Earth on ships Holding Oven

[splocious]

Hey all, just joiined the forum so please be kind. :Blushing

Ive not long started a job as a ships electrician and have been getting sent to the galley constantly to trace earths.

I have traced the earth to a holding oven. Oven works by keeping food warm from heating element submerged in water. This is obviously first port of call but

I cannot find any resistance to earth with the power off, however as soon as the power is on, earth indicator lights up. The element is also isolated by main switch so dont think it is the element.

Also, ships system is that of dual supply, ie both live and neutral are wires are live. For some reason at first contactor block, live wire is 230V and neutral is 5V. This should be 115V each.

Any assistance is much appreciated

cheers

 

[NozSpark]

Hey all, just joiined the forum so please be kind. :Blushing Ive not long started a job as a ships electrician and have been getting sent to the galley constantly to trace earths.

I have traced the earth to a holding oven. Oven works by keeping food warm from heating element submerged in water. This is obviously first port of call but

I cannot find any resistance to earth with the power off, however as soon as the power is on, earth indicator lights up. The element is also isolated by main switch so dont think it is the element.

Also, ships system is that of dual supply, ie both live and neutral are wires are live. For some reason at first contactor block, live wire is 230V and neutral is 5V. This should be 115V each.

Any assistance is much appreciated

cheers

Not that I've done anything on ships, or know how they are wired, it sounds like you have a centre tapped (earth) transformer... and I'd guesstat your problem is that you've lost your circuit earth or the earth to the piece of equipment that you are testing...... I guess you are testing WRT earth??

 

[Andy™]

Hey all, just joiined the forum so please be kind. :Blushing Ive not long started a job as a ships electrician and have been getting sent to the galley constantly to trace earths.

I have traced the earth to a holding oven. Oven works by keeping food warm from heating element submerged in water. This is obviously first port of call but

I cannot find any resistance to earth with the power off, however as soon as the power is on, earth indicator lights up. The element is also isolated by main switch so dont think it is the element.

Also, ships system is that of dual supply, ie both live and neutral are wires are live. For some reason at first contactor block, live wire is 230V and neutral is 5V. This should be 115V each.

Any assistance is much appreciated

cheers

sounds like a CTE supply. if you, you do not have a neutral. you have 2 lives. where are you testing the voltage to? if its earth, then it sounds like a dodgy connection. do you get the same readings elsewhere?

how have you tested the element to earth leakage?

 

[Evans Electric]

I'm all at sea with this one , sorry. :coat

 

[steptoe]

marine vessels are a totally different situation, and TBH not well covered I would think in this forum.

I have done a bit of work offshore, but I still dont think this will help you much.

on the installs I have worked on there is no fuse to blow (as such) but a light will indicate where the fault exists. no fuses to blow as that could be a safety issue as regards certain working.

remember, you may have a condition where the ship is somewhat like a car and uses negative earth.

what is you earthing arrangement,? IT.?

 

[septiclecky]

Hey all, just joiined the forum so please be kind. :Blushing Ive not long started a job as a ships electrician and have been getting sent to the galley constantly to trace earths.

I have traced the earth to a holding oven. Oven works by keeping food warm from heating element submerged in water. This is obviously first port of call but

I cannot find any resistance to earth with the power off, however as soon as the power is on, earth indicator lights up. The element is also isolated by main switch so dont think it is the element.

Also, ships system is that of dual supply, ie both live and neutral are wires are live. For some reason at first contactor block, live wire is 230V and neutral is 5V. This should be 115V each.

Any assistance is much appreciated

cheers

No neutrals on ships unless it is a 4 wire system.

Ships normally generate 400 volt 3 phase with 400/230 step down transformers so lighting circuits are across 2 phases to get 230 volts.

Gather you have the 3 light system on main switch board to check for earths so all 3 lights are half light when all ok but 2 are bright and 1 is out when you have an earth.

You will find that when the element is off it's ok but once the element is powered up the insulation breaks down and that is why a earth is being shown on the main switch board, just order and replace the element.

 

[splocious]

Thanks all,

Yes I am testing wrt Earth.

All terminal connections ok, been remade and problem persists.

Tested elements wrt earth and no leakage, They should also be electrically isolated when oven plugged in but powered off yet there is still an earth somewhere.

Worked offshore also and negative earthing system is used, doesnt explain 230V on one line and one 4 on other though in my mind.

 

[NozSpark]

Thanks all,Yes I am testing wrt Earth.

All terminal connections ok, been remade and problem persists.

Tested elements wrt earth and no leakage, They should also be electrically isolated when oven plugged in but powered off yet there is still an earth somewhere.

Worked offshore also and negative earthing system is used, doesnt explain 230V on one line and one 4 on other though in my mind.

It's like a disconnected floating earth... i.e. your earth wire is not connected to the transformer centre tap (at some point)

 

[splocious]

It's like a disconnected floating earth... i.e. your earth wire is not connected to the transformer centre tap (at some point)

Not quite following you. I understand that none of the lives are directly connected to earth as in a domestic sysem.

When measuring source 115V on each line when disconnected but 230V on one when connected and only 5 on other???

Forgive my ignorance if im being daft? :Blushing

 

[NozSpark]

It sounds like you have a centre tapped transformer with 115v, earth, 115v... giving you 230v across the outer phase taps. These voltage readings are are in relation to eachother, the 115 to earth.

Now if the earth wire is disconnected from the tranformer it's reference to the 115's is lost and it will float (with induced voltages from the phase wires!

HTH

 

[kme]

The septic 1 : +1

Is my memory too......a looooong time back (and I was comms then)

 

[septiclecky]

Not quite following you. I understand that none of the lives are directly connected to earth as in a domestic sysem. When measuring source 115V on each line when disconnected but 230V on one when connected and only 5 on other???

Forgive my ignorance if im being daft? :Blushing

Depending upon what voltage is used for lighting onboard ship eg 230v across terminals you should get approx 132v to earth on each phase when all is OK.

If you have an earth fault on one of the phases, depending upon which phase it is down to earth then when you test for voltage you would get 230v between terminals but would also get 230v on one terminal to earth but on the other terminal you would get 0v for a full earth fault if that phase is down to earth. If it is a partial earth fault then there is a partial voltage to earth on the phase to earth.

Remember when I first went to sea some 30 years ago it was all alien to me as shoreside electrics go straight out off the window and don't apply on ships when you have an earth fault.

 

[septiclecky]

It sounds like you have a centre tapped transformer with 115v, earth, 115v... giving you 230v across the outer phase taps. These voltage readings are are in relation to eachother, the 115 to earth.Now if the earth wire is disconnected from the tranformer it's reference to the 115's is lost and it will float (with induced voltages from the phase wires!

HTH

On ships no such thing as a Centre Tapped transfomer, transformers used are 3 phase Delta-Delta so no earth connection only earth connection is at ships genny.

 

[ProDave]

On a ship (made of metal) finding a Ground (better description than earth) should be easy, just about any bit of the ships metalwork will be ground.

You say you are "testing WRT earth" but which earth are you testing wrt?

If you have a probe on the case of the oven and are getting these strange results, then like others it sounds as though the oven has lost it's ground connection.

Try instead putting your ground probe on some part of the ships metalwork.

Check the earth continuity from ships metalwork to oven casing.

I assume they use some variant of 13A plugs and sockets, check the grounding at the socket and earth continuity of the oven's lead.

Also please explain what they mean when they send you to "trace earths" ?

Nobody is going to call an electrician and say "come and trace my earths" They are more likely to say come and find out why something is tripping, not working, or giving me an electric shock.

 

[Chr!s]

I was always led to believe that the system employed on ships was mainly a floating system

this would explain the difference in voltages on each line, i cant see it being a centre tapped 115 system though i may be wrong.

I think where earthed systems were employed the hull often had issues with corrosion.

Regards chris

 

[splocious]

On a ship (made of metal) finding a Ground (better description than earth) should be easy, just about any bit of the ships metalwork will be ground.You say you are "testing WRT earth" but which earth are you testing wrt?

If you have a probe on the case of the oven and are getting these strange results, then like others it sounds as though the oven has lost it's ground connection.

Try instead putting your ground probe on some part of the ships metalwork.

Check the earth continuity from ships metalwork to oven casing.

I assume they use some variant of 13A plugs and sockets, check the grounding at the socket and earth continuity of the oven's lead.

Also please explain what they mean when they send you to "trace earths" ?

Nobody is going to call an electrician and say "come and trace my earths" They are more likely to say come and find out why something is tripping, not working, or giving me an electric shock.

Ive been testing wrt the earth of the oven as opposed to the ships hull but that was after checking continuity and all was fine.

When asked to trace earths i mean, go to galley find offending appliance and then finds the cause of the earth and rectify.

ta

 

[ProDave]

Ive been testing wrt the earth of the oven as opposed to the ships hull but that was after checking continuity and all was fine.When asked to trace earths i mean, go to galley find offending appliance and then finds the cause of the earth and rectify.

ta

I'm sorry but to me "the cause of the earth" does not make sense.

What is the actual fault they are having? is something tripping, if so you should be looking for the cause of the fault.

If the oven shows good earth continuity then your supply can't be balanced at one point, and imbalanced at another, simply not possible.

 

[kme]

As previously said, marine systems are completely different to standard wiring, so much so that it can be difficult to "get your head around" the terminology & systemic quirks.

We used to crew minesweepers, and they had even odder wiring, as you couldn`t risk having a EM field around the hull, which could set off mines.

In fact, there were / are several "DG stations" around, which all RN vessels had to visit periodically, to have the hulls degaussed, specifically to counter mines.

Slightly off topic, just trying to illustrate that the correlation between ship- and shore- side electrics is almost nonexistant.

KME

 

[wozz]

I'm sorry but to me "the cause of the earth" does not make sense.What is the actual fault they are having? is something tripping, if so you should be looking for the cause of the fault.

If the oven shows good earth continuity then your supply can't be balanced at one point, and imbalanced at another, simply not possible.

i think he means the cause of the earth fault indicator to light, rather than as you say trip out which it may not do on a ship.

And kme post makes sense to me but that because i spend too much time watching the digital channel 'yesterday'. How we found out about the magnetic mine and de fused the first one is truely amazing.