Siemens ET 200S Manual page 273

Note
The PM-E 24–48 VDC, 24–230 VAC power module (6ES7 138-4CB10-0AB0) is
not a direct replacement for the device with the order number
6ES7 138-4CB00-0AB0 for AC applications because you have to select either AC
or DC supply voltage. In the case of DC applications, the new module is a direct
replacement because the default setting of the new parameter is "DC". If you want
to replace the device 6ES7 138-4CB00-0AB0 in AC applications, you have to
create a new hardware configuration and set the value "AC" for the load voltage
type parameter.
If the hardware configuration is not changed for AC applications, the SF status
LED remains on all the time. If the "No load voltage" diagnostic interrupt is
enabled, several interrupts are activated in each AC cycle. The electronic modules
that are connected to the potential group of this PM-E continue to function
normally, however.
Distributed I/O System ET 200S
EWA 4NEB 780 6024-02 07
Power Modules
10-7