An intermediate relay is required to carry out auxiliary functions... It is widely used in control and automation systems. The main purpose of the element is the distribution and switching of loads in power grids. A relay is needed to convert or transfer one signal to another. Used for both direct and alternating current. As a rule, the product is used to control more powerful devices: power contactors, actuators of the automation and alarm system. In this article, we will tell the readers of the site about how to connect an intermediate relay, providing a wiring diagram and video instructions.

Ways to turn on the device

How to connect a mechanism to the system? The device is connected to the electrical circuit in two ways:

When there is a normal stable voltage of the power supply, it should work reliably. In addition, their reliable operation is provided for in case of emergency voltage drop down to 40-60%. In particular, in the design, such a transformation element can be with one winding, two or three (the latter are extremely rare).

The connection of an intermediate relay is essential for any equipment or device. After all, this allows not only to automatically interrupt the circuit, but also with its help it is possible to expand the functionality of other relays that are located in this electrical circuit.

The durability of the device depends on the amount of time it has been triggered. That is, it is characterized by the number of cycles of operation and return to its original position. The degree of protection of the equipment from various undesirable factors that surround the structure is assessed by such a criterion as the transition time of contacts from one position to another.

Connection diagrams

After the intermediate relay has been installed in the electrical cabinet, it must be connected to the electrical circuit. For this, the contacts of the coil itself and direct contact elements are used. The relay has, as a rule, several pairs of contacts NO normally open and NC normally closed. The normal position is the absence of a signal to the coil. Since the coil has no polarity, the connection of the contacts is arbitrary.

Such an apparatus is installed in control and automation circuits. Located between the actuator (eg contactor) and the reference source. The figure shows electrical circuit devices:

The picture shows an intermediate relay without voltage supply. If you apply it, the contacts will switch. The voltage in the coil can be different: 220, 24 and 12 volts.

How to connect the device is shown in the figure below:

In some cases, an intermediate type relay is used as a contactor, then the installation diagram will look like this:

As you can see, the intermediate relay has three groups of contacts that control the load and one group for holding the current in the coil. You can install an additional contactor, then the device is connected first to the contactor.

Also, this unit can be connected to a motion sensor. Thanks to him, it is possible to connect several powerful lamps to the motion sensor system. Installation is as follows: the winding of the fixture is connected to the sensor, and the power contact switches the load in the luminaire system. How to install such a sensor is shown below:

Another option for installing an electronic starter is to a thermostat. The diagram is shown in the picture (click to enlarge):

In this case, the connection of the thermostat and the starter is made in sequential order to the first phase and the neutral wire (in the diagram they are designated as T1 and K1, respectively). The installation of the remaining contacts of the starter is carried out evenly between the other phases.

Hi Geektimes!

The management of powerful loads is a fairly popular topic among people in one way or another related to home automation, and in general, regardless of the platform: whether it be Arduino, Rapsberry Pi, Unwired One or another platform, turn on or off some heater, boiler or duct fan sooner or later has to.

The traditional dilemma here is what, in fact, commute. As many were convinced of their sad experience, Chinese relays do not have the required reliability - when switching a powerful inductive load, the contacts spark strongly, and at one point they can simply stick. We have to install two relays - the second is for safety net for opening.

Instead of a relay, you can put a triac or solid-state relay (in fact, the same thyristor or field controller with a logic signal control circuit and opto-decoupling in one case), but they have another drawback - they heat up. Accordingly, a radiator is needed, which increases the dimensions of the structure.

I want to tell you about a simple and rather obvious, but at the same time a rare scheme that can do this:

• Galvanic isolation of input and load
• Switching inductive loads without current and voltage surges
• No significant heat generation even at maximum power

But first, a few illustrations. In all cases, TTI relays of the TRJ and TRIL series were used, and a 650 W vacuum cleaner was used as a load.

The classic scheme - we connect the vacuum cleaner through a conventional relay. Then we connect the oscilloscope to the vacuum cleaner (Caution! Either the oscilloscope or the vacuum cleaner - or better both - must be galvanically isolated from the ground! Do not climb into the salt shaker with your fingers and eggs! They are not joking with 220 V!) And see.

We include:

I had to almost at the maximum of the mains voltage (trying to tie an electromagnetic relay to the zero crossing is a deadly task: it is too slow). A short burst with almost vertical fronts blew in both directions, noise flew in all directions. Expected.

Turn off:

A sharp drop in voltage across the inductive load does not bode well - the surge flew skyward. In addition, do you see this noise on a sine wave milliseconds before the actual shutdown? This is the sparking of the relay contacts that have begun to open, because of which they will one day become attached.

So, it is bad to switch an inductive load with a "bare" relay. What will we do? Let's try to add a snubber - an RC chain from a 120 Ohm resistor and a 0.15 uF capacitor.

We include:

Better, but not much. The ejection slowed down in height, but remained generally preserved.

Turn off:

The same picture. The debris remained, moreover, the sparking of the relay contacts remained, although it was greatly reduced.

Conclusion: it is better with a snubber than without a snubber, but it does not solve the problem globally. However, if you want to switch inductive loads with a conventional relay, install a snubber. The ratings need to be matched to the specific load, but a 1-watt 100-120 ohm resistor and a 0.1uF capacitor looks like a reasonable option for this case.

Related literature: Agilent - Application Note 1399, "Maximizing the Life Span of Your Relays." When the relay is operating for the worst type of load - a motor, which, in addition to inductance, has a very low resistance at start-up - good authors recommend reducing the passport life of the relay five times.

And now let's make a knight's move - we will combine a triac, a triac driver with zero detection and a relay into one circuit.

What's on this diagram? On the left is the entrance. When "1" is applied to it, the capacitor C2 is almost instantly charged through R1 and the lower half of D1; The VO1 optical relay turns on, waits for the nearest zero crossing (MOC3063 - with a built-in zero detector circuit) and turns on the D4 triac. The load starts up.

Capacitor C1 is charged through the chain of R1 and R2, which takes about t = RC ~ 100 ms. These are several periods of the mains voltage, that is, during this time the triac will have time to turn on guaranteed. Then Q1 opens - and relay K1 is turned on (as well as LED D2, shining with a pleasant emerald light). The relay contacts bypass the triac, so then - until it is turned off - it does not take part in the work. And it does not get warm.

Shutdown - in reverse order... As soon as "0" appears at the input, C1 quickly discharges through the upper arms of D1 and R1, the relay is turned off. But the triac remains on for about 100 ms, since C2 is discharged through the 100 kilohm R3. Moreover, since the triac is held open by current, even after VO1 is turned off, it will remain open until the load current drops in the next half-cycle below the holding current of the triac.

Turning on:

Shutdown:

Nice, isn't it? Moreover, when using modern triacs that are resistant to rapid changes in current and voltage (all major manufacturers have such models - NXP, ST, Onsemi, etc., the names start with "BTA"), the snubber is not needed at all, in any form.

Moreover, if you remember the smart people from Agilent and see how the current consumed by the motor changes, you get the following picture:

The starting current exceeds the operating current by more than four times. For the first five periods - the time by which the triac is ahead of the relay in our circuit - the current drops by about half, which also significantly softens the requirements for the relay and prolongs its life.

Yes, the circuit is more complicated and more expensive than a conventional relay or a conventional triac. But it's often worth it.

Switching is the turning on or off of an electrical appliance to the network. For this, disconnectors, switches, circuit breakers, relays, contactors, starters are used. The last three (relay, contactor and magnetic starter) are similar in structure, but are designed for different load powers. These are electromechanical switching devices. Newbies often have questions like:

“Why does a relay have so many contacts?”;

"How to replace a relay if there is no similar pinout?";

"How to choose a relay?"

I will try to answer all these questions in the article.

What is a relay for?

To turn on the load, you need to apply voltage to its terminals, it can be constant and variable, with a different number of phases and poles.

Voltage can be applied in several ways:

Detachable connection (insert the plug into the socket or plug into the socket);

A disconnector (how you turn on a light in a room, for example);

Via a relay, contactor, starter or solid-state switching device.

The first two methods are limited both in terms of the maximum switching power and the location of the connection point. This is convenient if you turn on a light or a device with a switch or an automatic device at the same time and they are located next to each other.

For example, I will give a situation, for example (a boiler) is a fairly powerful load (1 - 3 or more kW). The input of electricity is in the corridor, and in the same place on the electrical panel you have an automatic boiler switch, then you need to stretch a cable with a cross section of 2.5 sq. mm. 3-5 meters. What if you need to turn on such a load over a long distance?

For remote control you can use the same disconnector, but the greater the distance, the greater the resistance of the cable, which means that you will need to use cables with a large cross-section, and this is expensive. And if the cable breaks, it will no longer be possible to turn on the device directly on the spot.

To do this, you can use a relay that is installed directly near the load, and turn it on remotely. This does not require a thick cable, because the control signal is usually from units to tens of watts, while a load of several kilowatts can be switched on.

Switches and disconnectors - needed to manually turn on the load, in order to control it automatically, you need to use relays or semiconductor devices.

Areas of application of the relay:

Electrical installation protection schemes. For automatic input of energy protection against low and high voltages, Current relay - for the operation of overcurrent protections, permission to start electrical machines, etc.;

Automation;

• Security systems;

  For remote activation.

How does a relay work?

An electromagnetic relay consists of a coil, an armature and a set of contacts. The set of contacts can be different, for example:

Relay with one pair of contacts;

With two pairs of contacts (normally closed - NC, and normally open - NO);

With several groups (for load control in independent circuits).

The coil can be designed for different AC and DC currents, you can match your circuit so as not to use an additional source to drive the coil. Contacts can switch both direct and alternating current, the magnitude of the current and voltage is usually indicated on the relay cover.

The power of the load depends on the switching capacity of the apparatus due to its design; on powerful electromagnetic switching devices there is an arc extinguishing chamber to control a powerful resistive and inductive load, for example, an electric motor.

The operation of the relay is based on the operation of a magnetic field. When current is applied to the coil, the lines of force of the magnetic field penetrate its core. The armature is made of a material that is magnetically attracted to the coil core. A contact copper plastic and a flexible lead (wire) can be placed on the armature, then the armature is energized and voltage is applied to the fixed contact via copper buses.

The voltage is connected to the coil, the magnetic field attracts the armature, it closes or opens the contacts. When the voltage disappears, the armature returns to its normal state by a return spring.

There may be other designs, for example, when the armature pushes the movable contact, and it switches from the normal state to the active one, this is shown in the picture below.

Bottom line: The relay allows a small current through the coil to control a large current through the contacts. The magnitude of the control and commutated (through contacts) voltage can be different and does not depend on each other. This gives us a galvanically isolated load control. This provides a significant advantage over semiconductors. The fact is that by itself a transistor or thyristor, it is not galvanically isolated, even more so directly connected.

Base currents are part of the current switched through the emitter-collector circuit, in a thyristor, in principle, the situation is similar. If the PN junction is damaged, the voltage of the switched circuit can get to the control circuit, if it is a button, it's okay, and if it is a microcircuit or, they will most likely also fail, so an additional galvanic isolation is implemented through an optocoupler or transformer. And the more parts, the less reliability.

Relay advantages:

simplicity of design;

maintainability. you can audit most relays, for example, clean the contacts from carbon deposits and it will work again, and with a certain skill, you can replace the coil or solder its terminals if they come off the outgoing contacts;

complete galvanic isolation of the power circuit and the control circuit;

low contact resistance.

The lower the resistance of the contacts, the less voltage is lost on them and the less heating. Electronic relays generate heat, and I'll briefly talk about them below.

Disadvantages of relays:

due to the fact that the design is essentially mechanical - a limited number of operations. Although for modern relays, it reaches millions of operations. So the questionable point is the disadvantage.

response speed. An electromagnetic relay is triggered in a fraction of a second, while semiconductor switches can switch millions of times per second. Therefore, you need to be smart about the choice of switching equipment.

if there are deviations from the control voltage, there may be a rattling of the relay, i.e. the state when the current through the coil is small, for normal holding of the armature, and it "buzzes" opening and closing at a high speed. This is fraught with its quick failure. Hence follows the following rule - for relay control analog signal must be fed through threshold devices such as a Schmidt trigger, comparator, microcontroller, etc.;

Clicks when triggered.

Relay characteristics

To choose the right relay, you need to take into account a number of parameters that describe its features:

1. Coil operation voltage. The 12 V relay will not work stably or will not turn on at all if you supply 5 V to its coil.

2. Current through the coil.

3. Number of contact groups. The relay can be 1-channel, i.e. contain 1 switching pair. Or maybe 3-channel, which will allow you to connect 4 poles to the load (for example, three phases 380V)

4. Maximum current through contacts;

5. Maximum switching voltage. For the same relay, it is different for DC and AC currents, for example 220 V AC and 30 V DC. This is due to the peculiarities of arcing when switching different electrical circuits.

6. Mounting method - terminal blocks, output for terminals, soldering to the board or.

Electronic relays

A conventional electromagnetic relay clicks when triggered, which can interfere with you when using such devices in household premises. An electronic relay, or as it is also called, is devoid of this drawback, but it generates heat, because a transistor (for a DC relay) or a triac (for an AC relay) is used as a key. In addition to the semiconductor key, a binding is installed in the electronic relay to ensure that the key can be controlled with the required control voltage.

Such a relay for control uses a constant voltage from 3 to 32, and switches an alternating voltage from 24 to 380 V with a current of up to 10 A.

Advantages:

low control current consumption;

lack of noise when switching;

a larger resource (a billion or more operations, and this is a thousand times more than an electromagnetic one).

Disadvantages:

• may burn out from overheating;

  is more expensive;

  if it burns down, it will not be possible to repair it.

The picture below shows a good diagram of connecting the relay to the network and load. A phase is connected to one of the power contacts, to the second load, and zero to the second load output.

This is how the power unit is assembled. The control circuit is assembled as follows: a power source, for example a battery or a power supply, if the relay is controlled by direct current, is connected to the coil via a button. To control an alternating current relay, the circuit is similar, an alternating voltage of the required magnitude is supplied to the coil.

Here it is obvious that the control voltage does not depend in any way on the voltage in the load, also with currents. Below you see the control circuit of the central locking activators of the car with bipolar control.

The task is as follows, in order for the activator to move forward, you need to connect plus and minus to its solenoid, in order to move it back, the polarity must be changed. This is done using two 5-pin relays (normally closed and normally open).

When voltage is applied to the left relay, plus is supplied to the lower wire (according to the diagram) of the activator, through the normally closed contacts of the right relay, the upper wire of the activator is connected to the negative terminal (to ground).

When voltage is applied to the coil of the right relay, and the left one is de-energized, the polarity is reversed: plus through the normally open contact of the right relay is supplied to the upper wire. And through the normally closed contacts of the right relay - the lower wire of the activator is connected to ground.

This special case I gave as an example that with the help of a relay it is possible not only to turn on the voltage to the load, but also to carry out a variety of connection and polarity reversal schemes.

How to connect a relay to a microcontroller

It is convenient to use a relay to control the AC load through a microcontroller. But a small problem arises: the current consumption of the relay often exceeds the maximum current through the pin of the microcontroller. To solve it, you need to strengthen the current.

The diagram shows the connection of a relay with a 12V coil. Here, the transistor VT4 of reverse conductivity, it plays the role of a current amplifier, the resistor R is needed to limit the current through the base (it is set so that the current is no more than the maximum current through the pin of the microcontroller).

A resistor in the collector circuit is needed in order to set the coil current, it is selected according to the magnitude of the relay operation current, in principle, it can be excluded. A reverse diode VD2 is installed in parallel to the coil - it is needed so that the bursts of self-induction do not kill the transistor and the output of the microcontroller. With the diode, the bursts will go towards the power source, and the energy of the magnetic field will stop working.

Arduino and relay

For amateurs there are ready-made relay shields and separate modules. To secure the outputs of the microcontroller, depending on the specific module, opto-decoupling of the control signal can be implemented, which will significantly increase the reliability of the circuit.

A diagram of such a module is here:

We talked about the characteristics of the relay, and so they are often indicated in the markings on the front cover. Pay attention to the photo of the relay module:

10A 250VAC - means that it is capable of driving the load alternating voltage up to 250V and with a current up to 10 A;

10A 30VDC - for direct current, the load voltage should not exceed 30V.

SRD-05VDC-SL-C - marking depends on each manufacturer. In it we see 05VDC - this means that the relay will operate from a voltage of 5V on the coil.

In this case, the relay has normally open contacts, only 1 moving contact. The connection diagram to the arduin is shown below.

Conclusion

The relay is a classic switching device that is used everywhere: control panels in switchboard industrial workshops, in automation, to protect equipment and people, to selectively connect a specific circuit, in elevator equipment.

It is very important for a novice electrician, electronics engineer or radio amateur to learn how to use relays and make diagrams with them, so you can use them in work and households, implementing relay algorithms without the use of microcontrollers. Although this will increase the dimensions, it will significantly improve the reliability of the circuit. After all, reliability is not only durability, but also reliability and maintainability!

Content:

Electricity has long and firmly entered all spheres of life and work of people. Numerous devices have become widespread, including those designed for power management. These are various types of relays, which are electrical switches that connect or disconnect a circuit under predetermined conditions. All such devices differ in design features and types of incoming signals. Without them, the operation of modern industrial equipment and many other electronic equipment is impossible.

Principle of operation and purpose

All relays are electromagnetic switching devices, with the help of which the necessary adjustment of the controlled object is carried out. The device is triggered after a certain signal arrives at it. Electrical circuits regulated using relays are classified as controlled. The signal supply circuit from the relay to the device is called the control circuit.

All relays are signal amplifying devices. That is, the feed even small amount electricity to the equipment, causes a more powerful circuit to close. The relays can be operated on AC or DC. In the first case, triggering occurs when the input signal has a certain frequency. With constant current, the operating state of the relay appears when the current flow becomes one-way, or electricity moves in two directions.

Thus, the relay is directly involved in the closing and opening of the circuit. These devices control the supply of voltage to devices and equipment that consume electricity.

Currently, mainly electronic relays are produced, controlled by reliable microprocessors. Analog control of a relay includes a whole complex, which includes transistors, resistors and other components of microcircuits. The use of a relay completely automates work processes, since a set time interval is set after which the equipment is turned on and off.

General relay device

The simplest relay circuit includes an armature, magnets and connecting elements. When a current is applied to the electromagnet, the armature closes with a contact and further closes the entire circuit.

When the current decreases to a certain value, the pressing force of the spring returns the armature to starting position, as a result, the circuit is opened. More accurate operation of the device is ensured by using resistors. Capacitors are used to protect against sparking and voltage surges.

Most electromagnetic relays have more than one pair of contacts. This makes it possible to control many electrical circuits at once.

Classification and types of relays

All relays are classified according to various criteria:

• According to the field of application, they are divided into control relays, protection and automation of electrical systems.
• According to the principle of operation, they can be electromagnetic, magnetoelectric, inductive, semiconductor and thermal.
• Depending on the incoming parameter, the devices are divided into current, power, frequency and voltage relays.
• By their effect on the control part, they can be contact and non-contact.

Depending on the controlled quantities, relay designs are divided into several main types:

• Electrical. With their help, electrical circuits are switched on and off. They are indispensable when working with large power loads.
• ... These devices use a coil with a reed switch, which is a vacuum cylinder. Sometimes it is filled with a certain type of gas. The reed switch is located inside the electromagnet.
• ... These devices use the principle of linear expansion of metals.

There are other types of relays, for example, operating according to special circuits using special reactive components.

An electromagnetic relay is a switching device for switching electrical circuits with an electromagnetic field.

Areas of use

Electromagnetic switching is used in automation circuits, control of electric drives, electric power and technological installations, in control systems, etc. The electromagnetic relay allows you to regulate voltages and currents, perform the functions of memory and converting devices, and fix deviations of parameters from the set values.

Principle of operation

An electromagnetic relay, the principle of which is common to any type, consists of the following elements:

1. Base.
2. Anchor.
3. Coil of turns of wire.
4. Moving and fixed contacts.

All parts are attached to the base. The armature is rotatable and held by a spring. When voltage is applied to the coil winding, an electric current flows through its turns, creating electromagnetic forces in the core. They attract the anchor, which turns and closes the movable contacts with the paired fixed ones. When the current is turned off, the armature is returned by the spring. Moving contacts move with it.

Only reed relays differ from the standard design, where the contacts, core, armature and spring are combined in a single pair of electrodes.

The electromagnetic relay, the diagram of which is shown below, is a switching device.

It is typical and generally shows how electrical energy is converted into magnetic energy, which then overcomes the force of the spring and moves the contacts.

The electrical circuits of the coil and commutation are not connected in any way. Due to this, small currents can control large ones. As a result, the electromagnetic relay is a current or voltage amplifier. Functionally, it includes three main elements:

• perceiving;
• intermediate;
• executive.

The first of these is a winding that creates an electromagnetic field. A controlled current passes through it, upon reaching a predetermined threshold value, an effect on the actuator occurs - electrical contacts that close or open the output circuit.

Classification

Relays are classified as follows:

1. By the way of managing contacts - anchor and reed contacts. In the first case, the contacts are closed-open when the armature is moved. In reed switches, there is no core and the magnetic field acts directly on the ferromagnetic electrodes with contacts.
2. The control current can be direct or alternating. In the latter case, the armature and core are made of electrical steel plates to reduce losses. For direct current, devices are neutral and polarized.
3. The relays are divided into 3 groups according to the response speed: up to 50 ms, up to 150 ms and more than 1 s.
4. Defence from external influences provides for sealed, sheathed and open devices.

With all the variety of types presented below, the action of an electromagnetic relay is based on general principle switching contacts.

The device of the electromagnetic relay is hidden inside the case, only the terminals of the winding and contacts protrude from the outside. They are mostly numbered, a connection diagram is given for each model.

Options

The main characteristics of the relay are:

1. Sensitivity - switching from a signal of a certain power supplied to the winding, sufficient to enable switching on.
2. Winding resistance.
3. Actuation voltage (current) - the minimum threshold value of the parameter at which the contacts switch.
4. Drop-out voltage (current).
5. Response time.
6. Operating current (voltage) - the value at which guaranteed switching on occurs during operation (the value is indicated within the specified limits).
7. Release time.
8. Switching frequency with load on contacts.

Advantages and disadvantages

The electromagnetic relay has the following advantages over semiconductor competitors:

• switching large loads with small dimensions;
• galvanic isolation between the control circuit and the switching group;
• low heat generation on contacts and coil;
• small price.

The device also has disadvantages:

• slow response;
• relatively small resource;
• radio interference when switching contacts;
• the complexity of DC switching of high-voltage and inductive loads.

The operating voltage and current of the coil must be within the specified limits. At low values, contacting becomes unreliable, and at high values, the winding overheats, the mechanical load on the parts increases, and insulation breakdown may occur.

The durability of the relay depends on the type of load and current, frequency and number of operations. Most of all, contacts wear out when they open, forming an arc.

Non-contact devices have the advantage that they do not have an arc. But there are also many other disadvantages that make it impossible to replace the relay.

Electromagnetic current relays

The current and voltage relays are different, although their structure is similar. The difference lies in the design of the coil. The current relay has a small number of turns on the coil, the resistance of which is low. In this case, the winding is done with a thick wire.

The voltage relay coil is formed big amount turns. It is usually included in the existing network. Each device controls its own specific parameter with automatic switching on or by disconnecting the consumer.

With the help of a current relay, they control its strength in the load to which the winding is connected. Information is transferred to another circuit by connecting a resistance to it with a switching contact. Connection is made to the power circuit directly or through measuring transformers.

Protective devices are fast and have a response time of several tens of milliseconds.

Time relay

In automation schemes, it is often necessary to create delays when devices are triggered or to send signals for technological processes in a certain sequence. This is done using time delay switches, which have the following requirements:

• stability of exposure regardless of the impact of external factors;
• small size, weight and energy consumption;
• sufficient capacity of the contact system.

For the control of electric drives, high accuracy requirements are not imposed. The shutter speed is 0.25-10 s. Reliability must be high, since work is often carried out under conditions of shock and vibration. Power system protection devices must work accurately. Exposure does not exceed 20 sec. Actuation occurs quite rarely, therefore, high requirements for wear resistance are not imposed.

Electromagnetic time relays operate on the following deceleration principles:

1. Pneumatic - due to the presence of a pneumatic damper.
2. Electromagnetic - with direct current, there is an additional short-circuited winding in which a current is induced, which prevents the growth of the main magnetic flux when triggered, as well as its decrease when it is turned off.
3. With an anchor or clock mechanism, which is wound up from an electromagnet, and the contacts are triggered after the countdown.
4. Motor - supplying voltage simultaneously to an electromagnet and a motor that rotates the cams that activate the contact system.
5. Electronic - using integrated circuits or digital logic.

Conclusion

With the advent of the era of electronics, the electromagnetic relay is gradually being supplanted, but it still develops, reaching new possibilities. It is difficult to find an alternative to it in places where there are current and voltage drops when starting and disconnecting devices using electricity.