Mike Dolt Enterprises
Mike Dolt Enterprises
User: Aelectric, Location: Mass
Asked on: Monday, July 28, 2025 at 7:21 am EDT
Answered on: Monday, July 28, 2025 at 7:21 am EDT
Question: I have a large lakeside residential project I am on where there is up to 6 volts between equipment grounding conductor and the lake. There is also a couple amps on the grounding electrode conductor. Someone got a little tingle at the lake, and we were called in to investigate. There are (2) services feeding the property (total 4 buildings on the property). The generator, 600 amp main (for house), 400 amp main (for guest house, barn, and entertainment building) are all located next to transformer outside. The service to the house is almost 500' away, the other buildings are between 125'-300' away. The house is the closest to the lake and has a ufer ground that is just under 1 ohm, so that seems good. The equipment ground we are referencing voltage to the lake comes from the house. The odd part, is that as you increase load in the other 3 buildings, that voltage reference to the lake increases. Im not sure how often or even if this is an option but if the transformers neutral isn't perfectly center tapped, would that be enough to trickle some voltage back out to ground at the main service equipment area? Having a hard time figuring out why the 3 smaller building load increases the voltage and current at the main house. I was going to lift the equipment ground that is feeding the main panel in the house and see if that stops the voltage to the lake, identifying that is sending voltage in from main up by the transformer or if its coming from the house. Any other ideas would great and appreciate your thoughts. Thanks
Okay, this is a complex and potentially dangerous situation. Let's break down the problem and explore potential causes and troubleshooting steps. Safety is paramount. If you're not 100% confident in your abilities, consult with a qualified electrical engineer specializing in grounding and bonding before proceeding. Do not work alone.Understanding the Problem Voltage to Lake
The 6 volts between the equipment grounding conductor (EGC) and the lake is a significant concern. Even a small voltage difference can be dangerous, especially in a wet environment. This indicates a current flow in the grounding system, and the lake is acting as a low impedance path to ground.
Current on Grounding Electrode Conductor (GEC)
A couple of amps on the GEC is also indicative of current flowing through the grounding system. The GEC should only carry current during fault conditions or under unusual neutral imbalances.
Load Increase Effect
The fact that increasing the load in the other buildings increases the voltage reference to the lake at the main house is a key clue. It points to a shared grounding path and a neutral-ground voltage issue somewhere in the system.
Ufer Ground Resistance
The Ufer ground resistance of under 1 ohm at the house is excellent locally. However, it doesn't negate potential problems elsewhere in the system.
Tingle at the Lake
The "tingle" is the real-world symptom that demonstrates the risk and seriousness of the situation.
Potential Causes and Troubleshooting1. Neutral-Ground Bond Issues
This is the most likely culprit.
Multiple Neutral-Ground Bonds
There should only be one neutral-ground bond per service at the service entrance. If there are additional neutral-ground bonds elsewhere in the system (subpanels, generators, or other buildings), circulating currents will occur, flowing through the grounding system.
Check EVERY subpanel, the generator, and all other buildings for improperly installed neutral-ground bonds. Look for neutral (white) wires connected to the ground bus in subpanels. The most common cause is incorrect wiring in one of the subpanels. Compromised Neutral Conductor
A loose, corroded, or undersized neutral conductor somewhere in the system can cause a voltage drop, forcing current to return through the grounding system. This can be exacerbated by increased loads. Check all neutral connections at every panel and device.
Transformer Neutral Imbalance
As you mentioned, if the transformer's neutral point isn't perfectly centered, it can cause a slight neutral-ground voltage. While this is possible, it's less likely than multiple neutral-ground bonds or a compromised neutral conductor to cause the symptoms you're seeing. Have the utility company check the transformer.2.
Ground Faults
Hidden Ground Faults
A small ground fault in any of the buildings (perhaps in a wet location, a faulty appliance, or damaged wiring) could be injecting current into the grounding system. Use a megohmmeter ("megger") to test the insulation resistance of branch circuits and equipment in each building.
Equipment Grounding Conductor Issues
Check the continuity of the equipment grounding conductors throughout the entire system. Ensure they are properly sized and securely connected. A loose or broken EGC can force fault current to find alternate paths to ground (like through the earth and lake).3.
Stray Voltage
External Sources
Less likely, but consider whether external sources of stray voltage (nearby power lines, other electrical equipment) are contributing to the problem.
Troubleshooting Steps (Proceed Carefully and Methodically)1. Visual Inspection
Start with a thorough visual inspection of every electrical panel, subpanel, the generator, and the service equipment. Look for: Loose connections Corrosion Overheating Improper wiring (especially neutral-ground bonds in subpanels) Damaged or undersized grounding conductors2.
Voltage Measurements (with a high-impedance meter)
Neutral-Ground Voltage at Each Panel
Measure the voltage between the neutral and ground buses at every panel (main service, subpanels in each building, generator). Significant voltage differences indicate a problem. The voltage should be low, ideally near zero, at the service entrance. Elevated voltage in subpanels indicates a neutral current issue and that there are likely multiple neutral ground bonds.
Voltage Between EGC and Lake
Reconfirm the 6 volts between the equipment grounding conductor at the house and the lake.
Voltage Between GEC and Earth
Measure the voltage between the grounding electrode conductor (GEC) and a remote earth ground (use a ground rod driven far away from the existing grounding system). This can help identify the magnitude of the ground current.3.
Current Measurements (with a clamp-on ammeter)
Current on GEC
Reconfirm the 2 amps on the grounding electrode conductor.
Current on Individual Grounding Conductors
Use a clamp-on ammeter to measure the current on the equipment grounding conductors in each building. This can help pinpoint the source of the ground current.4.
Isolate and Test
Lift the Equipment Grounding Conductor
Carefully and temporarily disconnect the equipment grounding conductor at the house main panel. Monitor the voltage to the lake. If the voltage drops significantly or disappears, the current is likely coming from the service equipment area (where the transformer is). If the voltage remains: The current is likely originating within the house itself. Start checking branch circuits for ground faults. If the voltage disappears: Proceed to the next step.
Disconnect Feeders to Other Buildings
One by one, disconnect the feeders to the guest house, barn, and entertainment building at the main service equipment. Monitor the voltage to the lake. When the voltage drops, you've likely isolated the building with the grounding issue.
Isolate Branch Circuits
Once you've identified the building with the problem, isolate branch circuits within that building until you find the circuit that is causing the voltage.5.
Megger Testing
Use a megohmmeter to test the insulation resistance of branch circuits. This can help locate hidden ground faults. Disconnect electronics and motors before meggering to avoid damage.
Important Considerations NEC Compliance
Ensure that the entire electrical system is compliant with the National Electrical Code (NEC) and local codes. Pay close attention to grounding and bonding requirements.
Documentation
Keep detailed records of all measurements, tests, and modifications made during the troubleshooting process.
Professional Assistance
Do not hesitate to consult with a qualified electrical engineer specializing in grounding and bonding. This type of problem can be complex and requires specialized knowledge and equipment.
Utility Company
Contact the utility company and request that they inspect the transformer and service connections. They may be able to identify problems on their side of the service point.
Specific Steps to Take Immediately (Based on Your Description)1. Check for Neutral-Ground Bonds
Go to the subpanels in the guest house, barn, and entertainment building. Ensure that the neutral bus is isolated from the ground bus. There should be no connection between them (other than the EGC). If you find a connection (a bonding screw, a jumper wire), remove it.2.
Inspect the Neutral Conductor
Closely inspect the neutral conductor for the entire system (from the transformer to each building). Look for loose connections, corrosion, or damage.3.
Document Everything
Before making any changes, take photos and document the existing wiring configurations.
In summary, the most likely cause of your problem is multiple neutral-ground bonds in the subpanels, combined with a path for current to flow through the earth and the lake. Start by checking for and removing these bonds. If that doesn't solve the problem, proceed with the isolation and testing steps outlined above.Again, safety is paramount. If you are not comfortable performing these tests, consult with a qualified electrician or electrical engineer. Good luck, and please provide updates as you progress! Flag for review