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Topic Title: 3 phase RCD's
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Created On: 01 March 2014 12:17 AM
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 01 March 2014 12:17 AM
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robwmc

Posts: 2
Joined: 09 March 2012

I have a 3 phase 415v heater that needs protecting with an RCD, the 3 phase RCD's that I've seen have all been 4 pole. So will it still operate correctly without a neutral attached? Thanks in advance.
 01 March 2014 01:20 AM
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Zuiko

Posts: 521
Joined: 14 September 2010

L1 + L2 + L3 = N in a healthy 4-wire circuit.

If you have a balanced three-phase load, L1 + L2 + L3 = 0, then you do not need a neutral.
 01 March 2014 07:47 AM
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anastasis

Posts: 583
Joined: 01 September 2009

I would always check with the manufacturer of a 4 pole RCD before using it without a neutral connection. Some, for example, require a neutral supply for the test button. I don't think any will object to not have a neutral connection on the load side.

See this thread for a similar discussion: http://www.theiet.org/...s/f.....eadid=33102
And note what it says here: http://www.tlc-direct.co.uk/Pr...s/HGCD463U.html

Originally posted by: Zuiko

L1 + L2 + L3 = N in a healthy 4-wire circuit.

If you have a balanced three-phase load, L1 + L2 + L3 = 0, then you do not need a neutral.


The above equations treat the currents as vectors, which not everyone here may be aware of.
 01 March 2014 10:49 AM
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24Hour

Posts: 187
Joined: 06 April 2006

Anstasis is correct.
Without a neutral the test button will not operate, so how does the customer checkmit every 3 months.
That said it will actually trip in the corect fashion on fault mode without a neutral though.

-------------------------
Yes i do do 24/7 everyday of the FLAMIN year.
 01 March 2014 11:29 AM
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hertzal123

Posts: 303
Joined: 26 August 2007

Without a neutral a resistor must be fitted between 1 phase and neutral,so test button works.Forget the value,but hope this helps.
Regards,
Hz.
 01 March 2014 12:13 PM
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geoffsd

Posts: 347
Joined: 15 June 2010

Edit - Changed my mind.

Some RCDs have the test button between two of the lines.
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