135 V between Ground and Neutral


Old 10-21-19, 05:00 PM
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135 V between Ground and Neutral

Hi all,
I have moved into a flat in Spain and was wiring a wall lamp.

When measuring the voltage between ground and neutral I get a reading of 135V. (from live to neutral it is 230V).

This seems rather scary to me so I asked the electrician who did the instalation and he tels me that this is normal in a three-phase system.

Iīm not very clued up on 3phase systems, so I was keen to know if such a high voltage between ground and neural is ever possible (I donīt know if we have TT, TN...setup)

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Old 10-21-19, 08:38 PM
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The normal house current voltage in Spain is 230 volts (50 Hz AC).

I am not sure how 3 phase systems are set up in Spain but it is possible to have a 3 phase system with 230 volts live to live and a center symmetric ground. In such a system you might expect live to ground to be 135 volts for any of the three ;ive legs (aka phases). None of the three legs would be considered neutral in the U.S. sense and the ground would not be used for anything other than grounding..

(also conjecture) Given such a 3 phase 230 volt system a home might be fed with two of the live legs for a 230 volt supply to the home.

The "voltage of a circuit" is the highest voltage between any two conductors so what I referred to as a 230 volt 3 phase system has 230 volts phase to phase (live to live) for any two of the live legs.

Neutral in the U.S. sense means grounded conductor; neutral is correctly bonded to ground in just one location at the home, the panel where the first whole house disconnect is located. In the house in Spain that is the subject here, if you indeed have two legs of the 3 phase street secondary line coming into your house as your service and neither is grounded (which means neither is neutral in the U.S. sense), in reality live to ground is unpredictable voltage wise and may have only coincidentally been 135 volts the moment you measured it.

Another kind of 3 phase system that might be found supplying 230 volt house current (and called star or wye) might have 230 volts live to neutral and about 400 volts live to live. A home might be supplied with 230 volts from this system (called 400 volt 3 phase) by having one live conductor and the neutral in the service drop. Here, 135 volts would be meaningless other than to indicate a malfunction if encountered..


Last edited by AllanJ; 10-21-19 at 09:26 PM.
Old 10-23-19, 10:59 AM
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Thanks for your reply AllanJ

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