Among all the generator’s specs, the type of neutral bonding could be one of the most enigmatic for a person who only has little understanding of electrical engineering.
You may have come across the terms “floating” and “bonded” neutral. While they sound obscure to many people, they are an important factor when hooking up your portable generator to a transfer switch.
But, before we go into the specifics of a bonded and floating neutral, we must first explain what a “neutral” is, and how it is different from a “live/hot wire” and a “ground”.
Difference Between Live/Hot, Neutral and Ground
An electrical circuit consists of two wires. One carries the current from a source to a load, and the other returns this current back to the source. In any electrical circuit, this loop must be closed for the current to flow.
A wire that carries a current from a source to a load is called a “live/hot wire” – a current carrying wire.
A wire that returns the current back to the source is called a “neutral wire”, or simply neutral – current carrying wire again.
Contrary to these two, a “ground wire”, or just ground, is not a part of the electrical loop and only carries current in a fault condition. The ground wire is basically a protective wire, whose purpose is to ensure the safety of the system.
Bonded Neutral Generator
In a bonded neutral generator, the neutral is bonded to the generator’s frame. The transfer switch, must in this case transfer the neutral to meet the safety standards according to NEC (National Electrical Code) article 250.
The safety standards of the NEC article 250 require that the neutral must be grounded at the first means of disconnect (which means the nearest possible point), and cannot be grounded twice, to avoid induced transient voltages or currents.To elaborate, let’s take an example of a residential home circuit.
We are interested in connecting a generator to a home circuit. First, we must learn how a residential electricity system works.
In residential homes, all load is powered by a utility (an electricity distribution company). The power cables from the utility are connected to the electrical panel installed in homes (diagram below). The electrical panel distributes this power to each circuit within a home.
The electrical panel (also called distribution board) is a system that distributes current to different circuits within a home or a building. It contains separate fuses or circuit breakers for each circuit, often enclosed in a metal enclosure. All the neutral points are grounded at a single common point.
To shift the load from the home electrical panel to a generator, a transfer switch is used. The transfer switch always transfers (disconnects from the home electrical panel and connects to the generator’s terminal) the live/hot wire. So, only the neutral wire stays in question.
As per NEC standards, we cannot ground the neutral twice. Since the generator already contains a neutral bonded to the ground, the transfer switch must transfer the neutral from the home electrical panel to the generator’s neutral terminal (diagram below).
We can observe that the load is completely isolated from the home electrical panel and is mounted directly onto the generator. Thus, a bonded neutral generator behaves as an isolated or a stand-alone unit.
In a floating neutral generator, the neutral is not bonded to the generator’s frame. Therefore, the ground must be provided by the home panel. The transfer switch, in this case, does not transfer the neutral to comply with the NEC standards.
The load is transferred from the home electrical panel to the floating neutral generator in accordance to NEC article 250. As per the standard, neutral must be grounded once, and not more than once. However, the generator does not have a grounded neutral.
Therefore, the transfer switch does not transfer the neutral. It only connects the load to the generator’s neutral. The neutral from the generator is now connected to the load and is grounded via the home electrical panel (diagram below).
In a floating neutral generator, since the neutral is not bonded to the generator’s frame, both wires are normally current carrying wires. Therefore, both slots of the receptacles on the generator are considered live/hot receptacles.
If there is a short circuit between any slot of the receptacles and the generator’s frame, the return path, i.e. neutral wire, is not bonded to the frame. There will be no return path for the current to flow through. Therefore, all the short circuit current will flow through the metal frame into the ground and thus, providing safety from the short circuit current.
Floating neutral generators are used for systems which already have a grounded neutral, e.g. home electrical panels, some recreational vehicles etc. The generator is connected by means of a transfer switch that does not transfer the neutral.
There are no standards for a specific type of generator to have a bonded or a floating neutral.
Summary of Differences Between Bonded and Floating Neutral Generators
|Bonded Neutral Generators||Floating Neutral Generators|
|Neutral is bonded to the frame.||Neutral is not bonded to the frame.|
|Transfer switch transfers the neutral.||Transfer switch does not transfer the neutral.|
|Protects from transient voltages.||Protects from short circuit.|
|Mostly used in stand-by and open frame generators.||Widely spread in portable inverter generators.|
|Can be used both as an isolated unit and for systems with a grounded neutral.||Used for systems with a grounded neutral.|
How to check for Floating Neutral or Bonded Neutral?
As a standard practice, the type of neutral, bonded or floating, is usually clearly mentioned near the portable generator’s outlets.
Another simple way to check for the type of neutral bonding is to consult the generator’s manual or visit its manufacturer’s website. You can also call the manufacturer and inquire directly.
The type of neutral bonding can also be detected using a continuity tester. For this, first, turn the unit off. Now insert one lead of a continuity tester in the neutral slot of any AC receptacle (you can consult the user manual to find it) and attach the other lead to its metal frame. Continuity means that the neutral is bonded, and in case of discontinuity, it is floating.
The electromechanics behind bonded neutral generators are in a stark contrast to floating neutral generators. Hence, their respective applications may differ.
Therefore, we must first carefully determine the type of generator that we need before hooking it up. Any misjudgment can be very dangerous. However, it is worth noting that it is normally possible to convert the neutral.
You should never try to modify a generator on your own. It is not only dangerous but will also void the manufacturer’s warranty.
The installation of a portable generator on a home circuit should only be done by a licensed electrician. Under no circumstance, one should try and connect a generator to the home circuit by himself.
I think I’ve found a good bonding solution for my Champion 201083 portable generator. I first removed the bonding connection inside the generator per Technical Bulletin Number 2030001. Then I got an extra L-14-30P plug (like the one on the house to generator cable). I connected the plug’s ground pin to its neutral pin and labeled it “neutral bonding plug”. If I want to use the generator to run power tools via a standard extension cord, I insert the bonding plug and then connect the extension cord to one of the 120V GFCI outlets. The generator is now “bonded neutral” and safe to use with the power tools. If I want to power the house panel, then I have to remove the bonding plug in order to connect the cable from the house and the generator becomes “floating neutral” with the only neutral to ground bond taking place in the house electrical panel as it should.
It’s true that using a bonded neutral generator on a home panel box which is required to also have a bonded neutral will cause neutral current from the generator to evenly split between the neutral and ground conductors in the generator cable. If you have a 30A generator cable that is 20 feet long, the resistance of the parallel #10 conductors will be 0.01 Ohm. The voltage difference between the generator frame and the home panel box ground will be 0.3V maximum. Yes, it’s technically a violation of the NEC but I don’t think anyone will be electrocuted by 0.3V. Consider that a flashlight battery is 1.5V and a car battery is 12V.
Now consider if your generator is wired with a floating neutral and you are using it to power your electric drill with an extension cord instead of powering your home. Your drill develops a short circuit between the hot lead and the metal case which is tied to the generator frame via the grounding wire in the power cord. Your generator frame is now at 120VAC with reference to the neutral wire and this could be a very hazardous situation. The generator’s circuit breaker doesn’t trip because there is no connection between the neutral and ground to draw excessive current.
My thinking is that there is far less risk using a bonded neutral generator on a residential panel than there is using a non-bonded generator with an extension cord and other individual loads connected directly to the generator outlets.
Thanks for this article, it confirms my suspicions about the Westinghouse floating neutral portable generator… I was fine with the output until I measured the “hot” and “neutral” wires to ground — and found that the voltage (with or without a load) was approximately 60 volts AC in each case… Installing a good ground to the generator did not change anything – so I assumed that the neutral was “floating” from the inverter to the output receptacles…
Thanks for the article. It was very helpful. I see mine can be installed as a back uo without using a floating neutral if I disconnect the wire to the frame. I have a Siemens box and see there is a tremendous range in price for components. Do younhave any recommendations for brands for lockouts or receptacles?
EXCELLENT and concise article! In generator/RV circles, you will often hear floating neutral generators referred to as “floating ground” which is technically inaccurate, but it makes sense to RV’ers who are checking their generator with a meter: They get ~120VAC between the hot and neutral and expect ~120VAC between the hot and ground with little or no voltage between the neutral and ground. When they see >0VAC between neutral and ground, then <~120VAC between hot and ground, it is the ground that is "floating" (in their mind).
A lot of modern RV's have fault-test circuits that get angry when plugged into a floating neutral generator and disconnect the power. The "quick and dirty" remedy to this is to connect the neutral and ground together on the generator and make a crude bonded neutral out of it. If it doesn't trip any safeties on the generator (which it easily could, depending on how it's engineered) this should remedy the "fault" being seen by the RV.
People who try to replace the Onan in a motorhome with a portable generator run into this all the time (along with the expected challenges surrounding cooling, exhaust, etc.)
Hi Paul, I have a bonded neutral generator. Does grounding the frame into earth with a copper wire and rod make it safer or is it overkill? Thanks.
Hi Hans, it is always safer to ground your generator.
This is a good article but a few technicalities. The “neutral” you refer to for the return is the “grounded conductor” if the system is grounded, otherwise it is also a live conductor, as you pointed out. It is only a neutral if it occupies a center tap on the source – which it normally would be if it’s a 240V source or 3-phase source and you are referring to the 125V receptacle. The “ground wire” is the “equipment grounding conductor”. It should be clearly distinguished from the grounding electrode conductor. I’m not convinced that a bonded neutral and installation of a grounding electrode is better for safety. It’s essentially installing the first fault – and it’s the second fault that completes the circuit.
Wow, there are still people out there that think driving ground rods make you safe. Electricity leaves the source and returns to the source, otherwise, you do not have a completed circuit. Electricity does not try to go to ground (Earth). The impedance is simply too high due to the shell effect. The ground cannot clear a fault, ground rods are for transient voltage occurrences. If ground could clear faults we would not need GFCIs, or breakers for that matter, fault current would just magically disappear into earth, which it does not.
Ok I had an electrician hook up a portable generator with a bonded ground. He used a gfci switch circuit to feed the panel with neutrals and grounds. So it is tied in with a manual switch with a main disconnect for when generator is supplying power. Is this correct or should it be a floating ground. I’m questioning as per biulding code I believe it should be floating and the bonded ground should be removed and transfered.
I have a Westinghouse inverter generator with a bonded neutral, and a Reliance transfer switch that does not switch the neutrals. The Westinghouse support website has instructions for converting to a floating neutral. I am going to ground the generator for safety.
Are there any issues with people or equipment safety with a floating neutral if the generator is connected to a transfer switch and grounded?
Does it make sense to use a floating neutral on the generator when connected to a transfer switch or an RV, and converting to a bonded neutral when using the generator standalone to power tools?
Such modification should be done by a licensed electrician, as he will ensure that all electrical codes and safety standards are respected. But yes, it does make sense to rebond the neutral if not connected to the transfer switch, as this will allow for proper operation of your unit’s GFCI outlets.
Which type of generator is the safest for a residential generator? Also, should you ground your generator if it’s bonded with a metal rod. Great explanation of differences between bonded and floating neutral generators.
I am not sure what the hazard is of having the generator bonded and connected directly to the home main panel where it is bonded as well ( panel interlocked away from utility power). A code violation but not a significant safety hazard vs. inadvertently using generator without a bonded neutral (if I make it floating).
Hi Norm, I don’t think that there’s one “safest” type of portable generator for residential application. That being said, you may want to ensure that it has GFCI outlets. By choosing an inverter generator, you’ll provide clean power to your electronics. Grounding is a must for maximum safety. Moreover, make sure you don’t backfeed the grid.
This article made me understand differences between floating and bonded neutral generators . The only confusion is when I watch a video on Reliance pro transfer switch ,they connect the neutral to household panel from generator and don’t mention whether it’s floating neutral generator or bonded neutral.Are all portable generators floating neutrals.
PS great article Thank You
Hi Guy, not all portable generators have a floating neutral. We specify the type of neutral on every product sheet available on our website. Look inside the spec table (towards the bottom of each product page). If the type of neutral is flagged as “N/A”, it means that the manufacturer didn’t provide the information.