Will current feed back through ground on a marina circuit? 1

[TLindy]

Hello, I'm new to this forum and look forward to interacting with the members here.

I'm participating in a boat club who owns a marina with 240 slips. We have on average 30 boats per transformer (this is key to my question below), with most on a 30 AMP breaker, but a few on a 50 AMP breaker.

The concern over preventing Electrical Shock Drowning has become a real priority for our club members. I'm part of the team that is undertaking an effort to researching the viability of installing Ground Fault Equipment Protectors (GFEPs), 30mA trip, at each pedestal. We've done a great deal of testing with our new Fluke 368 FC and have discovered numerous boats that are errantly discharging amperage back through the ground instead of the neutral wire (The ground should read zero on a boat).

The concern is: There may be danger to another boater on that same transformer circuit who may be working their electrical system.

My question is this: When there is a boat, or even several boats on the same transformer, who have errant amperage on their ground, are they causing amperage on the ground within all boats on that transformer?

Consider that they didn't unplug their shore power cord or at least turn off their main "house" breaker, and because they are part of the same transformer circuit, may they be in danger of shock while working with their own ground cable on their boat?

Thank you!!

TL

 

[VEBill]

Fresh or salt water?

Which location? Local electrical Codes and practices vary.

---

Related to boats sharing a common ground, consider also marine galvanic isolator devices.

 

[TLindy]

VEBill, thank you for your response.

In answer to your questions, Fresh Water and WA.

We are intimately familiar with galvanic isolators, and even more relevant to this scenario, isolation transformers. But the real question is, "When there is a boat, or even several boats on the same transformer, who have errant amperage on their ground, are they causing amperage on the ground within all boats on that transformer?"

Sure, with an isolation transformer, this is a non-issue when connected to shore power. But outfitting 240 boats with such devices is not in our purview.

We simply want to know if it's even possible for other boats on the transformer to be in danger because a boat may have errant current moving through their ground.

Thank you again.

TL

 

[waross]

Metal hulls?
Propellers? Rudders? Swim ladders?
If the current is going in the water it has to be coming out.
It may be returning through the ground grid.
If other boats have any connection between their shore power ground and their submerged metal parts they may be in danger.
Another issue is erosion of grounded metal in the water.

My question is this: When there is a boat, or even several boats on the same transformer, who have errant amperage on their ground, are they causing amperage on the ground within all boats on that transformer?

It depends on the nature of the fault causing the ground current. The other boats may be acting as a return path or they may be acting as a shared electrode.
That is, with one type of fault, the leakage current may be returning trough the other boats.
With another type of fault, it may be causing a voltage rise on the grounding conductor and all boats on the transformer will be leaking current to ground.
A bad fault on one boat may cause problems with nearby boats on another transformer.
Most likely yes.
I would be inclined to unplug all the boats on a transformer and then plug them and do a current check on each one individually.
Be aware that some boats may have a problem all the time, some may have a problem when their onboard main breaker is on and some may only have a problem when a particular piece of equipment is in service.
Thinking out of the box;
Will it be feasible to monitor the ground return current to each transformer and sound a very loud alarm when someone plugs in a faultily wire boat?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VEBill]

If the Neutral to Ground connection was only at the shore transformer (at the associated service panel), and if every boat maintained strict isolation of their Neutral (not tied to Ground at their boat), then that should eliminate AC ground return currents.

Does that align with boat Shore Power wiring standards?

It can get complicated when on-board inverters are added to the mix. They're a very likely source of stray Neutral to Ground paths.

 

[VEBill]

The safety issue can be this (an example):

A given boat has locally connected the Neutral and Ground (at their boat). One likely cause is their on-board inverter, where they switch off only the Hot when on Shore Power, leaving Neutral and Ground tied.

This in itself perhaps doesn't cause any immediate and obvious symptoms.

Then, after time passes, their Neutral wiring develops a fault such as a broken wire, or loose or corroded connection. Common with boats.

Now all the return current is on the Ground path. This could cause overheated ground wiring, or cause shocks if a person gets in the path from the faulty boat to Earth Ground. Still might not be immediately obvious with low power loads.

It gets worse if the boat's Shore Power wiring Ground also develops a break. At that point their hull might become live via whatever loads are switched on.

There are endless scenarios, which is why Wiring Standards are so complicated.

 

[dpc]

All shore power connections from the same transformer are interconnected. The ground wires will all effectively be connected together, even if the breaker at the pedestal is switched off. This can create issues in older boats where ac and dc wiring is not properly isolated, where neutral and ground connections are tied together and where on board inverters are paralleled to the shore power system. Shock hazards for persons in freshwater are increased with the boat ac systems are not properly grounded increasing the risk of the boat's neutral/ground reaching line voltage potential. Unfortunately, the interconnected grounds between boats can cause serious corrosion issues so many boat owners intentionally do not connect their boat ground to the shore power ground. This increases the shock risk. Electrical systems on pleasure craft are often a complete mess.

In the US, marinas are covered in Article 555 of the National Electrical Code. If the system is being upgraded, likely the entire system may need to be brought up to current code requirements.

 

[TLindy]

VEBILL and WAROSS, thank you! Exactly the response/answer I was looking for.

All 240 boats in our marina are in fresh water, and most are fiberglass, with many being wood, and only two being steel (65'+ boats).

With our Fluke, we have tested every boat "dim" or in a state that didn't require the user to turn every circuit on (We're going to require all circuits on in an upcoming club rule). We are looking at the NEC 555.3 threshold for ground fault not exceeding 30mA. On occasion, we find a massive differential between the hot and neutral in isolation from the ground (Home made 30 AMP shore power cable). Then we check hot against ground (excluding neutral) and find that almost all of the current is errantly (for a boat) flowing back out through the ground. Yikes!

VEBILL nailed it with "A given boat has locally connected the Neutral and Ground (at their boat)." In one case, we found the DYI electrician had crossed a ground with neutral in the addition of a new circuit in his boat. So when that circuit was lit up (Battery chargers were on that circuit, so it was almost always lit up) he's dumping a lot of amps out of his ground, instead of his neutral. You likely know, on boats, the AC ground is also connected to the DC ground side, which is then connected to engine and through-hull metals. Some/most current certainly will follow the ground, but there's still a differential from hot to ground that shows, 200+mA is discharged into the water. 100mA in fresh water/near proximity is almost always lethal.

I think you both confirmed that there is a POSSIBILITY (I stress "possibility") that an errant current coming from a boat, out the ground, can affect other boats on that same transformer circuit. This is just another bullet in my chamber for the necessity of our club to $pend the monie$ for a complete retrofit to 30mA GFEP's.

Thank you very much for the effort you put into my question.

As a Mechanical Engineer, I consider myself electrically ignorant. I know electricity exists (and am a big fan!), but the particulars are something I can contract out to someone who claims to be an expert

TL

 

[stevenal]

Please install the Ground Fault Equipment Protectors. Also look at the latest 2020 NEC requirements for marina power, since NFPA considers this an important issue. Link