You sank my battleship?

[RampyElectric]

Ok here I am again.... my boss and I have another bet. Help me out guys.

A warship has electrical systems, which I assume are all bonded....but to what....the generator or source? What about the steel hull?

 

[petersonra]

warships are generally ungrounded. can't take a chance a ground fault would trash some critical system in the middle of a battle.

 

[hardworkingstiff]

So who won? Anyone? Did one of you say it was ungrounded?

 

[iwire]

Our Charlie B used to design ship board electrical systems, I don't know how much he can post about them.

I agree with Bob that most systems will be ungrounded and make use of fault lights.

 

[RampyElectric]

well not exactly, I am worse off than he though.... I said it was not only bonded.....but that it was bonded to the source/generator....but that I thought the hull would have to be bonded.

He said it would be bonded to the propeller.

ok this makes me wonder...how are overcurrent conditions or short circuit/ground faults cleared?

 

[hardworkingstiff]

ok this makes me wonder...how are overcurrent conditions or short circuit/ground faults cleared?

The 1st one is not cleared, but a fault indicator is displayed and it's time to locate the fault. A 2nd fault will start things popping.

 

[iwire]

well not exactly, I am worse off than he though.... I said it was not only bonded.....but that it was bonded to the source/generator....but that I thought the hull would have to be bonded.

He said it would be bonded to the propeller.

ok this makes me wonder...how are overcurrent conditions or short circuit/ground faults cleared?

I would expect all non-current carrying metal parts to be bonded together but never connected to the source(s).

Faults are not cleared in the conventional sense.

The first 'ground fault' will bond the source to the hull, this will not cause a trip but it should alert maintenance to go find the problem and fix it.

Keep in mind I am just going on how a landbased ungrounded system works, I may be off base with a ship.

 

[Rockyd]

See 240.12 and 240.13 for shipboard logic.

 

[tom baker]

Even though I was a mechnic in the Navy, we were taught that you can still get shocked from the ungrounded electrical system. There is no system bonding jumper, but the shock is from capacitacance (SP) charge to the metal hull. There were ground detector lights the electricians would monitor. The ships I was on, Bainbridge and Enterprise, were 440V. The Nimitz class and later are 4160V, as they had two reactors, were the Enterprise had 8. Everything was much bigger on the Nimitz. Charlie B was a electrical divsion officer on the Nimitz.
The next gen nuclear carriers will probably have electric motors (VFD) instead of tubines, as you can put the engine rooms anywhere with out regard to the prop shaft. If I recall the Enterprise main engines are 200,000 shaft hp. Top speed is 30 knots plus and much higher, as the enterprise has narrower hull than the Nimitz. The bainbridge is now razor blades. The Big E will likely be retired when the next generaton carrier is out. By the way there are 12 nuclear carriers with a crew of 5,000 w/ air wing.
Oh and the 120V circuits had two fuses. What I don't know is if they use GFCIs.

 

[Rockyd]

Tom,

I know where the "other Washington" is. Did sea trials and and was part of E division on a new Sub-tender we picked up at the yard in Bremerton. Do wonder if the "selective tripping" of breakers really held water - we had an FPE swithboard! We could only run thee of the four generators if we had switchboard all tied together, without exceeding specs.

 

[LarryFine]

What I don't know is if they use GFCIs.

Or AFCI's in the sleeping quarters.

 

[RampyElectric]

ok so let me see if I understand. If I had an outlet in my quarters....and the ungrounded conductor makes contact with the box or the ship's hull.....it would basically just stick there and the electricians mate would see it on a warning panel and come by and make a repair..... but where does the touch voltage go? And why does it take a second fault to disconnect the circuit?

 

[charlie b]

I am coming into this one a bit late. OK, here is some info that comes to my memory. But I can?t assert the percentage of truth in any of it. My last days of ?haze grey and underway? are 22 years in the past.
1. US Navy shipboard 120 volt systems are not grounded.
2. There is a ground detection system that will tell you if a single phase has an undesired connection to the hull. It is checked at least once an hour. It is possible that more modern ships have an automatic ground detection system, but I have no facts to offer on that topic.
3. All non-current carrying metal parts of all electrical systems are bonded to the hull. This could be with welds, bolts, or bond wires.
4. An overcurrent condition will trip the breaker in the due course of time, just as it would in a shore facility.
5. A short circuit will clear by immediately tripping the breaker. But that?s the same as shore facilities. By ?short circuit,? I am referring to Phase to Neutral or Phase to Phase.
6. The first ground fault will not clear, as several members have already described. The intent is that that first ground fault should be detected and isolated, before the second ground fault occurs.
7. The reason for an ungrounded 120 volt system is to maintain operation under battle conditions.
8. You can be electrocuted by touching a hot wire in an ungrounded system. Tom was right, and his reason was also right. But he misspelled ?capacitance.?
9. Fault coordination (i.e., the breaker nearest the fault trips first) is a design criterion. I have never had the opportunity to perform a fault coordination study for a vessel, Navy or otherwise. So I can?t give any information on how well it works.
10. During the time that I worked in the Marine Engineering arena, the most significant difference that I noticed in non-navy ships has to do with oil tankers. Any 120 volt branch circuit that has wires cross through what we would call a ?Class I Location? must have a breaker with a switched neutral. It?s like a 2-pole breaker, but the second pole does not connect to the ?other? phase. Instead, the second pole connects to the neutral bar. This requires a special construction of the panel.

I guess that?s enough sea stories for now.

Charles E. Beck,
Commander, USNR, Retired.

 

[iwire]

ok so let me see if I understand. If I had an outlet in my quarters....and the ungrounded conductor makes contact with the box or the ship's hull.....it would basically just stick there and the electricians mate would see it on a warning panel and come by and make a repair

First both conductors are ungrounded conductors.

The conductor will not flash like a normal short, you may see some spark from the capacitance Tom mentioned but no big boom.

..... but where does the touch voltage go?

Assuming the conductor stays connected to the hull now the entire ship is at the same potential as that phase that is now bonded.

It could stay like that forever.

And why does it take a second fault to disconnect the circuit?

Lets say the above short was on phase A, if the next fault is also on phase A nothing will happen. If on the other hand the next fault is on B or C you will have a phase to phase short through the hull and a Overcurrent device will have to open.

The advantage to the system is a single fault will not keep anything from operating.

 

[charlie b]

If I had an outlet in my quarters....and the ungrounded conductor makes contact with the box or the ship's hull.....it would basically just stick there and the electricians mate would see it on a warning panel and come by and make a repair

Correct. But the on-duty EM might not notice until the next time he or she took the hourly readings, and manually pushed the ground detector button.

..... but where does the touch voltage go?

Not sure I understand this question. There is, as Tom said earlier, a capacitance between the hull and the wiring system. If you were to touch a hot wire, the charge present on the capacitor would discharge itself through your body. If instead a hot wire makes a direct connection to the hull, that capacitance would be discharged through the point of connection.

And why does it take a second fault to disconnect the circuit?

You have no doubt seen systems that are grounded at points other than the center of a Wye. The ?corner grounded delta? and the delta that is grounded in the center of one winding are two that come to mind. A shipboard ungrounded delta system would just become a corner grounded delta, if you ground one phase. There is no fault path, no ?low resistance path? for current to flow from the source back to the source. Tell me what would happen to a corner grounded delta system, if you connected one of the other corners to ground? A fault, right? A breaker trip, right?

 

[RampyElectric]

wow.... man you guys blow me away. Its like have 10's of thousands of electrical brains to draw on. I get it now. Man thats neat. Thanks for the education, and thanks for not making me feel foolish for asking.
Aye Aye Commander.

 

[hardworkingstiff]

wow.... man you guys blow me away. Its like have 10's of thousands of electrical brains to draw on. I get it now. Man thats neat. Thanks for the education, and thanks for not making me feel foolish for asking.
Aye Aye Commander.

I feel the same way about this place.

 

[tom baker]

Thanks for helping out Charlie
Does any old Navy hand remember "120 volts your deadly shipmate?". I saw that many times at A school. If not that then victory at sea.

 

[NoVA Comms Power]

... Does any old Navy hand remember "120 volts your deadly shipmate?" ...

You don't have to be all that "old" to remember. :smile:

It was usually part of a double-feature, played along w/ a true "classic" ... Trial by Fire.

 

[charlie b]

But what was the name of that third film in the trilogy that all Navy personnel had to see? There was ?120 Volts, Your Deadly Shipmate,? and ?Trial by Fire,? and the story of the Melbourne/Evans collision.