Page 93 - Basic Course

KNX BASIC COURSE

1 Safety Low Voltage Networks

SELV (Safety Extra Low Voltage)

 Safety transformer

 Voltage range less than/
identical to 120 V DC or 50 V AC
 Safe insulation to e.g.
230 / 400 V AC

 SELV may not be earthed!

Figure 1: Safety Low Voltage Networks
General: for the bus and mains installation the relevant installation requirements of
the respective country shall be observed.

SELV stands for Safety Extra Low Voltage

Clearance and creepage distances: The clearance and creepage distances indicated
above apply for:

Pollution degree 2 (offices)
Overvoltage category 3 (permanently connected to mains, high availability)
Insulation material class 3

Permitted voltage range:

Alternating current (AC):  50 V
Direct current (DC):  120 V

No special protection against direct contact is required if the voltages do not exceed 25 V
AC or 60 V DC.

Earthing:
A SELV network may not be earthed!

Home and Building Management Systems KNX Association
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