Mains and Earthing

[ulindel]

Please explain,

By chance when a light socket was checked, was found that when the electrician put his meter across the Live and the Earth (Yel/Grn) wire
it showed that it was live,
the same as when he checked between Live and Earth wires.

When a check was made in the consumer unit, the same showed there too.

No additions or alterations were made to the house electrics recently.

Any explanations please?? Thanx, ulindel

 

[Screwi]

If you meter between live and earth - it will show live, as the meter is finding live through live and neutral through the earth - that is normal??

Your question needs to be better explained my friend ?!?

 

[fireman22]

did your electricain say this was wrong? or have you done it and thought it was wrong, my guess.

 

[ulindel]

Thanx Screwi & Fireman,

The electrician said was normal, but in my ignorance, the thought of touching metal parts earthed when his meter showed LIVE, is scary!!

Forgive the double check, but do I understand right, that this is a normal situation.

Thanx again.

 

[ninebob]

A current path between live and earth, when tested, should be positive. That is what earth is there to do.

In the absence of any fault condition, any metal earthed part you touch will not be live. If there is a fault, what has been demonstrated to you is that the current will flow to earth, and not to you when you touch a metal part.

So, nothing to worry about!

 

[ulindel]

Thank you Minebob,

Electrics are mindbogling and very confusing. When the others said that the meter reads "..... neutral through the earth ......", why in the plug we rewire the earth does not find neutral and blow the fuse?

Then comes to mind this friend who uses a small screwdriver, with a balb in it, which lights up if he touches a live wire with it and his finger stuck on the other end of the screwdriver???? How come his nose does'nt glow!

Thank you all for puting my mind at rest.

 

[Damocles]

His nose may glow if he drinks a couple of bottles of whiskey first.

 

[felix]

Then comes to mind this friend who uses a small screwdriver, with a balb in it, which lights up if he touches a live wire with it and his finger stuck on the other end of the screwdriver???? How come his nose does'nt glow!

This may sound odd to you but voltage does not cause electric shocks; current does. When you put volts across something that conducts electricity a current flows. Light bulbs conduct electricity and so do you.

If you're unlucky enough to put your finger on a live wire, current will try to flow through your finger and out somewhere to earth. If you're wearing rubber soled shoes and touching only the wire this current will be tiny because the rubber offers a high resistance to current flow. You might not even notice. If you're holding earthed metal with your other hand the current will be big and you'll know all about it!

That screwdriver has a big resistor in it as well as the little red bulb (proper name, neon bulb). When you put its tip on a live wire a tiny current runs through the resistor, the neon and you. It's so small you don't notice but it's enough to light the neon.

 

[jtaunton]

Remember, its differences in voltage that you need to watch out for, and the higher that voltage, the higher the current that will flow.

Your earth, netural, taps and, in theory, the actual earth are all tied together at a nominal 0V. Your live sits at an average of 230V with respect to neutral. Unless you've got a voltage across you, then no current will flow. If there are two resistances, one after the other (such as, say, you (being low resistance) and some rubber-soled shoes (being high resistance) then the amount of voltage across each is split in proportion to their resistances. If, for example, your rubber-soled shoes were 22 times more resistive than you are, then if you were to touch a live wire then there would be 10V between your fingertip and your feet, and then 220V across your shoes. You'll have to trust us though - don't go trying any of this.

So as felix says, don't go touching live and neutral and/or earth at the same time.

Same reason that a bird can sit on a power cable with no ill effects.

 

[ulindel]

Roger di fellows, will all be left to the experts (sparkies).

Helps sometimes to be inquisitive when doubts exist. Cheers.

 

[Damocles]

Certainly does. I still do not understand the question. I shall meditate in search of enlightenment some more.

 

[Big_Spark]

You should also remember that the 230V mains is only the rms value of the supply, the peak Potential difference is likely to be as high as 340Vac, this is all connected to how electricity is generated in a sinusoidal pattern by the alternators (simplified explanation)