IS CONNECTION TO EARTH OTHER THAN THE SERVICE EQUIPMENT HELPFUL IN PROTECTING SHOCK AND ELECTROCUTION PROVIDED IT IS BONDED

[bobby ocampo]

The fault to the grounded enclosure simply converts an ungrounded delta system to a corner-grounded system. A person touching the enclosure wouldn’t even realize a fault had occurred.

Code requires fault indicator

 

[bobby ocampo]

If you tried to convey your information using only equipotential bonding, and how you did that to make it safe for you to touch, certainly would read better to my eye.

Never did I say ONLY. Equipotential bonding or grounding will be safe because in solidly grounded there is arc flash and arc blast specially on 480 volts that OCPD operation is a must. However we can clearly see that connection to ground reduces the voltage to potential to earth which is considered zero potential. Proof is EGC in ungrounded system. Earth is not encourage to be the ONLY or SOLE return path to ground but paralleling with a lower resistance EGC will help. !. less current will flow to the EGC to prevent extensive damage because part of the current will flow to the ground. Kirchoffs current law.. While majority of the current will flow to the conductor with less resistance the total current will still be the same.

Discussing Earthing as safety related, made it all hard to read. I don't have any idea what the original objective was, what else was conveyed.

Clearly connection of a metal panel to ground for as long as it is bonded will help reduce impedance and return path to operate the OCPD to prevent arc flash and arc blast. Touch potential will be low or approaching zero if connected to the earth.

 

[bobby ocampo]

I am fine with people thinking it is grounded meaning it is safe.

Code requires it to be effectively grounded. If ground resistance is high it is not effectively grounded. If connection to earth is not effective it is not safe

To me that means it has an ECG to carry fault current, sufficient to trip the upstream device.

Agree. Part of the solution to make sure that the EGC will not be stressed is to connect parallel paths. The resistance of two parallel resistance is always lower than the lowest resistance.

I don't expect anyone wants to know the detail of how. The convention is for grounding to mean per code, EGC and an OCPD, solidly grounded and not some unicorn floating system.

Code allows UNGROUNDED and HRG systems maybe not in residential but in special commercial and industrial installations.

The convention for grounded to mean safe, works imo, people also assuming pro work to code.

Code requires effectively grounded

 

[bobby ocampo]

You ask about a bonded transformer, then provide a diagram, that shows a floating transformer output coil? Bonding a case to a ground rod, does not mean that the transformer coil is bonded, and realistically does nothing.

The connection to earth will in the metal panel will reduce the touch potential to approaching zero.

I would suggest that you obtain a copy of Soares Book On Grounding.

I have a copy of SOARES and CENGAGE, IEEE 142, IEEE 80

It has lots of illustrations and detailed explanations of all system types and how and why they are treated the way they are.

SOARES illustration concentrated more on solidly grounded. Comprehensive discussion on ungrounded is in IEEE 142 Chapter 1. Or Industrial Power system Handbook by BEEMAN Chapter on System Grounding

Principles of electricity is the same in low voltage as well in high voltage.

 

[bobby ocampo]

Additional grounding electrodes gets into a multi grounded situation which can cause serious issues. I think Mike Holt has done a great job of shedding light on “stray voltage” (technically stray current) which is either caused by or made worse by multiple grounds. With multiple rods present there are multiple paths and fault current can take multiple, sometimes undesirable paths. More grounds is not better.

Multiple connection of metal parts to ground does not create the stray potential or stray current. The connection of the neutral to ground other than the service equipment creates this problem. Connection to ground with bonding helps reduce the stray voltages because it will discharge excess voltages to zero potential. The problem is the neutral not the connection to earth.

This runs contrary to what utilities do which is the opposite theory…you can never have too many grounds,

Utilities recommend bonding with EGC all ground rods to be equipotential. The equivalent impedance of the EGC with the GROUND in parallel will reduce the equivalent impedance to allow OCPD TO OPERATE. Kirchoff's current law.

 

[bobby ocampo]

For me I think the issue is advocating or advising Earthing does anything safety related. If it's a safety concern, saying it's Earthed only conveys no information to me. And then if trying to say 'Earth it for safety' I would view it as a dangerous misunderstanding (typically coming for someone without an electrical background).

What is it that you don't understand?

That's how the statement would come to me, from someone who I do not expect to have a deep electrical background. So the issue of basically misinstructing the non technical audience jumps out at me. The next guy is just going to report what he heard or saw at the last instance 'I earthed it for safety'.

Again requirement is effectively grounded. Grounding or grounded to earth doesn not necessarily mean effectively grounded.

My concern would be, if you're going to touch it with your own hands, you'll figure it out I have no doubt there.

Only unexperience will touch with their hands. That is a stupid advice. Use a voltmeter.

My guess is you're writing in a manner of advising some else to touch it with their hands. The system is safe (for you) to touch because it is Earthed.

You use voltmeter to verify. Touch potential is reduced if connected to earth or paralleling of low resistance conductor will reduce touch potential

That statement is false and the opposite is true. Earthing is neither necessary or sufficient to make the electrical system safe.

Sorry for not understanding. Have a seminar on system grounding based on IEEE 142 Chapter 1

Earthing will have a duty to perform dumping lightning strikes and utility faults, overvoltages, during which time there will be a substantial step and touch potential surrounding the earthing system, as it functions now necessary.

Same application with reducting the touch potential when an ungrounded current carrying conductor touches a metal enclosure. SAME principles applies in reducting the touch potential. You can verify it with a voltmeter if you want to do the experiment. Use voltmeter before touching it with your hands

Which is why the bonding mats have to be connected to the switchgear as well as everything else, to limit the touch potential where the man must also function and now touch (feet on the concrete, throw the switch).

Basicaly to reduce the touch potential low resistance will reduce the voltage drop incase of a fault between the hand and the feet

Just saying you Earthed something bypasses everything else necessary to make it safe. That's what message the idiot public should get. There's a lot more to it. Hire pros if you want the thing touched.uch

Earthing requires bonding too to be effective because it help reduces the return path resistance to the source and reduces the touch and step potential as majority of the current will flow to the lower resistance EGC. The total current that will return to the source is the same using Kirchoffs current law.

 

[bobby ocampo]

Mike Holt has some old videos available online of different techniques of testing GES resistance.

And he does in fact show the lower the earth resistance of a GES at a service in the case of an open neutral it will reduce touch potential to conductive objects.

Lower resistance for the ground is safer. Code is only minimum requirement for safety, you can have it safer Compliance with the code does not necessarily mean efficient, convenient and adequate for good service.

But this is not the main point of the service neutral being grounded. Thats the reason the code only requires a 25ohm with one rod or 2rods and a 1000ohms. They don’t care. The fact that it’s grounded at the service has no significance in safety of personnel.

Code requires not more than 25 ohms. Lower than 25 ohms is better. In commercial and industrial installations ground resistance is required to be less than 5 ohms and to some specially electronics requires to be less than 1 ohm.

Dirt and ground rods play no role of safety against personnel in the scope of NEC.

If it does not play a role Code will not require a maximum value fot the ground resistance

 

[bobby ocampo]

If you have an ungrounded system, and an enclosure containing said system that is not connected to Earth, it is still very unlikely you would receive a shock by touching that enclosure.

Sorry to disagree. You will be electrocuted. Voltage to ground will be higher than 50 volts. Check with a voltmeter

There is a possibility, very slight at low voltages, that you would have some capacitive charging of the enclosure and could be shocked when touching it.

Sorry to disagree. Verify with a voltmeter. For 240 volts line to line, Touch potential is 139 volts more or less. For 480 volts line to line delta, voltage to ground is 277 volts. You will be electrocuted or receive a dangerous shock

Bonding everything together and connecting to Earth generally provides equipotential and eliminates these rogue capacitive charging currents between different components and or the Earth.

Equipotential is correct. Equipotential to the earth is approaching zero voltage

These concerns would be much more pronounced at medium and high voltages, very unlikely at under 600 volts.

You can try with a voltmeter. Greater than 50 volts touch potential is dangerous per IEEE 80

 

[Dsg319]

Lower resistance for the ground is safer. Code is only minimum requirement for safety, you can have it safer Compliance with the code does not necessarily mean efficient, convenient and adequate for good service.

Code requires not more than 25 ohms. Lower than 25 ohms is better. In commercial and industrial installations ground resistance is required to be less than 5 ohms and to some specially electronics requires to be less than 1 ohm.

If it does not play a role Code will not require a maximum value fot the ground resistance

Lightning and transients is why the code has us stick copper to dirt . The earth/dirt is not and will not ever be used as an effective ground fault current path. The NEC states this…..The math won’t allow it to.

 

[Dsg319]

Principles of electricity is the same in low voltage as well in high voltage.

No. A 100Kv wye system to earth fault might open a OCPD.

600volts and less you might as well forget it. Play around with ohms law and you will see.

 

[petersonra]

Code requires not more than 25 ohms. Lower than 25 ohms is better. In commercial and industrial installations ground resistance is required to be less than 5 ohms and to some specially electronics requires to be less than 1 ohm.

If it does not play a role Code will not require a maximum value fot the ground resistance

Read carefully what the code actually says about this. There is no minimum value for ground resistance.

After you have read carefully what it actually says, if you still think that it mandates a minimum ground resistance, read it again. Repeat as necessary till you figure it out.

 

[electrofelon]

Lower resistance for the ground is safer.

No not really. Granted this is a very common belief and misunderstanding the electrical world but the ground resistance really doesn't matter much. Please note when discussing this topic you have to differentiate between system earthing and equipment earthing. You can't really have an intelligent conversation just lumping them all together as "grounding".

For system earthing, you just don't need a low impedance Earth connection to accomplish what you are trying to accomplish. All you need is to just reference that conductor to ground and keep it from floating, and besides if this is an MGN distribution system it's already going to have a zillion earth connections.

For equipment earthing, dirt just has way too high of a resistance to accomplish much. Yes it can provide some equipotential from static and capacitive charges, but really provides no protection during any sort of fault event unless you are standing right on the electrode.

Is my understanding that lightning doesn't really "care" about the DC resistance to Earth

 

[paulengr]

Lightning and transients is why the code has us stick copper to dirt . The earth/dirt is not and will not ever be used as an effective ground fault current path. The NEC states this…..The math won’t allow it to.

The NEC has nothing to do with Earth as a path. It’s simple physics. The resistance between two ground rods is equal to rho / distance. So as distance grows the resistance goes to zero regardless of soil resistance.

This is one of those crazy things that doesn’t make a lot of sense. First, a myth: electricity takes the shortest path. If that is the case, Earth behaves like a wire. If we know specific resistance rho (ohm-feet) of the soil we can calculate rho x d / (area of dirt that is a conductor). Now that last part is tricky…how much area is involved? This is where we need to go back to the myth. The truth is electricity follows ALL paths proportional to their conductance. Conductance is just the inverse of resistance. In dirt it’s a 2-D system so the number of paths is proportional to the square of the distance. So going back to the formula we get d/d^2 or just 1/d so the resistance between two ground rods is rho/d. As the distance increases no matter how poor the soil is eventually the resistance goes to zero.

This sounds very “put there” but in average clay soils R is well under an ohm within about a mile. I’ve seen the same number show up in mines all over North America. In sandy-Rocky Western soils it might take a couple miles but even they eventually hit zero.

Utility distribution systems make effective use of this by using multi ground systems. Pole grounds mikes from the substation provide a good path back to the substation neutral.

 

[retirede]

Code requires fault indicator

I never stated otherwise. Your diagram didn’t show fault indicators.

 

[augie47]

Thank you "Mr Petersonra"
Similar to a plague of locusts, theses discussions are brought to light by the OP since 2008.
Those interested can perform a search.
As for now, since "Elvis has left the building", we will put it to bed.