Figure 3–14: CT/VT MODULE WIRING
3.2.5 CONTACT INPUTS AND OUTPUTS
Every contact input/output module has 24 terminal connections. They are arranged as three terminals per row, with eight
rows in total. A given row of three terminals can be used for the outputs of one relay. For example, for form-C relay outputs,
the terminals connect to the normally open (NO), normally closed (NC), and common contacts of the relay. For a form-A
output, there are options of using current or voltage detection for feature supervision, depending on the module ordered.
The terminal configuration for contact inputs is different for the two applications.
The contact inputs are grouped with a common return. The B90 has two versions of grouping: four inputs per common
return and two inputs per common return. When a contact input/output module is ordered, four inputs per common is used.
The four inputs per common allows for high-density inputs in combination with outputs, with a compromise of four inputs
sharing one common. If the inputs must be isolated per row, then two inputs per common return should be selected (4D
The tables and diagrams on the following pages illustrate the module types (6A, etc.) and contact arrangements that can be
ordered for the relay. Since an entire row is used for a single contact output, the name is assigned using the module slot
position and row number. However, since there are two contact inputs per row, these names are assigned by module slot
position, row number, and column position.
Some form-A / solid-state relay outputs include circuits to monitor the DC voltage across the output contact when it is open,
and the DC current through the output contact when it is closed. Each of the monitors contains a level detector whose out-
put is set to logic "On = 1" when the current in the circuit is above the threshold setting. The voltage monitor is set to "On =
1" when the current is above about 1 to 2.5 mA, and the current monitor is set to "On = 1" when the current exceeds about
80 to 100 mA. The voltage monitor is intended to check the health of the overall trip circuit, and the current monitor can be
used to seal-in the output contact until an external contact has interrupted current flow.
Block diagrams are shown as follows for form-A and solid-state relay outputs with optional voltage monitor, optional current
monitor, and with no monitoring. The actual values shown for contact output 1 are the same for all contact outputs.
B90 Low Impedance Bus Differential System