Electrical/galvanic Isolator Query

[JohnGH]

A friend has a boat that is new this year. The galvanic isolator has 2 red LEDs with are on, but not fully. They go off when the inverter is switched off, but as he is running a 240v fridge, the inverter is on most of the time. His understanding is that if the two lights are on then there is a leak. So my questions are: what exactly is an electrical leak and what can be done about it? I guess it might be nothing to worry about, but it would be good to know.

 

Any advice/explanation would be appreciated thanks.

 

John

[smileypete]

Best first step might be to buy a simple socket tester and plug it in when the inverter is running.

 

IF it shows 'no earth' then it's likely the inverter lacks a proper neutral to earth bond and that needs sorting for safety reasons, if the boat was bought new with inverter included the builder should have sorted it.

 

This is the sort of tester, the type with three lights, any leccy parts distributor/Maplins/Screwfix/Toolstation/Ebay should sell them:

 

http://www.amazon.co.uk/Green-Mains-Socket-Safety-Tester/dp/B003337BLM

 

Or get someone competent with mains to measure the earth to neutral voltage when the inverter is running, it should be 0V.

 

cheers, Pete.

~smpt~

Edited August 4, 2013 by smileypete

[nicknorman]

That shouldnt happen! It means that there probably a wiring fault somewhere. The LEDs illuminating means that some current is flowing from/to shore on the earth line. What I find confusing about your post is that presumably if he has the inverter on, he is not plugged in to shore power? If he is not plugged in to shore power and the GI LEDs come on, there is something fundamentally wrong with the electrical installation.

Edited August 4, 2013 by nicknorman

[by'eck]

A friend has a boat that is new this year. The galvanic isolator has 2 red LEDs with are on, but not fully. They go off when the inverter is switched off, but as he is running a 240v fridge, the inverter is on most of the time. His understanding is that if the two lights are on then there is a leak. So my questions are: what exactly is an electrical leak and what can be done about it? I guess it might be nothing to worry about, but it would be good to know.

 

Any advice/explanation would be appreciated thanks.

 

John

 

Think of a galvanic isolator as a low step that interrupts small stray voltages in either direction that otherwise may cause galvanic corrosion to the hull. Greater voltages are free to jump over the step so the earth connection its inserted within is maintained from a safety point of view.

 

FWIW this is achieved by back to back diodes.

 

The red LED's are there to indicate a fault with the earthing system or unit. Depending on model usually both on indicate an AC current leak, one on a DC leak.

 

To check unit disconnect shore power lead then use a digital multimeter set to diode test. It should give a reading around 900 to 1000 with probes in either direction with no more than 10% difference.

[blackrose]

If he is not plugged in to shore power and the GI LEDs come on, there is something fundamentally wrong with the electrical installation.

 

Or just something wrong with the GI installation? It should have been installed between shore earth and the consumer unit but it sounds like the inverter is running through it too.

 

http://www.safeshoremarine.com/assetts/diyinstallguide.pdf

 

That doesn't show the earth bond to the hull which should be on the consumer unit side as shown in this link:

 

http://www.safeshoremarine.com/diagram%20for%20earth%20wiring.pdf

 

I think the Smartgauge site has some better diagrams.

Edited August 4, 2013 by blackrose

[JohnGH]

Thanks for your replies, useful if a little over my head. Will pass the information on.

 

John

[trackman]

Galvanic corrosion, which is what the GI is there to protect against, will normally only happen if one is using a landline. It occurs when current from the landline circuit leaks through the hull to earth instead of going the proper way via the electrical circuit.

A GI is therefore only required when using a shore electric supply. It shouldn't be active when an inverter or generator on the boat are used as the electrical source.

As already remarked in other replies, it sounds as though there is a fault in the installation.

Of course, in the unlikely event of the boat being moored near an electrified railway or tramway, there might be other sources of galvanic corrosion, but they would probably not light up LEDs on a GI!