Most relays used in industrial circuits have the ability to have their contacts changed from NO to NC in the field. In other words, a technician can remove several screws and mount the contacts upside down and they will change from NO to NC, or vice versa. Fig. 1 shows an example of this type of contact. This feature makes adding NO or NC contacts very easy. It also makes it simple to change a set of NO contacts to NC at the time it's needed. Since these contacts are actually cartridges, additional sets of contacts can be added to a relay at anytime as long as there is room. In some cases a second deck is added to the relay so more contacts can be added.
Above: Fig. 1: Example of contacts that can be changed
from NO to NC in the field.
