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jakbeuk
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Three-Phase Three-Wire and Earth Supply, Earth Leakage Test

09/23/2018 7:58 AM

Hi People, I got a number of 3 phase outlets with Earth pin and NO NEUTRAL, that are currently protected by 3pole Type D, Circuit Breakers but no earth leakage protection.

What brands/manufacturers offers RCDs that will protect 3 phase outlets without neutral. (Clipsal 4pin 500Vac 50Amp)

These outlets are used for different loads of different sizes but not exceeding 50Amp.

Thanks for any assistance/ ideas.

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SolarEagle
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#1

Re: 3 Phase 3 Wire & Earth Supply, Earth Leakage Test

09/23/2018 1:31 PM

No problemo...

https://www.schneider-electric.com.sa/en/faqs/FA282621/

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spades
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#2
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Re: 3 Phase 3 Wire & Earth Supply, Earth Leakage Test

09/23/2018 5:09 PM

Be a bit cautious there.

These 3 phase RCDs generally pass all 3 phases through a toroid to accurately determine that equal currents are present in each phase - ie none flowing to earth etc., which is fine until you use only 2 of those phases for control purposes.

Manufacturers often recommend fitting a resistor when a neutral is not continued to the device, but this only permits the test function to work. Control equipment across 2 of the phases (which is the common method of control for 3 phase equipment where no neutral is present) creates an out of balance situation which can cause much nuisance tripping.
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rwilliams
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#4
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Re: 3 Phase 3 Wire & Earth Supply, Earth Leakage Test

09/24/2018 1:22 PM

The unbalanced current for controls or single phase L-L loading normally returns on the conductors that pass through the current transformer, so unbalanced phase loading will not upset a zero sequence current transformer.

However, the caution is appropriate insofar as the sensitivity of this method is much less than other ground fault detection methods, due to internal CT saturation and the inductive characteristics of the sensing device connected to the current transformer. Many of these combinations required actual component testing to predict the pickup point where the relay could sense a ground fault.
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TonyS
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#3

Re: 3 Phase 3 Wire & Earth Supply, Earth Leakage Test

09/24/2018 7:39 AM

A 3 pole RCD will work perfectly well with 2 phases so long as they are balaced.

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PWSlack
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#5

Re: Three-Phase Three-Wire and Earth Supply, Earth Leakage Test

09/25/2018 3:36 AM

All the equipment does is identify whether the sum of the currents passing through it at any moment exceeds the trip setting, and, assuming this sum current is passing along an earth conductor (which might be a human) trips to disconnect the supply for safety. So, anything that works with a <...NEUTRAL...> conductor will also work without it.

If in doubt, consult a qualified local Electrician.

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