How to Calculate Incomer Breaker Sizing for a 3 Phase 4 Wire 415V 50Hz UPS DB

check this please

Calculation & sizing the Circuit Breakers

a breaker protects wire from carrying too much current.....start there then move to the loads and their expected amperage draws, you're protecting wiring not machinery with a breaker

Give your client their money back and admit that you are incompetent.

haha

Are you not supposed to ask the correct questions being the designer/ installer of the system. There are very many pertinent data you have to submit before you can expect forum experts to offer the answer. How about getting data of required battery back up capacity and the charging voltage for a start?

Dear All

Simple thumb rule is current drawing capacity is 18 Amp.for 3-phase system.So take 32 Amp 4- pole ,is appropriate for its incoming rating.

The OP has not specified whether it is online or offline UPS, the power factor, crest factor, short term overload capacity of UPS, % Harmonics as per UPS vendor specification, peak charging current from dead charge, voltage at which charging takes place, % efficiency of the UPS, prospective fault current at both incoming and outgoing side, provision of double wound isolation transformer etc. As a designer/installer (client relationship), he is supposed to drive all these parameters and incorporate in the design. Very unfortunate that he is clueless about what is needed. In fact I am not sure whether he is asking how to determine the rating of UPS incomer switch or incomer rating of UPS distribution DB. Also as stated by other peers in the thread, the 8 Nos. 20 Amps TP outgoing MCB of UPS DB defies logic. Also not sure whether it Harmonic immunised series MCB and whether the neutral bus and conductors are rated for twice the current rating of main phases.

Impossible to be of help with such pathetic inexperience.

Your question is full of question mark. How can the incoming only 10kva only which required to serve 8 outgoing. Please be more specific.

British Standard 7671 again. <sigh>

From the data provided by you the 3phase 415VAC 10KVA power inverter will draw about 14A @ 415VAC and unity power factor. For you to get the MCB size @ input side, multiply 14A by a factor 1.5. That gives you 21A. As you know already, there is no 21A conventional MCB. So, go for a 25A MCB with 4poles. As for the battery charging and outage conductor, use a 25mm2 flexible copper type. That solves your problem. However, you have work to do on the DFB. Use your Clamp meter to pick the loads at startup, ramp up, and the continuous modes respectively. Multiply your ccontinuous load results each by a factor 1.35. That helps you to professionally select MCB sizes per load

Otherwise, if what you meant is the incomer at the UPS incomer, the average current per phase of a 3 phase 10KVA UPS is 14A @ 415VAC and unity power factor. Be professional in your choices. Forget the already existing UPS DFB MCB ratings of 20A each, 8 nos. Your incomer must not be more than 16A 3poles. So, total load per phase must not exceed 14A. Infact, you must not load the inverter beyond 80percent of 14A so that overload circuits don't respond too often. Please, do away with those junks of unreasonable MCBs. Make sure you properly distribute and balance the loads, so as to avoid line imbalances.

For 10 KVA UPS the out put current would depend upon UPS output voltage.

is output 3 Phase 380V / 400V / 415V etc.....