Ship Shore Power and Earth Ground 1

[CGSmith]

When a ship is on shore power, is anyone familiar with the standard practice for providing an Earth Connection? ABS talks about a requirement as does DNV. The requirement is vague (just says an earth terminal/connection is required) and I’ve never actually seen one on the ships that I’ve worked. Where is this connection typically placed? Is it a receptacle or just a lug somewhere on the hull? Very curious to see if anyone has dealt with this before. Thanks!

 

[waross]

It is most effective as grounding conductor in the shore power cable.

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

 

[catserveng]

Here is a link to a paper discussing the topic, in its reference section are a number of resources on the subject.

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8387443

Most vessels I deal with use low voltage (440-460VAC) shore power connections with a ground conductor in the shore power cable and a ground pin in the shore power connector. On the ships side of the system the connector ground conductor is usually connected to a dedicated ground lug attached to a structural member of the hull.

A lot of discussion on this issue in coastal areas with strict air quality standards, as more vessels are required to use shore power when in port.

You didn't say is this was pertaining to a low voltage or high voltage system, for high voltage systems the best reference I know of is IEC/IEEE 80005-1 HVSC (High Voltage Shore Connection) Systems.

Hope that helps, MikeL.

 

[CGSmith]

Thanks! The ship power class is 450VAC. Shore power specified is 505VAC. I didn’t see a conductor in the receptacle for ground which is what is making me wonder. All lines appear to lead to the switchboards. I’m wondering where that ground would connect. I’ll read through the IEEE document....thanks!

 

[crshears]

See

https://www.dcms.uscg.mil/Portals/1...C-Std-Spec-8635.pdf?ver=2017-05-15-153700-043

and

https://www.dcms.uscg.mil/Portals/1...C-Std-Spec-0450.pdf?ver=2017-05-15-153703-030

Hope this helps.


CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[crshears]

Should add FWIW that back when I was involved with single-phase 120/240V shore supply to a vessel I recommended use of both an isolating transformer and a galvanic isolator.

Shore ground was at a minimum to be connected to one side of the galvanic isolator, and possibly to the neutral tap of IT supply winding, although whether this was required by Code I never did determine...

Ship's hull/chassis were to be bonded to neutral tap of IT load winding, its housing, its magnetic core, and the other side of the galvanic isolator.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

One cannot assume that ship shore power grounding is identical to on-shore grounding.
On shore, grounding or bonding is to provide life safety.
Ship grounding should also eliminate any current from the hull through the water to the shore ground.
Allowing hull currents to flow through the water will lead to rapid corrosion.
Case in point:
A wharf built of sheet piling was used for ships under repair.
When welding on a ship was required, the welders just ran one welding lead onto the ship and used a hull return through the water.
After two years the sheet piling had to be completely replaced due to corrosion damage.
If there is a neutral current due to unbalanced single phase loads, the current may divide between the neutral conductor and the ground connection.
Improper grounding may lead to corrosion issues.

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

 

[crshears]

Well put, Bill; that's where I was going as well.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]