Floating system- Victron inverters

lazza · June 2012

HI Forum

I recently posted about an installation on the beach without grounding. The safest option and avoiding putting metal plates in the sand etc... as we had to be mobile anyway.... was to leave the system "floating".

I therefore disconnected the neutral cable from the ground connection within the inverter which is recommended by the manufacturer (see page 8 and Appendix B of the manual http://www.victronenergy.com/upload/...%20ES%20SE.pdf). However, when doing tests, whereas when the Neutral is connected to the Ground within the inverter, the voltage difference between the live wire and the inverter chassis was 230V. When "floating" it didnt drop to 0V... it was in fact at half that voltage ie 115V for both live and neutral wires.

As I didnt connect any PE wire to the inverter, there is no risk of potential difference between a plug socket ground and a plug socket live or neutral wire. However, between the live or neutral wire and the chassis of the inverter there IS a potential difference.. allbeit only 115V.

Why would this be? Is this dangerous

Thanks
Larry

BB. · June 2012

Re: Floating system- Victron inverters

It is leakage current (perhaps a little DC, but probably mostly AC coupling--possibly through filter capacitors).

It is not dangerous in the sense there will be no fire. However, it can be dangerous in terms of shock. Basically anything over ~5 milliamps (0.005 amps) through your heart can stop it.

So, if you were to grab "neutral" (or the hot) and something metal (chassis of inverter, either battery terminal, etc.), you will most likely get a shock.

Your volt meter uses a tiny amount of current to measure voltage so it is very easy to "measure" voltages to ground in floating circuits... If you are interested in seeing if it is a "solid" connection, you can take a low wattage 230 VAC filament lamp and connect it between neutral and chassis (and try hot to chassis too)... The bulb should not light (assuming it is leakage current).

If you want/need to protect against shock, you should be able to connect a RCD (aka GFI ground fault interrupter in US/North America) outlet which should detect >5mAmp and disconnect if somebody/something makes a AC power to metal (ground) connection and current flows.

One reason to connect Neutral to Chassis ground (assuming this is a metal chassis vehicle/trailer/etc.) is this will allow you to only put a breaker/fuse in the "Hot" lead... If there is a short between Hot and Chassis/Frame/etc. ground, then the fuse/breaker would pop. Without a neutral bond, the "first short" just becomes the neutral bond. Not really "hazardous"--Just makes a short between one leg of AC and Chassis "undetectable"...

Otherwise, in the US where we have split phase (Hot/Neutral/Hot--H-N 120, H-H 240), we use two pole breakers so that a short in either not will pop both breakers and kill both Hots.

But since you do not have a "center tap" neutral connection, you still should not need a two pole breaker for safety.

-Bill

niel · June 2012

Re: Floating system- Victron inverters

that does not sound good to me. i think you might try a ground even if not ideal. in giving this a bit of thought i concur the straight rod, even if shorter, can be a problem removing it. what i thought of is along the lines of a spiral dog anchor.
http://images.search.yahoo.com/images/view?back=http%3A%2F%2Fsearch.yahoo.com%2Fsearch%3Fei%3DUTF-8%26p%3Ddog%2Bground%2Bstakes&w=152&h=117&imgurl=www.bing.com%2Fimages%2Fsearch%3Fq%3Ddog%2Bground%2Bstakes%23focal%3Dbce077eee4b703b0dedac6cabe3a7da7%26furl%3Dhttp%3a%2f%2fimages.toolsdiy.co.uk%2fimages%2fthumbs%2f152%2f1266757500_camping_stake_1.jpg&size=&name=search&rcurl=http%3A%2F%2Fwww.bing.com%2Fimages%2Fsearch%3Fq%3Ddog%2Bground%2Bstakes%23focal%3Dbce077eee4b703b0dedac6cabe3a7da7%26furl%3Dhttp%3a%2f%2fimages.toolsdiy.co.uk%2fimages%2fthumbs%2f152%2f1266757500_camping_stake_1.jpg&rurl=http%3A%2F%2Fwww.bing.com%2Fimages%2Fsearch%3Fq%3Ddog%2Bground%2Bstakes%23focal%3Dbce077eee4b703b0dedac6cabe3a7da7%26furl%3Dhttp%3a%2f%2fimages.toolsdiy.co.uk%2fimages%2fthumbs%2f152%2f1266757500_camping_stake_1.jpg&p=dog+ground+stakes&type=&no=4&tt=115&oid=http%3A%2F%2Fts3.mm.bing.net%2Fimages%2Fthumbnail.aspx%3Fq%3D4827784378778094%26id%3D942411a29a3e9f33b08bc5d0e21a708c&tit=Dog+Tie+Out+Stake+Ground+Anchor+Camping+-+Garden&sigr=15tn14bdq&sigi=15m1e08i0&sigb=11r1h9p6r&fr=yfp-t-701

an example of one i saw was 16in long, but because it is spiraled it will afford a bit more contact area with the sand. keep in mind that this can be removed with a bar and just turning it like a screw and wetting the sand occasionally may help too even with better conductivity to the surrounding sand for the anchor. if this would prove to be not enough then 2 can be put into the ground and tied together with a short length of #6 wire.

now i do need to mention that there could be galvanic action between the copper in the connections and the anchor, but for temporary use this should not pose a problem if you take the connections off of the anchor when not in use.

vtmaps · June 2012

Re: Floating system- Victron inverters

I think Bill's explanation is most likely.
Another solution is to use an isolation transformer.
--vtMaps

BB. · June 2012

Re: Floating system- Victron inverters

It really depends on the system and the usage...

If this is an "enclosed" system that is only worked on by you/trained personnel--Then you can avoid the whole grounding issue and just let stuff float.

If this was, for example, powering a beach side stage with sound gear/instruments--Then you would want to do anything you can to prevent electrocution (fairly common with sound gear).

If this was an area subject to lightning strikes, then something into the ground/sand would be helpful (again, more important if a stage with people around).

-Bill

lazza · June 2012

Re: Floating system- Victron inverters

HI

Thanks for your replies. I will try what Bill suggests to see if the connection is solid or not. It's only really a risk at the inverter chassis... which in theory only we have access too.. but i dont like the idea of having 120V there.

About to post another thread on direction of energy flow in AC systems.... will put it in the correct topic

cheers
Larry

Cariboocoot · June 2012

Re: Floating system- Victron inverters

I get en Error 404 trying to look at that linked inverter so I'll hazard a question instead:

MSW inverter by any chance? One with the (-) pole tied to ground somehow? (Possibly by the RV wiring, not the inverter itself.)

BB. · June 2012

Re: Floating system- Victron inverters

Yes, the PDF Link is bad (cut and paste did not work correctly).

And Marc is correct to ask--If this is a MSW inverter, you cannot connect AC Neutral to "battery" ground as this will "short" the inverter.

And it may be possible that some TSW inverters cannot have grounded neutrals either--Always check the user/installation manuals to be sure.

-Bill

lazza · July 2012

Re: Floating system- Victron inverters

It's not MSW... definitely TSW

http://www.victronenergy.com/upload/documents/Manual%20-%20Phoenix%20Inverter%20Compact%202000%20-%20rev%2002%20-%20EN%20NL%20FR%20DE%20ES%20SE.pdf

is this link better?

BB. · July 2012

Re: Floating system- Victron inverters

Yes, Link works now.

-Bill

Floating system- Victron inverters

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