3 Phase 4 Wires System Can Apply 3 Poles CB?

You're not the only one.

Can you send copies of the schematics, plans, specifications, and purchase order to us for review? Oh, and specs for the CB's?

What color are the wires?

What gauge are the wires?

What polarity are the poles?

Yes, but there are cases in which a 3P+N CB is needed.

It might help more to say what the load is, rather than what it is not.

If you are not having secondary backup power (DG supply), then you can provide three pole breaker without switched neutral instead of 4 pole switched neutral breaker. The idea is to avoid providing multiple neutral earthing points.

I would expect the norm to switch the "hot" three wires and not the neutral. If the contactor failed to engage the neutral, unpleasant things could happen when the load was unbalanced. As every one else said, special cases do occur.

We may be getting too complex here assuming a neutral wire. Customer's can relay information in strange ways. Your customer, if like half of mine, may not be very well versed in industrial electricity and may be counting the ground as a "wire" not realizing he is setting off alarm bells because we are assuming that is a neutral conductor. So maybe you are getting three phases and a ground conductor (earth) - quite a normal situation. Check with your customer and verify what the fourth wire is.

Basically, for LV side, there is always come with 3Phase 4 wire where the 4th wire is a neutral. There are other method that we used for these situation. First you can use 4 pole MCCB which mean 3 phase + Neutral or you can used a 3 Phase MCCB with a neutral link at the side of the MCCB.

The neutral wire will be connected to the neutral link. But make sure that this is not for generator power system. For normal load it is o.k.