How many are too many?

How many e-stops can wire in series?

How many safety switches can you wire in series?

Can you daisy chain safety light curtains?

These are just a couple of questions that get asked quite often for safety circuit design. Here are some simple answers that I will be happy to give to you.

How many e-stops can wire in series?

Leuze ESB200 IP69K E-Stop with mechanical status indication

Since an emergency stop pushbutton is considered a complementary protective device you may wire them in series. But beware, this may lower the overall performance level for the circuit.

How many safety switches can you wire in series?

Leuze MC388 magnetically coded safety switch with LED status indication

ISO 24119 speaks about Diagnostic Coverage (DC) and the maximum achievable DC based on movable guards. To simply the standard this depends on how frequently the switch is used. 2-4 switches tied in series are possible with a medium DC which is required for PL d. A risk assessment will verify this.

Can you daisy chain safety light curtains?

Leuze MLC500 series light curtain set

Unless the light curtain has a cascading functionality (i.e. MLC520 cascade) or some special function (i.e. MLC530 linkage), this is not possible. Typically light curtains are wired independently and provide an individual pair of self-testing safety outputs. Another option would be to use a safety relay with multiple inputs (i.e. Leuze MSI-SR5B) or a programmable safety relay (i.e. Leuze MSI400).

If you have specific questions about your application or product please feel free to contact me directly at 248.446.2488 and I would be happy to help.

Rod Karch, Leuze Safety Product Specialist