Have you ever encountered a neutral cable being disconnected by a circuit breaker? Many electricians say that it is forbidden to interrupt the neutral cable, but it is possible to disconnect the neutral with a four-pole circuit breaker. In this article we are going to show what the NBR 5410 standard talks about sectioned neutral cable.
Tetrapolar Circuit Breaker
The circuit breaker is a protection device, which has the function of disarming when an electric short-circuit or overload current is identified, being essential to avoid accidents and damage to the cables.
There are several models and types of circuit breakers, for example, the monopolar, used in installations and circuits that have only a single phase, bipolar used in circuits or installations with two phases, three-pole suitable for installations and circuits with three phases and finally the tetrapolar for facilities and circuit with three-phase and one neutral.
The four-pole circuit breaker has four poles allowing the neutral cable to be disconnected. The big question for electricians is whether or not to disconnect the neutral cable, as the other circuit breakers do not allow the disconnection of the neutral cable.
Neutral at the circuit breaker
To find out if we can disconnect the neutral cable, we should always refer to the NBR 5410 standard. The NBR 5410 standard has a part that talks about the protection for the neutral cable, starting from item 188.8.131.52. There are cases where the neutral has to be protected against overcurrent and this has a little to do with the grounding system.
For TT and TN grounding cases, item 184.108.40.206.1.1 says that: When the section of the neutral conductor is at least equal to or equivalent to that of the phase conductors, it is not necessary to provide for detection of overcurrent in the neutral conductor or device disconnection in that conductor.
This is the most common case and because of item 220.127.116.11.1.1 that most professionals in the Electrical Industry understand that there is no need to use a circuit breaker for the neutral. In the item the phrase “not necessary” is used, that is, this phrase does not oblige and does not prohibit the use of a circuit breaker for the neutral.
The next item in standard NBR 5410, 18.104.22.168.1.2 says that: When the section of the neutral conductor is smaller than that of the phase conductors, it is necessary to provide for the detection of overcurrent in the neutral conductor, suitable for the section of this conductor.
These cases are very specific, normally used in industrial areas and in these cases it is mandatory to use a circuit breaker that cuts the neutral.
The standard still says something very important in item 22.214.171.124 that deals with the sectioning and closing of the neutral conductor, in this item the standard says that: When the sectioning of the neutral conductor is required, the opening and closing operations of the corresponding circuits must be of in order to ensure that the neutral conductor is not sectioned before or restored after the phase conductors.
Item 126.96.36.199 was placed exactly, because if there is a different closing or opening time between the phase and neutral cables, what we call interrupted neutral can occur. The interrupted neutral can cause the outlets to have a higher voltage than they should, causing serious accidents or even burning equipment.
Tetrapolar Circuit Breaker – When to use
Many electricians think that the four-pole circuit breaker is only used for electrical controls , but not! Four-pole circuit breakers can be used for the assembly of QTA’s, which are automatic transfer frames between network and generator.
In the QTA’s, the neutral of the electric network must be disconnected for the input of the generator neut