What are Current Transformer (CT) shorting blocks used for? Where can they be found? Are there any hazards of having the CT secondary open-circuited?


13 June 2022

Current Transformers require shorting blocks to be used when they are being installed or serviced

Product Line:
LV Transformers

Applies to Current Transformers (CT's) by SquareD/Schneider Electric

Current Transformers can produce very high voltage potentials at their secondary terminals if disconnected when primary current flow is present

Current Transformers must never be open-circuited when current may pass through their window.  Catalog # 3090TB4 for 4 pole and 3090TB6 for 6 pole shorting blocks used with CTs.  The hazard of electric shock, burn, or explosion exists on an open circuited CT.  Death, severe personal injury, or equipment damage can result if the leads are touched when the CT is open-circuited..  As much as 4000V on the secondary has been measured on large core CTs with an open-circuited secondary.  CTs must ALWAYS be shorted or connected to a burden such as a meter or relay, it must be  demagnetized or accuracy may be reduced.