In addition to the A and B connections, an optional, third connection may be present (the TIA standard requires the presence of a common return path between all circuit grounds along the balanced line for proper operation) called SC, G or reference, the common signal reference ground used by the receiver to measure the A and B voltages. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. The allowable common-mode voltage is in the range −7 V to +12 V, i.e. ±7 V on top of the 0–5 V signal range. Failure to stay within this range will result in, at best, signal corruption, and, at worst, damage to connected devices.