Ground wire and Equipment Grounding Conductor

[glennspark]

Yes and no. Most of the "stray voltage" and I put quotations around that for a reason, I am talking about is what many call voltage phenomena that they really don't understand. It could be from current carrying conductors in proximity to something, but for most NEC applications this doesn't happen because of the requirement in 300.3(B) which says:



Following that will ensure that magnetic fields around the conductors of a particular circuit will cancel one another limiting any induced current to other objects. So IMO that source of stray current is not much of a problem most of the time. What seems to be more easily overlooked is parallel paths for intentionally grounded current carrying circuit conductors to take, that is what makes up most of the "stray voltage" I am talking about and what seems to cause the most trouble and confusion. Any interconnection between those grounded current carrying conductors and other grounded objects beyond a single earthing point (generally at/near the source) are subject to introduce problems.

but current wants to go to earth....and the more parrallel paths you provide it with.....the better it gets...

dont forget that voltage remains the same in a parrallel circuit....the currents divide proportionally through each resistor...

 

[kwired]

i think that quotation may be to do with what we call `eddy current`...which can be induced in metallic enclosures where cables are using different entrys....for example one knockout is used for the phase...and another knockout is used for neutral...

i have come across this one quite a bit when carrying out condition reporting in the UK...its unqualified, incompetant inexperienced guys thats doing it...and it can cause enclosures to overheat due to recirculating currents...which can be nasty.

the solution:

1) make sure that all current carrying conductors of a circuit enter an enclosure through the same entry point

2) use a non ferrous bushing for each entry

3) cut slots between entrys to disrupt the eddy (this risks compromising the IP (ingress protection) of an enclosure though...

And NEC in general doesn't permit such an installation without using solutions as you mentioned, so this is not a problem with code compliant installations.

 

[glennspark]

Excuse my non-engineering background. They only thing that "dump(s) to earth" is lightning. Everything else is trying to get back to 'it's' source. Correct?

Not sure about sprites.
http://www.bing.com/videos/search?q...&mid=198F8E6C8190E35B7420198F8E6C8190E35B7420

in a healthy circuit currents are going back to its source....

in a short circuit fault....the currents will be going back to source...at a vastly increased magnetude...for the duration of the fault until the OPD clears it

for earth fault ...as the name suggests its general mass of earth that is providing the fault path....so current goes to earth...

 

[glennspark]

And NEC in general doesn't permit such an installation without using solutions as you mentioned, so this is not a problem with code compliant installations.

and this is where the NEC BS7671 meet...

both dont allow it...

 

[kwired]

but current wants to go to earth....and the more parrallel paths you provide it with.....the better it gets...

dont forget that voltage remains the same in a parrallel circuit....the currents divide proportionally through each resistor...

Current doesn't want to go to earth, it wants to return to it's source, earth just happens to be a convenient path to do so in many cases.

 

[jxofaltrds]

in a healthy circuit currents are going back to its source....

in a short circuit fault....the currents will be going back to source...at a vastly increased magnetude...for the duration of the fault until the OPD clears it

for earth fault ...as the name suggests its general mass of earth that is providing the fault path....so current goes to earth...

Tell me that I am reading this wrong.

 

[GoldDigger]

Current goes to earth and then comes back out again, I guess.

Tapatalk!

 

[glennspark]

sorry i think theres been some confusion here.

Current will flow to the lowest impedence reference it has...

what i meant to say was that general mass of earth can be used to form part of a fault path loop...hence TT

 

[glennspark]

Current goes to earth and then comes back out again, I guess.

Tapatalk!

hmm...if you says so...

 

[Archy Styrigg]

sorry i think theres been some confusion here.

Current will flow to the lowest impedence reference it has...

what i meant to say was that general mass of earth can be used to form part of a fault path loop...hence TT

Come on Limey,

Electricity will flow through any available path.
The magnitude of the current in each path is inversely proportional to the resistance of each path. :lol:

 

[suemarkp]

sorry i think theres been some confusion here.

Current will flow to the lowest impedance reference it has...

what i meant to say was that general mass of earth can be used to form part of a fault path loop...hence TT

I'd say current flows on all paths, and the amount of current flowing in each path is inversely proportional to the impedance of that path.

If you take a live wire and drop it onto the earth (or even push it a few inches into the earth), you're not going to have a very low impedance connection. But some current will still flow into the earth to get back to its power source (assuming a grounded power source). Because the earth has a rather high 'insertion loss", that makes the shock hazard worse in that there's a significant patch of earth around that live conductor that is higher voltage than the earth a few feet away. This creates the deadly step potential. Once you're 10 feet away from that wire in the earth (assuming the wire voltage is 600V or less), there is no step potential problem and the additional impedance for current to travel through the earth is quite low (the exit point to the power source could be feet or miles away with little change in impedance).

 

[glennspark]

lol...ayup archy....

 

[glennspark]

I'd say current flows on all paths, and the amount of current flowing in each path is inversely proportional to the impedance of that path.

If you take a live wire and drop it onto the earth (or even push it a few inches into the earth), you're not going to have a very low impedance connection. But some current will still flow into the earth to get back to its power source (assuming a grounded power source). Because the earth has a rather high 'insertion loss", that makes the shock hazard worse in that there's a significant patch of earth around that live conductor that is higher voltage than the earth a few feet away. This creates the deadly step potential. Once you're 10 feet away from that wire in the earth (assuming the wire voltage is 600V or less), there is no step potential problem and the additional impedance for current to travel through the earth is quite low (the exit point to the power source could be feet or miles away with little change in impedance).

yes and i`v already mentioned this.

regarding parrallel paths and how current divides proportionally...

 

[glennspark]

I'd say current flows on all paths, and the amount of current flowing in each path is inversely proportional to the impedance of that path.

If you take a live wire and drop it onto the earth (or even push it a few inches into the earth), you're not going to have a very low impedance connection. But some current will still flow into the earth to get back to its power source (assuming a grounded power source). Because the earth has a rather high 'insertion loss", that makes the shock hazard worse in that there's a significant patch of earth around that live conductor that is higher voltage than the earth a few feet away. This creates the deadly step potential. Once you're 10 feet away from that wire in the earth (assuming the wire voltage is 600V or less), there is no step potential problem and the additional impedance for current to travel through the earth is quite low (the exit point to the power source could be feet or miles away with little change in impedance).

spheres of influence....

voltage gradient...

 

[jxofaltrds]

The US uses TN-C-S.

Help me - why not TN-C-ST since we install an electrode at the installation end?

 

[glennspark]

Come on Limey,

Electricity will flow through any available path.
The magnitude of the current in each path is inversely proportional to the resistance of each path. :lol:

archy...i`v already mentioned about resistors in parrallel...and how currents divide proportionally

 

[glennspark]

I'd say current flows on all paths, and the amount of current flowing in each path is inversely proportional to the impedance of that path.

If you take a live wire and drop it onto the earth (or even push it a few inches into the earth), you're not going to have a very low impedance connection. But some current will still flow into the earth to get back to its power source (assuming a grounded power source). Because the earth has a rather high 'insertion loss", that makes the shock hazard worse in that there's a significant patch of earth around that live conductor that is higher voltage than the earth a few feet away. This creates the deadly step potential. Once you're 10 feet away from that wire in the earth (assuming the wire voltage is 600V or less), there is no step potential problem and the additional impedance for current to travel through the earth is quite low (the exit point to the power source could be feet or miles away with little change in impedance).

sometimes you see a load of dead sheep in field around pylons for no apparrant reason..this is due to the sphere of influence due to a fault around that pylon..this and the 4 points of contact (four feet/hoofs)