is appropriate to make a small excursion into denominations. According to the government’s order, the 380 values no longer exist. The networks available today will be gradually reduced to 230/400 volts. The first digit indicates the voltage of the existing phases relative to the earth potential. With a short-circuited neutral, it is more appropriate to use a second denomination. It characterizes the voltage between two adjacent phases.
220 or 230 volts are rms values. Effective voltage, the thermal effect of which is equal to the constant of similar parameters. The amplitude of the sinewave is approximately 311 V( 220 x 1.41).To find the span of the sinusoid between the two phases, we multiply the root of two by a full 380( 400) volts. Basic knowledge will help you choose the right terminal block to equip the existing network. The technical characteristics indicate the effective value of the voltage, not the amplitude.
As for the change of parameters, it was planned for 2003.However, the forums still frankly believe: the voltage of Russia is 220 volts. Using the help of a multimeter, simply determine the true state of affairs. The 230 volt probes found are not the inaccuracy of a power station, not a whim of local officials. Planned transition to the European standard. The fact is important to the owners of incandescent bulbs, such an increase in the effective voltage value immediately detrimental to the service life of the devices.
A nominal deviation of 10% is allowed, tightening of norms is planned, at the time of 2016, our plans remain a matter of the future. With regards to the frequency requirements are very harsh. Deviations from the specified 50 Hz are literally in fractions of a percent. Regarding the operating frequencies of the terminal block, the standard limits the upper value to the skin effect. The current flows around the surface of the conductor, causing a sharp increase in heating. Calculated limit values will have to be revised. High frequencies are almost harmless to human health.
In addition to the generally accepted standard voltage values, the following ratings are given: 277/480, 400/690, 1000 volts. Fits in the scope of GOST 30011.7.1 terminal blocks. The frequency is still 50 Hz. Denominations are used by heavy industry, less often by commercial buildings. On transport we will meet face values where higher. For such cases, the mentioned terminal strips are not applicable. Increased voltage will meet on the railway. The frequency can be 16.6 Hz.
The leaders of the voltage ratings will be power lines, substations, and hydroelectric generators. The inapplicability of weak terminal strips is obvious here. It is recommended to choose products according to the current values of currents and voltages.
Limit, nominal parameters
In addition to the above basic characteristics, there are others.
- The rated insulation voltage for household appliances is 500 V, in this case it will be much higher. Test values at times overlap operational.
- Rated impulse withstand voltage. The impulse transmits a relatively small energy, the parameter can be higher than the operating value. At the same time, the amplitude of the short current pulse is normalized( the voltage may not change).The mode is characteristic of the start-up of engines, especially asynchronous ones.
- The nominal connection capacity duplicates the information of the supported sections, indicating whether the installation of several conductors in one socket is possible. Along the way, the requirements for the wire are specified: rigid, flexible, special flexibility.
Marking pads contains information about the manufacturer, type of product. Other information is contained in the manufacturer's catalogs. If there is free space, information on supported sections is provided with reference to GOST with the table below, which decodes information. If the connective capacity does not meet the standards of official documents, technical information is immediately indicated. Then other parameters follow: isolation voltage, maximum pulse voltage. Operating conditions are available only in case of different from standard ones.
Terminal strip marking is unusual for electricians, where a complete list of parameters is easy to read, bothering to inspect the case for marking. This information is forced. Correspond to GOST - are passed by marking.
Classification of blocks
Terminal blocks are usually classified by the following features:
- Installation method. Today popular products mounted on DIN-rails. Sometimes, instead of a single pad, the owner buys the required number of individual single-pole terminal blocks. Switching nodes put below the automaton protection. Pads are screwed, inserted.
- The number of poles indicates how many lines we will pass through the block. The exception is the design with uninsulated pairs. Such terminal strips are used for grounding buses where the lines are to be connected.
- The method of terminating the cores of terminal blocks will allow to divide the family into threaded and non-threaded.
- According to the ability to receive prepared conductors. So called cores, supplied with tips, the finest copper threads which are soldered. Equipping multi-apartment networks, it is convenient to use unprepared solid veins. Installation rules do not provide for wiring qualities of particular flexibility. Consequently, the cores are solid - there is no need to complicate the task.
- The presence of different or of the same type of fixing nodes seal termination.
- Number of pins per pole. It is not always possible to conduct a straight line through the terminal block. Branching or even joining of lines is possible, the case of protective grounding.
- Operating conditions indicate the preferred location of the terminal block. The manufacturer does not guarantee the operation of the product.
Which block to choose
The terminal block is selected according to the installation conditions. The distribution box of modernity involves the installation of DIN-rails. The grounding bus is mounted on the side, top, bottom. It is common to place the terminal block horizontally. Insulation of the housing is not required, even the opposite: it is possible to reliably ground the metal parts of the equipment. It is not enough to simply fasten the block; use a special threaded clip located on the inside of the guard housing. For street performance.
With regards to home shields - options are possible. It is recommended to entrust the assembly to a specialized company. Correctly conduct the internal installation, place the automatic switches, RCD, mark labels. It will remain powered to connect the house wiring. For the ground bus conduct a separate vein, going to the area of the local circuit of the lightning conductor.