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Posted By Topic: RCD and Breaker wiring

Jun 16 2012 21:59

On a 2 pole RCD I know the neutral is (or at least normally is) on the right, and phase on the left, but are the phase and neutrals in meant to come from the top or bottom and does it matter. In wiring diagrams etc I've seen it both ways on RCD and breaker.

Jun 17 2012 10:10

I generally feed the protection from the bottom, ie from the bottom of a RCD to three MCBs with the supplied phase bar.

Jun 17 2012 10:16

Sometimes it matters, and sometimes not.

If either one matters, it should be marked on the unit - check the wiring diagram.

When it matters, it's often because of the test circuit. Test button gets supply from load side Active, and runs via resistor to line side N. If direction reversed, and test is fed from line side, then pressing the test buttom with the unit tripped or switched "off" will liven the load side N - an unsafe situation.

Jun 17 2012 10:20

Most RCDs are marked the correct direction for the current flow, some give a circuit diagram and terminal numbers to give this information.

But for all RCDs the wrong current direction will or can destroy the RCD.

As for the neutral pole, this often marked by the letter N or some give a circuit diagram and terminal numbers to give this information.

Jun 17 2012 20:59

As per above. Refer to link to the image:

(1) being the Live Side and (2) being the Load side. (1) Terminal is being fed BY the incoming active conductor and the max three MCB final circuits being fed FROM the (2) terminal. In from top out from bottom. Lower (N) connection feeds the corresponding PROTECTED circuits. Upper (N) connection is from incoming Neutral or non protected bus bar.

Jun 20 2012 22:49

RCD has no markings on the terminals but a tiny diagram that leads me to believe the input is through the top.
Aleck it looks like switching the unit off opens the trip circuit as well which prevents the unsafe situation you mentioned.
Thought about about using multi meter to confirm input from output by looking for trip circuit resistance on output while the switch is turned off and pushing the test button but it doesn't work on either side until you switch the unit on (then both show the trip circuit). I think this is because the trip circuit is being opened when you flick the unit off

Sep 03 2012 22:32

I have had this very situation today. Installing HAGER RCCBs which have phase on the left side of the breaker and neutral on the right. The top left terminal is marked '1', the bottom left is marked '2'.

According to the diagram on the unit, the test circuit resistor is fed from pin 2, which then goes to the TEST switch, and then to a set of contacts which are closed when the unit is active (not tripped). If the unit trips, these contacts open thereby disconnecting the TEST circuit as well.
The other side of these contacts goes to the N terminal on the bottom right.

The diagram printed on the RCD also shows the balance sense core being around the lower terminals (2 and N), with the contacts (cutoff) above the core, the output being 1 and N at the top.
This would make reasonable sense, that the sensing circuitry etc is on the incoming side BEFORE the contacts.

The installation instructions that come with the RCDs do not specify which side the supply should be fed in.

I have found out that Hager specify their units to be connectable with supply top OR bottom - it doesn't matter.
This may not be the case with every other brand though so it may pay to check with the supplier.

Sep 04 2012 07:08

NB just don't swap incoming and outgoing feeds on PDL plate mount (and probably RCD powerpoints) because that lets all of the smoke out of them!

Sep 04 2012 22:02

good point, brendon - funny how these things never work as well once the smoke has been let out!

Sep 04 2012 22:05

If you could invent a syringe to get the smoke back in - you would make a fotune!

Sep 04 2012 22:05

If you could invent a syringe to get the smoke back in - you would make a fortune!

Sep 05 2012 19:10

it must be possible, as they now have smoke in a can !!!!

Sep 06 2012 20:45

lol, you guys are hilarious.