Safety - Beijer Electronics BoX2 base Installation Manual

6.5. Safety

Power supply
230 V AC to 24 V DC
+24 V
1
0 V
4
Power supply
230 V AC to 24 V DC
+24 V
2
0 V
4
Distance?
Power supply
230 V AC to 24 V DC
+24 V
3
0 V
4
230 V AC
If a power supply that meets safety standards is used and only powers the BoX2 device, there is no
problem. See 1 in drawing above.
However, if a 24 V unit that also powers other units is used, there is reason to be cautious, see 2 in
drawing above. The device does not have insulation that meets safety requirements in the event of
a potential short circuit between 230 V AC and 24 V DC. It is assumed that the 24 V power supply is
secure, for example, SELV according to EN 60950 (protection against electric shock) and UL 950.
NOTE
Here is an example that explains why a secure 24 V DC power supply can be ruined
by mixing 24 V relay contacts with 230 V AC relay contacts in a smaller controller.
Check that the clearances and creepage distances between 24 V DC and 230 V AC
fulfill EN 60950 or UL 950. If not, input a separate 24 V unit into the device.
If there is a substantial distance between the relay contacts for 24 V DC and 230 V AC, it is OK to use
the same 24 V devices for all feeds. See 3 in drawing above.
Connect 0 V on the 24 V power supply to the ground, see 4 in drawing above. This offers three
advantages:
• Safety is increased. The 24 V power supply is not live in the event of a faulty connection or short
circuit between 0 V (24 V) and 230 V phase.
• Transients on the 24 V feed are connected to the ground.
• No risk that the 24 V feed is at a high level in relationship to the ground. This is not unusual since
there is high static electricity.
Beijer Electronics, MAEN274
BoX2 device
BoX2 device
BoX2 device
Small controller with expansion unit
COM1
Ch0
Ch1
COM100
Ch100
Ch101
5355
19
Additional Installation Tips
2023-09