Differential switch (life saver). The Importance of Verification.

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The differential switch, often called lifesaver, performs an important function for the protection of people, starting from the domestic to the industrial sector. In electrotechnics it is classified as a safety device, in fact it offers protection against electrical faults to earth or phase-to-earth electrocution.

The principle of operation, simplifying the circuit, can be explained as follows.

In normal operation, the current which passes through the phase and the neutral is the same, therefore the residual current device continues to operate without interruptions. The electrical appliance or set of appliances connected to the differential will absorb a certain current, but the sum of all the currents drawn from the phase must “return” from the neutral, in short.

In this figure the circuit is simplified because the magneto-thermal protection is missing, which we will deal with in another article.

If for some reason a person comes into direct contact with the live or neutral, there is a condition of direct contact fault: essentially the person acts as an electrical appliance and typically a dangerous electric current flows through the limbs. In this case the residual current device “feels” this change because a part of the current I1 flows in the person’s body as current I2. It follows that the current drawn from the phase does not completely “return” to the neutral, but a part is “drawn” by the person. If the difference between the current entering the phase and leaving the neutral exceeds a certain threshold, the circuit breaker “trips” and interrupts the flow of electricity, often saving people’s lives. This threshold is the rated differential tripping current and is stamped on the switch. In the civil field RCDs with current of 0.03 ampere (0.03A), or 30 milliampere (30mA) are used. In industry, on the other hand, different and programmable RCDs are installed in the tripping current, depending on various factors such as selectivity, the type of loads, the type of circuit protection.

If for some reason a person comes into direct contact with the phase or the neutral, there is a fault condition as in the following figure. In this case the differential switch will trip because the two currents I1 and I3 are different from each other and exceed the safety threshold.

The most common case, on the other hand, is due to a loss to ground of an electrical appliance. This may depend on various factors, loss of insulation, end of life failure, production defect, or due to causes attributable to the electrical system. Even a single outlet can contribute to ground fault or the electrical system itself losing insulation in some places due to various causes.

Maintenance. Because it’s important

We have seen how differential switches intervene and can in some cases be real safety devices for people, in any field: civil, commercial, industrial.

But how do I know if the differential will protect me when I need it? I’m sure it will work, after years of being active 24H?

The answer is there periodic check.

They exist today automatic reset differentialswith system self check, control and reporting. But these differentials, also due to the cost, or due to lack of information, are still little used, therefore the presence of manual switches represents the majority of installations.

There are certified tools and certain procedures to check every point of your electrical system, e we at RZ can do it thanks to our investments in proper instrumentation and professional trainingas people’s safety comes first. The legislation requires the differential switch to be tested on a monthly basis.

A very simple do-it-yourself procedure is to use the test button, present on the differential. This button, if pressed, gives rise to the fault condition and must trip the circuit breaker. Otherwise we strongly advise you to have your system checked by a professional.

Here’s how to do the do-it-yourself tests for the monthly differential check. Just press the test button, marked with a T.

Manual differential example 1

Manual differential example 2

#Electrical system #Renovations #maintenance

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