Normally the current transformer (CT) rating amps are assigned to the WattNode® meter during installation using the Modbus application software that will be used for acquiring the power and energy data. To save time or if the Modbus master cannot configure the CtAmps, the meter can be factory configured by ordering the meter with either of the following two options:
- Option CT=xxx – If the CTs for all three phases have the same rated amperage, use Option CT=xxx where xxx is the desired rating in amperes.
- Option CT=xxx/yyy/zzz – If the CTs for the three phases have different ratings, order Option CT=xxx/yyy/zzz where xxx, yyy and zzz are the desired ratings in amperes for phase A, B and C, respectively.
Whether the WattNode meter has the Option CT or not, it is always possible to field reconfigure the CT ratings using the CtAmps configuration registers.
Overriding Option CT
If you have a WattNode Modbus meter with Option CT and you need to change one or more CT ratings, it can be done using any Modbus-compatible application software by writing the required CT ratings to the configuration registers (see the manual for details):
- If the CTs for all three phases have the same rated amperage, write that value to the CtAmps register (1603).
- If the CTs for the three phases have different ratings, write the phase A, B and C amps to the CtAmpsA register (1604), CtAmpsB register (1605) and CtAmpsC register (1606), respectively.
The factory assigned CT ratings for phase A, B and C can be read via the OptCtAmpsA register (1724), OptCtAmpsB register (1725) and OptCtAmpsC register (1726), respectively.