There are times when you may want to test a WattNode in an office or laboratory environment, but you don’t have a voltage source high enough to power the WattNode meter. This page list five solutions:

  1. Use a control transformer to step-up 120 Vac to voltages as high as 480 Vac.
  2. Use a foreign travel adapter to generate 230 Vac.
  3. Use a programmable AC power supply.
  4. Use an AC power calibrator.
  5. Install the required voltage service.

Most of these solutions only provide single phase power. Items #3, #4 and #5 can provide three-phase power, but at considerable expense. The good news is that you can perform general WattNode testing for all models with only single-phase power.


All of these techniques involve lethal voltages ranging from 120 to 480 Vac. Only electricians or other qualified personnel should test WattNode meters because these voltage levels are dangerous! The green terminal block screws on the WattNode will have hazardous voltages whenever the WattNode is powered!

  • Always remove power BEFORE touching or using a screwdriver on any of the WattNode screw terminals.
  • If possible, use an insulated screwdriver as an added safety precaution.
  • Do not leave a WattNode meter powered in a publicly accessible location, unless it is mounted inside an electrical enclosure with the door closed and secured.

The following table lists the different WattNode models, the operating voltage range of their power supplies (in practice, the meter will operate somewhat below the rated minimum voltage), the power supply input terminals, and the maximum power draw of the meter.

Model Power Supply Operating Range Power Supply Terminals WattNode Power
WNx-3Y-208-xxx 96 to 138 Vac ØA, N 3W
WNx-3Y-400-xxx 184 to 264 Vac ØA, N 3W
WNx-3Y-480-xxx 222 to 318 Vac ØA, N 4W
WNx-3Y-600-xxx 278 to 399 Vac ØA, N 3W
WNx-3D-240-xxx 166 to 276 Vac ØA, ØB 4W
WNx-3D-400-xxx 320 to 460 Vac ØA, ØB 3W
WNx-3D-480-xxx 384 to 552 Vac ØA, ØB 4W
  • Note: WNx may be WNB or WNC
  • Note: -xxx may be -P, -FT10, -FT10-L, -MB, etc.

Control Transformer

Control transformers are normally used as step-down transformers to provide 24 or 120 volt control power from higher voltage electric services. They have multiple taps, which are selected to match the available voltage supply. A control transformer can be operated in reverse to step-up 120 volts to a higher voltage to power a WattNode meter. Control transformers are readily available from many electrical and HVAC distributors. For example, Functional Devices, Inc., sells a model TR40VA013 Transformer 40VA, 480/277/240/208 to 120 Vac which can provide 480, 277, 240, and 208 volts from a 120 Vac source.

Control Transformer
Control Transformer

Connect the WattNode meter to the appropriate primary terminals—common and the voltage tap corresponding to the meter’s voltage rating. Insulate the ends of the unused voltage taps with wire nuts or electrical tape. Connect the 120 volt secondary to a suitable line cord and plug.

Foreign Travel Adapter

Radio Shack and others sell transformers that step-up 120 Vac to 230 Vac for operating European appliances. You will probably also need a European style plug to match the output of the transformers or you can cut-off the European receptacle and connect the wire leads directly to the WattNode meter.

  • Voltage Valet Heavy Duty Step Up Transformer, 120 to 240 volts, 150 watts, Radio Shack, Model TU150UL, $52.49.

This will work for some, but not all WattNode models:

  • WNx-3D-240-xxx
  • WNx-3Y-400-xxx
  • WNx-3Y-480-xxx

In some cases, WNx-3D-400-xxx or WNx-3Y-600-xxx models may work, but 230 Vac is too low to guarantee operation.

Programmable AC Power Supply

Several companies sell AC single and three phase AC power supplies. Most can supply 0 to 270 Vac or 0 to 300 Vac. Even the smallest of these provides ample power for many WattNode meters. Unfortunately, they cost thousands of dollars (note: the prices are just estimates and may be out of date).


AC Power Calibrator

AC power calibrators are similar to AC power supplies, but are generally much more accurate, commonly can produce 600 Vac or higher, and can generally produce current signals or voltage simulations of CT outputs. They are excellent for testing wattmeters, but are generally priced in the tens of thousands of dollars. In some cases, it may be possible to find used units.

  • Fluke 6100A, 6100B, 6105A
  • Rotek Model 8100
  • Clarke-Hess Model 8080


Add Electrical Service

Depending on the service from your utility, you probably already have three phase power, at least 120/208 Vac. You can hire an electrician to add a three-phase breaker and install a three-phase outlet in your laboratory to power the WattNode meter. This has the advantage of testing with a true three-phase circuit, but only works with WNx-3Y-208-xxx and WNc-3D-240-xxx models. If you have (or can get) 277/480 Vac service, you could use this to test WNx-3Y-480-xxx and WNx-3D-480-xxx models. It is possible, but expensive to get a three-phase step-up transformer from 120/208 to 277/480. It is even more expensive to have the utility add 277/480 service.

See Also

Keywords: voltage, voltage range, control transformer, converter, step up, bench test