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#146606 02/02/07 02:05 AM
Joined: Jul 2002
Posts: 8,432
Likes: 3
Trumpy Offline OP
Myself and my Boss were having a rather lively argument yesterday over a submersible pump.
I certified a place recently where there was such a pump down 130 metres into the bore.
This pump-head is a 3-phase unit (230V) and has an Earth wire on it as well.
All the connections are hermetically sealed on it.
OK then, could someone please explain why it is required in my Boss's view that this pump be protected by a 4 Pole RCD @ 30mA.
Sure it is for a domestic water supply out in the rural parts of Canterbury, but there are lots of places here that don't have them (RCD's I mean).
What is your take on this?.

#146607 02/02/07 04:12 AM
Joined: Sep 2005
Posts: 153
There can be 2 reasons to use an RCD in your case (in a German application):

Mandatory: Grid is TT or earth short circuit is too low to switch device off after 5 seconds (long cable?).

Other: You will be able to detect faults of the pump earlier which usually consist in tightness problems and can cause earth leakages.

Looking at the actual price of an RCD from about 25 Euros (some 50 Kiwi dollars?) we'd always do it with here.

#146608 02/02/07 11:43 AM
Joined: Aug 2001
Posts: 7,520
Similar here in the U.K. under current rules. RCD if a disconnection time of 5 secs. cannot be achieved with fuses or MCBs due to loop impedance, otherwise not required.

#146609 02/05/07 06:02 AM
Joined: Dec 2004
Posts: 354
Trumpy, the compulsory RCD rule applies to houses. Does it apply to sewage and water pumps attached to the houses ?

I think that RCDs on external pump circuits are a luxury, and not a requirement.

#146610 02/07/07 08:05 PM
Joined: Jul 2002
Posts: 8,432
Likes: 3
Trumpy Offline OP
Hi Kiwi,
Yeah, I was wondering that myself.
I have never seen an external circuit to a house, such as a water or waste-water pump protected via an RCD.
Outside garden lighting where the lamps can be accessed yes, but something that is usually only accessible to competent persons, no.
Next thing being, this pump does not have a neutral (being 400V 3-Phase), so how would the RCD detect a leakage from Phase(s) to the required neutral?.
Even all the controls (Pressure switch, etc) are 400V.
I must say, I've never struck this problem before.
Same side of the coin, ever seen the price of a 3-phase RCD before?, they aren't cheap.

#146611 02/08/07 04:32 AM
Joined: Sep 2005
Posts: 153
RCD have been invented to check for earth leakages.

A false connection to the neutral is a partial or total short circuit. It can be detected by overcurrent protecting devices or more sophisticated current/power observing electronic devices. But never by an RCD.

Whether with or without neutral, an RCD will work as well, except for the test button. The way of connecting with correct test button function to such systems is often written on the device itself.

Price: So what is it down under?? In Germany we start with 25 € as said above.

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