Using FR 303 vs FR 304 as Main Switch in 3-Phase Installation: When and Where?

Hello ,
I would like an explanation when and where FR 303 or FR 304 should be used as
main switch in a 3-phase installation?

You raised a very important point - I am curious about other colleagues' opinions. According to the applicable regulations, fire protection switches in TN-S installations should disconnect all working conductors, i.e. L1, L2, L3 and N, while in receiving installations?
It is known that in fire protection, all current paths should be disconnected, and in installations located in explosion hazard zones, or if such are the requirements of the manufacturer of a device. The second issue is the selection of the apparatus - is the N pole disconnected last - and connected first?
In the PN-IEC 60364-4-473 standard Overcurrent protection measures (473.3.3) - there is a provision:
If disconnection of the neutral conductor is envisaged, the disconnection and reconnection should be carried out in such a way that the neutral conductor cannot be disconnected earlier than the disconnection of the phase conductors, and the neutral conductor should be connected at the same time as the phase conductors or earlier.
So closing is allowed if all contacts of the switch are switched on and off by a common lever - simultaneously.

In my opinion, the use of the FR 304 disconnecting the N (neutral) wire as the main switch in the "normal installation" is a mistake. I do not know about other colleagues, but I see a difference in the markings 3+N and 4-pole. Sometimes, however, logical thinking related to technical knowledge is missing - just like in the quoted standard.

Hello.

I agree with Akrzy74, I have had many cases that with 4-pole FR the contacts were unevenly connected. This, of course, caused damage to the receivers.

Regards.

For comparison - this photo -

Citation col. Piciu1

Quote:

I have had many cases that with 4-pole FR the contacts were unevenly connected. This, of course, caused damage to the receivers.

Me too. Switching off will occur instantly, but when we switch on, it may happen that we switch on two phases first - and the connection of the N contacts may take place later. Unfortunately, ordinary FRs have contacts that are switched on and off at the same time - just look at the contact diagram on the switch. Many electricians who assemble such devices do not know what the difference is (unfortunately) - let alone an "amateur" of electrics ...

I will quote PN-IEC 60364-5-53:2000
Selection and installation of electrical equipment. Switchgear and control apparatus.

531.2.1.1. Residual current protective devices should ensure disconnection of all active conductors of the circuit. In TN-S systems, the neutral conductor is not required to be disconnected if it can be assumed that this neutral conductor is at earth potential under the given supply conditions.

NOTE - The conditions for verifying that the neutral is at ground potential are under development.

It is true that this point concerns the RCD, but there is still talk about interrupting the N conductor. Maybe there is an answer here?

Maybe "a few more" sentences regarding disconnecting the neutral wire in the installation
Col. rumik_l wrote-

Quote:

I will quote PN-IEC 60364-5-53:2000
Selection and installation of electrical equipment. Switchgear and control apparatus.
It is true that this point concerns the RCD, but there is still talk about interrupting the N conductor. Maybe there is an answer here?

Maybe yes, maybe not
In TN-S systems, the neutral conductor can be isolated or connected. (60364-4-46).
If the cross-sectional area of the neutral conductor in a TT or TN network system is at least equal to or equivalent to that of the phase conductors, detection of overcurrents in the neutral conductor or equipping it with a current interruption device is not required.
If the cross-sectional area of the neutral conductor is smaller than that of the phase conductor, detection of overcurrents in the neutral conductor related to its cross-section is required. The consequence of detecting such a current should be the disconnection of the phase conductors - but not necessarily the neutral conductor.
Overcurrents are not required to be detected if two conditions are met simultaneously:
- the neutral conductor is protected against short-circuit current by a protection device for the phase conductors
- the highest predicted value of the current in the neutral conductor during normal operation is clearly lower than the long-term current carrying capacity specified for this conductor. (60364-4-473)

robsonoski wrote:

Hello ,
I would like an explanation when and where FR 303 or FR 304 should be used as
main switch in a 3-phase installation?

For now, this discussion doesn't explain anything. Because he can't explain. Well, unless Col. robsonski write what he is talking about.

Akrzy74 wrote:

I do not know about other colleagues, but I see a difference in the markings 3+N and 4-pole.

It probably means that N is then understood as the neutral pole, intended only for switching operations in the neutral line, incapable of making and breaking the short-circuit current.
In general, circuit breakers are divided into dependent and independent circuit breakers. In dependent, the speed of closing the contacts depends on the speed of moving the drive element. According to the standard, the N pole should close earlier and open later than the other poles. In circuit breakers with independent operation, the speed of closing the contacts does not depend on the speed of moving the drive element, and there it is required that all poles close practically simultaneously.