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Installation with Single / 2-Pole or 3/4 Pole MCB’s

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.

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.

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.

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