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I'm creating a portable test socket for electrical appliances that comes equip with a RCBO, power meter and possibly emergency stop button. My test socket will operate at max 240V AC and 10A. The purpose of the RCBO is to protect myself when I'm working on or fixing electrical appliances.

When searching for RCBO breakers, they seem to have different rated residual current varying from 10mA to 300mA with the most common being 30mA. I understand that in a household application where multiple devices are connected there can be some leakage current where the higher rated residual current RCBOs are used. However, in my case where the RCBO is connected close to a single appliance, which value is most suitable for me? And also to take note the 10mA RCBOs are almost triple the price of the 30mA version from my local supplier.

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For personal protection when working on equipment a 10 mA RCD/RCBO is best. If that is unaffordable then a 30 mA one should be adequate. A 300 mA model will not provide protection against electrocution. In the UK a 300 mA trip is used to provide protection against fire, not electrocution. Typically it would also be a time delayed design. Circuits fed from a 300 mA time-delayed RCD that need to provide protection against electrocution will also have a 30 or 10 mA normal speed RCD. Wiring outside the UK will follow the relevant local standards but a 300 mA trip won't protect you anywhere in the world.

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Those 300mA are selective, they are intended to supply multiple <30mA, they are not meant for direct touch protection RCD. For direct touch, a RCD of less or equal than 30mA is suitable.

The RCD is a very fine electro mechanical device, less trip current, more fine like a swiss watch, so the price is higher.

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