Parallel connection of relay protection voltages

Connecting relays in parallel to share voltage or current is generally not recommended due to unequal current distribution and high risk of relay failure.Key ConsiderationsCurrent Sharing Issues: When relays are connected in parallel, the current may not divide equally because each relay has slightly different contact resistance. The relay with the lowest resistance will carry more current, potentially exceeding its rated capacity and causing overheating or failure ( ). Failure Risks: If one relay fails or cannot energize, the remaining relay(s) will carry the full current, increasing the likelihood of contact welding or damage. This is particularly critical in protective relaying circuits where reliability is essential ( ). Voltage and Arc Concentration: During switching, the interrupting arc may concentrate on a single relay, especially if the relays do not operate simultaneously. This can lead to premature contact wear or failure ( ). Protective Measures: To mitigate risks, it is recommended to:Use relays with a current rating significantly higher than the expected load.Install fuses or current sensors in series with each relay to prevent overcurrent.Ensure simultaneous operation of relays to minimize uneven voltage or current stress ( ). Practical Guidance: Standards such as NFPA 79 advise against paralleling relay contacts to increase ampacity, except under very specific conditions where the relays are not switching current but merely holding a voltage ( ). Alternative Approaches: Instead of paralleling relays, consider:Using a single relay with a higher voltage or current rating.Employing solid-state relays or contactors designed for higher loads.Designing the protection scheme to distribute load across separate circuits rather than paralleling contacts. In summary, while parallel connection of relays may seem like a way to increase capacity, it introduces significant risks of unequal current sharing, contact failure, and reduced reliability. Careful design, proper rating, and protective devices are essential if parallel operation is unavoidable.