Beijer-electronics EXTER T150-st EN Manuel d'utilisateur télécharger pdf (Page 21)

Additional Installation Tips

Beijer Electronics, MAEN967 21

6.5 Safety

Most of the operator panels are fed with 24 V DC.

1. If you use a power supply that meets safety standards and only feeds the operator

panel, there is no problem.

2. However, if you have a 24 V unit that also feeds other units, there is reason to be

cautious.

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.

3. 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.

4. Connect 0 V on the 24 V feed to the ground. This offers three advantages:

–Safety is increased. The 24 V feed will not be live in the event of a faulty connec-

tion 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.

Example:

Here is an example that explains why a secure 24 V DC feed 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 operator panel.

5355

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

+24 V

0 V

230 V AC

COM1

COM100

Small controller with expansion unit

Ch0

Ch1

Ch100

Ch101

Distance?

1 2 ... 16 17 18 19 20 21 22 23 24

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Beijer-electronics EXTER T150-st EN Manuel d'utilisateur Page 21

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