Liebert UPS System user manual Selection of cables, Current carrying capacity of cables

Chapter 3 Electrical Assembly

Chapter 3 Electrical Assembly

This chapter introduces the connection methods of the power and signal cables.

3.1 Selection of cables

3.1.1 Current carrying capacity of cables

The current carrying capacity can be selected according to the voltage drop and permissible temperature increase.

Table 3-1 Current carrying capacity of cables

Current								Cross sectional area(mm2)
carrying
		1	1.5	2.5	4	6	10		16	25	35	50	70	95	120	150	185	240
capacity (A)
25 C	Rubber	21	27	35	45	58	85		110	145	180	230	285	345	400	470	540	660
°
	Plastic	19	24	32	42	55	75		105	138	170	215	265	325	/	/	/	/
35 C	Rubber	20	25	33	42	54	80		103	136	168	215	267	323	374	439	505	617
°
	Plastic	18	22	30	39	51	70		96	129	159	201	248	304	/	/	/	/

3.1.2 Selection of power cables

The power cables include input power cables of main circuit and that of the bypass, the UPS output cables, battery input cables, protective earth cables and the lightning protection cables.

1. Calculation of current of power cables

The first calculation method is done according to the following formula:

If the power factor is 0.80, the efficiency is 0.9, the minimum input voltage is 176 volts, output line to neutral voltage is 220V, minimum battery voltage is 324 V, bypass overload capability is 135% and that of the inverter is 125%,

2. Selection of cable cross sectional areas

Power cables are selected according to two factors - 3 – 5 A/mm2 current density and the maximum voltage drop be less than 3 W.

The cross-sectional areas of bypass input neutral cable and UPS output neutral cable should be 1.5 times of the phase cable. The cross sectional area of the

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