Current Transformer FAQ

Frequently Asked Questions

  • Can I extend CT wires?
    Yes, generally the CT lead wires can be extend by 100 feet or more, but longer wires can result in increased noise or interference, which can decrease accuracy. See Current Transformer Wire Extension.
  • How can I tell if I’ve wired up the CTs incorrectly?
    See the troubleshooting section of the manual for your meter or search for troubleshooting articles on this support site.
  • Do I need shorting blocks for the CTs?
    No, our CTs have internal burden resistors and only generate 0.333 Vac, whether connected to the meter or not.
  • Can a CTS-0750-005 be used on a 200 amp circuit?
    All CTS-0750-xxx model CTs function safely up to to 200 amps. A 5 amp model will have an output of 0.333 Vac at 5 amps, and the same model used at 200 amps will have a theoretical output of 13.33 volts. The temperature rise at 200 amps will be only a few degrees due to low current in the secondary winding. So long as the actual current does not exceed 5-6 amps, the WattNode meter should operate and measure correctly. WattNode meters can handle CT overvoltages up to 5 Vac without damage, but will not measure accurately beyond about 125% of normal CT rated current, or about 6.25 amps.
  • What is the maximum CT rated amps supported?
    This depends on the WattNode model. See Maximum CT Rated Amps for details.
  • Can I use split-core CTs outdoors?
    Split-core current transformers are not designed for outdoor use. An operating and storage humidity range is not specified and in a high humidity environment the silicon iron core laminations used many of our CTs can rust together and can not be opened. In humid environments, spraying a rust inhibitor, such as WD40, on the exposed laminations can help to prevent rusting.
  • What is the operating and storage temperature rating of CTs?
    The operating temperature for the ACT series is rated -30°C to +55°C all others are rated -10°C to +55°C and the storage temperature for all models is rated -40°C to +70°C.
  • What is the recommended absolute maximum current for CTT (solid-core) CTs?
    The UL listing allows for operation up to the following currents:
  • CTT-0750-xxx: up to 200 amps
  • CTT-1250-xxx: up to 800 amps
  • CTT-2000-xxx: up to 1,500 amps
  • CTT-3000-xxx: up to 3,000 amps