Generator grounding

[sapper]

Okay I work on generators every day and I always ground them before I will run them but I often come across people that don't ground them or that think if it is touching the ground it is grounded. This is not true.

I will be looking for a generator very soon (Honda EU3000) for my needs and I am trying to decide how to carry a grounding rod or plate in the vehicle when needed and how to retrive it quikly also.

How are people here doing it or are you one of the many I see not grounding it at all.

 

[Albin]

Don't ground.

I don't have the NEC to quote from, so I won't (should be in section 250). Basically, it's safer to not run a separate ground on portable gensets. I know, I used to do it too.

If I can find the specific reference tomorrow at work, I'll post it up.

Good luck.

 

[dwh]

Agreed. No need to ground a portable. The NEC doesn't really care unless it's feeding a building, in which case it's considered a "separately derived system" and the NEC has rules for that.

OHSA cares, but they don't require grounding if the metal parts of the gen are grounded to the frame - the frame is considered to be the ground and need not be connected to the planet (again, unless connected to a building). Here's OSHA's doc on the subject:

http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf


Now, neutral to ground BONDING is a different subject. Generally on a generator, the neutral should be bonded to ground. HOWEVER, this may not be so (probably isn't) on an -inverter- type generator. Most inverters (I'm referring to inverters here, not just inverter generators) don't have a neutral to ground bond, because they use a floating neutral. I haven't checked any Hondas, but my Honeywell inverter generator does not have neutral bonded to ground.

 

[sapper]

After reading the manual the generator is using a floating neutral.

http://www.hondapowerequipment.com/pdf/manuals/31ZT7610.pdf

"GROUND SYSTEM
Connections for standby power to a building electrical system must be
made by a qualified electrician. The connection must isolate the
generator power from utility power, and must comply with all
applicable laws and electrical codes. A transfer switch, which isolates
generator power from utility power, is available through authorized
Honda generator dealers.
Honda portable generators have a system ground that connects
generator frame components to the ground terminals in the AC output
receptacles. The system ground is not connected to the AC neutral
wire. If the generator is tested by a receptacle tester, it will not show
the same ground circuit condition as for a home receptacle."


With that though the ground itself is bonded to the frame which in the event of a short would become energized and why I want to ground it. Once you get hit by ground current once you will understand my desire to ground it. The ground is for the protection of life and without a path it will act like a capacitor until something "me or my family" provides a path for the current to flow.

"GROUND TERMINAL

The generator ground terminal is connected to the frame of the
generator, the metal non-current-carrying parts of the generator, and
the ground terminals of each receptacle."

 

[dwh]

Once you get hit by ground current once you will understand my desire to ground it.

Yea well...12 years as a full-time working journeyman - I think I recall being bit once or twice. Leaves a coppery taste in the mouth.


(Don't mind the caps - they're just my way of emphasizing. I'm not yelling. )

The ground is for the protection of life and without a path it will act like a capacitor until something "me or my family" provides a path for the current to flow.

Sounds good. But the question is; "Path for the current to flow TO WHERE?"

The current originates in the alternator or inverter. To complete a circuit, the current has to return to the source. You do not complete a circuit by shunting to the planet. Current from a generator doesn't magically flow toward the planet - there has to be a CIRCUIT. For this reason, a planet ground is irrelevant on a portable generator because current does not flow through it back to the source.

Unless...

The danger is CREATED once you've connected the gen frame to the planet. If you take a metal frame gen and set it on a concrete slab (assume no rubber feet), you have now created a potential path. From the gen, through you, through the concrete and back to the frame. The current can flow IN through the planet ground back to the source.

If the metal frame is not connected to the earth, such as on a vehicle or set on a slab of wood (or rubber feet) - then that potential path does not exist and neither does the danger.

The danger is; "Becoming a path from the generator's hot, to the generator's neutral or ground" - but a planet ground does nothing to protect against that because it is outside of the circuit path - and as shown in the example above, can even CAUSE the danger by creating a circuit path that wasn't there before.


So, what CAN happen with an ungrounded portable generator? Well, as an example - you plug in an extension cord, you plug an old Milwaukee drill (all metal) into that. There is a short and the drill handle becomes hot. You then touch the generator frame. You get bit.

Grounding the generator to the planet won't stop that. It won't protect you. It could even cause it to happen if you touch the planet since the planet is touching the frame. But a GFCI would protect you.

If you want to protect your family, use a GFCI instead.


(Of course, connecting a portable gen to a building - which is already planet grounded - automatically creates that "extra path" danger, so the gen frame is also required to be planet grounded.)

 

[sapper]

These are the definitions I use for the following terms; (all from the CEC, Canadian Electrical Code)

Ground fault circuit interrupter — a device whose function is to interrupt, within a predetermined time, the electrical circuit to the load when a current to ground exceeds a predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit

Ground fault circuit interrupter
Class A, when applied to a ground fault circuit interrupter (GFCI), is an interrupter that will interrupt the circuit to the load when the ground fault current is 6 mA or more but not when the ground fault current is 4 mA or less (when the ambient air temperature is less than –5 °C or more than 40 °C, the minimum tripping current may be 3.5 mA instead of 4) in a time
(a) not greater than that given by the equation where T is in seconds; and
I is the ground fault current in rms milliamperes for fault currents between 4 mA and 260 mA; and
(b) not greater than 25 ms for ground fault currents over 260 mA.

In addition, a Class A GFCI is to be capable of interrupting the circuit to the load, in keeping with the above requirements if the identified circuit conductor (neutral) becomes inadvertently grounded between the interrupter and the load.

The prime function of a Class A GFCI is to provide protection against hazardous electric shocks from leakage current flowing to ground from defective circuits or equipment. It does not provide protection against shock if a person makes contact with two of the circuit conductors on the load side of the GFCI.


Grounded — connected effectively with the general mass of the earth through a grounding path of sufficiently low impedance and having an ampacity sufficient at all times, under the most severe conditions liable to arise in practice, to prevent any current in the grounding conductor from causing a harmful voltage to exist
(a) between the grounding conductors and neighbouring exposed conducting surfaces that are in good
contact with the earth; or
(b) between the grounding conductors and neighbouring surfaces of the earth itself.

Grounding — a permanent and continuous conductive path to the earth with sufficient ampacity to carry any fault current liable to be imposed on it, and of a sufficiently low impedance to limit the voltage rise above ground and to facilitate the operation of the protective devices in the circuit.

Grounding conductor — the conductor used to connect the service equipment or system to the grounding electrode.

Grounding electrode — a buried metal water-piping system or metal object or device


10-002 Object
Grounding and bonding as required by this Code shall be done in such a manner as to serve the following purposes:
(a) to protect life from the danger of electric shock, and property from damage by bonding to ground noncurrent- carrying metal systems;
(b) to limit the voltage on a circuit when it is exposed to higher voltages than that for which it is designed;
(c) in general to limit ac circuit voltages-to-ground to 150 V or less on circuits supplying interior wiring
systems;
(d) to facilitate the operation of electrical apparatus and systems; and
(e) to limit the voltage on a circuit that might otherwise occur through exposure to lightning

 

[sapper]

A GFCI will not function if there is not a correct path to ground (or electrode). In order for a GFCI to work at all the current has to travel on the ground.

The bonding made at the frame with all non-current carrying parts is because it is required by code (CEC), and is the same for all wiring devices such as recepticals, conduit, juction boxes or any other metalic component which may potentially be energized even if VERY rare, or highly unlikely. This bonding conductor at some point should be connected directly to the ground buss or grounding conductor to reduce the chance of injury.

I agree that there should only be ONE (connection to ground electrode) made by the ground conductor as if there is more than one you could have a ground loop and the current/voltage may not dissipate correctly.

 

[dwh]

Excellent! I like it when people who deal with electricity do their homework.

However, your quotes of the CEC are a bit off the mark. In reverse order...

The quoted section on grounding mentions nothing about "separately derived systems". A portable generator (or an off-grid solar or wind or micro-hydro) is a separately derived system. In the case of a separately derived system -connected to a building- it does of course apply. Standalone/portable systems are different (unless connected to a building).


GFCI.

A GFCI will not function if there is not a correct path to ground (or electrode). In order for a GFCI to work at all the current has to travel on the ground.

Sorry, that's a common assumption, but it's totally incorrect.

If that were true, then a GFCI breaker would not function, since it has no ground connection. It has only hot and neutral:

I think perhaps you don't quite understand how a GFCI works. I assume you are familiar with a "clamp-on current meter" - such as a Fluke or Amprobe?

That's what a GFCI does. The current flow of hot and neutral are each measured and compared. In normal circumstances, the flow of current of the hot and neutral will be nearly equal. If the flow of current through the hot and the neutral become different - then a problem is indicated.

An imbalance between hot and neutral indicates that the current is flowing back to the source through some path "other than neutral". It could be flowing from your wife's hair dryer, through your wife, to the bathroom faucet, then through a pipe to the planet. It could be through your drill (my previous example) through you, back to the generator frame (IF neutral and ground are bonded in the generator, if they aren't, then the frame is not a return path). Either way, the GFCI does not measure - or use - ground to decide if a fault exists. All it knows is that the current is flowing from the hot, but is not returning through the neutral as it should.

Since the GFCI operates by detecting an imbalance in the current flow BETWEEN HOT AND NEUTRAL - grounding (to gen frame or planet) is irrelevant to its operation. It will operate equally well in an ungrounded RV as it does in an on-grid house.


HOWEVER; some GFCI -receptacles- use a "leak to ground" to TEST. Thus, without a ground, the GFCI WILL OPERATE CORRECTLY - but the TEST button won't do anything.

GFCI -breakers- however do not have any ground connection, so they test by leaking a bit of hot to NEUTRAL to create the imbalance for the test.


In a generator (or inverter) where the neutral is not bonded to ground, "ground" (the frame) is not a path to return to the source. Again, the GFCI will still operate correctly - detecting imbalance between hot and neutral - but again, if the GFCI device tests with a leak to ground, the test button does nothing.

EDIT: Now imagine that you ground the frame to the planet. The test button on the GFCI still does nothing, because the planet is NOT a path for current to return to the source (the alternator or inverter in the gen). You can ground the frame to the planet, but no current will flow through that path. Is it "grounded"? Mechanically it is. Electrically it is not.

 

[dwh]

The bonding made at the frame with all non-current carrying parts is because it is required by code (CEC), and is the same for all wiring devices such as recepticals, conduit, juction boxes or any other metalic component which may potentially be energized even if VERY rare, or highly unlikely. This bonding conductor at some point should be connected directly to the ground buss or grounding conductor to reduce the chance of injury.

All true. On a -building- which is grounded to the planet.

However, a separately derived system, for example a generator mounted on a truck (or trailer or pallet) is an entirely different beast and must be treated differently (again...as long as you don't connect it to a building or some other planetary grounded system).

 

[sapper]

I think I found the reference. I must admit that I mostly work on large Generators from 40kw to 1.5 MW and also large grids with combinations of gensets. My knowledge of GFCI's is weak as I do very little residental wiring and mostly industrial. I know enough to get by if I need too but I am sure there is room for improvement. I am glad to have a good discussion on the topic of grounding because it seems to be one of the most misunderstood topics when considering electrical. I really don't care if I am not meeting code 300 kms from any real road but I am concerned with the safety of my family.

10-206 Grounding connections for isolated systems (see Appendix B)
(1) For a wiring system or circuit required to be grounded and not conductively connected to a distribution system, the grounding connection shall be made at the source of supply, or on the supply side of the first switch controlling the system, and
(a) the grounding conductor shall not be smaller than that specified in Table 17 but in no case does it need to be larger than the largest ungrounded conductor of the system; and
(b) where two or more systems are employed, a common system grounding conductor shall be installed unless separate grounding electrodes are provided for each system, in which case the grounding electrodes shall be interconnected in accordance with Rule 10-702.
(2) Notwithstanding Rules 10-802 and 10-806, where a circuit is required to be grounded, and is supplied from a source having a rated output of 1000 V•A or less, the grounding connection shall be permitted to be made to the grounded metal enclosure of the power supply, or to the bonding conductor within the enclosure.


I still believe that if it is less than 1000 VA you should be fine without a ground, but anything larger than that should have a ground.

 

[GeoScum]

I'm going to agree with dwh and Albin here. Small generators should not be grounded to earth. The NEC (2008) reference for this is 250.34, and dwh has supplied the proper OSHA reference. The fact that Sapper does not understand the operation of a GFCI is telling. Also, the reference to the CEC is without context and as such it is difficult to judge its relevance.

Grounding is an exceedingly important concern, one that has had books written about it. If OSHA and the NEC feel that a small generator system is safe when:

1) it is not grounded to earth,
2) circuits are protected by correctly sized over-current protection devices
3) a GFCI is installed, then I accept that.

Using large industrial generators, often in parallel with other gen-sets, is not the same situation as the generators we may be expected to use. One is best advised to heed the directions of the manufactures, the NEC, other appropriate code enforcing AHJ's (Authorities having jurisdiction), OSHA and its equivalents.

While not specific to portable generators, there are situations where improperly grounded panels and circuits can become dangerous. Wilily-nilly grounding based on hunches and a incomplete understanding of electrical systems should be avoided.

 

[DaveInDenver]

I have the 2005 NEC here (it's the one I was tested to on my P.E. in 2008), some of the language changed in the 2008 and 2011 but they don't change fundamentally. You want a floating ground path unless the system you are connecting to is earth grounded, then you have to reference the generator to earth.

Don't ground.

I don't have the NEC to quote from, so I won't (should be in section 250). Basically, it's safer to not run a separate ground on portable gensets. I know, I used to do it too.

If I can find the specific reference tomorrow at work, I'll post it up.

Good luck.

250.34 Generators-Portable and Vehicle-Mounted
(A) Portable Generators. The frame of a portable generator is not be required to be grounded to the earth if:

(1) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.​

(B) Vehicle-Mounted Generators. The frame of a portable generator is not required to be grounded to the earth if:

(1) The generator frame is bonded to the vehicle frame.
(2) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(3) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.​

(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be bonded to the generator frame where the generator is a component of a separately derived system.

FPN: For grounding portable generators supplying fixed wiring systems, see 250.20(D).

250.20 Alternating-Current Circuits and Systems
System grounding is the intentional connection of one conductor of an alternating-current system to the earth so as to limit elevated voltage on conductors from high voltage surges imposed by lightning, line surges, or unintentional contact with higher voltage lines and to stabilize the phase-to-ground voltage during normal operation [250.4(A)(1)].

(A) AC Systems of Less Than 50 V. Alternating-current systems that operate at less than 50 V are not required to be grounded unless:

(1) The primary exceeds 150 V to ground
(2) The primary is ungrounded​

(B) AC Systems Not Over 600 V. Alternating current systems of the following types must have the neutral (X0) terminal of the power supply bonded to a suitable grounding electrode (earth).
Single-phase, 2- or 3-wire, 120 V or 120/240 V system
3-phase, 4-wire, 208Y/120 V or 480Y/277V wye-connected system
3-phase, 4-wire, 120/240 V delta-connected system (high-leg)

(D) Separately Derived Systems. Separately derived systems, which are required to be grounded by 250.20(A) or (B), must be grounded in accordance with the requirements of 250.30.

250.30. Grounding Separately Derived Systems
(A) Grounded Systems. Separately derived systems that operate at over 50 volts [250.20(A) and 250.112(I)] must be grounded to an effective fault current path to ensure that dangerous voltage, which can create a shock and/or fires from ground-faults, will not remain [250.2(A)(3)]. In addition, separately derived systems must be grounded to the earth to stabilizing the voltage during normal operation [250.2(A)(1)].

(1) Grounding - Effective Fault Current Path. To provide the low impedance path necessary to clear a ground-fault (line-to-ground fault), the metal parts of the separately derived system (equipment grounding conductor) must be bonded to the system grounded conductor (X0 Terminal). The bonding jumper used for this purpose must be sized in accordance with Table 250.66, based on the total area of the largest ungrounded (hot) conductor.

The neutral-to-case bond can be made at the source of a separately derived system or to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices.

(2) Grounding - To the Earth. A grounding electrode conductor, that connects the separately derived system grounded (neutral) conductor to a suitable grounding electrode [250.30(A)(4)], shall be installed in accordance with 250.30(A)(2)(a) or (b). Grounding electrode conductor taps as permitted by 250.30(A)(2)(b), shall be installed in accordance with the requirements contained in 250.30(A)(3).

Exception: The size of the bonding jumper for a system that supplies a Class 1 circuit from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived phase conductors and shall not be smaller than 14 AWG copper.

(a) Single Separately Derived System. A grounding electrode conductor for a single separately derived system must be sized in accordance with 250.66, based on the total area of the largest ungrounded (hot) conductor. This conductor shall connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(4). The grounding electrode conductor must terminate at the same point on the separately derived system where the neutral-to-case bonding jumper is installed [250.30(A)(1)].

Exception: A grounding electrode conductor is required for a system that supplies a Class 1 circuit from a transformer rated not more than 1000 volt-amperes. However, the system grounded conductor must be bonded to the transformer frame or enclosure in accordance with 250.30(A)(1).

(b) Multiple Separately Derived Systems. Where more than one separately derived system is connected to a common grounding electrode conductor as provided in 250.30(A)(3), the common grounding electrode conductor shall be sized in accordance with Table 250.66 based on the total circular mil area of the derived phase conductor from all separately derived systems.

(3) Grounding Electrode Taps. Grounding electrode taps from a separately derived system to a common grounding electrode conductor must connect the grounded conductor of the separately derived system to the common grounding electrode conductor and must be installed in accordance with (a) through (d) below.

(a) Tap Conductor Size. Each tap conductor must be sized in accordance with 250.66 for the derived phase conductors of the separately derived system it serves.
(b) Connections. All connections must be made at an accessible location by an irreversible compression connector listed for the purpose, listed connections to copper busbars not less than 1/4 in. x 2 in., or by the exothermic welding process. Tap conductors must be connected to the common grounding electrode conductor as specified in 250.30(A)(2)(b) in such a manner that the common grounding electrode conductor is not spliced.
(c) Installation. The common grounding electrode conductor and the taps to each separately derived system must comply with 250.64(A), (B), (C) and (E).
(d) Bonding. Exposed structural steel that forms the building frame or the interior metal piping in the area served by the separately derived system must be bonded to the grounding electrode conductor in accordance with 250.104(A)(4).​

(4) Grounding Electrode. The grounding electrode conductor must terminate to a grounding electrode that is located as close as practicable, and preferably in the same area of the neutral-to-ground termination of the derived system. The grounding electrode shall be the nearest one of the following:

(1) Effectively grounded metal member of the building structure.
(2) Effectively grounded metal water pipe, within 5 ft from the point of entrance into the building.​

Exception: The grounding electrode conductor can terminate any point on the water pipe system for industrial and commercial buildings where, (1) conditions of maintenance and supervision ensure that only qualified persons service the installation, and (2) the entire length of the interior metal water pipe that is being used for the grounding electrode is exposed.

Where effectively grounded metal member of the building structure or effectively grounded metal water pipe is not available, then one of the following electrodes must be used:
The metal frame of the building or structure, where effectively grounded, see 250.52(A)(2).

An electrode encased by at least 2 in. of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 20 ft of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than ½ in. in diameter, or consisting of at least 20 ft of bare copper conductor not smaller than 4 AWG, see 250.52(A)(3).
A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG, see 250.52(A)(4).
Rod and pipe electrodes not less than 8 ft in length, see 250.52(A)(5).
Plate electrode expose not less than 2 ft2 of surface to exterior soil, see 250.52(A)(6)
Other local metal underground systems or structures such as piping systems and underground tanks, see 250.52(A)(7).

FPN: Interior metal water piping in the area served by a separately derived system must be bonded to the grounded (neutral) conductor at the separately derived system in accordance with the requirements of 250.104(A)(4).

(5) Equipment Bonding Jumper Size. Where an equipment bonding jumper is run with the derived phase conductors from the source of a separately derived system to the first disconnecting means, it shall be sized in accordance with Table 250.66, based on the total area of the largest derived ungrounded (hot) conductors.

(6) Grounded (neutral) Conductor. Where a grounded (neutral) conductor is installed and the neutral-to-case bond is not located at the source of the separately derived system, the following must apply:

(a) Routing and Sizing. The grounded (neutral) conductor must be routed with the secondary conductors, and it cannot be smaller than the required grounding electrode conductor as specified in Table 250.66 based on the largest ungrounded supply conductor, but it is not required to be larger than the ungrounded derived phase conductor. For secondary phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded (neutral) conductor is not permitted to be smaller than 121/2 percent of the area of the largest derived phase conductor.

(b) Parallel Conductors. If the secondary conductors are in parallel, the grounded (neutral) secondary conductor must be sized based on the total circular mil area of all of the parallel conductors per phase. Where installed in two or more raceways, the size of the grounded (neutral) conductor in each raceway must be, based on the total area of the largest derived ungrounded (hot) conductors, but in no case smaller than 1/0 AWG are required by 310.4.

 

[sapper]

I have never worked with the NEC only the CEC and after some reading there are some huge differences in the 2 references. I guess I often think about things way too much but the CEC makes no direct reference to portable generators but only considers them isolated systems similar to transformer secondarys and UPS systems.

Because the unit I am looking at is capable of being run in parallel with another unit leads me to want to run a electrode and ground it.

Also the CEC never uses the term "cord-and-plug".

 

[dwh]

I really don't care if I am not meeting code 300 kms from any real road but I am concerned with the safety of my family.

Then GFCI is the way to go. If there is anything hinky going on, there will be an imbalance and it will trip. Bloody things can be touchy though, and trip for no apparent reason. Lot of people end up tossing them out because they get fed up with it.

10-206 Grounding connections for isolated systems (see Appendix B)
(1) For a wiring system or circuit required to be grounded and not conductively connected to a distribution system

Now see...that right there gives me pause. Being somewhat familiar with the mindset of The High Priests Of The Codex, that line there makes me think that somewhere else in the code, there is a reference to some system which is NOT required to be grounded. That might be what we're looking for. I've never seen a copy of the CEC though, so I'd have no idea where to find it.

 

[dwh]

Because the unit I am looking at is capable of being run in parallel with another unit leads me to want to run a electrode and ground it.

Pretty sure the Honda sync kit includes a ground-to-ground connection. Once they are paralleled, they are essentially a single portable generator and again, no need to planet ground.


I think the thing you keep missing is this part about the planet not being a ground path. Someone, who shall remain nameless (but not blameless), got me started making cheesy MS Paint drawings...