Inverter case earthing

[Loafer]

Dear Leccies

 

Is it acceptable to connect the inverter's exterior earth terminal to the 12V supply negative input to the inverter?

 

I'm currently earthing it to its own stud on the engine bearer nearby. I'm thinking that if there's any stray earth current it'll pass through some of my hull.

 

Ta.

[nicknorman]

Not really. If the battery -ve is well earthed to the hull it won't be a massive problem but in theory at least, the AC earth and battery negatives should be kept seperate until they connect to the hull. I think you should leave it as it is, after all where is this stray current you mention going to flow to? Where is the potential difference to make the current flow?

[WotEver]

Dear Leccies

 

Is it acceptable to connect the inverter's exterior earth terminal to the 12V supply negative input to the inverter?

Ta.

No.

 

There will always be a voltage drop along the battery cables so it ain't earth.

 

Tony

[Loafer]

Not really. If the battery -ve is well earthed to the hull it won't be a massive problem but in theory at least, the AC earth and battery negatives should be kept seperate until they connect to the hull. I think you should leave it as it is, after all where is this stray current you mention going to flow to? Where is the potential difference to make the current flow?

 

When I first installed it, there was a slight tingle from the case when I touched it and the surrounding steelwork. I think its a bit of capacitive coupling somewhere. I've just checked with my clampmeter and it's showing 0.4A along the earth wire. Presumably this is finding its way back to the battery negative via my engine bearers and block. I can't think of a reason why I can't shorten its journey and just connect it to the battery negative (at the inverter end of the cable). Ultimately it's connected to it anyway, innit?

No.

 

There will always be a voltage drop along the battery cables so it ain't earth.

 

Tony

 

You could say that about the earth cable itself, couldn't you?

[nicknorman]

0.4A seems a massive earth current. DC or AC?. Are you sure it isn't just the inaccuracies of the clamp meter?

 

Anyway, as I intimated, you could, and it probably wouldn't be an issue in practice, but it isn't the right way to do it. I'd be more concerned where this tingling and 0.4A was coming from. (Well, yes if you are going to be pedantic we know where it's coming from, the question is WHY?)

 

Just to explain why wotever and I are squeaking a bit, it's because if something were to happen to the -ve to hull bond then you would just have the earth connected to the battery -ve, and one of the things we try to avoid with boat wiring is the "contamination" of 12v systems with mains systems such that things that are only designed to be safe for 12v, suddenly have 230v on them following some fault condition on the AC side.

Edited February 6, 2016 by nicknorman

[WotEver]

You could say that about the earth cable itself, couldn't you?

Nope. There's no current flowing in the earth wire.

 

Whereas the -ve supply lead will have maybe 50A flowing.

[Loafer]

0.4A seems a massive earth current. DC or AC?. Are you sure it isn't just the inaccuracies of the clamp meter?

 

Anyway, as I intimated, you could, and it probably wouldn't be an issue in practice, but it isn't the right way to do it. I'd be more concerned where this tingling and 0.4A was coming from. (Well, yes if you are going to be pedantic we know where it's coming from, the question is WHY?)

 

Just to explain why wotever and I are squeaking a bit, it's because if something were to happen to the -ve to hull bond then you would just have the earth connected to the battery -ve, and one of the things we try to avoid with boat wiring is the "contamination" of 12v systems with mains systems such that things that are only designed to be safe for 12v, suddenly have 230v on them following some fault condition on the AC side.

 

It appears to be 0.5A on the DC setting, and .25A on AC setting. I don't know why it should be there. I'll take some more measurements tomorrow - plus disconnect the earth cable and see what voltage is there.

0.4A seems a massive earth current. DC or AC?. Are you sure it isn't just the inaccuracies of the clamp meter?

 

Anyway, as I intimated, you could, and it probably wouldn't be an issue in practice, but it isn't the right way to do it. I'd be more concerned where this tingling and 0.4A was coming from. (Well, yes if you are going to be pedantic we know where it's coming from, the question is WHY?)

 

Just to explain why wotever and I are squeaking a bit, it's because if something were to happen to the -ve to hull bond then you would just have the earth connected to the battery -ve, and one of the things we try to avoid with boat wiring is the "contamination" of 12v systems with mains systems such that things that are only designed to be safe for 12v, suddenly have 230v on them following some fault condition on the AC side.

 

Goddit, ta!

[cuthound]

If you have a normal multimeter as well as a clamp meter, the normal multimeter can usually read current, typically 5-10 amps. Make sure the multimeter is set to its highest amp range before connecting it.

 

This is done by putting it in series with the cable carrying the current you want to measure. Disconnect one end of the cable you want to measure. Connect one of the multimeter cables to it, connect the other multimeter cable to where the cable you want to measure came from.. Should be more accurate than a clamp meter.

[bottle]

Loafer

 

No teaching of how to suck eggs.

 

Assuming you have the Uni-t clamp meter, you are pressing the 'rel' (middle button) so that the display goes to zero, meter switched ON but not placed round cable, before taking reading.

[Loafer]

If you have a normal multimeter as well as a clamp meter, the normal multimeter can usually read current, typically 5-10 amps. Make sure the multimeter is set to its highest amp range before connecting it.

 

This is done by putting it in series with the cable carrying the current you want to measure. Disconnect one end of the cable you want to measure. Connect one of the multimeter cables to it, connect the other multimeter cable to where the cable you want to measure came from.. Should be more accurate than a clamp meter.

 

I don't have a normal multimeter. My UniT clamp meter has shown itself to be fairly accurate elsewhere, so I have no reason to doubt it.

 

 

Loafer

 

No teaching of how to suck eggs.

 

Assuming you have the Uni-t clamp meter, you are pressing the 'rel' (middle button) so that the display goes to zero, meter switched ON but not placed round cable, before taking reading.

 

 

Yes, I'm pressing the 'rel button,with the meter right next to the cable to be measured, then I clamp the cable and hit the 'hold' button, then bring up it to where I can read it.

[bottle]

 

I don't have a normal multimeter. My UniT clamp meter has shown itself to be fairly accurate elsewhere, so I have no reason to doubt it.

 

 

 

 

Yes, I'm pressing the 'rel button,with the meter right next to the cable to be measured, then I clamp the cable and hit the 'hold' button, then bring up it to where I can read it.

 

Well that throws that possible problem out the window.

[Loafer]

 

Well that throws that possible problem out the window.

 

Thanks for your trouble anyway, bottle!

[Paul C]

Definitely no. In certain fault conditions it could raise the negatives of every item in the 12V system up to 230V for a brief moment (I think). Basically, all mains side earths should be an independent run, then connected to the hull near BUT NOT THE SAME STUD AS the 12V side's hull bonding. I think when I wired my boat up I took the inverter earth to the consumer unit's earth bus, from there existed an earth strap to the hull.

[WotEver]

I think when I wired my boat up I took the inverter earth to the consumer unit's earth bus, from there existed an earth strap to the hull.

Absolutely the correct way to do it. Think about it, in a house you wouldn't run it back to a stake in the ground, you'd run it to the consumer unit.

 

Tony

[Loafer]

Hmm. My inverter earth is about a metre away from the rest of the boat's 'earths' (including the mains earth, which are all at the same point). The only different one is the inverter's earth, currently bolted to the same bit of engine bed frame, but just across the engine bay on the other side..

 

Does that sound normal?

[WotEver]

Does that sound normal?

It sounds better than many boats

 

Not best practice though.

 

For DC the batteries -ve terminal should be bonded (wired) to a single stud on the hull. The -ve busbar should connect to that same point. Everything that requires a -ve connection should obtain it from the -ve busbar.

 

For AC shore power the earth should go to galvanic isolator or transformer and the other side of that should go to the earth busbar in the consumer unit. That busbar should then be wired to a stud adjacent to the DC -ve stud on the hull. Any AC electrical circuits that require an earth should get it from the consumer unit busbar.

 

Tony

 

Edited for the AC earth arrangement and further clarity.

Edited February 7, 2016 by WotEver

[Loafer]

It sounds better than many boats

 

Not best practice though.

 

For DC the batteries should earth to a single stud on the hull. The -ve busbar should earth to that same point. Everything that requires a -ve connection should obtain it from the -ve busbar.

 

For AC the earth should go to galvanic isolator or transformer and the other side of that should go to a -ve stud on the hull adjacent to the DC stud. The earth busbar in the consumer unit should earth to that same stud. (It's fine to go from GI to busbar to stud too.). Any AC electrical circuits that require an earth should get it from the consumer unit busbar.

 

Tony

 

I'm going to have to digest that more thoroughly tomorrow. Currently I'm suffering a little from Wadworth's Syndrome.

 

Thanks Tony.

 

Will you mind if I ask you what you just said, sometime tomorrow, when I'm back on Earth?

 

The bit in red is causing the most stoppages in my head. Aren't they one and the same thing? i.e. battery negative, and battery 'earth'?

 

Why am I so thick at this time of a Sunday?

[WotEver]

Come back to it tomorrow and all shall become clear

[ditchcrawler]

It sounds better than many boats

 

Not best practice though.

 

For DC the batteries should earth to a single stud on the hull. The -ve busbar should earth to that same point. Everything that requires a -ve connection should obtain it from the -ve busbar.

 

For AC the earth should go to galvanic isolator or transformer and the other side of that should go to a -ve stud on the hull adjacent to the DC stud. The earth busbar in the consumer unit should earth to that same stud. (It's fine to go from GI to busbar to stud too.). Any AC electrical circuits that require an earth should get it from the consumer unit busbar.

 

Tony

Not sure that last bit is right, maybe a sketch

[WotEver]

Not sure that last bit is right, maybe a sketch

It wasn't really, so I've edited it

 

To y

[WotEver]

The bit in red is causing the most stoppages in my head. Aren't they one and the same thing? i.e. battery negative, and battery 'earth'?

I've now removed erroneous reference to 'earth' when talking about DC. Hopefully it's now clearer.

 

Tony

[Loafer]

I've now removed erroneous reference to 'earth' when talking about DC. Hopefully it's now clearer.

 

Tony

 

Ah, I'm not far off the right track then. It'll STILL require a re-read though. I'll attempt to navigate back to your original thread soon, but I'm not putting any money on it happening tonight!

Edit: Yes, it makes sense now. I must be sobering up. Always difficult when the cat is away!

Edited February 7, 2016 by Loafer

[WotEver]

Edit: Yes, it makes sense now. I must be sobering up. Always difficult when the cat is away!

It's not just you, my post makes more sense now anyway

[Loafer]

It's not just you, my post makes more sense now anyway

 

Phew. I hate it when it's just ME! Trouble is, that is quite likely whilst I'm in this partially-charged state. I'm sure my cells are sulphating as I type!

Holy cow. The rain here has just gone so heavy that I can't hear the telly!