EnergySafe Magazine Summer 2018, issue 49 - Page 10

10 Electrical Q&A  Your electrical questions answered! Compiled by ESV’s Electricity Technical Advisor, John Stolk energysafe continues its regular series featuring some of the questions that ESV receives on a range of electricity installation issues, some of them relating to gas installations. Also provided are the answers together with references to the Acts, Standards, Regulations and Clauses that apply to them. Question Answer Standard Clause Does anyone know exactly what rule applies to precisely how much sheath should be removed, behind accessories? Cables of a sheathed type need not be installed in a wiring enclosure. AS/NZS 3000:2007 Clause 3.10.1 Where the sheath of a cable is removed, the exposed insulated core of the cable requires to be enclosed. 100mm or less sheathing can be removed behind an accessory, when the rear of the accessory is enclosed in a wall cavity. What rule applies to precisely how much insulation can be removed when terminating conductors inside the tunnel of a light switch? The insulation on a conductor shall not be removed any further than is necessary to make the connection. AS/NZS 3000:2007 Clause I have come across a new switchboard that I needed to remove circuits from. I found that none of the stranded cables had been twisted and folded when originally terminated. I was under the impression that it is required to twist and fold to terminate. Or is it just best practice? The ends of stranded conductors shall be secured by suitable means, so as to prevent the spreading or escape of individual strands. They shall not be soft-soldered before clamping under a screw or between metal surfaces. AS/NZS 3000:2007 Clause I have been asked to install a horizontal outlet sideways (vertically). The Wiring Rules do not prohibit a horizontal socket outlet being installed vertically, but the installation must comply with the requirements of Clause 4.4 of AS/NZS 3000:2007/ AS/NZS 3000:2007 Clause 4.4 The Wiring Rules requires the automatic disconnection of supply in the event of an overload or short-circuit. AS/NZS 3000:2007 Clause 2.1.2(b) AS/NZS 3000:2007 Clause 6.3.3 Can anyone clarify if there is an AS/NZS 3000 clause that suggests this is not compliant? If I use a 25A magnetic only circuit breaker, does that mean my cable needs to be rated at 250A? The circuit in question supplies an old overhead crane that only has direct on line (DOL) single speed motors, due to the unnecessary excessive jogging by the operators the motors are constantly only drawing starting current. If I use a cable rated at 25 amps, is the cables insulation likely to melt? Anyone know what’s the logic behind earthing pools and wet areas Reo? Why would you want the Reo at Earth potential? Twisting stranded cable and folding all conductors is best practice. Magnetic circuit breakers offer predominantly short circuit protection only, not overload protection. The circuit breaker can only be used where overload protection is provided by another device. The cable size is determined by the temperature rise. The full load current of the motor must be known so that the overload relay can be set. The peak current during starting should also be known so that any adjustable instantaneous trip units in the circuit breaker can be set close to, but not below this current. Supplementary bonding is required to prevent voltage gradients being introduced within the pool and water circulation system. All extraneous conductive parts in zone 0, 1 and 2 including the reinforcement steel within the pool, decks and conductive parts in contact water filtration system are required to be connected together to prevent difference of potential between conductive parts. The equipotential bonding ensures that the conductive parts within the pool zones and in contact with the pool water remain at the same potential as a very low voltage is sufficient to present a hazard to a person immersed in water.