How many hard questions appear in the KNX Basic exam?

The KNX Basic exam mixes difficulty levels. Expect roughly 30 to 40 % of hard questions out of 60 to 100 total per session — practicing on questions filtered by difficulty is the best success indicator.

Should I start with hard KNX Basic questions?

Depends on where you are: if you're starting prep, begin with easy questions and ramp up. If you're 2 weeks from the exam and haven't seen any discriminating items, jump straight to hard KNX Basic questions to spot your gaps.

KNX Basic · Hard level

hard KNX Basic exam questions

KNX Basic Certification mock exam questions selected at hard level. Ideal for preparing for the discriminating questions you'll see on exam day.

Sourced bank~ 4 minHard

Hard level questions

Q01
On how many bits is the Group Address encoded inside a KNX TP1 telegram?
- A.8 bits
- B.16 bits
- C.24 bits
- D.32 bits
2. TP Topology· Kodierung der Gruppenadresse· Hard
▸
Correct answer
B — 16 bits
Learning tip
The Group Address is encoded on 16 bits in the TP1 telegram, regardless of the display structure chosen in ETS (Free, 2-level, 3-level). The display structures merely split the same 16 bits differently for human readability: Free uses 16 free bits, 2-level uses Main (5 bits) / Sub (11 bits), 3-level uses Main (5 bits) / Middle (3 bits) / Sub (8 bits). The wire-level telegram is identical in every case. A and C are wrong because 8 bits would be far too few and 24 bits do not appear in the TP1 frame. D is wrong because 32 bits is the Individual+Group total in some Extended-frame variants, not the Group Address alone.
Source: KNX Specifications V3.0.0 (public) — Telegram Format, Group Address field
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Q02
The Group Address space in KNX TP1 allows up to 65 536 different Group Addresses (2^16).
TrueFalse
2. TP Topology· Adressraum Gruppenadressen· Hard
Correct answer
True
Learning tip
A Group Address is encoded on 16 bits inside the telegram, giving 65 536 possible values. In practice, the address 0/0/0 is reserved as a broadcast, so 65 535 addresses remain available for application use. Whether the project uses the 2-level (main/sub) or 3-level (main/middle/sub) representation does not change the underlying 16-bit address space — it only changes how the bits are visually grouped in ETS.
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Q03
Activating Data Secure on a Group Address adds a per-telegram overhead (authentication and encryption) that reduces the usable application payload.
TrueFalse
9. KNX Secure· Data-Secure-Overhead· Hard
Correct answer
True
Learning tip
True. Each Data Secure telegram carries additional bytes for the sequence number, the MAC for authentication and the encryption envelope. Those bytes occupy room inside the standard telegram and therefore shorten the application payload that can be transported in a single frame. For long DPTs such as 14-character DPT 16 strings, this overhead can force fragmentation into multiple telegrams, which is an important sizing consideration for high-rate visualisations.
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Q04
In an installation predating 2018, a maximum of 64 sensors, actuators, line couplers and backbone couplers can be connected to a TP main line.
TrueFalse
2. TP Topology· Offizielle Musterprüfung 4· Hard
Correct answer
True
Learning tip
True. Before the 2018 update of the KNX TP specification, a main line was limited to a single segment of 64 devices (sensors, actuators, line couplers and backbone couplers combined), with no possibility to extend it via repeaters as a regular line could. After 2018, this restriction was lifted and the modern rule allows up to 256 devices in total per main line, in line with the rest of the topology. Legacy installations therefore still operate under the older 64-device cap.
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