220V Low Voltage Ship Supply

Have you read all you can in Wikipedia on this topic, Mildred?

You don't use the earth conductor for carrying current except during clearance of a fault. The answers to your questions are that, no, live to live is a single phase arrangement and they are not 110v to earth.

Amen....

GA from me too.

220 V is low voltage?

Yes. So?

No so! Here yes so!

Only by those that the skin has been toughened by salt water over a long period of time.

Actually low voltage is classified as any voltage less than 600V.

SAFETY BLURB: New NEC and OSHA regulations. require LV gloves be worn when working on any voltage greater than 50V.

You asked:-

Does this mean that the system is now a two phase system and the two phases are 180degrees out of phase? and would there now be 110v from phase to earth and 220v phase to phase?

In my Navy time, we transformed from 3 Ph. 440VAC (NATO Navy power standards) down to 120VAC phase to phase (if I remember correctly), for all domestic power and lighting. A Star/Delta transformer if I remember correctly.

Power is taken off across a single Delta field winding (if memory serves me!), between any two of the three connections L1, L2 and L3. My take is that its a single field and therefore a single phase.

Its a long time since I was in school for power Generation!!!

We never ever used a neutral.....simply not needed. 3 Phases and ground (the ship's hull....)

In my time, on 220VDC ships, the whole ships power was 220VDC for everything. Its also far less dangerous to life and limb.....(that will get someone "up in arms", but its true....!)

What is current (pun intended!) today I cannot say......Hopefully there is someone here more up to date....

Thanks for all of the input, I have been looking at some material. I found a drawing of what i am trying to explain i have attached it.

With reference to the drawing what would be the voltages provided to the circuits? I don't know how to calculate them, will some cancel due to different phase angles therefore it would be 110V?

I am also confused by what the circuit reference will be if both wires are 'hot' is there no reference and when one wire is positive the other is negative.

If these questions are stupid i apologise i have tried to read on my own some but i cant seem to gain the information i need.

All that circuit does is transform one set of RST in delta to a different voltage RST in delta. There is no earth reference, so your phase to earth voltages could be anything.

Positive and negative have little meaning in an ac circuit other than to look at something at any instant in time. Your voltages are alternating some tens of times a second. Nuff said?

The voltages across each of those separate single phase supplies will be 220v RMS, you will not see 110v anywhere there.

Google RMS voltage for more info on that term.

Some folks claim that because there are actually 2 phases then it should be called a 2 phase supply, but in reality, there is only one resultant sine wave voltage present, and so while single phase is arguably a better fit, the debate goes on.

As there is no earth connection to the transformer secondary then there is no earth reference for any of the live conductors.

A bit of reading on isolation transformers may assist you.

The common arrangement for achieving earthing and neutral is to have a star connected secondary with the star point connected to ground, but often a delta secondary is corner connected or even connected in high leg configuration.

Google those terms for more on the subject.

It's been a very long time for me since I sailed as Electrical Third but I seem to remember that with a Star winding from the center to each leg is based on 1.73. That is that each leg in a 220v system from center to end of leg would be 220 divided by 1.73 or 127 volts. All three legs should be feeding separate transformers and legs nearly of equal loads to keep a balanced situation.

You never, ever, never ground a shipboard electrical system

I think you may find yourself at odds with a number of authorities on that point.

Here's one Australian Maritime Safety Authority. See section 2.13 and particularly 2.13.1.2.2

Here's another DNV ship/HLSC electrical rules See section D400.

And another See section 2.1.4

Or this one Section 10.6.7

Or the Norwegian maritime authority See sections 3, 4 and 5.

shipboard electrical are floating grounds, no pun intending. Both black and white have voltage. Voltage will be measured to ground via capacitive coupling. If the hull were grounded, electrolysis would occur, in addition the hull could become charged posing a shock hazard to anything in the water

"in addition the hull could become charged posing a shock hazard to anything in the water"

I'm guessing that comment refers to when the vessel is connected to shore power as no such danger could exist if it were not.

So I will attempt to address the shore power issue only.

As seen by a person in the water, a ship's hull when connected to shore power becomes simply another class 1 single insulated appliance.

If this hull is not earthed and there is a sufficient leakage current to the hull due to failed insulation on the ship or similar cause, there will be a current flow back from the hull to the shore power main earthing conductor or to the general ground mass via the water (the shore power supply is referenced to that earth). Either way, the swimmer is in danger of electrocution.

Similarly, any person touching both the hull/superstructure and a grounded item on the pier, such as a gantry or the like would also be in peril.

Were no earth bond installed, an RCD may provide protection if there is one in place and working correctly, but the timely operation of an RCD even at 10mA is no guarantee of safety for a swimmer as, while the device may operate in time to prevent electrocution, the victim may be incapacitated for long enough to drown as many more vital organs can be traversed by the current due to the body's immersion.

Bonding of the hull to the shore power earth eliminates all of these concerns as the hull and earth are held at equal potentials and the mains breaker or RCD will operate if there is a fault detected.

It is for these reasons that bonding of the hull to earth is mandatory when connecting to shore power.

I'll repost that reply as I omitted a couple of key words that will make a difference to the intention. The changes are underlined for clarity

"in addition the hull could become charged posing a shock hazard to anything in the water"

I'm guessing that comment refers to when the vessel is connected to shore power via direct connection as no such danger could exist if it were not.

So I will attempt to address the shore power issue only.

As seen by a person in the water, a ship's hull when directly connected to shore power becomes simply another class 1 single insulated appliance.

If this hull is not earthed and there is a sufficient leakage current to the hull due to failed insulation on the ship or similar cause, there will be a current flow back from the hull to the shore power main earthing conductor or to the general ground mass via the water (the shore power supply is referenced to that earth). Either way, the swimmer is in danger of electrocution.

Similarly, any person touching both the hull/superstructure and a grounded item on the pier, such as a gantry or the like would also be in peril.

Were no earth bond installed, an RCD may provide protection if there is one in place and working correctly, but the timely operation of an RCD even at 10mA is no guarantee of safety for a swimmer as, while the device may operate in time to prevent electrocution, the victim may be incapacitated for long enough to drown as many more vital organs can be traversed by the current due to the body's immersion.

Bonding of the hull to the shore power earth eliminates all of these concerns as the hull and earth are held at equal potentials and the mains breaker or RCD will operate if there is a fault detected.

It is for these reasons that bonding of the hull to earth is mandatory when connecting to shore power if an isolation transformer is not used.

Very fine articles indeed. Page 14 of the Australian Maritime Safety Authority states that earthing for both AC and DC systems may be isolated and if so the steps taken to install them.

So we are both correct, but for safety of passengers, crew and hull, I prefer isolated "floating" systems.

There have been more than a few instances where swimmers have been electrocuted, both in marinas by faulty/defective wiring of adjacent ships, and along side boats with generators running.

As for using the hull for a DC return, that can lead to serious electrolysis, as well as interrupting the settings of a cathodic protection system. While the negative terminal is connected to ships hull nomimally through the engine block, a separate lead should be installed to prevent the hull from becoming a conductor.

There is really no such thing as an isolated hull, there will always be high impedance and capacitive couplings, and if that coupling becomes of sufficiently low impedance then shocks can occur.

The real problem with an isolated system is the necessity to detect and clear first ground faults as soon as possible. While the first one is not dangerous in itself, if it were to go uncleared and a second fault occurred in another phase or even in the other conductor of the same phase, then a fatality is possible.

While effective earth monitoring systems are generally employed on these vessels, the very fact that the first fault causes no inconvenience tends to make the operators complacent and slow to correct the fault.

Swimmers have been electrocuted in marinas due to incorrect use of earth bonding conductors or isolation transformers. An isolated hull with a first fault and no isolation transformer or earth bond to the shore can kill a swimmer. If the hull were using the IT earthing system that could not happen.

Again I make the point that the hull is not to be used for return currents, and have never said that it should be. The connection to the hull at one point only of the earth in an AC system, and the negative of a DC system will not cause any current flows or increase electrolysis in the hull.

I guess we will agree to disagree on this subject, but good debate anyway.

For me, none of your links worked.....with or without the "S".

As far as I remember, earthing a supply connection on a ship is considered an error and will need to cleared.

To "sense" these errors, a connection is made to ground via a low wattage bulb on each phase. When an earth fault occurs somewhere, the lamp will then light, the switchboard operator then needs to do some simple checks to find the area within the ship and send the electrician to the right area....

But I have never seen any other "deliberate" methods of grounding....possibly due to possible accelerated corrosion or something!!

Some good information here thank you. I suppose my question essentially was why, when using a meter to measure between ground (ships hull) and one of the live wires of the single phase, do we get a voltage of 110v.

to answer your question:-

"Because neither are connected to the hull...."