2PAC Mafia
Member
Hello,
last week I was working in a ferry boat for 350 passengers and at one electrical panel I saw a negative derivation to ground was indicated by a light.
I was checking that the derivation was probably caused by our company electronic system because when I switched off our power breakers the derivation light was off. I checked then our electronic system and I found -3V to ground. Our electronics installation always specify that negative of the battery must be isolated from ground, at least 4 Mohm. When I measured between ground and negative I measured 1.5 kohm aprox.
These boat has 4 engines with its electronic systems and only one of them was partially grounded (failure). I started looking for the partial short and I found that when I disconnected a cable harness going to the ECU the resistence changed and went to more than 4 Mohm so I supposed that caused the derivation. Then I checked again the light and it was still on, measuring with multimeter I still got the -3V.
My question is, how is possible that I got those -3V if I tested that ground and negative was already isolated???
Thanks.
last week I was working in a ferry boat for 350 passengers and at one electrical panel I saw a negative derivation to ground was indicated by a light.
I was checking that the derivation was probably caused by our company electronic system because when I switched off our power breakers the derivation light was off. I checked then our electronic system and I found -3V to ground. Our electronics installation always specify that negative of the battery must be isolated from ground, at least 4 Mohm. When I measured between ground and negative I measured 1.5 kohm aprox.
These boat has 4 engines with its electronic systems and only one of them was partially grounded (failure). I started looking for the partial short and I found that when I disconnected a cable harness going to the ECU the resistence changed and went to more than 4 Mohm so I supposed that caused the derivation. Then I checked again the light and it was still on, measuring with multimeter I still got the -3V.
My question is, how is possible that I got those -3V if I tested that ground and negative was already isolated???
Thanks.