Sparks Electrical News May 2018

DBs, SWITCHES, SOCKETS AND PROTECTION

15

FIND LEAKAGE CURRENTS WITHOUT TAKING EQUIPMENT OFFLINE

CIRCUIT PROTECTION RANGE GUARDS CONSUMERS AND ADDS STYLE

COMTEST offers Fluke 368 and 369 true-RMS leakage current clamp meters which help users de- tect, document, record and compare leakage current readings over time as a means of preventing un- planned downtime, and identifying intermittent GFCI (Ground Fault Circuit Interrupter) and RCD (Residual Current Device) trips, all without taking equipment offline. The Fluke 368 has a large (40 mm diameter) jaw for work with large conductors. The clamp’s jaw is ful- ly shielded to accurately capture very small leakage signals, and to minimise external electromagnetic in- terference. The device allows users to track changes in leakage current over time, helping to identify po- tential problems before they turn into major failures. Product features: • True-RMS measurements for accuracy when measuring complex, non-sinusoidal waveforms • 40 mm jaw opening

• Highest resolution of 1 μA, measures up to 60 A • Selectable filter function removes unwanted noise • Max/Min/Average readings and hold function • Forward-facing LED worklight for use in dark wiring cabinets • Backlit display; auto backlight off and auto power off for extended battery life • CAT III 600 V safety rating • Internal Memory Logging: up to 65 000 meas- urement points Designed specifically for industrial electricians and facilities maintenance technicians, the 368 and 369 are invaluable for general purpose electrical maintenance, as well as preventative and predictive maintenance and fault troubleshooting. Specific ap- plications include maintenance tests on motors and transformers and current leakage measurements for installation tests.

SCHNEIDER ELECTRIC offers installers Easy9, a stylish, prac- tical and affordable circuit protection range that adds value to the homeowner or small office user, through safety and style features. As homeowners and small offices add more electrical gadgets to their systems, the loads become higher and, when added to the lightning strikes, electrical surges and load shedding experienced in South Africa, can represent a fire and safety hazard. Circuit protection is therefore vital, safeguarding consumers against surge, short circuits, electric shocks and overloads. Schneider Electric has created a range that offers installers high quality and long-lasting protection, while its user-friendly design, availability and affordability is what makes it attractive to the homeowner. “Thanks to technology, today’s lifestyle is quickly evolving,” explains James Calmeyer, VP Building Business Unit, at Schneider Electric South Africa. “Customers’ comfort, leisure, safety and home business are completely dependent on electronics. However, this technology driven lifestyle is at risk due to nature and the severe threat of lightning. For example, in the event of a strike somewhere close to the supply lines, voltage rises from 230 to several thousands of volts. In a few microseconds, electronic components can be destroyed and all precious appliances damaged and left out of order. Just one Easy9 surge arrester however – located in the distribution switchboard, coupled with surge protection at the plug outlet – will protect equipment in the home from overvoltage caused by lightning. If installed correctly and by an accredited person, the surge arrester damps the spike, so that the voltage never reaches a level damageable for the electronics.” The Easy9 range includes switch-disconnectors, surge protection, earth leakage protection, as well as a full range of C curve miniature circuit breakers. In addition, its curved edges add to the elegance of a home or office. Schneider Electric has engineered Easy9 to be affordable without compromising on safety and reliability. All Easy9 products are manufactured in ISO 9000-certified plants belonging to Schneider Electric and are approved by independent authorities as compliant with local electrical safety standards. It has found its place in homes, industry, hospitals, airports and small offices. “It answers electricians’ need to have access to robust products that are widely available and will help them to complete their installations swiftly and professionally, with consistent design and connection features. It is a high-end device available at a mid-range price. “We work closely with electricians worldwide to help bring safe electricity to homes and buildings around the globe. With Easy9 electricians can take pride in delivering the enhanced safety and peace of mind their customers deserve. An advantage too is that it is a high-end device available at a mid-range price,” concludes Calmeyer.

Enquiries: sales@comtest.co.za

HOW TO SELECT THE RIGHT CIRCUIT BREAKER FOR YOUR INSTALLATION

S electing the correct Circuit Breaker (CB) for your distribution panel is crucial for the longevity of the instal- lation as well as the safety of those main- taining and occupying the premises. This ar- ticle addresses the selection of key breaker attributes such as voltage, current and kA rating. The voltage rating of a CB is determined by the highest voltage that can be applied across any two conductors in the circuit. It is important to select a circuit breaker with enough voltage capacity to meet the end ap- plication. A single phase ac circuit in South Africa is generally rated at 230 V and a sin- gle pole CB rated at 230 V can be used. A three phase ac circuit operates at 400 V and requires a Triple Pole CB rated at 400 V. Circuit Breaker Current Rating The next rating to consider is the amperage or ‘operating current’ of the breaker. CB’s are designed to operate at 100 percent of the required load. However, in order to offset the effects of heat generated by the system, it is good practice to select a CB at approxi- mately 125 percent of the required load. For example: If a supply of 250 A is avail- able from the transformer, the breaker of choice for the main incomer should be rated at 25 0A in order to protect the transform- er. However, the feeder breakers feeding a 25 A load should be rated at 32 A. Circuit Breaker kA Rating Finally the ‘kA rating’ or ‘fault level’/’rupturing capacity’ of the CB should be taken into ac- count. The kA rating of the CB indicates the maximum short circuit current that the CB can withstand without arcing or catastrophic failure. This current can be upwards of 100 times the required load and has the potential to cause major damage to property and personnel. Rating considerations Circuit Breaker Voltage Rating

on the nominal current, kA rating, number of poles required and whether the CB is SABS approved. By Brendon Swanepoel, 2nd Year Electrical Engineering Student, University of the Witwa- tersrand. Brendon is completing Switchboard Group’s six week Learnership and Training pro- gram offered to students looking to further their practical skills.

For Example: A circuit breaker rated at ‘6 kA’ means that the circuit breaker can withstand 6 000 amps of current during the brief time it takes to trip. Why is it so important to choose the correct kA rating? If the short circuit current is greater than what the CB can withstand, the contacts in the CB can weld together, preventing it from tripping. Another possibility is that the CB can explode, spewing dangerous plasma. So how do I calculate the correct kA? The maximum current that can flow through a circuit is determined by the size of the transformer feeding the circuit as well as the length of the cable run from the transformer. This is often called the downstream short circuit current. This will determine the maxi- mum kA rating required for the main circuit breaker. For example: A 500 kVA transformer that has a short circuit current of 35 kA at its ter- minals. The cable run from the transformer to the main breaker is 10m and is run with 90 mm² cable. The resistance in the cable limits how much current comes from the transformer, and so after calculations it was determined that the short circuit current at the end of the cable would be 26 kA. In this case, a 20 kA circuit breaker cannot be used in the installation. SABS Approved Dealers When selecting a CB, it is vital for it to be SABS or IEC approved. This provides the assurance that the CB’s have been tested to strict qual- ity standards and will operate in a safe manner as required. Well-known brands such as ABB, Schneider and CBI are all SABS approved and are regarded as high quality devices. Switch- board Group is a registered supplier of these products and the leading manufacturer of LV panels is South Africa. In conclusion a CB should be selected based

Enquiries: www.switchmanproducts.co.za

Photos taken at Switchboard Manufacturers Johannesburg

Breaker fitted to a DB with an under rated fault level

Enquiries: www.schneider-electric.co.za

SPARKS ELECTRICAL NEWS

MAY 2018