Hi All

I am looking for clarification on a wiring arrangement I have always considered good practice and commonly used, versus an arrangement I was recently informed of.

To my knowledge, if the secondary connections of an instrument current transformer are not connected and there is a primary current flowing on the measured circuit, then the secondary circuit of the current transformer should be shorted-out (i.e. a 'jumper' connection installed across S1 and S2 terminals of the current transformer), the S2 terminal usually also being connected to protective earth.

Whilst I don't have any reference to specific current transformer OEM wiring diagrams to refer, the general recommendation is to always ensure this arrangement due the hazards associated with a high-voltage that is generated across the secondary terminals (as the secondary current attempts to drive through a high impedance) when the circuit being measured has current flowing, as this will generally lead to failure (malfunction, breakdown of insulation, and potentially a fire) of the current transformer, and a hazardous voltage present at the secondary terminals up until that point in time.

Recently I was informed that an alternative way of dealing with this is to do away with the jumper wire, and simply earth the S2 terminal.

I am not convinced this is a safer or more effective solution and wondered whether anyone has an opinion on the suitability of the former versus the latter arrangement

Thanks in advance

Neil W