[Project] Fault Detection: Floating Neutral

[Project] Fault Detection: Floating Neutral is an algorithm that identifies homes with irregular Power Quality. Floating Neutral identifies homes that dip equal to or greater than 2V at the beginning of the start-up of a single-leg device with an inverse increase of voltage on the other leg.

If you’ve received a notification in the Sense app about a Floating Neutral issue, we’d like you to share details here in the Sense Labs community. Please answer the below questions surrounding your issue so we can continue to help users in the future with this issue.

Required information to include:

  • Did Sense detect a floating neutral in your home?
    • Did you receive a timeline notification or email from Sense OR discover it yourself in-app?
  • Did you notice any signs or irregularities prior to the issue being resolved?
    • E.g. Lights dimming or flickering
  • How soon after detection did an electrician come inspect the issue?
  • Was the issue resolved by an electrician or your utility?
    • E.g. electrician confirmed a floating neutral and replaced
  • What was the official diagnosis from an electrician or your utility?

Floating Neutral Resources

Below is more information about neutral issues that may be detected by Fault Detection: Floating Neutral. If you have suggestions for additional resources to add to this list, please reach out to @JustinAtSense.

7 Likes

Justin! An excellent and simple solution. You have some smart cookies working there. One note is that the “start-up of a single leg device” needs to be an event that does not require a previous device detection to qualify as “a single leg device”. A simple turn-on of any 120V device, known or unknown, should qualify in order to make floating neutral detection as reliable as possible.

The next question would be, since no one other than Flash can get to the main breaker quick enough to shut off the power before stuff gets fried - what exactly should the home owner do to protect himself from the threat of up to 240V applied to half of the circuit breakers? A high capacity whole-house surge protector connected to the main breaker won’t work because their MOV’s engage at higher voltages than many appliances can tolerate for the relatively long periods of time involved with an open or loose neutral. They would have too much leakage if they spec’d them to clamp low enough to help with neutral issues. They are by design a good tool to swat down very brief, very high voltage transients typical of lightning strikes.

2 Likes

The next question would be, since no one other than Flash can get to the main breaker quick enough to shut off the power before stuff gets fried - what exactly should the home owner do to protect himself from the threat of up to 240V applied to half of the circuit breakers? A high capacity whole-house surge protector connected to the main breaker won’t work because their MOV’s engage at higher voltages than many appliances can tolerate for the relatively long periods of time involved with an open or loose neutral. They would have too much leakage if they spec’d them to clamp low enough to help with neutral issues. They are by design a good tool to swat down very brief, very high voltage lightning-type transients.

I’m not aware of any off the shelf device that is made for this application. The controller for my standby generator has an option to immediately drop the load from the mains if the voltage on either leg is out of the specified limits, but this generator controller is made for industrial applications. One could put together a protection scheme for this using some monitoring relays and a big contactor, or a shunt trip circuit breaker, but the cost would be well into the thousands and would end up being difficult to physically install alongside typical residential service equipment.

I think for the typical homeowner, the most effective way to protect against floating neutrals is to proactively have your electrician inspect your service entrance equipment and replace/repair anything that looks loose or damaged. The electrician may also be able to look over the nearby utility equipment and suggest that they make repairs to anything that looks fishy.

2 Likes

Ultimately, this is the goal. A lot of folks are unaware of potential neutral issues, and we hope this can serve as a tool to help increase awareness for homeowners.

2 Likes

It’s also worth pointing out that in most cases, voltage imbalance and fire hazards from a floating neutral develop slowly over time as connections loosen and corrode. The sense monitoring feature will allow homeowners to catch and correct this problem before it becomes a hazard. Now, that won’t always be the case, as excavations and wiring mistakes can also cause an open neutral, but I’d say that the vast majority develop slowly over time.

5 Likes

That’s a great point @pswired and it begs the question: can the Floating Neutral fault detection lab probe the data deeply enough that in some cases the slow neutral degradation can be identified and “failure” preempted.

This reminds me of solar analysis to demonstrate panel degradation vs fixable weather effects like snow and dust. Hope Solar Labs are coming!

1 Like

My lights flicker when my instant on water heater turns on. I’m pretty sure it’s on 2 240v circuit breakers.
Sense has said nothing so far

@winfield100 Do you have a tankless water heater? I ask because these heaters can draw so much power that they can affect the voltage being delivered elsewhere in your home while running, which can cause lights to flicker. I’ve seen suggestions from folks to upgrade lightbulbs in this scenario, and if that doesn’t work, consulting an electrician might be the best move.

Upon further looking, we realized the flickering lights when the tankless water heater goes on, are LED’s on a dimmer switch.
It appears to be the dimmer
Thank you for your kind response

1 Like