Additional Installation Tip s
7.5 Safety
4
1
2
4
3
4
Power supply
230 V AC to 24 V DC
Power supply
230 V AC to 24 V DC
Power supply
230 V AC to 24 V DC
Operator panel
Operator panel
Operator panel
Distance?
Small controller with expansion unit
+24 V
+24 V
+24 V
0 V
0 V
0 V
230 V AC
COM1
COM100
Ch0
Ch1
Ch100
Ch101
5355
If a power supply that meets safety standards is used and only powers the operator
panel, there is no problem. See 1 in drawing above.
However, if a 24 V unit that als o powers other
unitsisused,thereisreasontobe
cautious, s ee 2 in drawing above. The opera
tor panel does not have insulation
that meets safety requirements in the eve
nt of a potential short circuit between
230 V AC and 24 V DC. It is assumed that the 2
4 V power supply is secure, for
example, SELV according to EN 6095
0 (prot ection against electric sh o ck) and
UL 950.
Note:
Hereisanexamplethatexplainsw hyasecure24VDCpowersupplycanberuinedby
mixing24Vrelaycont actswith230VACrelaycontactsinasmallercontroller. Check
thattheclearancesandcreepagedistancesbetween24VDCand230VACfulfill
EN60950orUL950. Ifnot,inputaseparate24Vunitintotheoperatorpanel.
If there is a substantial distance between the relay contacts for 24 V DC and
230VAC,itisOKtousethesame24Vdevicesforallfeeds. See3indrawing
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.
BeijerElectronics, MAEN330
25
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