I've just bought a 4th floor apartment in an old (1820) building in Spain. Neither my apartment, nor the building as a whole, has any earth circuit.

I'm looking for practical, technical advice on what steps I can take to minimise risks of injury or equipment damage caused by this arrangement. Longer term, can anybody suggest what installing a building ground circuit would entail? My apartment backs onto a small service courtyard (called a "patio" here), so for example, it's relatively easy for me to run a cable to ground level.


The service input goes to an old Siemens schutzschalter which is labelled as 30mA. The output of the Siemens goes to a single 20A circuit breaker which then feeds all of the lights and sockets in the apartment.

Pressing the Test button on the Siemens has no effect, so I'm guessing that's not giving me a whole bunch of protection. Since it's wired directly to the supply, it will take time to organise the electricity company to intervene. Therefore, is it reasonable for me to add a second RCB (https://www.bricodepot.es/productos/electricidad/proteccion-electrica/proteccion-modular/diferencial-bipolar), alongside the breaker to provide the RCB protection? There is ample space in the consumer unit for it.

I should also explain that the whole apartment is scheduled for renovation, including rewiring. Thus I'm looking for what I can do quickly to address any safety issues for the interim.


mains ===> Siemens ===> 20a breaker ====> lights and sockets


mains ===> Siemens ===> New RCB ===> 20a breaker ====> lights and sockets

  • 1
    Read about en.wikipedia.org/wiki/Residual-current_device. Aug 15 '17 at 14:31
  • 1
    Many European countries opted to use ungrounded electrical systems in residential locations. That does not necessarily make them unsafe. See Jim Stewart's link for RCD's used in Europe.
    – ArchonOSX
    Aug 15 '17 at 16:34
  • I don't know how the service panels in Spain are designed, but in a US you would not be able to put an RCB in series with a 30A standard breaker without improvising. What we would do (and what I have done on two of my house's circuits) is to replace the existing standard breaker (in your case a 30 A) with a combination breaker which protects against overcurrent and ground fault. I think you should see if one of these (in the 30A over-current rating) is available for your electric panel. Aug 15 '17 at 22:01
  • @JimStewart sorry - typo, it's a 20A breaker. thx for the suggestion. The service panel is wide enough to accommodate both the existing breaker and the proposed RCB without needing to improvise.
    – pinoyyid
    Aug 15 '17 at 22:14
  • The service panel may be wide enough, but what I was getting at was does it have the connection points which allow putting in another breaker? Perhaps in your panel the breakers are just connected by short pieces of wire and so it is possible to just put in another breaker. The breakers I am familiar with engage spades which are connected to a bus bar. The output side does just have a set screw for the wire which goes to the hot wire of the circuit, but the input side doesn't have a connection for a wire. I know that there are other types of breakers and maybe yours is one of those. Aug 16 '17 at 0:02

Look in your electrical panel and see if you have any combined residual-current / over-current breakers. And check to see if any of your wall receptacles are residual-current receptacles.

Depending on the wiring arrangement in your apartment it might be cheaper to use residual current device receptacles for the ground fault/residual current protection. One RCD receptacle properly placed would protect the entire circuit downstream.

On the other hand, the easiest thing would be to replace each of the over current breakers with a combined residual-current/over-current circuit breaker. If you have a single master breaker for the apartment, you could replace that one breaker with a combined breaker, but if you then have a ground fault anywhere, the power for the entire apartment would be cut off. This would be very inconvenient.

  • @ajeh the OP said "earth circuit" meaning a ground circuit. I am pretty sure the building has plenty of electric circuits.
    – ArchonOSX
    Aug 15 '17 at 19:02
  • Earth circuit or ground. And no read the link you will find they do things differently.
    – Ed Beal
    Aug 15 '17 at 19:05
  • thx for the response. I've updated the question with a bit more info on the current setup.
    – pinoyyid
    Aug 15 '17 at 20:47

RCDs. Done.

An RCD detects ground faults, which includes "electrical shocks to humans".

In Europe, there are several types of RCD in general use - whole house and individual-circuit. RCDs which protect humans should trip at around 8 milliamps, give or take. RCDs designed to protect the house (not the humans) are rated higher, at 35 milliamps give or take. This means a ground fault in that range (8-35 milliamps) would nonetheless continue to shock the human, could stun the human, and in rare instances can kill - especially if the stun causes secondary effects (drowning or falling).

Grounds have several purposes, but the raison d'être was to try to solve the electrocution problem. Grounds provide an auxiliary path back to source, to help the ground fault flow enough current to trip the breaker. If that seems like a round-about way to solve the problem, you are right, but that was all they had at the time.

RCDs are arguably a better way to solve that problem, since they more directly act on any ground fault, even one too small to cause an over-current trip of the breaker. Grounds have their usefulness, but I wouldn't lose any sleep in an ungrounded house with good RCD protection.

  • thx for the response. I've updated the question with a bit more info on the current setup.
    – pinoyyid
    Aug 15 '17 at 20:47
  • both answers are correct, so many thanks to Harper and Jim. Upvoted
    – pinoyyid
    Aug 16 '17 at 12:19

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