Okonite wire and cable - electrical fomulas for determining amperes, horsepower, kilowatts, and kilovolt-amperes
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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

Single-Phase

Two-Phase*
Four-Wire

Three-Phase

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

 


ENGINEERING TECHNICAL CENTER

Every effort has been made to ensure the accuracy of this presentation.
However, information is subject to change. Not responsible for typographical errors.

The Okonite Company
102 Hilltop Road
Ramsey, New Jersey 07446
Phone 201-825-0300
Fax 201-825-3524
info@okonite.com

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