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Topic Title: 4 pole rcds
Topic Summary: No Neutral
Created On: 15 October 2009 07:13 PM
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 15 October 2009 07:13 PM
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bakey1959

Posts: 767
Joined: 24 October 2006

Don't ask why, but we have ended up with 4 pole rcds supplying 3 phase + Earth sockets (no neutral).
Because of this, the test button on the RCD does not trip them and we have been told that it is possible and safe to connect a certain size resistor between the neutral and earth to facilitate this function. Does anyone know of such a practice?
 15 October 2009 08:39 PM
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rocknroll

Posts: 8824
Joined: 03 October 2005

In the older RCD's the internal test resistor was connected between N and L2 or L3 so it was difficult to test a 3P + E supply.

Now the test resistor is placed in between the L2 and L3 pole so 2P + E, 3P + E and 3P + N + E supplies can be tested:

See;

http://i641.photobucket.com/al...cknroll/MWSnap186.jpg

(You will notice that the test resistor is connected between the L2 and L3).

If it is an older RCD (check manufacturers details first) then connect a resistor between the N and L1 terminal on the load side.

30mA RCD - 2200/2400 ohm 2 Watt resistor
100mA RCD - 1000/1200 ohm 2 watt resistor

Just a few more points:

I would remove the resistor after the test personally, the reason I said connect to L1 is because unless you have schematic of the RCD you dont know whether the manufacturer has connected the internal test resistor between N and L2 or L3 and this will cause an error, manufacturers dont connect the internal resistor to L1 so thats a clear pole for your test.

Remember this only a functional test to see if the mechanism works only.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 16 October 2009 at 12:20 AM by rocknroll
 16 October 2009 05:00 AM
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ebee

Posts: 5664
Joined: 02 December 2004

Go on then rock.
Someone had to ask.
Why the figures for the resistors?

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 16 October 2009 10:38 AM
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rocknroll

Posts: 8824
Joined: 03 October 2005

The resistors should give you a simulated fault current of around 1 - 5 Idn

30mA 30 - 150mA
230 / 2400 = 100mA (approx)

100mA 100 - 500mA
230 / 1200 = 200mA (approx)

George says: I = V / R

You could use a bit of wire and put the full system fault current across the RCD if you want but I suspect you could end up in casualty with a big-boned matron sitting on your chest trying to fish the test button out of your nose with a pair of long-nosed pliers.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
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