Unbonded my generator and started a fire!

CORRECTIONS, thanks to the folks who commented below: 0:08 – Unbonding is removing the ground strap that connects ground and neutral, not ground to frame. 3:25 – The generator is a single phase, so it couldn’t run “out of phase.” Instead of 120v going to each leg, most or all of the 240v was going to one leg, and almost none to the other.

A 120/240 generator cannot go out of phase as it only has one phase. What probably happened is loosing the neutral caused the power being consumed to find an alternate route back to the generator. Meaning that instead of 120 -N - 120. you had for example 50-N-190. Those surge protectors operate by clipping any over voltages. depending on the specific component (a metal oxide Varistor is usually used and rated around 140-150v) will cause the Protector to try to protect. IN this case the Surge it was seeing wasnt due to power issues as a fault in the wiring of the cable. Glad you found what caused it.

Definitely a classic example of a floating neutral. A couple years back went on a service call in a late 1970s home, where the TV, DVR, DVD player and stereo system in living room smoked up so bad it set off the smoke detectors in the hallway and master bedroom after a 1500 watt electric fireplace had been running for over an hour, plugged into a different outlet on the other end of the living room. Come to find out, all the receptacles were backstab connection and part of a multiwire circuit (L1 & L2, sharing a common neutral) and the neutral burned up on a receptacle upstream, making everything downstream into a series 240V circuit and depending on the load balancing, voltages applied accross the load can range from nearly 0, to nearly 240. Also pointed out to the homeowner and corrected, the two single pole breakers controlling the multiwire branch circuit, by installing an identified handle tie to ensure that if either leg trips the entire circuit is dead, protecting anyone working on it thinking its dead when in fact one leg is still hot, evidently this wasn't required when the home was built. This whole catastrophe could have been avoided, had article 300.13 (B) of the NEC been applied which states that for multwire branch circuits, the continuity of the grounded (neutral) conductor shall not depend on connections to receptacles, lamp holders and so forth, where the removal of such devices would interrupt continuity. What this means, is that the neutral on those receptacles should have been connected via a pigtail

This was one of my arguments for not unbonding my generator, having more or less a redundant neutral. In the end I did unbond it and have not had any issues, but this video shows the importance of having a good solid connection all the way around.

I think the biggest lesson here is to always test before you need it. After making any changes, test and verify. Glad you weren't hurt.

Don't confuse neutral with ground. Ground only carries current when something is wrong. Neutral carries all the unbalanced current between L1 and L2.

The surge protector did catch on fire because it had a very /low/ resistance. Not high resistance. The MOVs inside go low resistance when exposed to over voltage, and they are supposed to short out and blow your fuses. It can be dangerous supplying power from a generator as it might no be able to make enough short-circuit current to trip thr fuses.

You are like a electrician detective. Glad it was only a couple of surge protectors that burned and not you home.

Nice detective work. Thanks for the info.

Side note: 250.30 of the NEC requires separate bonding wire to the service panel when connecting a generator in this situation if the neutral remains connected to the grid. However, if the transfer switch also separates the neutral from the grid, then the generator needs to be internally bonded.

Before you unbonded your ground at the generator, your neutral current was flowing through the ground conductor in the extension cord and the bonding jumper. So it was a related problem and unbondining your generator is correct. A ground rod would NOT have mitigated this problem even if you had connected it directly to your service entrance rod. That would have made the neutral current flow through your ground rod wires.

Thank you for everything! I’m glad you and your family are safe 🙏

As others have said, thanks for sharing the story and glad everyone is ok. Sharing these experiences helps others.

When the neutral get loose like that one leg goes high, the other one goes almost to zero volts like you said on the video and everything is connected in series between the two phases. The culprit is the loose neutral connection. It can also happen on the utility side of the installation.

Thank you, thank you, thank you. I have been stressing about the floating neutral question for about a month now and I am almost finished with the complete installation of my system. You answered my questions and really gave me down to earth answers. I'm good now. Thanks man.

Personal experiences - the best lessons for those of us who are still learning! Thank you!

Good info. Thanks for sharing !! So glad the damage was minimal!! Ride safe!!

Thanks for sharing! Glad everyone is OK!

I am not an electrician, but have been doing home renovations for 30 years. I installed a 120 volt Coleman RV heat pump in my kitchen ceiling. I also installed a dedicated duplex outlet for this purpose. However, when I turned on the heat pump the first time, it ran but was noisy. So I shut it off and went to inspect the heat pump itself. The motor case was extremely hot. I troubleshooted the possibilities, and found I had connected the neutral to the neighboring breaker, so the circuit was 240 volt. OOOPS.. Five years later, by some magic, the heat pump is still working. Oversight happens to everyone, so your extension cord failure is not a surprise, but glad you figured it out. (PS: during the course of home renovations, I found many many electrical and plumbing faults, done by the "PROFESSIONALS".)

Great info. Glad the family is safe.