User guide

Additional Installation Tips
6.5 Safety
Most of the operator panels are fed with 24 V DC.
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
Ifyouuseapowersupplythatmeetssafetystandardsandonlyfeedstheoperator
panel, there is no problem. See 1 in drawing above.
However,ifyouhavea24Vunitthatalsofeedsotherunits,thereisreasontobe
cautious, see 2 in drawing above. The operator panel 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 feed is secure, for example, SELV
according to EN 60950 (protection against electric shock) and UL 950.
Example:
Hereisanexamplethatexplainswhyasecure24VDCfeedcanber uinedbymixing24
Vrelaycontactswith230VACrelaycontactsinasmallercontroller. Checkthatthe
“clearancesandcreepagedistancesbetween24VDCand230VACfulfillEN60950orUL
950”. Ifnot,inputaseparate24Vunitintotheoperatorpanel.
If there is a substant
ial 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 feed to the ground , see 4 in drawing above. This offers
three advantages:
• Safety is increa
sed. The24Vfeedwillnotbeliveintheeventofafaulty
connection or s
hortcircuitbetween0V(24V)and230Vphase.
• Tr a ns ie n ts o n
the 24 V feed are connected to the ground.
• No risk that th
e 24 V feed is at a high level in relationship to the ground. This
is not unusua
l since there is high static electricity.
BeijerElectronics, MAEN011A
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