When it comes to choosing a home automation machine, many people usually rely on the total power of the appliances connected to the branch/area and put in a good supply of current to protect themselves from false alarms. Not every electrician knows about the time characteristics of the current. In this article we will go a little deeper into the theory, consider some important points and derive the simplest rule from all the above mentioned, which will help us to be sure of reliable and timely triggering of the safety automatic machine.
First of all, the automatic machine is designed to protect the wiring against fire and destruction. Electrical devices, as a rule, the dispenser does not protect, nor does it protect a person from electric shock – this function is performed by a differential switch or a differential automaton. So, if it protects the wiring, then the rating should not be overrated to avoid unnecessary tripping – if the wiring is in danger of fire or destruction, no power reserve should be mentioned! Simple wisdom: if you want reliable protection and minimal tripping, increase the cross-section of conductive wires within a reasonable range.
There is a misconception that if the wiring withstands a current equal to that of the machine, then everything is fine and there will never be a fire. This is far from the case. In the last article we superficially touched upon the topic of wiring and automatic machines, but the main thing is that we got acquainted with the table, which specifies the currents for different cross sections of wires. Now we will use this table and see which wires have the nominal value of which machine can be protected.
Modern automatic machines have two built-in protections: an electromagnetic breaker and a thermal breaker, each of which performs its important function. The EMC is designed to protect against short-circuits and sometimes faulty electrical appliances. The short-circuit current is very high and very dangerous for wiring, metering devices, so it is necessary instantaneous operation of the machine, usually the time of operation of the electromagnetic release does not exceed 0.1 seconds or less (depending on the class of current limit of the machine), depending on the particular device. The tripping current of such a tripping device is 5-10 times higher than the nominal tripping current! Naturally, it will not protect against slight overload. For protection against overloads the thermal breaker is intended. Time of its operation is considerably longer than at magnetic, however the thermal release even from insignificant overloads operates. The thermal release can also be triggered in a second, or it can “think” for a whole hour. So, if 5-10 multiple overloads within 0.1 second of the wire such machine will survive, then the whole hour “hang” under a current 1.5 times the nominal value of the machine can not every wire! Therefore, let us pay attention to a slower but more sensitive protection – the thermal breaker of the dispenser.
There is no specific figure corresponding to the rating of the dispenser, only the time and current characteristic from the dispenser manufacturer. We will not consider the graphs today, so as not to make even more confusion, we will consider only two important values: conditional non-disconnection current 1.13in and conditional release current 1.45in. Conditional non-detachment current is the current at which the automaton is guaranteed to operate for at least one hour (for automats with a nominal value less than 63A). In fact, to install the electrician and all additional devices you better use the services of nyc electric company.