This document explains why there can be confusion when some of the installation manuals which recommend using a 2-pole or 4 pole MCB when installing a range of UPS systems, such as Smart UPS and Easy UPS. It also sets out when a single or 3 pole MCB may be used.
Technical Description
At Schneider Electric we strive to make our UPS systems as versatile as possible so that they can be used in TN-S, TN-CS, TT or IT Networks.  There are also some rare cases where an electrical supply delivers 240V using 2 phases.  Therefore, many European Regulations such as the NFC 15-100 in France or the REBT in Spain will require the MCB to disconnect both phase and neutral in the event or a fault.
This would also be the case in countries where the prevalent earthing system is the TT network.
Solution:
The best solution in such cases is always to comply with local regulations.  In many of the installation manuals, it states that a typical MCB for such an installation would be a 2 or 4 pole breaker.  In this case, what is meant is that a 2 or 4 pole breaker is commonly or regularly used in such an application. It does not state that this breaker
type is mandatory.  In an area where the earthing network is a TN-CS or TN-S it is perfectly acceptable to use single pole for a single-phase installation or a 3-pole breaker in the case of a 3-phase installation. From the installers’ point of view, it doesn’t make sense to modify the distribution board to accommodate other breakers types.
First of all, it would require a major reworking of the way electrical panel boards are designed and manufactured, and since this has never been a problem, there’s no incentive to do this.
On the output RCBO's may be required and they are always double pole.
To summarise, for countries where the earthing system is a TN-S or TN-CS, we can advise customers that a single or 3-pole breaker is permissible if it complies with  local regulations.