Electronics > Beginners
Isolation transformer ground and safety questions
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macboy:

--- Quote from: rs20 on May 16, 2015, 11:12:03 pm ---
--- Quote from: Shock on May 16, 2015, 11:02:07 pm ---For instance, cutting of a ground/earth pin for a device plugged straight into the wall would isolate the ground/earth between the wall and the device only. But it would eliminate the protection of a residual current circuit breaker device installed in the room or switchboard.

--- End quote ---

I'm being super-pedantic here, but the RCD still protects (or at least activates) against touching live in the device with one hand and touching any other earthed device/water pipe, right? I'm just nitpicking one point, everything else you said is spot on.

--- End quote ---
You are correct. An RCD (a.k.a. GFI or GFCI) does not depend on a connection to earth/ground at all. It trips based on a difference in current between the live and neutral conductors. Any difference is assumed to be some leakage to earth (perhaps through a human body) and this trips the device.  Fault current to earth absolutely does not need to pass through the earth connection of the protected outlet/socket/circuit. It can take any path to earth, and in the case of a dangerous fault, that path is unlikely to be back through the circuit's earth conductor.
pcmad:
you can get ground from the water pipes in your house
helius:

--- Quote from: pcmad on September 03, 2019, 01:32:38 am ---you can get ground from the water pipes in your house

--- End quote ---

It's more correct to say that you may be able to get some kind of grounded node on the main water service pipe. But not all water pipes are made of metal; some metal pipes may have no electrical connection to ground; if there is an electrical connection to ground, it may be of high impedance and therefore not trip the circuit breaker in case of a fault; and if there is a fault to a high-impedance water pipe, and the circuit breaker is not tripped, you have created an additional touch hazard throughout the building!
When a low-impedance Protective Earth is not required, it may be reasonable to tie to the water service pipe, but knowing that is the case is not a job for newbies.
themadhippy:
In the uk its not permitted to use water pipes as an earth electrode unless  its a private water supply not connected to the public supply.
helius:
As an example of an application that allows water pipe connections, the customer unit for FTTH (fiber to the home) in this area includes a ground clip for the water service pipe. The entire unit is Class II: it is powered by 48 VDC from an isolated supply, and is all plastic-encased. Since it is Class II, there is no Protective Earth required; the ground clip is for noise suppression only and because the device would otherwise float at an undefined level to the equipotential zone of the building.
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