Conductor sizing between main distribution block and submain busbar within an enclosure

[Timon_]

Greeting, In Linergy catalogue (Reference LVYED213001EN) on pages 6 and 7 there is a depiction of submain busbars of several rows being fed from main distribution block. How are cross section and insulation material properties of these conductors being determined given that they are not overload protected and possibly not short-circuit protected due to cross section being decreased?

[RHH]

Hello @Timon_ ,

I do not know how the insulation thickness etc. is tested and determined as I am not a manufacturer of these distribution blocks.
There are probably standards and regulations for this. Perhaps Schneider Electric could give a full answer.

However just like your head switch in your panel, is just a ''switch''. There is no protection from the standard switch.
The standard switch will burnout by exceeding its capable Amperage, this will be the same for your distribution block.
Thats why most of the panels are protected by fuses at the transformer side or main switchboard. (Or if protection is not at the transformer, main switch of the panel = fuse / breaker).

Your distribution (blocks) do not need to have protecting capabilities as the protection is at your transformer (feeding side) or your breakers (user side). It only has one use, that is distributing currents to your breakers.

[Timon_]

Hello, @RHH. My question wasn't about main distribution block which is downstream of the main switch/main circuit breaker as sizing it is pretty straightforward because as you've mentioned it most likely is being overload and short-circuit protected by either main circuit breaker or some other device upstream. My question was about how do you size busbars and their conductors immedietly downstream of main distribution block (for example comb busbars connecting multiple MCBs and conductor suppying it) which aren't short-circuit and overload protected.

As for conductors and their insulation material properties which aren't short circuit protected I think I found the answer. Looks like according to IEC 61439-1 such conductors with 70deg C PVC insulation have to be routed away from any combustible materials. 90deg C PVC ones don't have any particular requirements.

[RHH]

Hey @Timon_ ,

Correct, what I was trying to say is there are no regulations concerning the busbars in the meaning of protection.

Cause they don't have to. They are not there to protect anything and the chance of being the concern or cause of an defect is slim to very low, as panel builders follow IEC while building and wiring them. However the bigger copper/aluminum (250A+) rail bars have a max. kA value that can be hightened with more supports closer to eachother.

As in the standard regulations state; you need to wire the mcb's with the correct copper/cable thickness for the amperage.
As far as I know of, most of the bars I know are fit for 80A. (industrial) But this is not a certainty with lots of different bars out there.

I didn't know of and about the certain thickness and insulation requirements, thanks for the involvement and insight in that matter. As I previously mentioned someone would know about these specification exactly from the manufacterer, like Schneider Electric.

We as panel builder standardized 90 degrees in wiring etc. a while ago, might be the reason we have not been looking into the specifications that deeply anymore. Again thanks for the heads up!

[PascalL · Accepted solution]

Hello @Timon_ 

Regarding  question : How are cross section and insulation material properties of these conductors being determined given that they are not overload protected and possibly not short-circuit protected due to cross section being decreased?

Regarding cross-section about rating, the cables are sizing at the same rating of the distribution block. They are tested according that performance with the IEC61439-2 as built-in components.

Regarding cross section about short-circuit, the cable are sizing taking to account about the coordination performance between upstream and down stream performance. The worst case performances has been tested.

The standard IEC61439-1/2 precise :

8.6.1 Main circuits

The busbars (bare or insulated, see 3.1.5) shall be arranged in such a manner that an internal

short-circuit is not to be expected. They shall be rated at least in accordance with the requirements concerning the short-circuit withstand strength (see 9.3) and designed to

withstand at least the short-circuit stresses limited by the protective device(s) on the supply side of the busbars.

This rule is important because if not, we should size for example the cross section of connection to distribution block or MCCB breakers connected to the distribution busbar with the same cross section of the main busbar dimensioned to ICC or ICW.

Best regards,

PascalL.

pascal.lepretre@se.com