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Generally, there must be an overcurrent protection device (circuit breaker or fuse) protecting each phase conductor connected to the WattNode® meter’s voltage input terminals (green, five-position screw terminal block).

In some cases, the circuit being monitored is already protected by fuses or circuit breakers and there is no need for additional protection for the meter. Also, the WattNode Module (WND-M1-MB) has high-impedance voltage inputs and is UL Listed without the need for overcurrent protection.

WARNING! Only qualified personnel or licensed electricians should install the WattNode meter. The mains voltages of 120 Vac to 600 Vac can be lethal! A WattNode meter installation must comply with all applicable electrical safety codes.


  • If you are monitoring a branch circuit with existing circuit breakers or fuses sized to protect a #14 or #12 AWG gauge wire, additional overcurrent protection may not be needed. Note that the largest gauge wire that will fit in the WattNode meter’s voltage input terminal block is #12 AWG, which is typically protected by a 20 amp breaker.
    1. If more than one phase conductor is connected to a meter, a multi-pole circuit breaker is preferred over fuses because if there was a line fault the breaker would disconnect all of the phases.
    2. If the meter is located some distance from the existing overcurrent protection device, you should install a disconnect switch or panel mounted break inside the meter enclosure to provide a convenient way to turn off the voltage when working on the meter.
  • If the meter’s voltage inputs need to connect to a circuit with a wire size larger then #12 AWG, you have two choices:
    1. Tap off of a higher current circuit using an overcurrent protection device rated for 20 amps or less.
    2. Find a circuit with #12 AWG or smaller wire that is on the same phases as the circuit you wish to monitor and connect the voltage inputs to this circuit. In this case you do not need additional overcurrent protection because the existing protection device will protect the conductors feeding the WattNode voltage inputs. The only downside to this approach is that if this circuit is turned off or interrupted, the meter will lose power and stop working, even though the load being monitored may still be powered.
  • For installations where multiple WattNode meters are installed in one enclosure, it is common to power all of the meters from one 15 or 20 amp circuit breaker. This has the advantage that you can turn the meter power on and off without interrupting other circuits. This does require space in the panel—usually a three pole breaker in commercial buildings or a two pole breaker for residential service.

Because the WattNode voltage input terminal block is only rated for one wire per terminal, the proper way to connect all the meters to the circuit feeding the enclosure is to run individual wires from each meter’s voltage inputs and connect these wires to the voltage source using a power distribution terminal block or appropriately sized wire nut connectors. The current transformers for each meter are then installed on the branch circuit conductors feeding the load being monitored by that meter.

Keywords: over-current protection, fuse, breaker