RCDs: Neutral - Earth Faults 

In NL we use one RCD for every 4 MCB's. And indeed 2p RCD's. They recommend RCBO's for outdoor units like airconditioners, outside lighting and solar panels.

Where you from ? Romainia ? They use cow shit to build houses

RODALCO2007 Virtually everything has RCDs now, as regulations require it for cables concealed in walls. The other options being to use armoured cables, steel conduit or having concealed cables more than 50mm below the surface - all of which are far more inconvenient and expensive than fitting an RCD. Cookers and similar are a problem, such as where a new consumer unit is fitted and the cooker which worked perfectly before now trips the RCD on a regular basis. Have also seen the same problem with people buying a new cooker, where it's been stored in a damp environment before delivery.

***** Thanks for your reply. In New Zealand a hotwater cylinder and range/cookers don't have to be on a RCD because of the leakage issues encountered sometimes with enclosed elements. Values are often around 10-15 kO.hms. and the element has still plenty of life left in them. The NZ standard also requires 2 RCD's at least to avoid loosing all power in the house.

greetings, I'm well late to the party here, but nonetheless I thought you would be interested to know The AS/NZ 3000 wiring rules are just about to have a new edition released, with one of the big changes being RCD everything. Every circuit needs its own individual RCD, including water heaters, ovens and cookers. One other big change is that if anyone who is working at a domestic residence needs to do work in the roof, they need to shut the power off to the whole installation which is interesting. you can follow this link for a preview of the planned revisions. www.commerce.wa.gov.au/energysafety/new-wiring-rules

We still use GFCIs at the receptacle here in the States, even though GFCI breakers are perfectly acceptable and code compliant. The big thing now here are AFCI's (Arc fault breakers). They are required at the breaker panel on almost every circuit in residential installations these days. (They've been required since 1999 in bedrooms, but now are required everywhere). I hear they aren't a requirement yet in the UK, I presume because you guys protect all cables with metallic sheathing. In any case, studies have shown that around 50% of electrical related home fires in the U.S. are a result of arc faults (series more than parralel) hence the new requirement. Here most homes use non-metallic plastic sheathing rated at 90C. While it's safe cable, it's still non-metallic sheathed meaning it is feasible that it can be damaged in the wall (errant nails or rodent chewing), thus the potential for unseen arcs which normal breakers won't detect. Some metro areas require metal sheathing for residential applications. Chicago is one city with very strict standards in that regard. (Here states and local munincipalities have the authority to override the national code with their own code). It makes sense in those areas because if one condo or apartment building burns, the whole block burns. It doesn't make as much sense in the country where your nearest neighbor is a mile away. We also have many very old homes here. It is not uncommon to see old homes with "knob and tube" wiring from the 20's. It is legal, but if renovation is done it must be brought up to code. And we have tons of homes from the 50's to 70's using wiring code from back then. Grounding has been code since the early 60's I believe, but there's still many homes out there without an earth ground circuit (all receptacles are two prong). Some unscrupulous people will install 3 prong receptacles in an old home without a ground circuit, thereby creating a "bootleg" ground. This is achieved by connecting the neutral to the metal electrical box. This will trick the inexpensive receptacle testers into reporting there is a proper ground. These cheap testers are used by most home inspectors, and creates a dangerous situation for an unknowing home buyer.

Clive, I don't think anything John has said would explain why your disconnected live wire would feel tingly. This may be because the disconnected live conductor was capacitively coupled to another circuit that ran alongside it for a few metres.

I'm by no means an expert. When you say the earth is so poor. What reading would you describe as poor? Thanks

The white lead is an earth connection and it is usually used by the TEST function of the RCBO... which creates a deliberate imbalance to earth in order to cause the RCD part to trip. If you don't connect it, the TEST function usually doesnt work. Some RCBO's are designed so that they don't require that earth connection

I would be looking to see if you have a shared neutral on your lighting circuit

DjResR They used to be optional here as well, but over time, more and more things have required them, and today almost all circuits in a house must have an RCD.

The Volex ones were made to go either way - on those consumer units it was usually one RCD at each end of the row of MCBs, the left RCD had L on the right, the right RCD had L on the left. The two RCD were identical other than the placement of the 'L' label, and that's why they had a stick on label rather than it being moulded/printed on. Supply in on the top for those - for most RCDs that doesn't usually matter either.

@@jwflame Thanks for your reply John, that is very helpful information. I had taught some electrical installation classes many years ago but did not remember dealing with consumer units or their contents. Currently facing the installation of consumer units in a summer house and a cellar - for lighting and power. Thanks again. JS.

Having multiple RCDs/GFCIs is not necessary, provided the house one is a 30mA type. However if the pool already has them fitted there is no reason to remove them either. The only minor problems can be that if they have a test button on them, pressing this may trip the main house RCD as well, and if a fault occurs it may not be the pool one which trips, the house one could trip first, or both could trip. The ground probes is an unusual design and should not be necessary either, the circuit already provides an earth connection. Even if the probes were required, just shoving a probe into the ground is next to useless, as it has to be tested to confirm the impedance is low enough. In some locations, earth rods have to be many metres long to be effective, or other methods such as buried grids must be used.

Senal Devasurendra If the earth is connected, then it's either due to voltage drop in the neutral, there is a fault between line and earth somewhere, or the test meter has a very high input impedance so the 80V measured is not actually there. Or a combination of all three.