Earth Faults

LukeB · 04-19-2008, 09:04 AM

Hi,

Can anyone give me some advice on detecting earth faults on a insulated distribution system, 24vdc?

My electrical experience and knowledge is not that vast, and although I have some great electrical books, I would like to get some input from anyone out there that has exp with this problem.

Thanks..

K1W1 · 04-19-2008, 10:11 AM

Hi,

First of all how do you know you actually have an earth fault in your insulated distribution system ( I assume by this wording you mean the negative of your 24V System is not connected to the hull anywhere)

LukeB · 04-19-2008, 10:47 AM

Hi Kiwi,

Thanks for the reply. We have Earth Fault Indicators on the 24v panel, and as I understand when one light ( + or -) illuminates brighter than the other, this indicates that there is fualt. In my case, the + light has illuminated, which mean there is a fault on the negative side of the 24v system. I am not really sure of how to go about testing to see where the fualt is?
Thanks

K1W1 · 04-19-2008, 11:04 AM

Hi,

That's the answer was looking for.

You are going to have to turn off all your 24V Stuff one circuit at a time till you find the lights stay on the same.

A short cut might be if you know something that has been wet or a squashed/damaged cable amongst your 24V Stuff.

It can be time consuming but there is no really fast way to find it unless you get lucky with what I suggested above.

What is your boat made of?

The Reverend · 04-19-2008, 12:35 PM

I would suggest switching off all the circuits and then turn them on and off individually as the fault could be cumulative.

As mentioned above look out for things that can get wet or crushed.

K1W1 · 04-19-2008, 04:15 PM

Hi,

Turning everything off isn't a bad idea if you have no idea how long there has been a fault and there maybe several problems, I took it for granted that this guy was paying attention to his monitoring system and this was an early indication.

Also don't forget to include the engines and engine control system in your circuit isolation.

What brand of boat are you dealing with here? I ask this knowing that some well known boat builders use 24V Control for their switchboards and this could be very difficult to isolate in one go.

AMG · 04-19-2008, 05:33 PM

I once had this problem and it turned out to be the start motor for a Northern Light genset. The shaft inside had come out of position due to a material failure and caused an earth connection. Caused a lot of trouble too...

Because the starter was "tricky" at times, we replaced it and found out.

LukeB · 04-21-2008, 06:38 AM

Hi all,

Thanks for all your replies..
Firstly, Kiwi to answer your question, the boat has a steel hull. Secondly, as you mentioned, I have been through the entire 24v system as you mentioned however the fault did not leave. I take it, that this would imply that I have more than one fault?

As for how long the fault has existed. Checking for earth fault is party of my daily Eng/Rm check, so the fault is new. The strange thing is that I have not carried out any work on anything on the 24v system over the last week. I guess this could mean that it could be a terminal that has come loose due to vibraition or water ingress perhaps..

I will try switching off the entire system as the Reverend suggests and see if I have any luck that way.

cheers

Ju52 · 04-22-2008, 01:01 AM

Hi
if you have diffs between lights,

1. change the lights ... there are lights with different brightness :-)
2. measure the voltage ... should be the same, if not you have to search

If you have a wiring plan, start at the sources and measure the voltage at all points you can find. if you will find a voltage drop you are now near the leak

I hope this can help a little

AMG · 04-22-2008, 02:51 AM

Quote:

Originally Posted by Ju52

Hi
if you have diffs between lights,

1. change the lights ... there are lights with different brightness :-)

For those who have not seen this kind of ground fault indicators, there are normally two yellow lights next to each other on a panel. When they glow with different brightness you have a problem. You can also have a pushbutton which makes them glow equal, to make it easier to see if there is just a small leak. We have had this installed by Alewijnse in Holland.

LukeB · 04-25-2008, 03:01 PM

still no luck guys...will keep you updated on my progress though. I havnt been able to give this 100% of my time as ive had a whole bunch of other maintenance projects to sort out..

C4ENG · 04-26-2008, 05:40 PM

I had a 24v earth leaks before in the ER of a larger yacht. I turned off all the breakers and looked through every thing I could imagine and came up with nothing. I had 2 contracting electricians then try to help me at seperate times with no luck. I gave up and decided the boat was just going to have to live like that.

TSI AV · 04-27-2008, 03:23 AM

Hi everyone,

My two cents:

1. Once I had a 24 V earth fault. Reason found: due to vibration, a "+" cable from battery was slightly damaged and was in touch with ship's hull.

2. Another time it was a battery charger.

3. Then it was in a fire detection system.

I trace such faults beginning with turning off all circuits, one by one.
If no results, start disconnecting lines in 24V system and measure resistances.

The "Earth fault detection system" itself may cause problem as well or give a false indication.

If Your system includes a traffo 220/24 - rectifier, charger then problems may be there.

Just take Your time, trace it logically, excluding circuits step by step.

P.S. Could be great, if You post some scanned drwgs if possible.

rgds,

Andrei

Electrospot · 05-03-2008, 04:13 AM

Hi there, be also aware for capacitors used in electronic equipment, they will be showed as an earthfault. Those capacitors are connected between neutral and earth and will be shown as a major fault. Electrospot.

K1W1 · 05-04-2008, 10:59 AM

Quote:

Originally Posted by Electrospot

Hi there, be also aware for capacitors used in electronic equipment, they will be showed as an earthfault. Those capacitors are connected between neutral and earth and will be shown as a major fault. Electrospot.

Hi,

Welcome to YF.

You have a good point in your post but I think it has been established here that the fault he is asking about is in the 24V DC System so the capacitors in electronic equipment should not be involved at this stage. When posting here please be aware that some of the people asking questions only have a very basic understanding of what the are asking about which is why they are asking for help. It is easy to confuse by suggesting complicated remedies when it is usually simple things that cause faults like these.

Please don't take my post as a criticism or any sort of personal attack it is not intended as such at all.