Inverter earth

[dor]

Peiople have mentioned here using these little 150 - 300 watt inverters from Maplins and the like for running TVs etc. They usually plug into a lighter socket.

 

Does anyone bother about linking the earth to the hull? I believe that is the normal practice for larger inverters. I suspect that the earth & neutral are linked anyway to the negative DC input, but what is the recommended way of using these?

 

Also, in view of the proposed BSC amendment: "d. It is proposed a check will be made to ascertain that a residual current device is installed in 230V systems.", presumably these would need to have an RCD to be compliant. Anyone use an RCD with these? (although I think this will be an "advisory").

Edited February 19, 2005 by dor

[bottle]

Peiople have mentioned here using these little 150 - 300 watt inverters from Maplins and the like for running TVs etc. They usually plug into a lighter socket.

 

Does anyone bother about linking the earth to the hull? I believe that is the normal practice for larger inverters. I suspect that the earth & neutral are linked anyway to the negative DC input, but what is the recommended way of using these?

<{POST_SNAPBACK}>

 

If these use a "lighter socket"(12 volt) there will not be any provision for earth, also televisions/radios and similar do not require an earth. If you open the plug, if not sealed, you will not find an earth wire. the reason for this is, the chasis of this type of equipment is used as the return.

[NB Willawaw]

I would use an earth wherever possible. If there is a short circuit inside the appliance being driven, due to overheating, worn cable, loose connection brought on by vibration, etc, the case or chassis of the appliance can become live without blowing a fuse or overloading the inverter. That is, until you touch it and then you will become its route to earth with electrifying results.

If you connect an earth to the inverter and therefore the appliance though the earth wire in the mains power lead between the inverter 230V output and the appliance, the instant the live wire inside the appliance accidently connects with the chassis, it will short to earth through your earth connection using the hull/water as a ground path and your inverter should trip out.

 

Before buying, check to see if the inverter has an earth connection on its AC side and make sure the model you buy has some form of overcurrent protection on its output side.

 

Best Regards

 

Mark

 

NB Willawaw - Stoke Bruerne (GU Northbound)

[John Orentas]

Mark

 

The significant point that was being made by Bottle is that most appliances do not have a provision for an earth connection. In fact few will have a metallic case and the days of a chassis are long gone.

 

Most appliances we buy these days are made for, or to be compatible with the 230 volts 2 phase systems in use in the vast majority of other countries.

 

This concept of Live, Neutral and Earth is a very British one. Few people in Europe would understand the difference between neutral and earth, I am not sure that I do as they are invariably connected together.

 

However I have become embroiled in similar discussions before so I think I will step back from it this time.

[NB Willawaw]

I understand your point and I guess it depends on what the appliance is going to be. Certainly washing machines, mains fridges, etc will have an earth connection to their metalwork, but it is quite possible that modern TV's etc might only have live and neutral wired. A lot of equipment comes pre-wired with moulded leads and plugs these days and its not always easy to see.

At 300W, the appliance is more likely to be a TV, etc.

However, please remember that most houses, which these appliances are designed for, have RCBO's fitted in their consumer units these days.

 

In summary, I would use an inverter with overcurrent protection and a 30mA RCD in the AC circuit and if there is provision for an earth on the inverter itself, I would use it and connect it back to the hull.

 

Please bear in mind that RCD's measure an imbalance between live and neutral currents and can be nuisance triggered by some devices.

 

Sudden changes in electrical load can cause a small, brief current flow to earth, especially in old appliances. RCDs are very sensitive and operate very quickly; they may well trip when the motor of an old freezer switches off. Some equipment is notoriously `leaky', that is, generate a small, constant current flow to earth. Some types of computer equipment, and large television sets, are widely reported to cause problems.

 

Persistent nuisance tripping, or an RCD that won't switch on at all, are causes for concern. Either can indicate an intermittent or permanent live-earth fault somewhere in the circuit (e.g., a faulty appliance flex).

 

Regards

 

Mark

NB Willawaw - Stoke Bruerne (GU Northbound)

[bottle]

Any earth is only supplied for safety reasons.

 

There is not one piece of electrical equipment that requires an earth.

It is used where the outer casing is made of conductive material i.e. metal.

The earth supplies the least resistence for electrical flow for when a fault in the insulation breaks down. this could be any fault but usually is a live supply connecting to the metal casing. If the earth was not available the casing would be live, then if you touch it you complete the cicuit (and your eyes lightup )

 

Electricity (230volt mains) is generated by generaters that supply 3 phases. To try and explain this: there are three coils surrounding a rotating magnet which induces the coils with the voltage. Each coil has two ends (obvious) one end of each coil is connected to a common point therefore making the neutral / earth.

 

 

An inverter is a transformer and there is not any physical connection from input to the output. THIS STATEMENT IS WRONG PLEASE SEE FOLLOWING POSTS

Edited February 20, 2005 by bottle

[maffi mushkila]

<snip>

An inverter is a transformer and there is not any physical connection from input to the output.

 

NO SIR!

 

I have to differ there.

 

An inverter changes DC to AC. It can be static or rotary.

 

A transformer, transforms one AC voltage to another AC voltage it too can be static or rotary. It can transform high voltages to low voltages or low to high. Can also be used as Isolation transformers by having two coils of equal size giving the same output as input.

 

To change AC to DC you need a transformer, a suitable rectifier and smoothing circuit. This is then a Transformer Rectifier Unit (or wall wart as I have recently heard them called) or mobile phone charger.

 

An auto transformer, will, if the secondary half of the coil becomes open circuit apply the full input voltage across the load. Your statement implies that this does not happen.

http://www.canalworld.net/forums/index.php...&cmd=si&img=129

 

An Inverter is not a transformer though it 'may' contain one.

Edited February 20, 2005 by maffi mushkila

[bottle]

NO SIR!

 

I have to differ there.

 

An inverter changes DC to AC. It can be static or rotary.

 

A transformer, transforms one AC voltage to another AC voltage it too can be static or rotary. It can transform high voltages to low voltages or low to high. Can also be used as Isolation transformers by having two coils of equal size giving the same output as input.

 

To change AC to DC you need a transformer, a suitable rectifier and smoothing circuit. This is then a Transformer Rectifier Unit (or wall wart as I have recently heard them called) or mobile phone charger.

 

An auto transformer,  will, if the secondary half of the coil becomes open circuit apply the full input voltage across the load. Your statement implies that this does not happen.

 

An Inverter is not a transformer though it 'may' contain one.

<{POST_SNAPBACK}>

 

 

Maffi

 

You are correct if you look at the time I posted it I think I may have been inverted if not tranformed.

[maffi mushkila]

Maffi

 

You are correct if you look at the time I posted it I think I may have been inverted if not tranformed.

 

No excuse in a Court of Law if the family of some hapless soul sue you for your misinformation causing the death of their loved one.

 

I have added a pic to the post.

 

And what are you doing up at such an ungodlt hour?

Edited February 20, 2005 by maffi mushkila

[bottle]

Maffi

 

been back and edited the post. Am I safe from the Caw now.

 

Have been to a dinner party.

[maffi mushkila]

Maffi

 

been back and edited the post. Am I safe from the Caw now.

 

Have been to a dinner party.

<{POST_SNAPBACK}>

 

 

No! coz I have also been back and edited my post and now it is correct "Law"

 

 

Nah nah

Edited February 20, 2005 by maffi mushkila

[bottle]

No! coz I have also been back and edited my post and now it is correct "Law"

Nah nah 

<{POST_SNAPBACK}>

 

 

I am speechless

[maffi mushkila]

I am speechless    

 

 

Sir

I am sorry to hear you are in such a predicament.

 

However I am in a position to assist you.

 

I have at my disposal several speeches of some great quality.

 

I would be willing to part with one or more for a financial consideration.

 

Shall we say 50 sovs a piece?

[maffi mushkila]

My apologies to any of the 18 guests that are reading this I have got my stupid head on today and been out in the sun.

 

 

Those of you who are members will know that I only have the one head so no apology is felt necessary.

Edited February 20, 2005 by maffi mushkila

[bottle]

I am sure I will recover but as usual we have wandered

 

Has the info supplied answered the original problem?

[maffi mushkila]

I am sure I will recover but as usual we have wandered

 

Has the info supplied answered the original problem?

<{POST_SNAPBACK}>

 

 

1. Of course we have, its what we do.

 

2. You ask me like I should know.

[dor]

Going back to the original question: If I was installing a fixed inverter, I would certainly link the earth to the hull, and use an RCD. However, with these little inverters, that you probably use for just one device, I just wondered if it really needed a separate earth to the hull. They don't generally have an earthing stud on them, so presumably rely on the negative dc input to earth.

They are widely used in vehicles where presumably it is not a problem. The question arose from reading the electrical safety section of the new BSC details, that recommends an rcd.

[bottle]

Dor

 

As you now understand, I'm sure, if the item you are using does not have an earth terminal an earth is not required. If it is possible for "you" to touch any part that could become live i.e. a metal casing then an earth is required.

 

An example in a domestic situation is a ceiling light fitting an earth wire is routed all the way to the ceiling rose but is not continued to the lamp holder unless it is metal.

 

An RCD is always a good idea. This should not ever be rated above the cable capacity but can be lower.

 

Sorry that we wandered of subject

[dor]

No prob Bottle.

 

I think if I was going to use an RCD with one of these, I would hard-wire the earth back to a separate earthing post rather than rely on the internals of the inverter. Incidently, talking to a friend yesterday, he says his TV works better on one of these little 150watt can inverters than it does off his 2000 watt pure sine wave jobby.

[John Orentas]

Bottle.

 

Don't confuse an RCD with a circuit breaker. The RCD doesn't have a current rating as such. It detects a current imbalance as with a person conducting to earth. (Residual current device)

 

A circuit breaker detects a current above it's fixed rating and breaks the circuit, it must be reset manually. (rather like a resettable fuse).

 

An RCD does not give protection against over-current or short circuits.

A circuit breaker does not give protection against electric shock.

Edited February 20, 2005 by John Orentas

[PhilipL]

I was always under the impression that RCDs (Residual Current Device) also acted as overcurrent trips, MCBs (Mininiature Circuit Breaker). However as I didn't know what an RCBO was I had to look it up, and they are Residual Current Breaker with Overcurrent protection.

 

So it seems that now you can have RCDs with or without overcurrent protection, and the ones with overcurrent may be described as RCBOs. For example on the Index Marine website they sell RCDs with or without overcurrent protection and the ones without are described as RCD only.

 

I don't know whether or when things changed, and how you would tell the difference if you already have one. If no one else knows I can probably find out at work,

 

Phil

[John Orentas]

Phil

 

Come on let us not complicate thing unduly, yes you can get combined units. You don't need to find out at work, if it is an RCBO it will have printed on it RCBO.

[bottle]

Dear All

 

I think the best thing to do is put in all the protection possible and earth anything that can be.

 

The protection equipment market is changing rapidly so try to get expert advice where ever possible.

 

Electricity is a wonderful thing but you cannot see it or smell it. You can certainly feel it if it bites though.

[PhilipL]

Phil

 

Come on let us not complicate thing unduly, yes you can get combined units. You don't need to find out at work, if it is an RCBO it will have printed on it RCBO.

<{POST_SNAPBACK}>

 

I believe that it's cheaper to buy a combined unit than to buy seperate devices so I think it's reasonable that people should be aware that they exist. The only disadvantage is the RCBOs normally seem to be single pole wheras RCCBs are normally double pole.

 

What I'm suggesting that an old RCD which has overload protection may not be marked RCBO, because that is relatively recent term. The names of these devices has changed over the years. Originally ELCB, then RCB, then RCD. I think that we now have RCCB and RCBO which are both types of RCD. I for one need to know, so I will ask at work,

 

Phil

[John Orentas]

Phil

 

I have been taken to task a couple of times for adding unnecessary complexity to some of these issues, I was not directing any criticism at you. Many of these devices have been re-named to reflect the fact that they operate in a rather different manner.

 

I personally would not recommend the use of combined devices on a boat because if /when they trip, you never will never quite know why. Was it an overload, short circuit or was it a potentially more serious live to earth fault.

Edited February 20, 2005 by John Orentas