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Some cable related terms you may be confused

December 21, 2019

Cable are ubiquitous in our daily life and it is more complicated than what you think it is. As a purchaser, it will be very helpful if you know more infor about this industry.

low voltage power cable, medium voltage power cable, control cable, electrical wire

 

Cable are ubiquitous in our daily life and it is more complicated than what you think it is. As a purchaser, it will be very helpful if you know more infor about this industry. Below we collect and share some infor with you.

 

WHAT IS VOLTAGE RATING?

The voltage rating of a cable is the highest voltage that may be continuously applied to a cable construction in compliance with the relevant cable standard or specification.

Voltage rating figures for cables are normally expressed in A.C. RMS. (Alternating Current Root Mean Square) and are written as a figure Uo/U (Um)

Uo = Rated voltage phase to Earth

U = Rated voltage phase to phase

Um = Maximum system

 

WHAT IS AC AND DC?

Electrical current flows from a point of positive charge to a point of negative charge whilst essentially the electrons flow in the opposite direction.

AC stands for an alternating current. Essentially the polarity of the supply is changing with time and as it does the current flows in one direction and then the other. Mains power generation is typically AC - most generators are based on an alternator which creates an alternating current as the wire stator turns within a magnetic field. AC power transmission is also preferred for high voltage mains transmission because it is relatively easy to step down the voltages for various applications with transformers. The frequency of this alternating direction for mains supply in the UK is 50Hz, or 50 cycles per second.

DC stands for direct current. Here the current flow is in the one direction only and does not alternate. This is typical of the sort of current produced by a battery. Power generated by photovoltaic panels is DC and would need to be converted with a power inverter to be used for standard mains applications. DC power, once generated, is very useful in speed control motors

 

WHAT IS VOLTAGE DROP?

A voltage drop in an electrical circuit normally occurs when a current passes through the cable. It is related to the resistance or impedance to current flow with passive elements in the circuits including cables, contacts and connectors affecting the level of voltage drop. The longer the circuit or length of cable the greater the voltage loss. The impact of a voltage drop can cause problems such as motors running slowly, heaters not heating to full potential, lights being dimmed. To compensate for voltage drop larger cross-sectional sized cables may be used which offer less resistance / impedance to current flow.

Voltage drop can be calculated from the formula:

Vd =mV/A/m x I x Ib ÷ 1000

Where:

mV/A/m = the voltage drop per metre per amp

I = the length of the circuit conductor

Ib = the design current

The allowable voltage drop for low voltage installations supplied directly from a public low voltage distribution system is 3% for lighting and 5% for other uses.

 

WHAT IS LOW VOLTAGE, MEDIUM VOLTAGE, HIGH VOLTAGE AND EXTRA HIGH VOLTAGE?

Definitions vary somewhat but a general guide to the voltage categories are as follows:

Low Voltage: up to 1000V

Medium Voltage: between 1000 V and 35 kV

High Voltage: between 35 kV and 230 kV

Extra High Voltage:from 230 kV and above

Zhenglan Cable Technology Co., Ltd manufactures low and medium voltage power cables. Welcome your inquiry.

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