There is a simple circuit for connecting a voltage relay in conjunction with a contactor. Many masters are delighted with such an invention, since at first glance the scheme has some advantages, but in reality it is not and there are several hidden negative moments.
What is the advantage
A legitimate question: why add a contactor to the circuit if you can limit yourself to only a voltage relay? Then, that the contactor is able to withstand a solid load, which the relay simply will not "pull". And such a scheme can already be attributed to the most primitive, but still automation.
What other advantages of the relay / contactor bundle:
- It makes no sense to buy a relay of a large rating, because in this circuit it is necessary exclusively to control the contactor.
- The contactor can be connected to wires from powerful consumers, such as hobs, instantaneous water heaters, autonomous heating boilers, etc.
It turns out that you can save on relays, and the circuit itself can be performed more competently. But not everything is so simple, because any switching device has one important indicator - the response time, and this is important in this case.
The very reverse side of the coin
Firstly, any additional element in the electrical panel is bad. A simple rule not only of electrical engineering, but also of any other technical industry: the more elements, the more likely it is that some will fail. So there was one voltage relay - a device that is quite complex in itself, and also a contactor appeared.
Secondly, this is the response time and in this circuit everything depends on the contactor. The voltage relay for a few milliseconds sends a signal to the control winding of the contactor, which also needs time to "think". And modern electronics are so sensitive that such a delay can be quite enough for the failure of several small capacitors. Therefore, seemingly insignificant milliseconds should also be taken into account.
And insignificant, but still a minus. A place. Yes, yes, to install the contactor, you must order a spacious electrical panel, since this device is notable for its volumetric dimensions. It turns out that all the savings on a smaller relay rating will be spent on the purchase of a contactor and another, more voluminous shield. A legitimate question arises: is there really so much benefit from such a scheme that it exceeds all the disadvantages?
Does it make sense to install a voltage relay in conjunction with a contactor?
No, it doesn't make any sense. The contactor will only add problems and money spending both at the purchase stage and in the future, in the event of possible malfunctions. Therefore, the best option is to install a separate voltage relay. By itself, the device will cope no worse than in conjunction with a contactor.
And then you don't have to buy a more capacious cabinet, a contactor, install it, check the operability and further monitor the correct operation of the devices. It turns out that there are only pluses from the choice of one voltage relay than with an additionally installed contactor.