EV Charging - You Tube Video RCD Protection

Only a few characteristics demand 30mA RCD additional protection of a circuit - generally those supplying sockets (≤32A), bathroom circuits, domestic lighting circuits, or the most common soft sheathed cables concealed (<50mm deep) in walls, So a circuit supplying a charge point is not likely to need 30mA RCD protection of itself unless the new cable is concealed in a wall and even then that can be side-stepped by using a wiring system with a concentric c.p.c. (e.g. SWA).

There are a number of good reasons to avoid putting a charge point after an existing RCD - discrimination is perhaps one, risk of nuisance tripping to the the extra leakage from the EV is another, but perhaps the most significant is that d.c. residual currents (that can result from EVs under some circumstances) can cause AC type RCDs to misbehave, and many existing RCDs are AC types. All RCDs on the supply side of EV charge points need to be either type A (presuming the the charge point somehow prevents d.c. residual currents exceeding 6mA) or even type B.

There are other reasons why an RCD might be needed - e.g. on TT systems, but that's less usual. On TN systems MCBs are normally perfectly adequate to prevent electric shock under normal earth fault conditions (provided Zs is within specification).

On TN systems isolation can be provided by a single pole MCB entirely properly - as long as it can be locked off (almost all MCBs can be with the appropriate attachment), it need not be local to the equipment it controls.

   - Andy.

Only a few characteristics demand 30mA RCD additional protection of a circuit - generally those supplying sockets (≤32A), bathroom circuits, domestic lighting circuits, or the most common soft sheathed cables concealed (<50mm deep) in walls, So a circuit supplying a charge point is not likely to need 30mA RCD protection of itself unless the new cable is concealed in a wall and even then that can be side-stepped by using a wiring system with a concentric c.p.c. (e.g. SWA).

There are a number of good reasons to avoid putting a charge point after an existing RCD - discrimination is perhaps one, risk of nuisance tripping to the the extra leakage from the EV is another, but perhaps the most significant is that d.c. residual currents (that can result from EVs under some circumstances) can cause AC type RCDs to misbehave, and many existing RCDs are AC types. All RCDs on the supply side of EV charge points need to be either type A (presuming the the charge point somehow prevents d.c. residual currents exceeding 6mA) or even type B.

There are other reasons why an RCD might be needed - e.g. on TT systems, but that's less usual. On TN systems MCBs are normally perfectly adequate to prevent electric shock under normal earth fault conditions (provided Zs is within specification).

On TN systems isolation can be provided by a single pole MCB entirely properly - as long as it can be locked off (almost all MCBs can be with the appropriate attachment), it need not be local to the equipment it controls.

   - Andy.