Earthing On Boats.

[little lad]

I am a commercial catering engineer and was sent to do a repair on a commercial oven on board a ship. The fault was that someone had received a shock off the unit. On arrival found that water had over boiled on top plate and customer received shock. Unit is a 3 phase and earth between phases was 380v and to earth for each phase was 120v. All these reading were taken from buzz bar inside unit. On doing a continuity check could not get a reading. There is 13a outlets on the wall around the galley. I inserted a plug tested and it inicated no earth. I was wondering is the device correct (plug tester) also how does a earth actually work on a boat. I have advised the site not to use any appliances and that they should contact a marine electrician this is for personal needs.

Thanks.

 

[SLIPSHOD & SLAPDASH]

Maybe it needs an earth rod  :coat

 

[steptoe]

yer, boats are funny beasts wrt earthing arrangements,

is this a leisure craft?

oil rigs/RN etc etc work really different,

 

[Andy™]

FFS. your 'time served' and your asking if a plug in tester is suitable!? how about getting someone competent instead

 

[little lad]

Hi step toe. It's a a small cruise ship.

Hi Andy. If you actually read the post I actually advised the customer do this. Also with the plug tester was advised that the plug tester would not recognise a earth on a ship because the plug tester is not designed for testing on ships.

Thanks.

 

[Andy™]

a plug in tester is not designed for 'testing'. well, maybe for a DIYer

great for a quick visual indication of the circuit being live, but that about it

 

[steptoe]

Hi step toe. It's a a small cruise ship.

Hi Andy. If you actually read the post I actually advised the customer do this. Also with the plug tester was advised that the plug tester would not recognise a earth on a ship because the plug tester is not designed for testing on ships.

Thanks.

do you know what the earthing type is?

IT ?

what do you class as small? 200tonnes?

 

[little lad]

Hi Andy no not sure at all what time of earthing the ship has. Also not sure on weight but it is 45.7m long.. If that helps.

Hi Andy the tonnage is 1065.

 

[steptoe]

most marine systems of that sort of size work similar to a car,

ie, neutral is earthed to the chassis/hull

tbh, its fairly specialised stuff, and a long time since Ive had anything to do with it,

you need to ascertain if its fuse protected or continual service,

ie, on a rig, or RN ship when a fault occurs there will not normally be a fuse to blow, but a light to illuminate to show a fault,

why? well, you wouldnt want a gun platform on a destroyer to stop working in the middle of a battle, or a pump going down on a rig could have devastating consequences.

 

[septiclecky]

Well it's not TT, TNC or TNC-S for a start.

Ships normally don't have a neutral to get 230v it is derived from 3 phase 400-230 step down transformers.

Sounds daft but when I was at sea never knew a fuse/mcb to go on a earth fault even when the was a full earth.

Earth faults where shown on the main switchboard by 3 lamps, when all was OK all 3 lamps would be half lit but when a earth fault developed on a phase the other 2 would increase in brightness whilst the phase with the earth fault would go dimmer

 

[steptoe]

Well it's not TT, TNC or TNC-S for a start.

Ships normally don't have a neutral to get 230v it is derived from 3 phase 400-230 step down transformers.

Sounds daft but when I was at sea never knew a fuse/mcb to go on a earth fault even when the was a full earth.

Earth faults where shown on the main switchboard by 3 lamps, when all was OK all 3 lamps would be half lit but when a earth fault developed on a phase the other 2 would increase in brightness whilst the phase with the earth fault would go dimmer

yer, that would be the norm on a normal ship for fault 1

on some when fault 2 occurs there may, or may not, be a fuse.

 

[apprentice87]

Hi All,

Out of interest, if it is 380 between phases, how is it only 120 between any one phase and "earth"?? should it not be 220, especially if neutral is tied to "earth" [the hull]

Could the neutral have come disconnected from the hull, so now, it is floating about all over the place, [tis on a ship!! ha ha] dependant on the way loads are balanced between the phases?? or do ship electrics not work like that.

If a ship does not have the usual OCPD's. how do they "contain" faults, you know, so that a simple fault in a gun platform for example, does not burn out miles of wiring???

 

[Steve3948]

Well if you've ever watched the "Deadliest Catch" many boats seem to have burn outs in control panels and mcb boards.

Interesting thread this though as I have never done any work on any kind of floating vessel and never really thought about it.

 

[septiclecky]

Hi All,

Out of interest, if it is 380 between phases, how is it only 120 between any one phase and "earth"?? should it not be 220, especially if neutral is tied to "earth" [the hull]

Could the neutral have come disconnected from the hull, so now, it is floating about all over the place, [tis on a ship!! ha ha] dependant on the way loads are balanced between the phases?? or do ship electrics not work like that.

If a ship does not have the usual OCPD's. how do they "contain" faults, you know, so that a simple fault in a gun platform for example, does not burn out miles of wiring???

If you read my previous posting ships don't normally have neutrals so it is not tied to earth as it would on land based installations.

To get 220v you go across 2 phases so a reading of around 120v to earth is correct

Marine Electrics are a totally different ball game to electrics shoreside

 

[SLIPSHOD & SLAPDASH]

If you read my previous posting ships don't normally have neutrals so it is not tied to earth as it would on land based installations.

To get 220v you go across 2 phases so a reading of around 120v to earth is correct

Marine Electrics are a totally different ball game to electrics shoreside

Thanks for that,  something new for me . I have never looked at 'boat electrics' and do not intend to in the near future.

 

[apprentice87]

Ooh, yes, thanks for that!! Learn something every day!!

john..

 

[Marvo]

most marine systems of that sort of size work similar to a car,

ie, neutral is earthed to the chassis/hull....

This is rarely the case unless the hull is non-metallic. Marine networks usually have a floating neutral (if there is a neutral..and excuse the pun) to help prevent corrosion.

 

[steptoe]

Well, you can call it what you want, I was only using the term neutral for simplification,

I'll say star point then from now on.

 

[NozSpark]

If a metallic hull was part of the electrical system then it would suffer really badly from galvanic corrosion and the sacraficial annodes would have to be enormous

 

[SLIPSHOD & SLAPDASH]

I am finding this thread very interesting , although it will probably be as much use to me as section 740.

I also  think my post,  #2  was highly amusing :coat