AC Grounding &/or Bonding

[Traveler 45C]

It seems that Hatt used the bonding ckts as the AC grounding path (green wire) in the older boats.

I replaced the water heater last night. Hatt supplied the hot and neutral wires in the usual fashion, but no grounding (green) wire. The heaters case was connected to the bonding ckt.

Is this the correct method of grounding/bonding by today’s standards? Or do I need to also run an additional grounding wire (green)?

[Traveler 45C]

Does Hat in their prints perhaps show where the ac ground goes?

Yes. My schematic clearly shows a connection between the heaters grounding (green) wire and the ship's ground bus bar. However, no such wire was connected to the heater, only the bonding wire (also shown on the schematic).

Given that the bonding ckt should also be connected to the ship's ground bus bar, electrically the heater is grounded. But something about this method bothers me. If something should go wrong with the bonding ckt there would not be a safe path for fault currents back to ground. It seems to me that having a redundant grounding wire ran directly to the ship's grounding bus would be safer. I just don't know if it is required or not.

[Nonchalant1]

It matters when your boat was made. Earlier Hatts did not have the isolation transformers so they were made with real grounding wires. In any case there is a difference between "ground" and bonding wires. AC and DC ground should be connected to the bonding system only at one single point on the boat.

[REBrueckner]

The above posts are essentially correct.
Nigel Calder has always called for the same essential ground to bonding connections for at least 30 years, isolation transformer or not. But there existed for a while a two wire system aboard some boats, called a floating ground used with an isolation transformer....in that case the negative is NOT grounded....its just brought back to the isolation transformer secondary. My prior 1961 Matthews had that system.

All ac ground wires should be brought together at an ac bus bar; all dc ground wires should be brought together at a dc bus bar. Then a single heavy wire is connected from each of those bus bars directly to a single point on the bonding system, usually to the thru hull bolt which is connected to an external copper ground plate if there is one.

The reason that a single point of connection is utilized between electrical grounds and the bonding circuit is to minimize stray electrical voltages and resulting currents which may cause zincs to deterioriate and underwater metals to suffer.

[Trojan]

At the panel in older boats not using an isolation transformer both black and white wires exiting the panel are terminated through a pair of breakers. All of the AC circuits are isolated. In the panel ahead of the breakers. The white and green wires are tied together. The green is used as a safety wire and for electrolysis protection.
With the use of the isolation transformer the white and green are still tied together and are treated the same except that the electrolysis protection is not required or provided.
It does not make any difference whether the voltage is 120 V or 240 VAC. They still require twin breakers for circuit isolation. The green is still used as a safety ground wire.
BILL

[Traveler 45C]

You are correct; the neutral and grounding wires should not be tied together onboard when power is supplied direct from the dock. However, they will be if power is supplied through an isolation transformer (at the secondary), the generator or inverter.

I don't have an iso xfmr.

It is my understanding that all equipment should have an insulated return to a common grounding point. Also that all equipment in contact with the water should be bonded.

In the event of a fault, the grounding wire would become current carrying and have a direct path to the grounding bus. If no grounding wire is connected, only a connection from the heater case to the bonding system (my boat's original setup), all bonded metal becomes hot.

Even though a connection to the bonding ckt is 'electrically' the same as connecting a separate grounding (green) wire, on a boat this shouldn't be done. No equipment should be using the bonding system as a ground return as these connections could possibly be at different electrical potentials due to the physical connections varying resistances and could induce stray voltages in the bonding ckt. A separate grounding wire direct to the grounding bus avoids inducing any stray currents.

Knowing all of this, it surprised me that there was no grounding wire provided for the water heater, only a bonding connection. Now that I'm thinking about it, there are no grounding wires to ANY elec outlet or the A/C system, I bet the fridge and stove are the same.

Maybe Hatt didn't know about stray currents back in '72.

[TedZ]

[QUOTE=Traveler 45C;143348]You are correct; the neutral and grounding wires should not be tied together onboard when power is supplied direct from the dock. However, they will be if power is supplied through an isolation transformer (at the secondary), the generator or inverter.


Well said but this is NEC talk and has been debated here to tears. The ABYC says one thing and depicts another. Many folk feel differently on these issues. TZ


I don't have an iso xfmr.

It is my understanding that all equipment should have an insulated return to a common grounding point. Also that all equipment in contact with the water should be bonded.


Agreed but this can become very confusing by not using the term "neutral" and "neutral buss." TZ


In the event of a fault, the grounding wire would become current carrying and have a direct path to the grounding bus. If no grounding wire is connected, only a connection from the heater case to the bonding system (my boat's original setup), all bonded metal becomes hot.


Well this trips breakers in allegedly all but the dock side power scenerio. Naturally one can see why it would be nice to wire grounds through to dockside in marine situations. It really boils down to whether our power pedestals in a marine world are really a sub panel. My contention, put a little differently is that the power pedestal source is our utility supply to the environment, our boats and should not be considered a sub panel. Then it becomes simple and safe. TZ


Even though a connection to the bonding ckt is 'electrically' the same as connecting a separate grounding (green) wire, on a boat this shouldn't be done. No equipment should be using the bonding system as a ground return as these connections could possibly be at different electrical potentials due to the physical connections varying resistances and could induce stray voltages in the bonding ckt. A separate grounding wire direct to the grounding bus avoids inducing any stray currents.


Of course. Again, "neutrals." TZ


Knowing all of this, it surprised me that there was no grounding wire provided for the water heater, only a bonding connection. Now that I'm thinking about it, there are no grounding wires to ANY elec outlet or the A/C system, I bet the fridge and stove are the same.

Maybe Hatt didn't know about stray currents back in '72.[/QUOTE

I don't know what Hatteras knew but it is a dynamic world and through mistakes and sometimes tragedies, standards get updated. TZ

Ted

[Traveler 45C]

Sorry, but not the neutrals TedZ. I was specifically referring to the grounding (green) wire, not the white one.

Without an iso xfrm, the neutrals on my boat should not be connected onboard.

[TedZ]

Great.

This confuses me...

"Knowing all of this, it surprised me that there was no grounding wire provided for the water heater, only a bonding connection. Now that I'm thinking about it, there are no grounding wires to ANY elec outlet or the A/C system, I bet the fridge and stove are the same."

and

"It is my understanding that all equipment should have an insulated return to a common grounding point. Also that all equipment in contact with the water should be bonded."


So you mean here that there are not two green wires assuming the bonding wire is green also. And the outlets only have a white and a black wire?

OK I wouldn't have guessed that was what you meant. My fault.

Ted

[Traveler 45C]

So you mean here that there are not two green wires assuming the bonding wire is green also. And the outlets only have a white and a black wire?

The heater has a hot (black), neutral (white) and bonding wire (green, connected to the bonding ckt), no grounding wire (green, insulated return to the common ground point). The outlets only have hot and neutral.

Sorry if I wasn't more clear or got my wire names crossed