TN-C-S earth fault

135

02:00:38

Circuit consists of a domestic supply of 230V ac @ 50Hz with a TN-C-S earthing arrangement.

Ze = 0.35Ω. This is the maximum impedance external to a domestic installation with TN-C-S earthing in the UK. Ze equal to or less than this allows the protective device to operate within the permitted time for safety (0.4s for a consumer unit, 5s for a distribution board).

Switch simulates a line-to-earth fault. In a TN-C-S system under fault conditions, fault currents could be as high as 30,000A. A UK consumer unit with a 16kA conditional fault current rating can only handle up to 16,000A; anything higher will blow up the protective devices.

In the circuit, the simulated line-to-earth fault current is 657A (rms).

published 6 years ago

rich11292000

6 years ago

What is typical amperage and max for UK domestic system? We have 200amp 240vac is USA, but older natural gas houses as low as 100amp

rich11292000

6 years ago

At work is a 55uH 3 phase reactor to protect a 480vac/2000amp generator. 22000a max short circuit. 3.5 tons

reniz77

6 years ago

@rich: the typical fuse rating in the mains cutout of modern residential units is 100 A, which is enough to supply 6 A for lighting, 32 A for ring final circuit socket-outlets, 40 A for shower, 32 A for cooker, and 3 × 16 A for water heater and 2 storage heaters, taking into account diversity in usage

reniz77

6 years ago

@rich: the conditional rating of consumer units in domestic is 16 kA prospective short circuit current

faceblast

6 years ago

those currents are huge

faceblast

6 years ago

australia runs on 240V with 80A mains per phase. 15A for ovens, airconditioners, hot water. 10A for outlet rings, lighting

reniz77

6 years ago

@faceblast: depends on the power ratings of appliances used in your country. In our flat, we have an 8.5kW shower that we sometimes use in full blast in the winter. Using P=I×V, that would be 8500/230=37A, thus needing a 40A circuit-breaker

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