This applies only when power is supplied from a three phase transformer.
Be sure to turn off power to the meter before making any of the changes suggested here. It is very easy to blow a meter if working hot.
The voltage and current references for the meter must be properly matched or that phase will only report half the power actually used. This means that if the wire that goes through CT1 is not connected to the VAC1 voltage input, half the power used will not be recorded. This happens because the two phases are 120 degrees out of phase and the meter sees it as 0.5 power factor. With a single phase transformer, the two legs are 180 degrees out of phase which causes an insignificant error.
The alarm causes the red LED on the meter to flash about once a second. It will happen whenever the meter senses negative power and a power factor below about 0.8. It needs about 60 watts flowing through each leg for this to happen. If you see the alarm, the first thing to check is that the CTs are on in the right direction (label toward the load). If it is not and the load is causing a low power factor, the alarm will be active (flashing). Swapping the black and white CT wires should fix the problem rather than having to remove the CT. Having the CT on backward also disables the alarm to that it will not activate if the phases are not properly matches.
If the alarm is active and the CTs are all in the right direction, it means that at least two of the CTs are not properly paired with their voltage inputs. Turn off power to the meter then reconnect the CTs after properly tracing the wires.