Mains voltage at home

[hazel]

I'm scratching my head trying to figure out how my house is wired. Hope you all can help me:

Mains is supposed to be 220 to 240VAC from LINE to NEUTRAL. I measure 227VAC so it's ok BUT here's waht is puzzling me:

I measure:
- 128VAC LINE to EARTH
- 128VAC NEUTRAL to EARTH

How this can be possible? I must assume there's no real EARTH at home?

I'm building a dual power supply for a project and burnt a couple power transformers in a few seconds

Thanks in advance!

 

[JohnRoberts]

Where exactly are you probing "earth"?

Just like ground is not 0V, earth is not a low impedance, or 0V.

JR

 

[hazel]

Where exactly are you probing "earth"?

Just like ground is not 0V, earth is not a low impedance, or 0V.

JR

I live in an apartment so I'm probing at Wall plug where I do my DIY stuff

 

[Gold]

If earth was the center tap of an isolation transformer that would account for the measurements. I don’t know anything about EU mains wiring so it’s a pure guess.

 

[JohnRoberts]

I live in an apartment so I'm probing at Wall plug where I do my DIY stuff

I am not familiar with house wiring in Spain. If your plugs have a third lead for "Safety Ground" this should be bonded to neutral at the distribution (fuse box).  Your measurement look like perhaps the safety ground is floating, if it is a safety ground.

My house has floating safety grounds (not good) and I can read random voltages on the floating safety ground connection, but it is high impedance so not much current.

JR

 

[hazel]

I am not familiar with house wiring in Spain. If your plugs have a third lead for "Safety Ground" this should be bonded to neutral at the distribution (fuse box).  Your measurement look like perhaps the safety ground is floating, if it is a safety ground.

My house has floating safety grounds (not good) and I can read random voltages on the floating safety ground connection, but it is high impedance so not much current.

JR

I sometimes read random values between 35 and 45VAC between neutral and ground and find it excessive but 128VAC is crazy.
I'm wandering if this would be an issue when building and testing power supplies.

Had massive grounding noise issues with a DIY Phono preamp at home in the past and it was dead silent at my friend's house who is a retired engineer and told me about doing his own earth connection

 

[JohnRoberts]

I sometimes read random values between 35 and 45VAC between neutral and ground and find it excessive but 128VAC is crazy.
I'm wandering if this would be an issue when building and testing power supplies.

Had massive grounding noise issues with a DIY Phono preamp at home in the past and it was dead silent at my friend's house who is a retired engineer and told me about doing his own earth connection

Perhaps it is a language thing but earth and safety ground are two different things.

In the US home mains wiring has safety ground bonded (connected) to neutral at the fuse/breaker panel. That same neutral/safety ground node is also connected to earth ground with a ground rod (metal spike driven into the dirt.)

Phono preamp noise is often about local noise fields, but a floating safety ground is not optimal.

Note: that actual noise voltage on a high impedance floating wire is not very meaningful.

JR

 

[PRR]

> Mains is supposed to be 220 to 240VAC from LINE to NEUTRAL

What is "Neutral"? Why would a homeowner care? This is truly a Power Company concept.

In your home, what you want is two wires 230V apart so your lights and appliances work.

And you would like a Safety Earth to connect to, so that if a live wire comes in contact with your appliance cabinet, it will blow a fuse and save your life.

It would be perfectly reasonable to give you 230V Center-Tapped. In fact that is said to be "better for sound". It is also how I get power in the US, plus the center-tap is rated for normal current and I can run my 115V toys from it.

Another option is 3-phase wYe, where the hot conductors are not quite in-phase with each other.

Translated to 128V to center, this gives 222V across your "230V" legs, which is in-sight of your 227V, but just enough off to cast doubts. Maybe the apartment building only takes 2 of the 3 legs and that unbalances the feed.

Or it could be there is NO connection to utility Earth, and you see the effects of all the appliances plugged-in which in a large building would tend to be equal both sides (but more likely 113V than 128V).

In any case, this should not matter. You must assume that *either* of the power wires may be "hot". This means you will be fine if both are hot. As they are on all my 230V appliances, and in Balanced Audio Power.

> burnt a couple power transformers in a few seconds

*Build a Lamp Limiter!!* A power transformer should NOT care if its primary leads are hot, or which way. Even if you "ground" the transformer, 500V difference from ground will not puncture the insulation. You may be mis-wiring the transformer. A lamp-limiter will delay the smoke and light an alarm.

My last (known) major screw-up was a 120V:24V wired backward: 120V on the 24V winding. It sucked so much current the office lights dimmed, which alerted me "something wrong". If the office had better wiring I might have left it powered until the smoke got out.