Using earth (ground) as 0V return wire

I bought this...

after SWMBO fell and fractured two vertebrae. Excellent range and loud enough to wake the dead ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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I love to cook with wine.     Sometimes I even put it in the food.

, hi-fi, TV, etc. I have a few spare buttons so I'm using one as a 'Shed Si gnal' so that SWMBO can summon me indoors occasionally. The simple oscillat or circuit, feeding a miniature speaker, has its own DC power supply in the shed (workshop) and its 0V line is earthed. So is the 0V line of the RC un it in the lounge. Therefore I assumed I could simply run just the signal wi re to the shed, without an accompanying 0V line, as that's provided by main s earth.

yes, if you don't mind your device seeing full mains during a fault event

0V. Is that a consequence of my wire-saving approach, and if so, why?

It would take quite a bit of current, mains or dc, to produce that V drop. You've not given much detail on that.

NT

Possibly separate grounding rods, and some underground chemistry?

That sounds like free energy to me.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

, hi-fi, TV, etc. I have a few spare buttons so I'm using one as a 'Shed Si gnal' so that SWMBO can summon me indoors occasionally. The simple oscillat or circuit, feeding a miniature speaker, has its own DC power supply in the shed (workshop) and its 0V line is earthed. So is the 0V line of the RC un it in the lounge. Therefore I assumed I could simply run just the signal wi re to the shed, without an accompanying 0V line, as that's provided by main s earth.

0V. Is that a consequence of my wire-saving approach, and if so, why?

Probably you're seeing electrochemistry, and multiple alloys of grounding posts in the electric grid connections in your neighborhood.

If it were critical, you could receive the oscillator signal through a capa citor with a tone decoder (NE567) and disable the speaker when the frequency was wrong. Or, you cou ld use a cordless phone's 'locate handset' feature instead of outdoor runs of wire .

give it up. Too much hassle for too little gain. Run two wires. Or run an air line with a whistle on the end. You don't say how far, but there are numerous cheap wireless devices that could be used. toy walkie talkie?

Thanks all. I'll probably end up simply running another wire, although it's a hassle. But curiosity is the main driver. There's thick copper mains ear th wire between the lounge and my heavily equipped shed workshop. I suspect I'm missing some obvious point and will investigate more methodically and report back.

I don't follow the warning about mains voltage? That must be equally true a bout a variety of my other circuits, including test equipment, in which the 0V line is connected to mains earth. If 240V touches an earth wire at poin t X then I assume it triggers the circuit breaker and quickly cuts all powe r to all circuits and appliances at X, Y and Z throughout the house.

Re the comments about 'stakes' etc. Are those relevant here? I confess I've never really understood the whole topic of Earthing, but surely the pertin ent point is the one I just made, about there being a physical network of h eavy wire linking all the mains sockets on my property?

Terry, East Grinstead, UK

If you've got power lines, use something like X10 or a power line network connection.

's a hassle. But curiosity is the main driver. There's thick copper mains e arth wire between the lounge and my heavily equipped shed workshop. I suspe ct I'm missing some obvious point and will investigate more methodically an d report back.

about a variety of my other circuits, including test equipment, in which t he 0V line is connected to mains earth. If 240V touches an earth wire at po int X then I assume it triggers the circuit breaker and quickly cuts all po wer to all circuits and appliances at X, Y and Z throughout the house.

ve never really understood the whole topic of Earthing, but surely the pert inent point is the one I just made, about there being a physical network of heavy wire linking all the mains sockets on my property?

When a live to earth fault occurs, a current of 10s/100s/1000s of A flows. The resulting voltage on the earth wiring depends on details, but is freque ntly near 240v/120v, ie your earth becomes live until the fuse/breaker acts . Connecting low v equipment to this means 2 things:

1. all touchable LV bits are briefly live
2. in some circumstances you also get 240/120v across your low voltage elec tronics

US experience with neutral grounded cookers does seem to show the risk to b e very small, as long as the appliance does not electrically connect to peo ple eg via headphones, bathwater, etc. If it does of course it's liable to be fatal.

NT

What kind of meter did you use ?

At least some analog multimeters in DC position shows something when feeding it with completely symmetrical AC.

So if you have PEN (separate PE protective ground and N neutral) there will of course be some voltage drop across the PEN due to the AC load, that might well show up as a negative voltages on some multimeters.

In a PEN (TN-C) environment

do not use PE as signal reference. Use separate signal ground or better a balanced connection or in this case some wireless means.

Since Terry is in Europe, here are some relevant issues:

• The distribution transformator might be 1 km away from the customer, with the secondary star point (PEN) grounded with several grounding stakes close to the transformer.

• A common PEN conductor in addition to the three phases are routed to each building (TN-C).

• In the old days, the PEN conductor was directly routed to each mains socket, in which was split to the Neutral N and protective earth contact PE at the socket.

• In more recent standards (TN-C-S) the splitting is done at the mains entry panel or after the meter. Local grounding electrodes are used from this point. If the PEN conductor from the distribution transfer to a house is lost, at least some of the PEN current will flow through the dirt ground if there is an unbalanced load.

Since we do not know the age of Terry's shed, it is hard to say, if TN-C with common PEN is used or TN-S with separate PE and N connectors are used. Based on the meter reading, my guess is that TN-C is used.

Thanks for the helpful follow-ups.

The RC output travels through four screw connector blocks between house and shed and I discovered that one had broken loose. So presumably that had a lot to do with the odd measurements I was getting (on a couple of DMMs). In fact at one stage I was reading about 100 V ac! Going to a few mV when I loaded it with a 1k resistor. Were those readings due to capacitive coupling?

So I think the earthing issue was something of a red herring. What's more, I later found I'd overlooked a 0V wire I had installed between RC and shed about a decade ago...

@upsidedown: Thanks for that detailed explanation, although some of it will need more study. The house is about 24 years old.

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Terry, East Grinstead, UK

Ages ago, had a small house where the doorbell (buzzer type) would not work, because one of the wires was broken in the wall above the push button switch. Did not want the mess of breaking the outside wall to get to the wire, and mechanically impossible to run another wire. So,i wired the appropriate switch side to the lath(wire) that was available as an earth/ground point, and in the back of the house added a wire from a cold water pipe near the buzzer. Perfect solution. If you can manage to keep the circuit isolated from others, you can at least prevent ground loops and if the drive/signal is "large", the receiving end will not "care" about an attenuated/noisy input signal.

*** Yes, these could easily develop 1V. Also any atmospheric static electricity (cloud bases) will atttract its opposite on the ground. *** Bullshit. You know better. Voltage is not energy. The earth is not a 0 impedance conductor, typical ranges are 10 to 1000 ohm-meters, so any amperage you could get would be miniscule. *** Art

... and any energy you extract eventually comes at the expense of your electrodes aka ground stakes.

Put the siren between the NPN collector and the 14V supply, and NPN emitter to 0V.

Proper operation is more likely if the shed supply 0V is connected to the 'lounge' supply 0V - whether by mains earth cable or otherwise...

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Cheers, 
Chris.

I recently had the same problem. I just replaced the unit with a wireless doorbell.

Yep. Works like a champ.

A volt is a terrible thing to waste.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

It's a revolting waste currently, especially when lost in the ome.

NT

yes..the vampire sez..zee stake vill kill me..