Category Archive for: «Protection»

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Which type of residual current device (RCD) to use and when?

Total earth loop impedance We know how (very) important the total earth loop impedance Zs is in the reduction of shock risk. However, in TT systems where the mass of earth is part of the fault path, the maximum values of Zs given in the IEE Regulations may be hard to satisfy. Added to this, […]

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Erection Procedures of Earthing Arrangements (TNC, TN-S, TNC-S and TT)

Earthing of low voltage networks The earthing of low voltage networks in the UK is largely determined by the Low Voltage Supplies. However, if the incoming supplies are at 11kV and the transformers are in the ownership of the user, the LV supplies may be earthed in a less conventional way using a high impedance. […]

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Practical calculations of lightning strikes frequency

Frequency of lightning strikes We distinguish between the following frequencies of lightning strikes which can be relevant for a building or structure: ND – Frequency of direct lightning strikes to the building or structure;· NM – Frequency of close lightning strikes with electromagnetic effects; NL – Frequency of direct lightning strikes in utility lines entering […]

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What’s Really Important When You’re Designing The Low Voltage Switchgear?

Requirements on the Switchgear Here what’s important when you’re designing the low voltage switchgear: Device Application in the Supply Circuit Short-circuit strength Release (Trip Unit) Device Application in Supply Circuits (Coupling) Device Application in the Distribution Circuit Device Application in the Final Circuit 1. Device Application in the Supply Circuit The system infeed is the […]

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Comparison Of Neutral Earthing Methods

Methods Of Neutral Earthing (Index) There are several methods for system earthing which can be generally divided into: Insulated earthing Solid earthing Impedance earthing through resistor, reactanse or arc-suppresion coil Comparison table INSULATED NEUTRAL SYSTEM (No Intentional Earthing) The neutral is not earthed directly. In reality,the electrical system is earthed through the system capacity to earth. […]

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Lightning And Surge Protection For Cable Networks And Antennas For TV (Part 2)

Continued from part one: Lightning And Surge Protection For Cable Networks And Antennas For TV (Part 1) Protective Mechanisms If an antenna is protected by isolated air-termination systems it means: – That in the area of flat roofs an air-termination rod will be installed with the required separation distance s, putting the whole antenna arrangement (mast and […]

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Lightning And Surge Protection For Cable Networks And Antennas For TV (Part 1)

Protective Mechanisms IEC 60728-11 complies with the state of the art and offers easy, standardised and effective protective mechanisms against the effects of lightning strikes into antennas. Antennas installed according to this standard do not increase the probability of lightnings to strike the object under consideration. Nor is an antenna system installed according to this […]

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National Fire Alarm Code Defined By NFPA 72

Smoke And Fire Alarms NFPA 72 is the National Fire Alarm Code. The importance of installing smoke and fire alarms in homes is supported by results from exhaustive investigations of home fires indicating that measurable quantities of smoke come before detectable quantities of heat. In other words, smoke generally comes before fire. Because this is […]

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Equipotential Bonding For Metal Installations

Design of the earth-termination system for equipotential bonding The electrical low voltage consumer’s installation requiring certain earthing resistances (disconnection conditions of the protective elements) and the foundation earth electrode providing good earthing resistances at cost-effective installation, the foundation earth electrode is an optimal and effective complement of the equipotential bonding. The design of a foundation […]

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Surge protective categories defined by ANSI/IEEE C62.41

ANSI/IEEE C62.41 Three different surge protective classes or zones have been defined by ANSI/IEEE C62.41, Recommended Practice on Surge Voltages in Low Voltage Power Circuits. These classes are illustrated in the pictorial diagram Fig. 12-1. Category C (outdoors) Category C (outdoors) is the region outside the home or building that includes external conductors, and it extends […]

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