Grounding Rod For Portable Generators Necessary?

[grsthegreat]

Grounding rods are not there to establish the lowest voltage potential between any metallic objects attached to the house ground system and earth ground? Since when is that not the main reason for them? Have you ever measured the voltage difference between earth ground and the building ground system? There is test equipment (that I have) that is specifically designed to measure this and determine whether the ground system is functioning correctly. There would be no purpose of the grounding system in the case of a wet basement floor or carport, in the case where a metal item becomes electrified through a fault in the insulation, if the ground wasn't at the same voltage potential as earth ground.

that is the definition of a ground rod, however the NEC does not want portable generators to have ground rods....gets back to the old multiple sources to ground issues.

Heck, even a large permanent generator only has the case grounded to a ground rod. the unit itself establishes its ground from the wires run to the buildings panel.

 

[tcartwri]

The one instance of needing to ground a gen set that I have experienced, is powering anything with an AC to DC power supply, like a desktop computer. Without the ground the chassis on the computer is floating and can develop a lethal voltage relative to earth. I have experienced a shock from this first hand. It's not fun.

The other application that immediately comes to mind is an inverter welder which is something our members will likely come across at some point. I would assume it has the same risk, although I don't know for sure.

 

[Hivoltage98]

I grabbed this from http://www.spgs-ground.com/information/purpose-of-grounding


What is the Purpose of a Ground Rod?
A ground rod or a ground field’s only purpose in life is to have a designed electrical path to dissipate a static discharge voltage (such as Lightning) to earth.

If you place a current probe around the conductor going to earth or the ground rod itself you should never see any current flowing on the conductor. If current is seen flowing on the conductor going to earth a ground fault exists. Another term that could be used is leakage current. In either case there is a parallel path back to the voltage source through the earth that crates the loop for current to flow on the earth ground conductor.

Always remember current will always return to its voltage source.

AC will seek a path to the AC source, DC will seek a path to the DC source and a Static Discharge (Lightning) will seek a path back to its source usually earth. If a return path is not designed for that return path or multiple return paths exist current will seek its own paths back to its voltage source.

When current seeks and find its own paths back to its voltage source usually it will pass through equipment. It the voltage passing through that equipment is higher then its operating threshold that equipment will fail and an outage of some type will take place.

Purpose Of Grounding
Personnel Safety

Effective bonding and grounding of all conductive components, including metallic frames and raceways, should reduce voltage potential differences among the components during normal operation, fault conditions or lightning strikes.

Proper grounding of power sources should prevent system source voltages from permanently appearing on metallic frames that personnel physically come in contact with. Effective grounding will maintain a minimum voltage difference between metallic objects that personnel may touch simultaneously. The protection system must be designed to allow protection devices to operate quickly and safely when voltage faults occur.

All metallic parts of any isolated ground plane shall have the ground plane designed so that shock voltages are not transmitted to personnel.

Equipment and Distribution Circuit Protection

To prevent electrical fires and limit damage to equipment and associated circuit conductors, the Building Safety Protection System shall provide a low resistance/impedance path for lightning currents to flow to earth when lightning strikes. The Building Safety Protection System shall provide a sufficiently low resistance/impedance path for fault currents so that circuit breakers and fuses can quickly and safely remove voltage to the faulted circuit.

Electrostatic Discharge (ESD)

Electrostatic Discharges (ESD) should be reduced by maintaining low resistance/impedance paths between grounded points throughout any ground plane. Metallic parts of any isolated ground plane are bonded and grounded so they cannot store electrostatic charges. This should reduce electrostatic discharge problems by maintaining all equipment at the same voltage potential during a lightning impulse.

Equipment Operation

The equipment should always operate properly and safely when connected to the Building Safety Protection System.

 

[grsthegreat]

well, anyone that wants to drive a ground rod everytime they decide to run their generator out in the back 40 to repair a fence......have fun.

also for your enjoyment
http://ecmweb.com/site-files/ecmweb.com/files/archive/ecmweb.com/images/archive/0900groundrods.pdf


in some places ground rods disappear after some time..eaten up.

also at a recent meeting with our local utility co, it was mentioned that some ground rods...depending on soil, can take many years to reach their proper potential (ohm rating). so in theory, placing a ground rod in for a temporary power panel is a useless waste of time and material....but we still have to do it.

 

[tcartwri]

My example was working in dessert conditions BTW.

 

[ishiboo]

Grounding rods are not there to establish the lowest voltage potential between any metallic objects attached to the house ground system and earth ground? Since when is that not the main reason for them? Have you ever measured the voltage difference between earth ground and the building ground system? There is test equipment (that I have) that is specifically designed to measure this and determine whether the ground system is functioning correctly.

As I said, its main purpose is lightning/static dissipation... check out HiV's post above.

The NEC requires a maximum resistance to ensure that the ground rod can participate in that fashion effectively, or two rounds must be driven if you cannot test.

There would be no purpose of the grounding system in the case of a wet basement floor or carport, in the case where a metal item becomes electrified through a fault in the insulation, if the ground wasn't at the same voltage potential as earth ground.

The grounding rods serve no purpose there. They will not flow enough current to trip a regular breaker as they have a very high resistance compared to a "good conductor".

Where a metal item becomes insulated, the EGC connected to the metal case should allow the fault current to flow back to the main panel, meter can, or wherever neutral/ground are bonded. When this happens, the short travels over the EGC, the breaker trips and everything is fine. The ground from the ground bar to the ground rod, and ground rod itself, are not used for clearing the fault and unnecessary for that particular purpose.

GFCIs are used to better protect people from wet circumstances or ground faults. Despite the name "ground fault", a GFCI does not use the grounding rods and need not have a grounding wire to function... in fact, they are the accepted way for replacing a 2-wire ungrounded outlet when no ground wire is present and its not feasible to get one there.

 

[ThomasH]

They don't want portable generators to have ground rods because that would establish multiple ground systems which are probably at different ground potentials. You are always supposed to have power sources grounded to the same ground system as the house system in order to minimize any differences in potential. By minimize, I mean keep them all within a few volts of each other.

 

[ThomasH]

Ground rods serve no purpose in grounding the case of a metal object that might become electrified? Wow. There is a reason that the ground lead is tied to the neutral at some point in the system, either at the main panel or at the meter. That provides the trip point for the breaker, and the tie to the ground rod attempts to keep the case at earth ground potential. At least close enough not to electrocute someone.

 

[ishiboo]

Ground rods serve no purpose in grounding the case of a metal object that might become electrified? Wow. There is a reason that the ground lead is tied to the neutral at some point in the system, either at the main panel or at the meter. That provides the trip point for the breaker, and the tie to the ground rod attempts to keep the case at earth ground potential. At least close enough not to electrocute someone.

Nope. The neutral and ground wires are tied together to clear faults, as I said. That happens without the ground rods.

Your idea is a common misunderstanding, but a misunderstanding none the less. The ground rods are for lightning/static dissipation.

 

[ThomasH]

Well you have your opinion and I have mine. Since I used to design electronic gear that had to be grounded in order to protect the operator (put the case and the physical ground at the same voltage potential) I trust my opinion. Let's hear some evidence to refute that grounds are mainly, or at least also, used to remove a hazardous voltage potential from touching metal and an earth ground. Sorry, but without real evidence, yours statement doesn't hold water.