Inverter Earthing.

[canals are us?]

Today I have bought a victron 3000 multiplus inverter and charger and bought all the cables and fuses. I purchased 95mm2 positive and negative cables to connect to the batteries along with a mega fuse holder and 400a fuse to go into the positive cable to the batteries.

I also bought a 6mm cable to run the 4 amp output to charge the engine starter battery cable along with a 5 amp fuse and holder.

The thing I didn't fully understand is where do I earth the inverter too?

The manual says that relay H engages/disengages when shore power is connected/disconnected and in disconnection the case becomes the earth/ground, so needs earthing from this point, for when you are not using mains AC but using the inverter AC.

 So from the earth point on the case, to where should it be connected too? Didn't seem to fully specify! What size earth cable should I use?

I am planning to pay a boatyard, once I have cut the cables to size to get them to crimp them, as I bet the crimping tool needs to be heavy duty and I bet expensive!

Many thanks. James

[Robbo]

Your consumer unit (so on the output of the Victron) should have a earth to the hull.  That’s all that’s needed.

[nicknorman]

If you read the instructions carefully, it says the inverter must be earthed by the incoming power earth conductor, and/or by the stud. So provided you have the expected connection to hull from eg the earth in the consumer unit, this will be connected to the earth of the inverter and so no need for an additional cable from the stud. Incoming and outgoing power earth conductors are connected together in the unit so it doesn't matter whether the connection to earth/hull is on the input or output conductors.

We don't have a consumer unit in our installation, we have a galvanic isolator with a connection between its boat side and the hull in addition to the earth conductor that goes to the combi. The power then routes to the Combi, and then to a single RCBO. However lots of people have a full Consumer Unit and that is probably the best place to make the earth connection to hull.

Edited January 31, 2018 by nicknorman

[Alan de Enfield]

19 minutes ago, canals are us? said:

....today I have bought a victron 3000 multiplus inverter and charger and bought all the cables and fuses. I purchased 95mm2 positive and negative cables to connect to the batteries

Your 3000w Inverter, on full power, will be drawing around 300 amps from the battery - your 95mm squared cable is rated at around 220 amps in conduit, or 328 amps 'clipped in air'.

Just think about your cable installation method.

You may well say "I'll never be running the inverter on full power", but one day a family member, a friend, or someone you have sold the boat to may just do it.

Having a 400a fuse will not give any protection to 220 amp cable - which do you think will 'blow' first ?

Edited January 31, 2018 by Alan de Enfield

[nicknorman]

^^^ depends on the thermal rating of the cable insulation.

Edited January 31, 2018 by nicknorman

[Slim]

27 minutes ago, canals are us? said:

Today I have bought a victron 3000 multiplus inverter and charger and bought all the cables and fuses. I purchased 95mm2 positive and negative cables to connect to the batteries along with a mega fuse holder and 400a fuse to go into the positive cable to the batteries.

I also bought a 6mm cable to run the 4 amp output to charge the engine starter battery cable along with a 5 amp fuse and holder.

The thing I didn't fully understand is where do I earth the inverter too?

The manual says that relay H engages/disengages when shore power is connected/disconnected and in disconnection the case becomes the earth/ground, so needs earthing from this point, for when you are not using mains AC but using the inverter AC.

 So from the earth point on the case, to where should it be connected too? Didn't seem to fully specify! What size earth cable should I use?

I am planning to pay a boatyard, once I have cut the cables to size to get them to crimp them, as I bet the crimping tool needs to be heavy duty and I bet expensive!

Many thanks. James

A hydraulic crimper on e bay is about £25. 

 

 

Frank

[canals are us?]

39 minutes ago, Alan de Enfield said:

 

Thanks everyone 

My boat has a mains consumer unit with an RCD trip and MCB's with an Earth terminal strip. I certainly hope the hull earth bond is connected to this earth strip terminal.

It seems that you are saying I don't need to run a separate earth cable from the earth lug point on the inverter case to the consumer unit earth point, as the inverter earths itself inside the unit?

The cable is rated and has printed on it 95mm 2. 500AMPS 70 o C CABLE. Is this suitable? I plan to just clip it to the wall. Thanks, I'll have a look for a hydraulic crimper.

Many thanks. James

Edited January 31, 2018 by canals are us?

[WotEver]

1 hour ago, Robbo said:

Your consumer unit (so on the output of the Victron) should have a earth to the hull.  That’s all that’s needed.

Just so. 

This question crops up regularly due, I think, to the ambiguous wording in the Victron manual. It speaks of ‘disconnecting the earth’ which sounds scary (and is, if it were true), but as Robbo and Nick have explained, you only need the one hull bond on the output (achieved by the consumer unit bond in most cases).

31 minutes ago, canals are us? said:

My boat has a mains consumer unit with an RCD trip and MCB's with an Earth terminal strip. I certainly hope the hull earth bond is connected to this earth strip terminal.

It should, but if you don’t know for sure then I suggest you check to confirm. 

[WotEver]

33 minutes ago, canals are us? said:

The cable is rated and has printed on it 95mm 2. 500AMPS 70 o C CABLE. Is this suitable?

How long is the cable run?  95mm² will carry the current without catching fire but the voltage drop at 3kVA load will be well over a volt if the inverter is 10m from the batteries. If it’s only 5m from the batteries then the drop will be around 0.6V

[canals are us?]

2 minutes ago, WotEver said:

Just so. 

This question crops up regularly due, I think, to the ambiguous wording in the Victron manual. It speaks of ‘disconnecting the earth’ which sounds scary (and is, if it were true), but as Robbo and Nick have explained, you only need the one hull bond on the output (achieved by the consumer unit bond in most cases).

It should, but if you don’t know for sure then I suggest you check to confirm. 

It could be worded better. Only ever removed the cover twice. Once to wire in a Galvanic isolator. Ie earth wire from shore line socket to GI then to Earth terminal bar in consumer unit. Other occasion to add a new MCB and circuit for an immersion heater.

I'll follow the earth cables and see where they go. Any idea where the earth bond to hull would be on a Liverpool boat from 1998? Around engine beds may be a good look. 

James

[WotEver]

Just now, canals are us? said:

I'll follow the earth cables and see where they go. Any idea where the earth bond to hull would be on a Liverpool boat from 1998? Around engine beds may be a good look. 

The usual advice is “adjacent to but not concurrent with the battery negative bond”. That is simply because it’s nice and logical and is the first place you’d look (as you yourself just stated). However, it could be anywhere, even to the stud securing the CU to the hull. 

Simple check. Ensure nothing is plugged into any socket and disconnect the shoreline. Now with a multimeter check the resistance from the earth busbar to the hull. It should be a very low (virtually zero) resistance. 

[canals are us?]

2 minutes ago, WotEver said:

How long is the cable run?  95mm² will carry the current without catching fire but the voltage drop at 3kVA load will be well over a volt if the inverter is 10m from the batteries. If it’s only 5m from the batteries then the drop will be around 0.6V

That's great news as cable cost £80! Less than 2 metres, as plan to fit the inverter on the bulkhead wall with the existing batteries to the side in a cupboard. Modern trad with engine under the floor. Though best location for inverter to allow airflow and inverter cant be above the batteries, as old charger was in the cupboard above batteries and charger got a bit warm so opened the cupboard doors.

James

[WotEver]

2 minutes ago, canals are us? said:

That's great news as cable cost £80! Less than 2 metres, as plan to fit the inverter on the bulkhead wall with the existing batteries to the side in a cupboard. Modern trad with engine under the floor. Though best location for inverter to allow airflow and inverter cant be above the batteries, as old charger was in the cupboard above batteries and charger got a bit warm so opened the cupboard doors.

James

That sounds fine

[smileypete]

1 hour ago, Alan de Enfield said:

Your 3000w Inverter, on full power, will be drawing around 300 amps from the battery - your 95mm squared cable is rated at around 220 amps in conduit, or 328 amps 'clipped in air'.

Just think about your cable installation method.

You may well say "I'll never be running the inverter on full power", but one day a family member, a friend, or someone you have sold the boat to may just do it.

Having a 400a fuse will not give any protection to 220 amp cable - which do you think will 'blow' first ?

Victron call for 2x50mm2 and a 400A fuse so 95mm2 sounds reasonable:

https://www.victronenergy.com/upload/documents/Manual - MultiPlus 3k 120V Ve.Bus enabled - rev 00 - EN.pdf

No point using conduit for large conductors, cable tray would be better.

[Alan de Enfield]

2 minutes ago, smileypete said:

Victron call for 2x50mm2

And that always 'worries' me - it only takes one terminal to make a poor connection and you have every amp trying to get down a 50mm2 cable.

[smileypete]

17 minutes ago, WotEver said:

How long is the cable run?  95mm² will carry the current without catching fire but the voltage drop at 3kVA load will be well over a volt if the inverter is 10m from the batteries. If it’s only 5m from the batteries then the drop will be around 0.6V

According to Mr Victron it'll go down to 9.5V so 0.6V added on top is still below the min 10.5V terminal voltage for 12V batts.

2 minutes ago, Alan de Enfield said:

And that always 'worries' me - it only takes one terminal to make a poor connection and you have every amp trying to get down a 50mm2 cable.

Maybe but Victron manufacture thousands of combis.

If you can't make reliable connections, then step 1 is to find out how to make them reliably!

 

Edited January 31, 2018 by smileypete

[WotEver]

Just now, Alan de Enfield said:

And that always 'worries' me - it only takes one terminal to make a poor connection and you have every amp trying to get down a 50mm2 cable.

I agree. And that one 50mm² cable will be ‘protected’ by a 400A fuse 

Okay, it’s extremely unlikely to happen but still not a great piece of design imho. 

2 minutes ago, smileypete said:

According to Mr Victron it'll go down to 9.5V so 0.6V added on top is still below the min 10.5V terminal voltage for 12V batts.

Yup, but they don’t explain that the current increases with every drop in voltage. 

Besides, my point was that 5m was okay. 

[canals are us?]

When I wire things up I always think the less connections the better!

James

[smileypete]

1 minute ago, WotEver said:

I agree. And that one 50mm² cable will be ‘protected’ by a 400A fuse 

Okay, it’s extremely unlikely to happen but still not a great piece of design imho. 

Yup, but they don’t explain that the current increases with every drop in voltage. 

I'm sure they've taken it into consideration.

[WotEver]

1 minute ago, smileypete said:

I'm sure they've taken it into consideration.

So am I, but they don’t explain it. 

> 340A at 3kVA at 9.5V. 

[smileypete]

16 minutes ago, WotEver said:

So am I, but they don’t explain it. 

> 340A at 3kVA at 9.5V. 

Well contact them and ask if you like, then share their answer with us.

I'm sure 99% of their customers, including marine electrical specialists, trust the install instructions...

Edited January 31, 2018 by smileypete

[WotEver]

Just now, smileypete said:

Well contact them and ask if you like, then share their answer with us.

I'm sure 99% of their customers, including marine electrical specialists, trust the install instructions...

So what’s your point?

[smileypete]

1 minute ago, WotEver said:

So what’s your point?

Trust the install instructions?

[WotEver]

Just now, smileypete said:

Trust the install instructions?

Who said I didn’t?

[smileypete]

11 minutes ago, WotEver said:

Who said I didn’t?

The bit where you said 'still not a great piece of design imho'

Maybe, but it's what the install instructions say...