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.

 

[ishiboo]

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.

This is not an opinion, it's simple fact... but unfortunately you've gotten confused with the distinction (or personal lack thereof) between grounding rods with the equipment grounding conductor (EGC) in this discussion. I never stated that grounds were not used to clear a fault and prevent someone from being injured, in fact I detailed it earlier. The discussion was whether or not grounding rods were required, NOT whether or not the EGC provides an added safety margin - I already explained it does! You seem to have slowly strayed from grounding rods to the EGC. The two are connected and interact at times but are distinct components with different purposes.

What you're referring to is clearing a fault as I explained before, for example if a washing machine developed a short internally it could electrify the metal frame and then the outside metal case of the machine, so that anyone who touched it became part of the circuit. With a separate EGC connected to the electrically isolated case/frame, that EGC would complete the circuit creating a full short between hot and ground, and that current would immediately trip the breaker. In an ideal situation this would happen before anyone was already touching the device and prevent a shock. The grounding rod(s)/UFER/etc. serve essentially no purpose for that situation, which is why they're not required or recommended for safe operation of a portable generator. The EGC is tied to neutral and bonded to the frame.

If you removed this bond and relied on a ground rod to clear a fault, you'd be dead, as the ground has too high of a resistance (and is not part of the circuit, right?) to flow enough current to trip the breaker.

 

[ThomasH]

The conversation was originally how you stated, and then drifted into the purpose of the ground. Of course a small current flowing through someone is not going to trip a 20 amp breaker. I never stated that equipment grounds and grounding rods are the same thing, that is silly. I stated several purposes for the grounding rods, which I have seen no evidence presented by you that what I stated is not true. By the way, all chassis becoming hot are not due to failed insulation, some of the equipment that I designed had voltage potential from magnetically induced voltage. Once again, the purpose of the ground connection was to protect the operator from voltage on the chassis that might shock them, but would NOT trip the breaker due because it was high enough to trip a breaker, but would electrocute a person.

I stand by my answer, regardless of your opinion. Actually, you have argued about a difference with no distinction. I have never argued that home electrical systems don't need a bonded neutral somewhere in the system to protect against dead shorts.

 

[grsthegreat]

yeiks... what has anything from the above have to do with ground rods on PORTABLE generators. PORTABLE generators rely on GFCI protected outlets...and GFCI protected outlets DO NOT REQUIRE A GROUND TO OPERATE

 

[ishiboo]

The conversation was originally how you stated, and then drifted into the purpose of the ground. Of course a small current flowing through someone is not going to trip a 20 amp breaker. I never stated that equipment grounds and grounding rods are the same thing, that is silly. I stated several purposes for the grounding rods, which I have seen no evidence presented by you that what I stated is not true. By the way, all chassis becoming hot are not due to failed insulation, some of the equipment that I designed had voltage potential from magnetically induced voltage. Once again, the purpose of the ground connection was to protect the operator from voltage on the chassis that might shock them, but would NOT trip the breaker due because it was high enough to trip a breaker, but would electrocute a person.

I stand by my answer, regardless of your opinion. Actually, you have argued about a difference with no distinction. I have never argued that home electrical systems don't need a bonded neutral somewhere in the system to protect against dead shorts.

I never said you did, you've simply changed the discussion from one to the other. You'd like me to refute your imagined ground rod purpose that's fine, but once I do so will you waste your time presenting evidence to disprove my opinion the earth is flat?

Let's Google "purpose of grounding rods" which should start us out. The first result is pretty clear. It's a company which specializes in grounding/shielding. HiV posted the same text earlier.

Here's your statement:

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?

Their statement:

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.

Wow! That was pretty straightforward, no?

It goes on to explain a pretty important piece of the puzzle:

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.

Why is this important? The earth is NOT a part of the source/circuit/etc. of the generator unless you make it, so it's a poor return to the source (the alternator).

For the most part, the rest of this thread is in agreement with NEC, OSHA, etc. that grounding rods are not necessary for portable generators... and I'll stand my ground... pun intended.

 

[ThomasH]

Yes, we both agree. You are arguing about something else. Another distinction without a difference. Of course, portable generators do not require a ground due to GFCI receptacles installed on them.

If you are talking about that specifically, then perhaps you shouldn't make blanket statements about washing machines and other things in general, and then say that you are talking about generators.

Enough of this sillyness.

 

[ishiboo]

:beer:

Yes, we both agree. You are arguing about something else. Another distinction without a difference. Of course, portable generators do not require a ground due to GFCI receptacles installed on them.

Not at all. Portable generators do not require a ground because they have little need for protection from lightning/static/etc., having a relatively small amount of conductors attached to them and the unlikeliness of lightning. A ground rod would not provide added safety due to not having a GFCI, and the GFCI is not what makes a ground rod unnecessary.

Your house has a comparatively huge area with lots of appliances/electronics/etc., antennas, and is connected to the power grid with hundreds of miles of lightning-attracting steel towers, cables and everything else... it's best to make sure the lightning has a good place to go, or it chooses its own route.

If you are talking about that specifically, then perhaps you shouldn't make blanket statements about washing machines and other things in general, and then say that you are talking about generators.

Enough of this sillyness.

You're in over your head I said the primary purpose of ground rods was lightning protection, you argued that it was something completely different which it's not. Then you started arguing "grounding" being necessary instead of "ground rods" and presented an example where the EGC in your mind needed a ground rod, so I gave an example of where/how/why the EGC works... now you're mad, packing up your toys and going home?

Have a :beer: and relax. Great discussion but IMHO it's important not to leave inaccurate safety information on the table for others to pick up. If it were clear cut for everyone we wouldn't have 8 pages on it, but there is in the end both fact and fiction.

 

[ThomasH]

Uh huh. Another distinction without a difference. I never said that that it was a sole purpose, re-read my post.

Enough already, go bother somebody else. This is why I don't post too often here, as there are a few people that want to argue endlessly about made up straw man situations and then throw in childish insults. I know what my engineering background has taught me over 40 years. You don't have to agree, that's fine.

 

[ishiboo]

Definitely will drop it, but I did not mean to throw any childish insults so I'm sorry if you took it that way. :thumbsup:

 

[Wolfman]

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.

This discussion seems to have slowed down, but I hope someone else can comment on the above quote. I am currently looking into welders for running with a generator. The comment above has me curious about whether inverter welders need grounding rods connected to generators more than non inverter based welders...

 

[ishiboo]

This discussion seems to have slowed down, but I hope someone else can comment on the above quote. I am currently looking into welders for running with a generator. The comment above has me curious about whether inverter welders need grounding rods connected to generators more than non inverter based welders...

Not an issue, which is why neither the NEC nor OSHA requires nor even recommends it. Tons of people run inverter welders and plasma cutters off portable generators without issue, as well as RVs with computers, etc. Inverters and switching power supplies are completely different animals and neither cause the ground to float.

Be careful sizing your generator appropriately for the welder at hand... some manufacturers provide wattage recommendations for them which is a big help. Remember the rated output current is different than the maximum current.

If you're really concerned, as a simple test drive a ground rod and connect it to a DVM, with the other side connected to the generator chassis/frame which is grounded.