TP Installation KNX Basic: exam questions with worked answers

Questions for the "TP Installation" topic

1. Q01

   What is the electrical classification of the KNX TP bus power supply?

   • A.230 V AC
   • B.12 V DC
   • C.30 V DC SELV
   • D.48 V DC PoE

   5. TP Installation· Busspannung· Easy

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   Correct answer

   C — 30 V DC SELV

   Learning tip

   The KNX TP bus is powered at 30 V DC SELV (Safety Extra Low Voltage). This voltage simultaneously powers the low-consumption devices and carries the differential telegrams superimposed on the DC level. Choice A (230 V AC) is the mains voltage, not the bus. Choice B (12 V DC) is too low and not a KNX value. Choice D (48 V DC PoE) is an Ethernet-related standard with no KNX TP equivalent. The SELV classification permits routing in the same conduit as other low-voltage cables.

   Source: KNX Specifications V3.0.0 (public) — TP1 Physical Layer

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2. Q02

   A bus termination (end-of-line resistor) must be installed at each end of a KNX TP segment, in the same way as for an RS-485 bus.

   TrueFalse

   5. TP Installation· Verkabelung· Medium

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   Correct answer

   False

   Learning tip

   False. KNX TP does not use any bus termination, which is one of its major differences from other differential buses such as RS-485 or CAN. As a result the physical topology can freely combine line, star and tree shapes without termination constraints. Only the closed-loop (ring) topology is forbidden.

   Source: Porto KNX — TP Installation

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