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Planning guideBasic electric principlesStarting currentThis is the current which is required during the start-up operation ofa machine to overcome friction losses and starting torques. Thestarting current can be up to seven times that of the nominal current,depending on the type of start-up. When there is instability in theelectric mains or for larger motors, corresponding devices must beprovided to reduce the starting current. These could be soft starters,frequency converters, etc. Designing the motor as a star-delta motorcan already reduce the starting current.Operating modes (in acc. with DIN EN 60034-1)See “Operating modes” chapterIndividual run signalIndicates the fault of the individual pump and demonstrates an exactevaluation method for building control systems.Motor protectionFor a safe operation of a motor, this must be protected against unacceptablehigh warming. Such an unacceptable warming can resultfrom faults which increase the motor current and strongly heat upthe motor:• Overload• Phase failure• Undervoltage• BlockingThese faults can be recognised by an overload relay or a motor protectionswitch which then switch off the motor. Overload relays andmotor protection switches may only be set to the maximum nominalcurrent of the motor.First digitOverload relayPrinciple of operation:The thermal protection is ensured by bimetals which heat up as themotor current flows via heating windings. For every conductive lineto the motor, a separate bimetal with corresponding heating windingis provided. If the power consumption of just one motor winding exceedsthe predefined value over several seconds, the generated heatwill deform the bimetal which then triggers the latch and switches offthe motor contactor. Also, if a phase fails (irregular heating of the bimetalstrips), the motor is switched off after a short period of time.After a thermal triggering has taken place, the switch can only beswitched on again after the bimetals have cooled down sufficiently.Overload relays don't switch off the motor directly, they have a contactfor relatively low switching frequencies. This contact activates acontactor which then switches the motor off in the event of a fault. Incontrast to the motor protection switch, an overload relay does nothave a short-circuit trip. This is why safety fuses should be installedin the supply line for one or several motors which are protected byoverload relays. Moreover, the reactivation of overload relays can bedone manually or automatically. The reactivation should be donemanually in order to avoid a permanent switching on and off whenthere is a fault.Motor protection switchWith motor protection switches, motors can be switched on and offunder normal operating conditions. The thermal triggering is basedon the principle of the overload relay. However, the operator is in aposition to switch off the motor during operation or in the event offault. Moreover, most motor protection switches have an additionalmagnetic quick triggering which protects the downstream line andthe motor against short circuits. With lower currents, these switchesare short-circuit proof, i.e. a back-up fuse may not be required.Other faults which lead up to an increased heating-up:• Dry-running of motors that may only operate in a submerged state• Unacceptable high fluid temperatures / ambient temperature• Unacceptable running times in short-term operationThese faults do not influence the current consumption of the motorand can therefore not be recognised by the upstream overload protection!For such faults, temperature sensors are used which are directlyimbedded in the component to be protected (motor winding).Protection measures (DIN VDE 0100-410)Protection classes:(DIN EN 50529 / VDE 0470 Part 1)The type of protection which a housing offers to e.g. protect againstdirect contact, is defined by the IP (International Protection) codes.This is made up of the “IP” and two digits (e.g. IP 54).First digit:• Protection of people against contact with dangerous parts• Protection of the equipment against ingress of solid foreign matterSecond digit:• Protection of the equipment against the ingress of waterSecond digitIndex Protection against contact Protection against foreign matter Protecton against water0 No protection No protection No protection1 Protection against contact with the backof the hand2Protection against touching with fingers3Protection against touching with toolsProtection against solid foreign matter50 mm diameterProtection against solid foreign matter12.5 mm diameterProtection against solid foreign matter2.5 mm diameterProtection against vertically drippingwaterProtection against dripping water fallingat a tilted angle (15°)Protection against spraying water fallingat a tilted angle of up to 60°4Protection against solid foreign matter Protection against splashing water fromProtection against touching with a wire1.0 mm diameterall directions5 Protection against touching with a wire Dustprotected Protection against water jets6 Protection against touching with a wire Dustproof Protection against strong water jets78– –– –Protection against temporary submersionin the waterProtection against permanent submersionin the waterWilo Water Management catalogue – 50 Hz – Drainage and Sewage – Waste water collection and transport – Edition 2012/2013 – Subject to change without prior notice13