Dry contact wiring is a common method used in electrical systems, but it often confuses people who are not familiar with electrical wiring. A dry contact refers to a contact that is not energized by voltage. It is also known as a volt-free contact or a relay contact. Dry contacts are commonly used in control circuits to communicate with other devices without the need for a high voltage supply. In this article, we will explore the basics of dry contact wiring and provide an easy-to-follow diagram for better understanding.
What is a Dry Contact?
A dry contact is essentially an electrical switch with no voltage. It is a switch that does not have a power source or a supply voltage, so it is not connected to any power source. This is why it is called a “dry” contact. Instead, a dry contact relies on the use of another device to supply the power necessary to open or close the circuit. For example, a relay or a PLC (Programmable Logic Controller) can be used to energize a dry contact.
Dry contacts are commonly used in control circuits to communicate with other devices without the need for a high voltage supply. An example of this is a thermostat, which uses a dry contact to switch on the heating or cooling system to maintain a desired temperature.
Why Use a Dry Contact?
There are several reasons why you might want to use a dry contact in your electrical system. One of the most common reasons is to isolate the control circuit from the power circuit. This means that the control circuit is not affected by any changes in the power supply, ensuring that the system operates independently and reliably.
Another reason for using a dry contact is to protect sensitive equipment. By using a dry contact, you can ensure that the equipment is not damaged by voltage surges or power spikes that could occur in the power circuit.
Dry Contact Wiring Diagram
To better understand dry contact wiring, it is helpful to have a diagram to follow. Below is a simple dry contact wiring diagram:
| Dry Contact Wiring Diagram | |
|---|---|
| Device A | Device B |
| NO1 | NO2 |
| COM1 | COM2 |
Device A could be a thermostat or a sensor, while Device B could be a contactor or a motor starter. NO1 and NO2 stand for normally open contacts, while COM1 and COM2 stand for common contacts. In a normally open contact, there is no connection between the contacts until the contact is closed. Once the contact is closed, the circuit is complete.
When the contact in Device A is closed, it energizes the coil in Device B, which in turn closes the contact between NO2 and COM2. This allows power to flow to the load connected to Device B.
FAQ
What is the difference between a dry contact and a wet contact?
A dry contact is a contact that is not energized by voltage, while a wet contact is a contact that is connected to a power source or a supply voltage. A wet contact is also known as a live contact.
Can a dry contact be used to switch on a light?
Yes, a dry contact can be used to switch on a light. However, it would require an external power source to supply the necessary voltage to the light. This makes it more practical to use a wet contact instead.
What is the advantage of using a dry contact?
The advantage of using a dry contact is that it enables you to isolate the control circuit from the power circuit, protecting sensitive equipment and ensuring reliable operation.
What devices are commonly used to energize a dry contact?
Relays and PLCs (Programmable Logic Controllers) are commonly used to energize a dry contact.
Can a dry contact be used to switch on a high voltage circuit?
Yes, a dry contact can be used to switch on a high voltage circuit. However, it should be used with caution and appropriate safety measures should be taken to prevent electrical shock or injury.
In conclusion, dry contact wiring is a simple and effective method used in many electrical systems. By using a dry contact, you can isolate the control circuit from the power circuit and protect sensitive equipment, ensuring reliable operation. The dry contact wiring diagram provided in this article should help you to better understand and implement dry contact wiring in your own electrical systems.
