Understanding old marine wiring gronding er, lack of.

[sparkyinak]

Hello all, this is my first post on the website. I am an electrician up in the fine state of Alaska.

As part of my duties, I assist in the upkeep of four floating bunkhouses that are on steel barges that were built in the 80's or early 90's.

My experience is in residential, commerical, and industrail wiring so I have taken a crash course in to the marine wiring whelm in the last few years. Although I am confident in my understanding on marine wiring, one thing that has been elusive to me is the grounding on these barges.

I have been trying to piece the history. These systems on the barges have been goobered and rehash to fit someones mood and I inherited their mess. Here is what I know and what I think.

I do believe when the barges were origionally built, the electrical system was a paralelled (2, 20kW gensets) ungrouded system. This is indicated to me by the fact the original control panel still has a ground fault detection system (no longer connected) and the electrical panels throughout break the neutral when open. What I believe is through the years as these systems were modified, the distribution system was converted to a grounded system but left the panels as they were so the breakers still open the neutral.

Since the system is a grounded system and the gensets are not paralled anymore, I feel that there is no need to break the neutral any more. I feel that the switched neutral is a relic of the old ungrounded days. I would like to do away with the switch neutral breakers since each neutral takes a space in their small panels and we are running out of spaces to add more.

Without putting anyone on the spot, is there any reason to keep on breaking the neutral on a grounded sustem that is on a steel vessel (barge)? If I do remeber correctly, emergeny electrical systems are ungrounded and require the ground detection systems and stuff. I do not have that requirement with my barges. Any thoughts? any insight would be muchly appreicated. Thanx

"Good judgement comes from experience. Experience comes from bad judgement." - unknown

 

[VEBill]

Would breaking the neutrals have anything to do with Shore Power hook-ups?

 

[sparkyinak]

doubt it. When on shore the bond is open on the barge and is bonded in the harbor.

"Good judgement comes from experience. Experience comes from bad judgement." - unknown

 

[flexoprinting]

I think the purpose of always breaking the neutral is for safety reasons, just in case a boat docks somewhere and the supply connection has been wired wrong.

If the neutral and hot get swapped the circuit will still be hot with only a standard breaker opening the black lead.

 

[sparkyinak]

A circuit breaker only protects what is down line from the breaker. Good or bad harbor power will not change it. The wiring within the barge will make the difference. I even scratched out a couple of senerios. Pending on several issues, either a double bond or shore power will trip, not the breaker on the panel unless I overlooked something.

"Good judgement comes from experience. Experience comes from bad judgement." - unknown

 

[VEBill]

It seems that you're assuming that because the neutral is being switched by the breaker, that it would only be disconnected via an overcurrent fault. My understanding is that it's intended to be opened at the same time as the hot, and therefore the breaker is the obvious, logical and safest place to open the neutral.

In other words, think about when the breaker is opened manually (for example).

Combined with un-trustworthy grounding and external power, it makes sense to open the 'neutral'.

 

[rovineye]

These are the recommendations from IEEE Std 45, (Recommended Practice for Installations on Shipboard.)


11.29 Overcurrent protection of conductors
Except as otherwise recommended in 7.8 and 18.3 (steering systems), overcurrent protection by fuses or circuit breakers should be provided for all ungrounded conductors. Fuses should not, and circuit breaker overcurrent trips need not, be provided for the neutral conductor of a three-wire grounded system, but provision should be made for feeder disconnect including the neutral.
The purpose of overcurrent protection for conductors is to open the electric circuit if the current reaches a value that will cause an excessive or dangerous temperature in the conductor or conductor insulation. A grounded conductor is protected from overcurrent if a protective device of a suitable rating or setting is in each ungrounded conductor of the same circuit. For ac systems over 600 V, fuses should not be used for overcurrent protection.

7.8.3 Feeder cables—overload and short-circuit protection For each distribution circuit, a circuit breaker with a pole for each conductor should be provided, except for three phase grounded systems where the grounded conductor need not be opened. Circuit breakers of the power or molded-case type should be used and are preferred. Fused switches may be used up to 200 A. Overcurrent protection should be provided for all ungrounded conductors. Fuses should not be, and circuit breaker overload trips need not be, provided for the neutral conductor of a three-wire dc grounded system.

 

[flexoprinting]

Hi guys

See the 2nd page.

http://bluesea.com/files/resources/technical_briefs/ten_deadly_conditions_part_2.pdf

 

[sparkyinak]

Thanx for all the good info. I do inderstand all this. The issue I have is I think I know why they broke the neutral at each circuit not just the feeder. I feel thet it is a relic of an old ungrounded system. It is that I am not 100% certain of it and if I go replace it and missed something. I would be in deep doo doo. I may have a lead on the original construction drawings which I am chasing as we speak. Thanx

"Good judgement comes from experience. Experience comes from bad judgement." - unknown