Electrical Formulas For Determining Amperes, horsepower, Kilowatts, and Kilovolt Amperes of Cable

Voltage Rating

The selection of the cable insulation level to be used in a particular installation shall be made on the basis of the applicable phase to phase voltage and the general system category as outlined below:

100 Percent Level - Cables in this category may be applied where system is provided with relay protection such that ground faults will be cleared as rapidly as possible, but in any case within 1 minute. While these cables are applicable to the great majority of cable installations which are on grounded systems, they may be used also on other systems for which the application of cables is acceptable **provided the above clearing requirements are met in completely de-energizing the faulted section.

133 Percent Level - This insulation level corresponds to that formerly designated for ungrounded systems. Cables in this category may be applied in those situations where the clearing time requirements of the 100 percent level category cannot be met, and yet there is adequate assurance that the faulted section will be de-energized in a time not exceeding 1 hour. Also they may be used when additional insulation strength over the 100 percent level category is desirable.

173 Percent Level - Cables in this category should be applied on systems where the time required to de-energize a grounded section is indefinite. Their use is recommended also for resonant grounded systems. Consult the manufacturer for insulation thickness.

**In common with other electrical equipment, the use of cables is not recommended on systems where the ratio of the zero to positive phase reactance of the system at the point of cable application lies between -1 and -40 since excessively high voltages may be encountered in the case of ground faults.

Electrical formulas for determining amperes, horsepower, kilowatts and kilovolt-amperes
DESIRED DATA	ALTERNATING CURRENT			DIRECT CURRENT
DESIRED DATA	Single-Phase	Two-Phase* Four-Wire	Three-Phase	DIRECT CURRENT
Amperes when kva is shown	kva x 1000 E	kva x 1000 2 x E	kva x 1000 1.73 x E	kva x 1000 E
Amperes when kilowatts are shown	kw x 1000 E x pf	kw x 1000 2 x E x pf	kw x 1000 1.73 x E x pf	kw x 1000 E
Amperes when horsepower is shown	hp x 746 E x %Eff x pf	hp x 746 2 x E x %Eff x pf	hp x 746 1.73 x E x %Eff x pf	hp x 746 E x %Eff
Kilovolt-Amperes	I x E 1000	I x E x 2 1000	I x E x 1.73 1000	I x E 1000
Kilowatts	I x E x pf 1000	I x E x 2 pf 1000	I x E x 1.73 x pf 1000	I x E 1000
Horsepower	I x E x %Eff x pf 746	I x E x 2 x %Eff x pf 746	I x E x 1.73 x %Eff x pf 746	I x E x %Eff 746

*In three-wire, two phase balanced circuits, the current in the common conductor is 1.41 times that in either of the other conductors.

E = volts Ų-Ų; I = amperes; % Eff = percent efficiency in decimals; pf = power factor in decimals;
kva = kilovolt-ampere; hp = horsepower; kw = kilowatts

General Information Electrical Formulas

Voltage Rating

Electrical formulas for determining amperes, horsepower, kilowatts and kilovolt-amperes

General Information
Electrical Formulas

Electrical formulas for determining amperes,
horsepower, kilowatts and kilovolt-amperes