Electrical Question No.25 - Load Calculation and diversity factor
one mcc panel contains feeders for 4 nos 5 hp motor,2 nos 10hp motor,3 nos 3hp motor,3 nos 1.5 hp motor.what will be the amps rating of incoming feeder?

#1
Thu, October 23, 2008 - 18:44
The connected load of an electrical installation is generally more than its actual maximum demand at any time. The reason is the liberal provisions made for loads that are to be used occasionally - spare feeders, maintenance power sockets and some reserve capacity available with most of the outgoing feeders. Moreover, some of the feeders may be operating under loaded. To design a switchgear assembly, particularly for its incoming feeder and the busbar ratings, based on the connected load would be neither economical nor prudent, and the protective scheme too would under-protect such a system.
Based on experience, IEC 60439-1 has suggested a multiplying factor, known as the ‘diversity factor’ as noted in Table 1. This factor depends upon the number of outgoing circuits and is defined by the ratio of the maximum loading on a particular bus section, at any time, to the arithmetic sum of the rated currents of all the outgoing feeders on that section. This factor also helps to determine the most appropriate and economical ratings of the main equipment, such as the transformer, cables or the bus system, associated switchgear and the protective devices
The values of Table 1 are based on a general assumption, and may vary from one installation to another depending upon the system design, the derating factors considered and any other provisions made while choosing the rating of a feeder (outlet), as noted above. It is therefore recommended that this factor be specified by the user, depending upon likely capacity utilization, to help the switchgear assembly manufacturer to design a more economical busbar system. In the absence of this, the factors as indicated in Table 1 may be applied.

For your question we can write:

Total load power is : 4 x 5 + 2 x10+ 3 x 3+ 3 x 1.5 = 53.5 hp =39.4 kw
Total load current is : 80 A ( in three phase system )
Diversity factor is : 0.5 ( 4+2+3+3=12 >10)
Maximum loading in incoming is : 80 x 0.5 = 40 A

Typical values for planning power requirement

Without air conditioning                80 … 120  W/m2
With air conditioning                     120 … 150  W/m2
Per workplace                              2.5-3.0  KVA

Schools and universities

Schools general                                                           30...50  W/m2
Humanities departments                                          50...75  W/m2
Science departments                                                 120 … 200  W/m2

Hotels and dwellings

Large buildings                                                40 … 80  W/m2
Per hotel room or dwelling unit                        3.5-4.5  KVA

Hospitals

Depending on size and facilities                   60 … 120  W/m2
Up to 50 beds, per bed                                3.5 - 4.5  KVA
Up to 105 beds, per bed                              3.0-3.5  KVA
Up to 250 beds, per bed                              2.0-3.0  KVA
Up to 300 beds, per bed                              1.5 -2.0  KVA

Department stores

Without air conditioning                                      100 … 150  W/m2
With air conditioning                                            150 … 200  W/m2

Exhibition halls

For exhibitors' power                                           25 … 50  W/m2
For hall lighting                                                    40 … 80  W/m2

Industry

Chemicals                                                             200 … 500  W/m2
Rolling mills, iron and steel                                  200 … 400  W/m2
Metalworking                                                       100 … 300  W/m2
Textiles                                                                  50 … 150  W/m2

#2
Mon, February 7th, 2011 - 15:35
Could we apply this factor if in a factory each branch is connected to a motor which operates throughout the day?. Will it be more appropriate/accurate to record Amps for the duration of 8 hrs  or so using a power analyser or data logger and select the maximum load?. A value of 0.5 may be too low in certain cases.

#3
Mon, February 7th, 2011 - 16:41
1- No
2-I agree you, the best diversity factor shall be obtained via field measurement and verifications.
3- It is related to actual cases

#4
Tue, March 29th, 2011 - 11:08
how i can calculate the divercity factor for socket panel and lighting panel and also for mcc panel

#5
Tue, March 29th, 2011 - 15:16