I recently did a Google search on how to ground a portable generator. Even with years of electrical experience, I found all the articles to be confusing and overly complicated. Or the opposite, not providing sufficient or correct information. I’d think that if you don’t know much about wiring and electric codes, terms like neutral bonded, separately derived system, and ground fault current path, can be more than just a little confusing.
In this article, I intend to clarify the issues surrounding generator safety with regard to grounding and neutral bonding. The process of grounding a generator isn’t too complicated. Knowing when to ground a generator and why this is important, can become quite technical. My hope is to explain all this in a manner that anyone can understand. To achieve this, I’m first going to explain what grounding is and why it is important.
It may not always be necessary to ground a portable generator. So, I’ll also cover this aspect. Do you need to ground your generator?
Understanding Electric Grounding
Alternating Current (AC) is generated by pulsing electric energy between a live source (the generator’s stator) and a neutral source (the alternator casing). A portable generator will, in most cases, have a neutral bonded frame. All metal components will be bonded to the frame, as these conduct electricity. The manufacturer will connect the conductive materials of the generator, like the gas tank, engine, and frame, to the alternator by means of an electric conductor of a suitable gauge. This would be copper wire.
The purpose of neutral bonding is to create a local, or stand-alone, grounding at the source (the generator). This method of grounding is to prevent electrical interference and ensure the safe operation of Ground Fault Circuit Interrupter (GFCI) breakers. This is an essential safety feature for any electric equipment that may cause a shock or electrocution.
You may often hear the term floating neutral (or ground), especially when connecting power to an RV. This is the situation that I’ve just described. In other words, the neutral is bonded to the generator and not connected directly to the earth. The same will apply to the electric connection to your RV. The neutral or ground is connected to the body of the RV and not the earth. Essentially, a floating neutral does not make direct contact with the earth. Connecting a generator, or inverter to a boat means that there can only be a floating neutral. The boat cannot be connected directly to earth, because it floats on water.
An Earth or Grounding electrode (grounding rod) is used predominantly for lightning protection and is required when the generator supplies power to a structure, like your home. This is known as ground fault current path. Grounding is also used to prevent electrical signal interference for radio and television signals. This is the opposite to a floating neutral. A copper conductor is connected to the neutral bonding at the generator and to an electrode, or rod that is driven a suitable distance into the ground (earth).
Generators used on a jobsite are subject to OSHA regulations and contractors need to be familiar with these. But I will explain what this about. For example, if a generator is used on a vehicle, or trailer, the neutral bonding needs to be attached to the vehicle.
So, before continuing, I want to clarify the distinction between Grounding and Neutral Bonding or a Floating Neutral. Grounding a generator means connecting an additional connection between the generator frame and the earth, by means of a metal rod that is driven into the ground. Neutral bonding means only connecting the alternator, and metal components of the generator, to the frame.
Do you need to ground your generator?
If you’re using extension cords plugged directly into the generator receptacles, there is no need to ground the generator, using a ground rod. If you’re using the generator on a jobsite, OSHA regulations require that these outlets be equipped with GFCI protection. Additionally, if the generator is placed on a conductive surface, like a metal trailer, it needs to be bonded to the surface on which it stands.
An RV, with a floating neutral, also doesn’t require a ground connection. Though, the neutral or ground connection of the RV has to be connected to the generator and not the shore power, or any other power source.
When connecting a generator through a transfer switch to a building, like your home, it becomes a little more complicated. This is where the term separately derived system becomes important. Remember that installing a transfer switch should be carried out by a licensed electrician. But I’ll explain it any way.
A transfer switch allows you to safely switch between the main electrical supply and your portable, or standby generator. Though not all transfer switches work in the same way. Some may have a common neutral, that is permanently connected to both the generator and the utility power. This means that the neutral is not switched, the circuit is never broken. Only the hot circuit is switched between mains and generator power. The neutral connection to the generator is always connected to the permanent earth grounding of the home. In this case, there is no need to connect an additional grounding electrode.
A separately derived system refers to a generator transfer switch that breaks both the neutral and hot connection. When the power supply is transferred to the generator, it is no longer connected to the main neutral supply to your home. The connection to the grounding of your house wiring is, therefore, separated from the generator supply. In this case, you will need to install additional grounding for the generator.
The situations I’ve outlined above are the general safety requirements for portable generator grounding. You may decide to ground your generator, even if it is not strictly necessary for your safety. A good example of this would be a generator used for outdoor music events. Signal interference from an unbalanced current will cause unwanted noise emitting from the sound system. A ground rod will balance the current to the earth, thereby eliminating the noise interference. If your generator at home causes a buzz on your stereo, or a distorted image on your TV, grounding the generator could be the solution.
How to Ground A Generator
A step by step guide
Upon deciding that it’s necessary to ground your portable generator, you’ll want to do this correctly, safely, and in compliance with electrical codes. This is what we’ll be covering in this section of the article.
What do you need?
- Grounding Rod – I’ve seen a lot of conflicting information with regards to grounding rod requirements, so I want to clarify this. A grounding rod needs to be at least 8’ in length and ½” in diameter (for a copper grounding rod). Many websites state that the rod should be at least 4’, but this incorrect. The rod needs to be driven at least 4’ into the ground. The difference in length is to account for the angle of the rod as it enters the earth. This will be become more apparent when we get to the installation of the ground rod. Grounding rods are usually copper but, essentially, any conductive metal will work.
- Copper wire – The length of the copper wire used to connect the generator to the ground rod is not important. You only need a suitable length of wire to reach a convenient location for the ground rod. The gauge of the grounding wire is important. The electric code specifies at least #6 or #8 copper wire for a domestic grounding rod. Though, for most portable generators this could be overkill. If you’re unsure, and want to play it safe, stick to these recommendations. A grounding wire can never be to thick. Though, it must never be too thin. The copper wire used to ground your portable generator must, at least, meet the AWG requirements for the maximum output of the generator. A 40A (4,800W @ 120V) should use a minimum #12 wire.
- Lugs and connectors – It’s common for DIY electric installations to wind the wire around the ground rod and neutral bonding nut. I don’t recommend this. You should either use metal connector lugs or solder / weld the wire to the rod. The connection to the generator should be done using a ring lug that securely fits around the bolt used for the neutral bonding.
- Tools required – the tools needed for this installation are quite basic and are probably in your toolbox at home or on a jobsite. You’ll need to either solder the wire or compress the lugs. You may need to cut the wire to length. You will also need a mallet to knock the rod into the ground.
Installing your grounding rod
The rod needs be driven at least 4’ into the ground using a mallet. In hard ground, some water to soften the ground will make this easier. If the ground is rocky, you may have to drive the rod in at an angle. This angle may not exceed 45°. Driving an 8’ rod into the ground at an angle of 45° will mean that it will reach the required 4’, if the entire length of the rod is driven into the ground.
Attach the copper wire to the rod. If you want to solder or weld the wire, wrap it securely around the rod before doing so. If you choose to use a bolt and a lug, you’ll need flatten the top of the rod first and drill a hole big enough for the bolt to fit through. You can flatten the rod either by grinding it with angle or bench grinder, using a file or rasp, or by heating the rod and beating it flat with a heavy mallet and anvil.
The other end of the wire needs to be connected to the grounding nut on your generator. This should be easy to identify. Your owner’s manual will usually have a diagram to help in this regard. Loosen the bonding nut and attach the grounding wire using a suitable lug. Make sure that all existing wires at the neutral bonding nut are in position before securely fastening the nut.