How to use your Stray Current Sensor (SCS)


Marine Surveyor’s of North Georgia Stray Current Sensor (Ground Fault Sensing Module) Installation, Testing and Operation.

First: The dock pedestal connection is checked for voltage, polarity and ground systems to ensure there is not a problem with the dock wiring or the physical connection. I use the Ideal Circuit Analyzer with adapters to do so. Vessel must be considered to be in serviceable condition with no apparent electrical  issues like blowing breakers, lights going dim, smelling smoke! That is “not” what the sensor is built for. Both pedestal and vessel breakers are turned off before installing the sensor. Connect the pedestal and SCS receptacles first (turn right) and pre-load the cable end so it  holds the connection in the lock position. Install the cable lock around the pedestal then through the enclosure wrist pin and pull tight. Cable lock also takes the weight off of the connection, prevents the sensor from falling into the water and secures it for days while being rented. Then connect the vessel shore power cord and SCS receptacles and must be made with a tightened coupler and seal ring. Check the vessel connection as well before you start testing.

Second: With all breakers off at the dock and the boat, the sensor is installed between the dock pedestal and the owners shore power cord. The dock side breakers are then turned on and the sensor is tested by pressing the test button. Once the sensor audio and visual alarm is activated manually by the test button the sensor is then reset by pressing the reset button and the audio and visual alarm turns off. The sensor is now on standby for monitoring the vessels AC systems.

Third: The surveyor, electrician and / or owner then operate all of the AC appliances by turning on the vessels breakers one at a time and manually turning on the appliances and components. When testing intermittent appliances and components they have to be operating automatically. Refrigerator door is opened so it turns on, the hot water faucet needs to be opened to flow cool water through the hot water heater to activate it, twelve volt systems need operated to get the battery charger to turn on. Inverter systems are a big concern and have to operate their internal battery charger. Any other systems that turn on automatically must be tested when running. The reason why chargers and inverters are extremely important to test is because they are directly dumping the AC current into the DC side through their operating circuit board when faulty. These appliances and components are the most common source of electricity entering the water through the bonding system or a direct connection to the DC electrical system. This is very dangerous if not lethal for someone entering the water near a vessel that is considered “HOT”.

Fourth: Once the stray current sensor audio and visual alarm activates from sensing a ground fault exceeding .030 ma, (ABYC and NFPA threshold requirements) a clamp meter is then installed on the external wiring of the sensor enclosure. These external wires are hot and neutral only “without the ground wire for a clean signal” for the clamp meter to measure the actual amount of stray current in the vessel.  You then clamp meter the ground wire only to get your second reading. These numbers combined should cancel each other out. Meaning a 1.250 amp reading in your hot and neutral wire and a 1.250 amp reading in your ground wire tells you the ground is good and the Stray Current of 1.250 amp is going back into the dock shore power system as it should. If the numbers do not add up to be the same the difference is going into the water. If there is a reading in the hot and neutrals and “not the ground wire” the ground system for the vessel must be checked immediately before any more testing is done with power to the vessel. Turn the dock and vessel breakers off before continuing.

The ground wire and in-line galvanic isolator (if present) need to be tested with an ohms meter to ensure the ground fault wire connection from the boat to the dock pedestal is good. Disconnect the sensor bullet connector for the ground wire and then locate the ground bus bar behind the main panel. Install an ohms meter in between. You must know the ohm resistance of the galvanic isolator (if present) to ensure proper operation and continuity and is usually labeled on the unit itself. Once the ground is properly inspected and repaired if necessary you can now go back to testing the vessel.

One thing for sure if the clamp meter is registering a higher reading with every breaker you turn on then there is a direct connection of the neutral wire and the AC ground system somewhere in the vessel. This connection is usually installed deliberately and is found behind the main breaker panel and must be disconnected immediately after the dock main breakers and vessel main breakers are turned off as the vessel is not wired to ABYC, NFPA standards or NEC codes. Sometimes the neutral and ground connection it is very difficult to find and could take hours to find it. Old air conditioner electric fan motors are a big problem because they scatter metal brush dust throughout the inside of the grounded steel housing of the fan motor creating a neutral and ground connection.

The only time an AC ground wire is to be connected to a AC neutral wire in a marine environment is at a power supply. Simply stated only what creates or provides AC power, marina transformer feeding the dock power, generator and inverter.  Not what uses power, washer, dryer, hot water heater etc.

Fifth: Once the components that are creating the stray current sensor alarm to activate are located it must be confirmed the appliance or component causing the sensor to activate does not have a (green) ground and a (white) neutral “connection”. Some product manufactures and / or electricians will make that connection not knowing the ABYC, NFPA standards and NEC code that stipulate to never connect the two. Connecting the ground and neutral wires apply to house hold wiring and house hold appliances only. Neutral wire electricity directly dumping into the ground system will activate the stray current sensor alarm.

Sixth: When all appliances are operated on board and the sensor does not activate use the three prong male plug that deliberately has a neutral and ground connection wire looped out and back in the plug. Plugging into any powered 15 amp receptacle will create a ground fault and set off the sensor to prove that it is monitoring the AC system. You must first make sure the outlet is wired correctly and there is no reverse polarity so when you plug in the three prong plug with the neutral and ground connection it does not short out and hope fully popping a breaker. If the breaker does not pop for any reason that could start a fire on board the boat. So make sure whatever outlet you plug into does not have reverse polarity.

Seventh: It is suggested that the sensor is left connected to the vessel for a couple of days when the owner is staying on board. The owner will now be able to test the vessel for a long period of time manually and giving intermittent appliances and components time to cycle several times to prove themselves to be operating correctly. If the sensor does not activate the alarm in this period of time the vessel can be considered eligible to remain docked at the marina or private residence and connected to the dock shore power supply.

In addition: Vessels should be tested for AC stray current at least once a year with a clamp meter with all AC electrical appliances running for a quick reference for proper or improper AC appliance and component operation. Clamp metering is not as precise a measurement for stray current as the “Stray Current Sensor” ground fault sensing module because clamp metering the entire cord involves the ground wire. The ground wire will distort the magnetic field reading for the hot and neutral wiring from electricity entering it from either the owner’s vessel or another vessel attached to the same shore power daisy chained ground system. You can also get residual from the marina itself.

If you have any questions about how to operate or trouble shoot your vessels electrical system using the Marine Surveyor’s of North Georgia Stray Current Sensor please do not hesitate to call Mike Griffin Cell# 678-977-8844.