Cross-Section Wire Selection in Switchgear: Guidelines for Overcurrent Circuit Breakers

Hello,

I would like to make sure that the cross-sections of wires in the switchgear before the overcurrent circuit breakers are selected in the same way as for the installation behind the circuit breakers?

Thanks in advance for the information!

wtct wrote:

I would like to make sure that the cross-sections of wires in the switchgear before the overcurrent circuit breakers are selected in the same way as for the installation behind the circuit breakers?

And are there any other protections besides those in the transformer station???

Cross-sections are selected due to:
- long-term load capacity
- voltage drops
-mechanical strength
- overload capacity
- short-circuit conditions
- and fire protection

... And if the conditions mentioned above by a colleague bartekfigure are the SAME before and after the circuit-breaker, then the entire section of the installation is made with the SAME cross-section.
Especially since the current before the circuit breaker is the same as after the circuit breaker.

Rzuuf wrote:

Especially since the current before the circuit breaker is the same as after the circuit breaker.

In normal working condition yes. But not in an emergency.

lordpakernik wrote:

Same.

The same (in the sense of methodology), but the protection against the conductor in question should be taken into account! I do not know any new regulations in this matter (if anyone knows, please complete), but according to PN-57/E-05022, the following conditions had to be taken into account in the use of protection at branches:

- cross-section of the branching cable (i.e. "behind the circuit-breaker" in the example described) not smaller than 3 consecutive standardized cross-sections from that supplying the switchgear,
- wires from the branch to the protective device must be protected against mechanical damage (in my opinion, the cover is the switchgear housing),
- the cable cannot pass through a room with an explosion hazard (here the switchgear is rather not built in such a room),
- the length of the section in non-industrial facilities cannot exceed 1m (in a small switchgear it is not a problem, in a large one not necessarily).

So to sum up, with a small switchgear in an apartment/house it is important to take into account the condition with cross-sections. If a 10 mm² wire enters the switchgear, you cannot use less than 2.5 mm² in front of "eSami" (subsequent cross-sections (6, 4 and 2.5), even if it is a lighting circuit, then 1.5 mm².

This cross-section must be converted to the same material for different cable materials). Of course, it may be that the previous protection is suitable for the section from which the branch is made - this must be checked when making the switchgear.

TWK wrote:

In normal working condition yes. But not in an emergency.

The emergency operating state, i.e. short-circuit conditions, may be different.

zbich70 wrote:

And are there any other protections besides those in the transformer station???

There is an RCD in front of the overcurrent circuit breakers and a 20 A overcurrent circuit breaker in front of the meter.