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# mains electricity question

#1
04-27-06, 05:21 AM
Member
Join Date: Apr 2006
Posts: 14
mains electricity question

Hi all,

I live in spain where the electricity mains are 220V 50Hz. I live about 400 metres from town and have a cable which contains 2 wires with a diameter of 10 (not sure what the ten stands for) that runs to my house and delivers mains current. I supply the third ground wire at site with a buried copper pole.

recently i have been experiencing problems when running a high amperage device. for example, when i use the oven or the 1 hp water pump, the voltage will drop to below 200 volts. The local electrician recommends that i change cables and use 3 wires with a rating of 25 in copper (or 50 in aluminium) to bring the electricity, still at 220v. could anyone explain to me what this means in layman's terms? i had thought the three wires would mean 380 volts, but he says no, it would still be at 220v. How could this help? I know that with a thicker cable the voltage drop would be less, but could someone explain about the three wires?

I hope this is coherent.

thx.

#2
04-27-06, 06:44 AM
Member
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
Note to others answering this question: in Europe, it is quite common for the supply to a home to consist of a _single_ hot leg and a neutral, rather than the split supply common in North America. It is also common for three phase power to be available at the distribution transformer.

bardos,
Three wires can mean one of two things:
It can mean that your electrician is suggesting that two phases along with the neutral be supplied to your home. This gives you the choice of using a single supply leg (220V) or both phases (380V). Also, for a given conductor amp capability, adding the additional phase leg essentially doubles the amount of power that may be delivered to your home. It is also possible, though I believe unlikely, that the third wire would be used for split single phase service (440V) similar to that used in the US.
_or_
It can mean that your electrician is suggesting that a separate 'ground' conductor be provided in addition to the 'grounded' neutral. This third wire is simply for safety, and does not increase the power available to your home.

Unfortunately, I don't know enough about electrical supply in Spain to say for certain which of the above possibilities is what your electrician is suggesting.

The sizes quoted (10, 25, and 50) are the _areas_ of the conductors in square millimeters. A 10mm^2 conductor is slightly smaller than a 7AWG conductor. A 25mm^2 conductor is slightly smaller than a 3AWG conductor.

A certain amount of voltage drop is always to be expected when you run any load. However if the amount of voltage drop has recently _changed_ with the same loads, then this suggests that something has broken, either a bad connection to the wires, or a break in the wires. If your supply conductors are underground aluminium conductors, then a small cut in the insulation can lead to corrosion of the wires and a slow increase in wire resistance and voltage drop.

-Jon

#3
04-27-06, 09:40 AM
Member
Join Date: Jan 2006
Location: PA
Posts: 1,909
Originally Posted by bardos
The local electrician recommends that i change cables and use 3 wires ..., still at 220v. Could anyone explain to me what this means in layman's terms? i had thought the three wires would mean 380 volts, but he says no, it would still be at 220v.
Third wire could be a safety ground or a third phase (grounded corner delta or a second arm from a wye).

> How could this help?
That is a good question. If the neutral is not grounded at your house, then it helps a lot. If it is three phase, it just brings you twice as much power.

> I know that with a thicker cable the voltage drop would be less,
Correct... much less.

> but could someone explain about the three wires?
You'll have to ask the purpose of the third wire. I don't know what is likely in your country.

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