Rcd as an emergency stop unit?

Question

Could I use a 3 phase rcd as an emergency contactor by putting the neutral through stop buttons and then down to earth?

Answer 1

Go to http://www.tlc-direct.co.uk/Technical/Di...

That should answer your question very well.

Personally, I wouldn't.

Answer 2

The above gives all the technical stuff but not what you want to know, the answer is no you shouldnt use the RCD as an emergency stop by earthing the neutral, the risk of the device not tripping would be too high,  just fit a contactor and put the coil supply through an emergency stop button.  

Answer 3

RCDs operate by measuring the current balance between two conductors using a differential current transformer. The device will open its contacts when it detects a difference in current between the line conductor and the neutral conductor. The supply and return currents must sum to zero, otherwise there is a leakage of current to somewhere else (to earth/ground, or to another circuit, etc.).

RCDs are designed to prevent electrocution by detecting the leakage current, which can be far smaller (typically 5–30 milliamperes) than the currents needed to operate conventional circuit breakers or fuses (several amperes). RCDs are intended to operate within 25–40 milliseconds, before electric shock can drive the heart into ventricular fibrillation, the most common cause of death through electric shock.

In the United States, the National Electrical Code, requires GFCI devices intended to protect people to interrupt the circuit if the leakage current exceeds a range of 4–6 mA of current (the trip setting is typically 5 mA) within 25 milliseconds. GFCI devices which protect equipment (not people) are allowed to trip as high as 30 mA of current. In Europe, the commonly used RCDs have trip currents of 10–300 mA.

Residual current detection is complementary to over-current detection. Residual current detection cannot provide protection for overload or short-circuit currents.

RCDs with trip currents as high as 500 mA are sometimes deployed in environments (such as computing centers) where a lower threshold would carry an unacceptable risk of accidental trips. These high-current RCDs serve more as an additional fire-safety protection than as an effective protection against the risks of electrical shocks.

In some countries,[1] two-wire (ungrounded) outlets may be replaced with three-wire GFCIs to protect against electrocution, and a grounding wire does not need to be supplied to that GFCI, but the outlet must be tagged as such. The GFCI manufacturers provide tags for the appropriate installation description.

  Important note regarding TN-C earthing system

According to IEC 60364:

RCD should not be used in a TN-C system (per definition, RCD would not provide necessary protection in circuits with L-PEN wiring)!

When an RCD is used in a TN-C-S system, a PEN conductor should never be used downstream (instead, separate PE and N wiring is required).

Answer 4

woulnt that make it trip straight away?