What is a Floating Neutral Generator?

A bonded neutral power generator is required by code when you have a "separately derived electrical system" where the power transfer switch also breaks the power grid neutral conductor - thus also breaking electrical continuity between the power neutral and the earthing electrode system.

In my two years of deployment in Iraq some 15 years ago... we derived all of our electrical power from large diesel generator sets (< 1 megawatt typical) using European mains voltages & frequencies (3-phase 415/240 @ 50~Hz)

Where all transfer switching between generator sets used 4-pole transfer switching that switched all 3 phases as well as the neutral... all generators had bonding jumpers installed across the neutral and the earthing conductors/electrodes... as such, this is what is commonly referred to as a "separately derived system" as the neutrals are separately derived and isolated from each energy source by means of the transfer switch.

In my experience, generators with floating neutrals are both dangerous and deadly - as the likelihood of fault currents present will cause the shorted phase to drop to zero, whereas the solidly connected neutral across the entire installation will have a line voltage potential on it to ground or earth... the remaining phases will then have an elevated voltage potential in reference to ground or earth... in a 3-phase system; that would mean a voltage potential that is 1.732x the typical line voltage from phase to earth under abnormal mains line fault circumstances. Under this same condition though, all 3 phases will have what appears to be a "normal" line voltage reading between all phases to neutral - but not to earth or ground.

It is still the best and the safest practice to bond the neutral to the frame of the generator set and also ensure that the generator set is also effectively grounded too.

Your incoming utility service is only served with phases & neutral conductors - and no earthing or grounding conductor - as the neutral conductor of the service feeder is bonded twice - once on each end of the service feeder - on the utility side at the power transformer - and at the customer side - at the service entrance (meter and/or disconnect switch or main switchboard/panelboard or load center, where the main circuit breaker or disconnecting means exists... however - when designing or installing a provision for an auxiliary power source (such as a generator for emergency power) a transfer switch is recommended for complete isolation from the grid to prevent the dangerous condition of backfeeding the utility - and placing utility workers in danger upstream that are working on the power lines, as well as creating dangerous voltage potentials upon restoration of grid power after a power outage.

The incorporation of a power transfer switch or an approved or listed circuit breaker interlocking mechanism is also required by the National Electrical Code (NFPA-70) to ensure safety and integrity of the installation.

Separately derived neutrals are best by far - but requires a 3-pole (or a 4-pole for 3-phase-4-wire service) double-throw manual safety switch for typical 120/240 single-phase 3-wire electrical services, and they're more expensive than their 2-pole counterparts, of which will only offer a solidly connected neutral termination that is not separately derived or offering total isolation from the power grid during an outage.

Ungrounded 3-phase-3-wire "delta" systems where the electrical system is intentionally ungrounded would be the exception to having a generator set without any grounding performed... although generator sets with 3-phase delta configured alternators are extremely rare... typically in a hospital setting - where a possible use for an ungrounded 480-volt, 3-wire "delta" service is utilized could use a large "WYE" to "DELTA" isolation power transformer installed between a generator set with a 3-phase-4-wire WYE alternator and the transfer switch for the ungrounded 480-volt "DELTA" electrical system.

3-phase generator sets are typically rated in kVA with a calculated power factor of 0.8 or 80%. Power transformers are also rated in kVA.

120/240v generator sets are typically rated in kW - whereas the power factor is 1.0 or 100%.

Can you explain how to connect 2 generators together so they act like 1 generator. example: your air compressor needs 12000 watts. And you have 2 generators with 8000 watts each. the 2 of them could do the job, But 1 can not. Tell us how/if it can be done?

Good video

091423: Why do I have continuity between hot & neutral when bonding plug inserted?

Great video Ben, thanks for being so thorough in the explanations and experiments

Useful, but there is a solution. Champion has a 2 minute video that shows you how to convert a one of there floating ground generators to bonded. They also insist that for safety the generator needs to be attached to a 8ft ground rod regardless of whether it is one of their neutral floating or bonded generators. However I have seen that not recommended elsewhere, at least for bonded.

Hey great video! I always love your details.
I have been searching for an answer perhaps you can help.
I have a Westinghouse 12,500 portable generator installed to 50amp power inlet to 100amp panel with interlock no ground rail in panel, shielded cable.
When on generator power my Bath and kitchen gfci's blinking red and no power. What can I do to fix this?

really enjoy your videos, I thought I was subbed already but wasnt...re-subbed

While the suggestion of bonding the neutral of a genset to the ground appears to make things safer I disagree. A portable generator has no ground. The hazard is simply resolved by using modern GFCIs on the generator. I use pigtail GFCIs whenever I directly plug into a portable generator even if the outlet is a GFCI. The hazard of using a bonded neutral generator directly tied into the distribution panel of my home is much more dangerous. Any generator I own will be a floating neutral. I disagree completely with your assessment of it not being a big deal. It is a big deal.

I made a cord to hook into my house, when I had the neutral connected it made the house 220vac, I cut the neutral and it works fine.

Thank you so much, you really explain amazingly well

Good video... lot's of food for thought. I especially liked the circuit schematic being shown.
Totally friendly suggestion.... get a pair or lineman gloves... 1KV would be fine for playing with generators for recreation and house power... an ounce of precaution....

Even the folks that write The National Electric Code have difficulties with grounds and bonding.

I encountered a strange situation with a Chinese generator. It is a three-phase generator. The neutral conductor is connected to the housing and grounded. It worked for a year and suddenly stopped producing electricity. When I separate the connection between the neutral wire and the ground, it works. I think the problem is in the generator itself, maybe the winding is short-circuited. I ask for your opinion.

I just watched your video. I always enjoy how you explain things. So, I have a 3000 watt inverter Honda generator about 15 years old. I've always used it with extension cords with no problems. However, I just made an extension cord to plug into the 20 amp outlet (L6 receptacle). I used a metal box and #12 wire and receptacle and I wired it as I would a house, Hot and neutral to the receptacle and the ground to the ground on the plug and the box. Now I am wondering if I should disconnect the ground to the box and bond it to the neutral? As a side note ,I tested it with my plug in tester and it showed an open ground. Even on the outlets on the generator.

Good info yet over my head. I just bought the exact generator to install in my school bus conversion and will be using a couple extension cords and also charging my solor batteries. So should I be concerned with the way it is from the factory ?

Hi Ben, nice video thank you for sharing your knowledge.

I'm going to back up my home electrical power with an inverter/generator. My generator comes from the factory with a bonded neutral so I need to do something to avoid using the generator neutral bonding along with the neutral bond in the home electrical panel. What if I just leave the ground wire from the panel to the connection box for the generator power floating - not connected to the generator? Will that fix the problem without having to modify my generator? Is it okay to do this?

Put it simply the generator neutral phase was not grounded to the chassis. Complicate the whole issue by calling it a floating Neutral??? KISS!

Exelente

Thanks for the very informative video. My generator is apparently not bonded. The neutral has no connection to the ground in the receptacle. The chassis appears to be just floating as there is no connection to anything. Running the generator and touching a hot lead to the chassis, nothing happens. It seems entirely possible there is a chance the chassis could become hot if there was a fault and then through me via the ground connection in the panel. Boy, am I confused.

why do you have to ad a grounding plug to an inverter gen. and how can you avoid it to use it like a regular plug

THANK -U

The reason it is confusing is because you call it "ground" even though it just means body or frame of system. It has NOTHING TO DO WITH GROUND.

Now you get to reset all your Clocks 😂

My generator has on the front ‘neutral bonded to frame’ written on the front. Should I connect the ground wire attached point on the generator to a ground point like my house ground? Any other considerations to be concerned about? I use an interlock as well on my main panel. But as you’ve pointed out, it only disconnects the two legs and not the neutral in the main box.

What is the app on your phone to read your currant wattage consumption? I would like to know how many watts my house is using while hooked to my generator. I have not been able to do that yet! What is the best way to know the wattage being pulled from my generator? Thank you so muh.

What is that app that measures watts being used?

If someone has a bonded neutral generator and hooking it up to a house with the cord why can’t you leave the neutral disconnected and just wire in the ground and both hots ?

So I have a generator with a floating neutral that plugs into a 50 amp inlet receptacle. The 50 amp inlet is wired to a 12,500 watt Reliance Controls Protran Transfer switch, which is wired to my main panel. The main panel has mixed neutrals and grounds on both the neutral and ground bus bars, the ground bus bar is grounded to the panel box, via the big green ground screw. Also, both the neutral and ground bars are jumpered together by a copper rod. Now since the transfer switch itself has breakers, does this make my main panel the second means of disconnect when the transfer switch is in generator mode? Do I need to add a separate ground bar and unground the panel box and get rid of the copper bar joining the ground and neutral bars?

On some Champion duel voltage generators they use a floating neutral and a multi contact switch to parallel both 120 vac windings to increase the amperage for the 30 amp 120 vac socket for campers and small RV's. So if you would bond ground to neutral with the switch to 120 vac you would get a direct short. When the switch is at the 240 vac setting the switch also bonds the neutral of one side of the 120vac winding to ground. With that being said most of the Chinese generators come out of the same major factory. So they don't have a bonded neutral. Remember China home power is 220 vac. So split phase is not used.

Excellent. Well explained. Clear and concise.

yes code reqiures an earth ground, but it does so to prevent electricity from other systems from entering your generator system (ie 480 lines that fall from overhead or more likely lightning strikes ; ps great job on video

Nicely done.Thanks.

You need a proper GFCI breaker on the AC outputs.

It’s always good when you have a machine that can kill you to have “bad documentation.”

center tap?...looks like 2 separate coils....

Very informative & confirming my studies, thanks.

To make a long story short, if you're going to use your generator to backfeed power into your house wiring, first turn off the main breaker from the utility company... very important! Then, and ONLY then fire up your unbonded generator into your house wiring at some point. Your grounds and neutrals will automatically be bonded by your home's electrical panel. When utility power is restored, shut down and disconnect your generator FIRST, then you can turn the power company's main breaker back on.

1. The major conclusion I took from this is that the floating neutral generator is only appropriate when I'm using it to power a system that already has the neutral and ground bonded at some point further down the line. Correct?

2. The corollary I'm trying to figure out is what to do when connecting my RV (or other 120v equipment) directly to the generator... It seems clear enough (to me) that neutral and ground should be bonded in this case. But is the grounding rod still required? Or is bonding neutral to the frame sufficient? (I'm still a bit unclear on this part)

Sorry but I'm confused. After watching this video, I went to my harbor freight predator 3500 generator and tested the 120v/30amp receptacle, with my Klein MM700 ohm tester touching the red lead to the neutral and the black lead to the ground bolt/terminal, and it HAD continuity. But when I tested the other 2 plugs (120v/20amp) receptacles I could not get continuity. How is that possible? I tried each several times. I bought this generator to connect to my small single wide trailer home at power outages. I just pull the lead/wire from the main income PGE box and connect an extension cord from the generator to the trailer side lead/wires that I disconnected from the main PGE box. So, I basically only have the generator as incoming power, the fuse box is inside the trailer. Do I need a bonded or floating ground generator and do I need a earth ground rod? Thanks for your video.

no.... but what you didn't do is go inside and see how much power is on your home's ground wires... i bet its not nothing

..somehow I don't think the Chinese would be very concerned about that

This is why you don't buy Chinese bran generators! The electrical safety of your appliances. The risk of fire to your home/work. The potential to leak fuel. The problems with overheating. The increased risk of carbon monoxide poisoning and electrical shock. Moreover, these Chinese brands don't ever recall products and follow up with consumers like Harbor Freight, Home Deport, or Amazon do.

One important point that I believe you should have mentioned in the video is that the reason they are not connecting the neutral to ground is they can get a higher output rating since they are forcing all current through the one line. MarkMannM2

How long would 40lb of propane power that thing? Thanks!

most inverter generators have bonding ... esp if they got a GFCI duplex.