I was wondering what are the disadvantages of floating ground (for example the chassis of a caravan) over earth ground. It's seems to be safer to left unearthed a chassis in order to break the grounding loop that exists in an electric shock event

It is related to the electric potential of the floating ground? it is worst for the electric appliances? If there's no electric shock with a 'live' chassis because there's no closed circuit.. why should the chassis be earthed?

 

I was wondering what are the disadvantages of floating ground (for example the chassis of a caravan) over earth ground. It's seems to be safer to left unearthed a chassis in order to break the grounding loop that exists in an electric shock event

It is related to the electric potential of the floating ground? it is worst for the electric appliances? If there's no electric shock with a 'live' chassis because there's no closed circuit.. why should the chassis be earthed?

Because it is "single fault tolerant". If there is a single fault (short between either live or neutral and earth) then it goes unnoticed. If there is a second fault, with no other safety devices, then it can be lethal.

 

we live on the surface of the planet (like "fleas on the back of the planet'). practically - we are constantly in the contact with it.

it is known that current follows favours the path of least resistance... but things have different conductivity/resistance... this makes the situation complex. and goal with safety is to make things simple and predictable - always.

by purposely making conductivity of all relevant parts high (low resistance) and connecting things together, a pretty universal reference potential is obtained. this is the earth potential.

this way when there is a fault (melted terminal, lose wire, punctured cable insulation etc.) and the LIVE wire is to touch something - it is likely to touch something that is already grounded/bonded (which is why electrical panels and even the panel doors need to be grounded/bonded).

since this situation is clearly unwanted (a failure), properly designed circuits will respond to it immediately - the unwanted connection will cause short and trip/blow upstream fuse/breaker. then the circuit is no longer live and that makes it SAFE and someone will need to find out what happened and fix it. yes this is inconvenient for someone to do a follow-up and the blown fuse may cost a bit but the cost is low (price if coffee instead of costing someone his life).

if the live wire contacted something that was NOT grounded, no fail safe mechanism would be triggered and that something would be electrified. in other words it would just be waiting for someone to approach and touch it, likely killing the unfortunate person. worse, this can cause chain effect - rescue people may fall into the same trap and get killed to. not all - someone may have proper gear (shoes, gloves) and seem unaffected. but the next person unaware of this (and rushing to assist) would still get killed. this is unacceptable.

this is why countries around the world have developed regulations which pretty closely match each other in terms of requirements and proper practices.

so if you are designing piece of the equipment, you are REQUIRED to follow the local electrical code. you may THINK that YOU are safe and that YOU know how to not get hurt, but this is not enough. it is all about protecting not just YOU but EVERYONE ELSE too. and the standards spell it out what is legally required to make something safe. and there are cases where floating circuits are allowed but there are conditions/restrictions when and where this is acceptable (therefore - read and understand the applicable standards). which is why you would be legally liable for all your work, specially if it leads to injury, death or even material/property damages.

 

Ungrounded doesn't mean no electric shock or voltage potential danger. Floating grounds can be static shock hazards causing fires and fuel explosions, that's why you see grounding chains and the like on fuel trucks.

 

it is known that current follows the path of least resistance..

Really? So if I parallel a 1 Ohm resistor with a 2 Ohm resistor, all the current flows through the 1 Ohm one?

Current follows ALL possible paths.

 

yup, TS was asking about grounding appliance which deals with mains but static electricity is another side of the coin. anyone working with dust collection, shot peening, sand blasting etc should know why the equipment and ductwork must be grounded.

 

Really? So if I parallel a 1 Ohm resistor with a 2 Ohm resistor, all the current flows through the 1 Ohm one?

Current follows ALL possible paths.

sigh... fair enough, thank you language police.

precise language is important so i corrected that statement.

 

It also depends on what you are designing. A simple AC appliance is far different than a piece of electronic equipment. It is important that you understand grounds, have a grounding approach, and keep thinking "safety" (i.e. what happens if there is a fault in the equipment and someone touches it while standing on the floor. A related discussion can be found here for audio equipment systems. https://www.cascadetubes.com/2020/01/13/grounding-philosophy/

 

Really? So if I parallel a 1 Ohm resistor with a 2 Ohm resistor, all the current flows through the 1 Ohm one?

Current follows ALL possible paths.

Let me get back to you on that. I just sent a text to Kirchhoff asking him about how that would work. Kirchhoff has some rules about that and soon as he returns my text I will have a good answer.

Ron

 

Power tools are designed and manufactured with understanding of both concepts.

Household appliances and industrial equipment are usually electrically bonded to earth ground. If there is an electrical fault and the chassis becomes live then the circuit breaker or ground fault circuit interrupter (GFCI) should trip and disconnect power.

Some tools are manufactured and advertised as double insulated. This means that there are two layers of insulation to avoid the tool ever becoming live.

Edit: BTW, I am not sure what you mean by "floating ground". There is no such thing. You can have a floating power supply or a floating COMMON. Ground is ground, not floating.

 

sigh... fair enough, thank you language police.

precise language is important so i corrected that statement.

I called it out because it is a common misunderstanding among beginners. I don't want to see it reinforced.

 

What word "ground" could mean to others.

 

So the question begs where is earth ground on a ship, a large ship? While I can't speak globally here in the US residential power delivery has the Neutral and Earth Ground bonded at the entry point. Tools and appliances do not have a path between earth ground and neutral, there is no bonding.

Shipboard power on large ships use what is known as an "insulated neutral" system. As the name implies, the neutral phase wire is totally insulated from (and therefore not earthed to) the ship’s hull.

This is some interesting trivia. I spent time on US war ships and primarily Aircraft Carriers. The single phase 120 VAC 0 Hz. outlets were 60V - 0V - 60V. Obviously Neutral and Ground were not tied together.

Ron

 

What is "ground" on an automobile or airplane?

 

If you were to hook up your caravan to the mains supply and not have the chassis of the caravan grounded/earthed, then a fault could result in the caravan chassis becoming live without a fuse or other overcurrent device operating.

Whilst this might not be a problem to someone in the caravan, someone outside touching the caravan is likely to receive an electric shock.

 

What is "ground" on an automobile or airplane?

Same as on a ship. Ground is merely a point of reference. All we need to do is remove the word earth preceding the word ground.

Ron

 

So the question begs where is earth ground on a ship, a large ship? While I can't speak globally here in the US residential power delivery has the Neutral and Earth Ground bonded at the entry point. Tools and appliances do not have a path between earth ground and neutral, there is no bonding.

Shipboard power on large ships use what is known as an "insulated neutral" system. As the name implies, the neutral phase wire is totally insulated from (and therefore not earthed to) the ship’s hull.

This is some interesting trivia. I spent time on US war ships and primarily Aircraft Carriers. The single phase 120 VAC 0 Hz. outlets were 60V - 0V - 60V. Obviously Neutral and Ground were not tied together.

Ron

Britain (and Europe) also bonds neutral and earth at the entry point.
Britain uses a similar system to the aircraft carriers on (outdoor) building sites. Power tools are all 110V and are supplied from the 230V supply via a transformer wired 55-0-55V, with the centre-tap earthed. As far as I know, the same system is not used in Europe.

 

The bottom line for me is to be safe around electrical energy. We just had three people killed from high voltage wiring.

 

in time everything fails. the overhead wires are exposed to elements which obviously does not help.
some are underground but that has own set of + and -.

existing systems meant to prevent things like this are not sensitive enough. there was a young man that was helping clear the branches near power lines and unfortunately he got electrocuted. the system detected something was wrong but was sending test couple of test pulses, each of them turning the body of the young man more crisp. perhaps running fiberoptic cable inside power wire would be more reliable way to detect wire break and disable line and rendering it safe.

 

Britain (and Europe) also bonds neutral and earth at the entry point.

I guess things have changed since I was involved in that issue.
Back then, the supply authority would only allow an Earthed conductor (neutral) to be connected at supply transformer only.
All neutrals & Earth had to be isolated from each other in the residence or building supplied.
They would not connect until this was tested as such.