Earthing AC Inverter Supplies

[Serenity Malc]

Yello,

 

I was thinking that when a 12/240v inverter goes to bypass when shore power is applied, the earth path continues through. Yes ? No ? How does an inverter deal with earth function when the boat is running from the inverter without shore power please ?

 

Many thanks in advance for any well informed replies or web links.

 

Cheers Malc.

Edited August 13, 2013 by Serenity Malc

[BEngo]

The inverter, or any generator doesn't really care about earth at all, but rather the earth is a safety part of the installation package. The purpose of the earth is to provide a low-resistance path back to the generating device in the event of a fault. This will then cause various protective devices to trip.

 

For the CEGB (or whatever they are today) it involves connecting the star point of the AC generator to a BIG plate buried in the earth. One cable is then taken off the star point and one from the other end of each of the 3 generating coils which are connected to it. Your house is then supplied with the cable from the star point and a cable from the outside end of one of the generating coils via various transformers. If, like me you live in the sticks, the house will have its earth wire connected to a rod into the ground. If you live in a town then the electric supply boyoes usually put another earth plate into the local sub-station and run cables from this to the domestic installations. At the substation the star-point cable (the neutral)will be bonded to this earth plate. The exact details of how this sub-station earth is connected to your home vary- sometimes it is a separate cable (or the cable sheath) sometimes just the neutral is provided and the house earth wire is connected to that. The Wiki on earthing ( http://en.wikipedia.org/wiki/Earthing_system) is not too bad once you grasp the technical jargon. In the event of a fault the electricity goes from the live wire through the fault and then through the earth wire to the ground and back to the generator. The RCS and the fuses/circuit breakers will detect this and shut off the power.

 

For an inverter (or a single phase generator) there are several output arrangements ( Have a look at Gibbo's post 7 in http://www.canalworld.net/forums/index.php?showtopic=19060&st=0) but in the simplest there are just two wires- these are the neutral and live and since it's AC it doesn't initially matter which we call which. However to get a path back to the inverter for any fault current the earth wire in the sockets has to be connected to one of these. The output connected to the earth cable then becomes the neutral and we have a neutral-earth bond just like the CEGB.

 

Sometimes this N-E bond is fixed, sometimes it's a relay, typically in a pass-through inverter.

 

Hope that helps

 

N

[nicknorman]

Yello,

 

I was thinking that when a 12/240v inverter goes to bypass when shore power is applied, the earth path continues through. Yes ? No ? How does an inverter deal with earth function when the boat is running from the inverter without shore power please ?

 

Many thanks in advance for any well informed replies or web links.

 

Cheers Malc.

 

In summary, the shore earth is passed through the inverter when its in pass-through mode. When its in inverting mode, normally a (programmable) relay operates to connect neutral to the earth of the inverter (which should be connected to hull at some point)

[Theo]

What very clear and informative answers!

 

N

[Serenity Malc]

Yello,

 

Thanks Bengo ..... I did my apprenticeship with SEEBoard a long time ago, but things on land don't change much. Your answer to my question appears to be that when the AC is provided by non shore power inverter means, the neutral earth bond is replaced by a neutral / earth relay within the inverter ?

 

Many thanks gentlemen ....... Malc.

[BEngo]

Yello,

 

Thanks Bengo ..... I did my apprenticeship with SEEBoard a long time ago, but things on land don't change much. Your answer to my question appears to be that when the AC is provided by non shore power inverter means, the neutral earth bond is replaced by a neutral / earth relay within the inverter ?

 

Many thanks gentlemen ....... Malc.

Yes, maybe. There are several ways to skin this cat. It's normally a relay in a pass-through or multi-purpose inverter so that the shore-earth can be connected automatically when shore power is available. In a stand-alone it can be a relay or it can be hard-wired. It is even possible to have inverters where the earth floats and there is NO N-E bond. Gibbo suggests you only want to use these with double insulated equipment. I wouldn't want one at all.

 

N

[by'eck]

In summary, the shore earth is passed through the inverter when its in pass-through mode. When its in inverting mode, normally a (programmable) relay operates to connect neutral to the earth of the inverter (which should be connected to hull at some point)

 

Just to add the shore power earth path is broken by the relay when it connects inverter neutral to boat earth/hull.

 

This is relevant in a situation where the shore power lead is still connected to pedestal but not live.

[Keith M]

Yello,

 

I was thinking that when a 12/240v inverter goes to bypass when shore power is applied, the earth path continues through. Yes ? No ? How does an inverter deal with earth function when the boat is running from the inverter without shore power please ?

 

Many thanks in advance for any well informed replies or web links.

 

Cheers Malc.

 

Having read the posts I feel there is is some confusion

Only Inverter / Chargers switch the Shore or Generator earth

If we are talking just about just an inverter the bond is normally hard wired

 

Keith

[nicknorman]

Having read the posts I feel there is is some confusion

Only Inverter / Chargers switch the Shore or Generator earth

If we are talking just about just an inverter the bond is normally hard wired

 

Keith

 

I think in general that is true, but to be picky isn't the determining factor whether or not it has a pass through function (ie 2 sets of mains connections) rather than whether its a Combi? I think some inverter-only devices have pass-through? Edited August 14, 2013 by nicknorman

[by'eck]

I think in general that is true, but to be picky isn't the determining factor whether or not it has a pass through function (ie 2 sets of mains connections) rather than whether its a Combi? I think some inverter-only devices have pass-through?

 

Yes, UPS devices for example.

[Keith M]

I think in general that is true, but to be picky isn't the determining factor whether or not it has a pass through function (ie 2 sets of mains connections) rather than whether its a Combi? I think some inverter-only devices have pass-through?

 

Having work with in the power electronics industry for nearly 30 years

I have never come a crossed an inverter with a pass through function

The only inverters which I have seen in that time have one input which is DC and then AC outputs but still a earth - neutral bond is required

 

Yes, UPS devices for example.

 

A UPS is a from of inverter / charger. The main input is AC and the secondary input is from the DC battery

 

Both Mastervolt and Victron inverter / chargers have the ability to act as a UPS

 

Keith

[by'eck]

 

Having work with in the power electronics industry for nearly 30 years

I have never come a crossed an inverter with a pass through function

The only inverters which I have seen in that time have one input which is DC and then AC outputs but still a earth - neutral bond is required

 

A UPS is a from of inverter / charger. The main input is AC and the secondary input is from the DC battery

 

Both Mastervolt and Victron inverter / chargers have the ability to act as a UPS

 

Keith

 

Hi Keith

 

I bow to your greater knowledge. Until a few weeks ago I would have agreed with you, but it has been pointed out to me that some UPS (not Combi) devices don't have a charger facility just an inverter with AC pass through. I believe Catweasel on this forum has one. Sterling also offer a low noise UPS one for AV equipment.

[Keith M]

Interesting

 

How is the inverter battery re-charged?

 

Keith

[by'eck]

Interesting

 

How is the inverter battery re-charged?

 

Keith

 

Not mentioned but with separate charger I guess. Lets face it you would probably need to provide the batteries so why not the charger.

Edited August 15, 2013 by by'eck

[nicknorman]

Perhaps its to do with the solar feed in market? Your batteries are charged only by solar, then discharged into the inverter when there is charge available, else the mains is passed through to keep the lights on?