Eaton MDN-408 Instructions For Installation, Operation And Maintenance

I.B. 2C12060H08For more information visit: www.EatonElectrical.comInstruction BookEffective: May 20063-9 MDSL LIMITERS/BLOWN LIMITER INDICATIONAn overall description of Magnum DSL circuit breakerswas provided in sections 3-1 and 3-1.1. More detailedinformation is provided here relative to application, cur-rent limiters and blown limiter indication.If current limiters are sized in keeping with Table 3.8recommendations, the circuit breaker will function andinterrupt routine fault currents. Infrequent high faults arecleared by the limiters. The limiters protect the circuitbreaker on faults above the rating of the breaker. Thelimiters will blow below the circuit breaker short-time rat-ing, if the fault currents equal the system maximumcapacity.In some applications the current limiters are sized small-er than necessary for protection of the MDSL circuitbreaker in order to provide protection from downstreamequipment. When this is done, the current limiter willblow on fault currents which could have been satisfacto-rily interrupted by the basic circuit breaker.3-9.1 MDSL CURRENT LIMITERSDo not replace limiters with sizes other than permittedby Table 3.8. MDSL current limiters have been testedand approved by Underwriters Laboratories, Inc. for usein MDSL circuit breakers when applied according toTable 3.8. They are not electrically or physically inter-changeable with current limiting fuses of any otherdesign.The current limiters are held in place in an extensionprovided on the back of the circuit breaker (Figure 3-67).This extension makes the circuit breaker six inchesdeeper than the corresponding Magnum DS circuitbreaker. The current limiters can only be removed fromthe circuit breaker and replaced when the MDSL circuitbreaker is removed from its associated compartment.For this reason there is no fixed mounted version of theMDSL circuit breaker.3-9.2 BLOWN LIMITER SENSINGThe blown limiter indicator provides a visual indicationon the front of the MDSL circuit breaker when a currentlimiter in any phase has interrupted a short circuit. It isthe visual element of the circuit that insures that the cir-cuit breaker will be tripped when any current limiter hasblown. This prevents single phase power from beingapplied to a three-phase load.The indicator itself is a red pop out button located on thelower left portion of the breaker’s front cover (Figure 3-68). A transformer is connected in parallel with the lim-iter. When a limiter is blown, the resulting voltageacross the open limiter energizes the transformer. Thetransformer feeds a PC board to provide an output tothe direct trip actuator to trip the circuit breaker, and anoutput to the indicator causing the button to pop out.Page 53Figure 3-67 Magnum DSL Circuit Breaker (Side View)Figure 3-68 Blown Fuse Indicatorwww . ElectricalPartManuals . com