Inverter update from a few days ago

[Csail]

Reply from Inverter company-

connect to your bonding circuit, usually the bat neg , about a 15 amp cable
-----Original Message-----
From: STERLING POWER PRODUCTS [mailtoublic@sterling-power.com]
Sent: 04 July 2007 01:07
To: help@sterling-power.com
Subject: FW: sterling-power.com Form Submission Results







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From: sterling-power.com [mailtoublic@sterling-power.com]
Sent: 03 July 2007 18:14
To: STERLING POWER PRODUCTS
Subject: sterling-power.com Form Submission Results



Contact from sterling-power.com





Message I have got your 1800w inverter on my yacht. I lost the instructions but basically where should the earth wire be attached to. Some people say the battery negative and others say a plate under the hull in the water? Also what size earth wire?
Regards,
Andy

 

[steve_cronin]

csail, me old matey....

.. best to just give Charlie a ring and talk "interactive" to him, honest!

Steve Cronin

 

[Csail]

Re: csail, me old matey....

Charlie?

 

[Anonymous]

Re: csail, me old matey....

[ QUOTE ]
Charlie?

[/ QUOTE ]Charles Sterling. He wrote to me to tell me that he doesn't answer emails, as a policy, as they get so many and it takes too long. His written English is a bit frayed which maybe explains it.

 

[boatmike]

I don't dissagree with this advice and in fact it does not conflict with what I said previously BUT the terminology needs to be clarified as it could easily be misunderstood.

IF your battery negative is fully bonded to a hull plate, and IF the wiring to the hull plate is greater than 15 AMP then it is possible to pick up an earth on any part of the bonding system. HOWEVER it is often the case that battery earths on boats are NOT bonded to a hull plate and in fact there are arguments for and against doing so, in which case to connect 240V earth to battery negative could be dangerous. It is however still GOOD PRACTICE to earth to a seperate hull plate, OR take your earth lead directly to the same hull plate. In fact if you were to build a commercial vessel to Lloyds or DNV spec it would be insisted upon.

What you have to consider is that you need to supply a direct earth of lower resistance than other wiring on the vessel so that any stray current will go directly to earth and nowhere else. This is still best done with a seperate earth wire for AC, even if it is goes to the same hull plate as the DC.

 

[rogerthebodger]

[ QUOTE ]
What you have to consider is that you need to supply a direct earth of lower resistance than other wiring on the vessel so that any stray current will go directly to earth and nowhere else. This is still best done with a seperate earth wire for AC, even if it is goes to the same hull plate as the DC.

[/ QUOTE ]

Mike, for that to work on protect the user the neutral supply of the inverter must also be connected to the common earth point as well as the case of the appliance because if the neutral is not connected the "stray current" will not have a return path.

Have a look at

this and this

 

[boatmike]

I am slowly losing the will to live here! This is not complicated. With any three wire household system you have live, neutral, and earth. Thats why we have 3 pin plugs. As we are talking AC both neutral and earth carry power. The earth system is connected to any appliance that requires an earth (the exception being as several people have pointed out most double insulated appliances which don't) Consider the humble microwave oven increasingly found on boats. This is NOT usually double insulated and the casing could become live if there was an internal short in the appliance. However, as the casing is connected to earth this will, provided that the system is grounded to a hull plate, short to ground through a low resistance earth wire rather than through some poor sod who grabs hold of the handle. It's got sweet FA to do with neutral and it would be stone raving bonkers to connect the earth and neutral wires together anywhere. Sorry if you don't agree but I don't believe even in SA anyone would deliberately connect neutral to earth on a household installation and it would be even more stupid on a boat as any break in the neutral line could cause the primary circuit to flow through the earth wire and make the casing of the microwave or WHY live. There is a lot of misunderstanding caused by the use of RCDs which protect entirely differently by sensing the PD between live and neutral and tripping where a difference shows a short in the system. RCDs are excellent, but having built many ships and commercial vessels I can confirm that neither Lloyds nor DNV would certify an installation where the AC system was not grounded to a hull plate regardless primarily to ensure that ANY stray current anywhere on the vessel that tries to run to earth can do so recognising that the same circuits supplied by a genny or any other devices at sea can also be supplied from shore power. The genny and I believe most inverters do indeed have a ground line which is I believe internal to the genny or inverter is connected to neutral and therefore provides a return path for stray current as you rightfully point out is required, but not to connect this to ground renders the earth line redundant.

 

[ean_p]

Not only in SA but in the UK too..............and most other place's

 

[rogerthebodger]

[ QUOTE ]
It's got sweet FA to do with neutral and it would be stone raving bonkers to connect the earth and neutral wires together anywhere.

[/ QUOTE ]

Well that how nPower in the UK do it and if they didn't the earth leakage current would have no where to go.

[ QUOTE ]
There is a lot of misunderstanding caused by the use of RCDs which protect entirely differently by sensing the PD between live and neutral

[/ QUOTE ]

Yes and if by "PD" you mean potential differance i,e, valtage you are very wrong.
A RCD (residual current detector) some times called RCCD (residual current circuit disconect) or commonly called ib SA earth leakage measures the different in current flowing in the line and neutral cables and tripe if the different in current exceeds 30 mA. In a household instulation this leakage current can only flow down through the earth connection of the appliance through the ground and back to the neutral of the substation by the connection of the neutral to the earth at the substation.

Now in an invertor instulation the invertor replaces the substation and so the neutral of the invertor must be connected to the earth line to the appliance to allow any earth leakage current to return to the neutral and cause the RCD to trip buy the fact of a differance in the current in the live and neutral of the RCD or if not RCD is fitted bu a short circuit triping the breaker or bloeing the fuse whichever fitted.

[ QUOTE ]
I can confirm that neither Lloyds nor DNV would certify an installation where the AC system was not grounded to a hull plate regardless primarily to ensure that ANY stray current anywhere on the vessel that tries to run to earth can do so recognising that the same circuits supplied by a genny or any other devices at sea can also be supplied from shore power.

[/ QUOTE ]

I have no argment about that as the main point IMHO is the last bit "any other devices at sea can also be supplied from shore power" as shore power will have its neutral line connected to earth at the substation and so must the generator and invertor to give the same level of protection

 

[fireball]

But Live is only dangerous when you can realise the Potential Difference ...

Not that I'm going to try it, but I would think I could quite happily sit on my boat with an inverter with isolated earth holding onto the Live wire - so long as there is no return to the Neutral wire I will not get an electric shock.

Our Inverter runs through the shorepower socket - so is partially protected by the RCD there - there is no earth connection on the inverter, I assume that if the case becomes live it blows a fuse ... We can turn it off remotely anyway...

 

[rogerthebodger]

[ QUOTE ]

But Live is only dangerous when you can realise the Potential Difference

[/ QUOTE ]

Correct

[ QUOTE ]
so long as there is no return to the Neutral wire I will not get an electric shock.

[/ QUOTE ]

Also correct but your hair may stand on end

[ QUOTE ]
so is partially protected by the RCD there - there is no earth connection on the inverter

[/ QUOTE ]

If the RCD is between the inverter and the aooliance on the boat yes but if the RCD is in the shpre side supply before the shortpower socket the no it will not protect you when the inverter is in use.

Again if the case of a mains power device has a short from the live side and the supply neutral is connected to the earth (ground) the supply side of the RCD, the current will flow down the live wire to the case and back to the neutral connected through the earth.

The current will flow in the live side of the RCD and not in the neutral side and the RCD will trip. The return is flowing down the earth connection and not through the neutral side of the RCD.

If no RCD is connected the current will rise to the level of the breaker or fuse and trip or blow the breaker or fuse either will then make the circuit safe.

If there is no earth / neutral connection at the supply you would not get a shock unless you cane into contact with the neutral and what is the real problen is that you would not know of the live / case fault in the appliance.

The problen is the fact of the assumption that if the case of the appliance is connected to earth that the installation is safe. In a domestic installation that assumption is correct as the neutral is connected at the supply substation (npower). Now on a boat the supply (excliding shore power) is independant and there the connection ot the neutral to earth of the supply (inverter / generator) connot be assumed and if this connection is not thee you may or may not get a shock but a fault will not automatically trip the safty breaker.

In South Africa all mains installations must by law have a RCD (earth leakage) I don't know the current UK regs but when I lived in the UK 25 years ago it was not a legal requirement.

 

[fireball]

Our inverter is only a measly 300w - it has a 13amp plug (and fuse) which is left in - runs up to the shorepower board - and plugs in instead of the shorepower - before the RCD

 

[rogerthebodger]

300 W id still enough to kill

RCD's trip at 30 mA mush above that can kill and even below can if the person has a week heart.

I was told Volts Jolts but mills (millamps of current) Kills

Pls check that the earth is connected to the neutral at the inverter bu disconnecting the inverter from both shore power socket and battery con test with an ohmeter a short betweer the earth pinh and the neutral of the inverter and the the earth pin of the shore power socket is connected to the earth pins of all the appliances you are using.