paulkirk avatar image

Earthing a Victron 500VA inverter

I have just purchased a Victron 500VA inverter and in the instruction manual, it states that the device must be earthed. Could someone who understands the product explain why please?

My application is as follows:

I have a small (2 m X 2m) wooden walled concrete floor remote building in the U.K. with no a.c. mains power. It houses some equipment related to astronomy -

a telescope mount requiring 18V DC supplied by a switch mode PSU

A camera requiring 12v DC supplied by a switch mode PSU

Some microcontroller related control hardware 5V DC - supplied by a switch mode PSU

a 300W , 240V dehumidifier for sucking the moisture out....

Because there's no a.c. mains, I've set up two 12v lead acid batteries in parallel and I charge these via solar panels and an MPPT controller.

The Victron 500VA inverter will be used to provide mains power from the 12V batteries and the SMPS mentioned above are powered by this.

Thanks very much for an explanation of why the Victron must be earthed.

victron products
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3 Answers
mikedonner avatar image
mikedonner answered ·

Grounding my equipment was a big hold up and source of confusion and frustration for me. You'll get on the internet everything from you don't need it to you'll kill yourself and/or start a fire. Static build up was something i didn't want and grounding solves that. I told myself numerous times "screw it I just wont ground it" then was worried back into wanting to solve it. So I grounded everything, batteries included. Glad I did the peace of mind was worth it.

I think the two main issues are a wire coming loose and charging something metal and static buildup.

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gerry-mcg avatar image
gerry-mcg answered ·

See this discussion here

It appears to centre around the concept of a floating earth

It is perfectly normal to have floating neutral on inverters and generators but it is very important to understand that this means there is no positive and neutral wires, they are both live. Each wire is carrying 115V but out of phase, one wire is -115V whilst the other is +115V, which means that when you plug something in it gets 230V, this being the difference between the two wires. The wires rapidly swap between + and - to give the 50Hz 230V supply your device needs.

This 2x115V is considered safer than 1x230V where you have no proper grounding of appliances. When connected to an EHU the grounding comes through the 3 wire connection to the hook up. When using an inverter without hook up we do not have a grounding, unless we bash a big metal stake into the ground and bond it to the motorhome chassis.

UK mains sockets often have switches on them but this only disconnects the brown wire not the blue one, similarly if the plug fuse blows it will only cut off the brown wire. This is known as single pole switching. If you have a floating neutral inverter single pole switching does not make the device safe because the blue wire is still live, as one canal boater found out the hard way when he turned a plug off and opened up an appliance without unplugging it. You may have noticed that continental motorhome sockets do not have switches on them, they only allow 2 pole switching, which disconnects both wires.

It is also worth noting that many UK RCDs only have single pole switching so they are of no use with a floating neutral inverter. 2 pole RCDs can be found but I have yet to see one on a plug in RCD device. 2 pole switching is safer but unsurprisingly costs more.

In summary neutral bonding is safe but different.

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paulkirk avatar image
paulkirk answered ·

Thanks for the replies. I hadn't realised about the 2 phase 115v context, that's important information. It's useful that the manufacturer states that the inverter must be earthed, but knowing why is also important. I'll probably research how to create an effective earth and earth it as Victron states. Once earthed I can also use a single pole RCD

thank you very much for the answer.

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