Are they really that bad? When I saw that they were being recommended, I wondered how one would run an arc-welder.
They don't work on ring-mains because every socket is supplied by two different paths, it's not very good at detecting a loose connection on one side.

My experience is that large brushed motors trip them every time. I suppose it would take a lot in built-in intelligence to distinguish between legitimate danger condition and some perfectly good uses.

 

BACK TO THE ROBOT MENTIONED IN POST #1
I see now that the question IS ABOUT THE 5KW INVERTER OUTPUT!! The is robot is powered bt a 48 volt battery pack!! As I now understand, there is no mains connection to the robot.
At least that is what I get from post #1!

"The 5KW inverter output has 3 terminals, line, neutral and PE"

If that is the case then the green wire serves no purpose, safety or other wise!!
Until one or the other output terminals is connected to the robot frame, there is no serious shock hazard from the contact with a single AC power conductor.

The sole purpose of that green wire safety connection to earth ground is to assure that there will be no serious voltage between the exposed conductive portions of a device and earth ground, BECAUSE one side of the mains voltage is tied to earth ground.
Inside the robot that is not the case.

 

BACK TO THE ROBOT MENTIONED IN POST #1
I see now that the question IS ABOUT THE 5KW INVERTER OUTPUT!! The is robot is powered bt a 48 volt battery pack!! As I now understand, there is no mains connection to the robot.
At least that is what I get from post #1!

"The 5KW inverter output has 3 terminals, line, neutral and PE"

If that is the case then the green wire serves no purpose, safety or other wise!!
Until one or the other output terminals is connected to the robot frame, there is no serious shock hazard from the contact with a single AC power conductor.

The sole purpose of that green wire safety connection to earth ground is to assure that there will be no serious voltage between the exposed conductive portions of a device and earth ground, BECAUSE one side of the mains voltage is tied to earth ground.
Inside the robot that is not the case.

The inverter in the TS's application has three outputs.
An IT earthing system is single-fault-tolerant. When properly working, either side of the 230V output can be touched and no shock will occur (but, obviously, a shock will occur if both 230V outputs are touched at the same time)
Being single-fault-tolerant means that the first short to chassis will go undetected, but at that point the system turns into a TT earthing system. One wire is now live with respect to the chassis, and will present a hazard. Of course, it is an extra hazard if one were expecting no shock from touching either wire.
This is the reason that IT earthing systems are banned in most applications apart from an isolating transformer with a single output.
If the TS wanted to use an IT earthing system it would require earth-fault detection, to detect if either 230V conductor had been shorted to chassis. An RCD (or ground fault interruptor if you prefer) isn't going to do that, because for an IT earthing system with a single short to ground there isn't any fault current to earth (because it has become a TT earthing system)

 

The inverter in the TS's application has three outputs.
An IT earthing system is single-fault-tolerant. When properly working, either side of the 230V output can be touched and no shock will occur (but, obviously, a shock will occur if both 230V outputs are touched at the same time)
Being single-fault-tolerant means that the first short to chassis will go undetected, but at that point the system turns into a TT earthing system. One wire is now live with respect to the chassis, and will present a hazard. Of course, it is an extra hazard if one were expecting no shock from touching either wire.
This is the reason that IT earthing systems are banned in most applications apart from an isolating transformer with a single output.
If the TS wanted to use an IT earthing system it would require earth-fault detection, to detect if either 230V conductor had been shorted to chassis. An RCD (or ground fault interruptor if you prefer) isn't going to do that, because for an IT earthing system with a single short to ground there isn't any fault current to earth (because it has become a TT earthing system)

Certainly correct! BUT there is a simple and easy way around the stated issue: "Ground Detector lights." They were mandatory in many GM assembly plants where we put our testing machines. A very simple system that was totally effective. On the door of the electrical controls system cabinet were two amber 120 volt (800T series) pilot lights, wired in series across the isolated 120 volt supply. The junction between the two lights was always solidly tied to the system GROUND, which WAS NOT tied to that isolated 120 volts from the large control transformer. The operation was that if either side of the 120 volts became "grounded" that amber light would go out and the other would get brighter. So the warning would be spotted even with the panel closed. Cheap and easy and very reliable.

 

Certainly correct! BUT there is a simple and easy way around the stated issue: "Ground Detector lights." They were mandatory in many GM assembly plants where we put our testing machines. A very simple system that was totally effective. On the door of the electrical controls system cabinet were two amber 120 volt (800T series) pilot lights, wired in series across the isolated 120 volt supply. The junction between the two lights was always solidly tied to the system GROUND, which WAS NOT tied to that isolated 120 volts from the large control transformer. The operation was that if either side of the 120 volts became "grounded" that amber light would go out and the other would get brighter. So the warning would be spotted even with the panel closed. Cheap and easy and very reliable.

It may be simple, but the effect is to turn the IT system into a TT system with a centre tapped supply.
In the USA you have succeeded in reducing the available voltage to 60V which is almost to the level that is considered safe.
On a 230V supply, you would have, instead of live and neutral, two 115V lives, each with an output impedance set by the lamp. Filament indicator lamps are not easy to get any more, and would a neon be bright enough? You could use a relay coil, but that would still require 10mA.
Just to add to the complexity, and the TS doesn't state the country in which is machine is to be used, British regulations would require 110V power tools if used on a building site, supplied from a transformer with its centre-tap earthed.

 

In a battery powered robot with an onboard inverter the probability of an accidental connection to the robot frame of one side of the inverter output is not very likely. AND, where did the 230 volts appear??? Only Ian mentioned that, I guess he resides in a 230 volt country. I was addressing the 120 volt world. AND the AB company is able to provide the required bulbs for their pilot lights from an eternal source.

 

AND, where did the 230 volts appear???

In the attachment on post #9

 

In the attachment on post #9

I read that attachment. It is a publication relating to robots in general. I saw noting to say it was referencing this particular robot assembly.

AND an interesting caution was given:
clean, newly regulated voltage and to block power-line noise, not to create a
permanently separate ground.


Once this bond is made, all 12V ground returns from logic boards, sensors, and other
low-power devices should follow the star topology, connecting back to the SPG. For
organizational clarity, it is acceptable to create a secondary, low-power ground bus
bar for the 12V systems, which is then connected via a single, appropriately sized wire
to the main SPG stud. This maintains the hierarchical star structure.
2.4 The AC Domain (230V) and Inverter Safety
Grounding the DC-AC inverter on a mobile platform involves two separate and distinct
connections, and the safety philosophy is different from that of a stationary building.

1. Equipment Ground Connection (Safety Earth):
The inverter chassis will have a dedicated grounding lug, often marked with the protective
earth symbol (⏚), "GND," or "FG" (Frame Ground). This lug must be connected with a
dedicated wire directly to the SPG stud on the robot chassis.5 This is a non-negotiable safety
requirement. This connection serves as the "equipment grounding conductor".24 Its purpose
is to bond the inverter's metal case to the rest of the robot's metallic structure. In the event of
an internal inverter fault where a "hot" 230V AC conductor touches the case, this ground wire
provides a low-impedance path for the fault current to flow. This massive current flow should
immediately trip the inverter's internal fuse or circuit breaker, de-energizing the output and
preventing the entire robot chassis from becoming live at 230V.5
2. Neutral-to-Ground (N-G) Bond:
In a stationary building, the AC Neutral wire is bonded to the Earth ground at a single point,
typically the main service panel, to establish Neutral at a safe, near-zero potential.24

On a mobile, untethered platform, you should NOT create this bond yourself.

Most inverters designed for portable or vehicular use are "floating neutral" or
"isolated output" systems, where neither the Line (Hot) nor the Neutral AC output is
referenced to the inverter's chassis.24
Creating an N-G bond on the robot can defeat the operation of integrated safety
devices like Ground Fault Circuit Interrupters (GFCIs) or Residual Current Devices
(RCDs).28 A GFCI works by precisely measuring the current flowing out on the Line
conductor and returning on the Neutral conductor. If it detects any imbalance
(meaning some current is "leaking" to an alternate path, like the equipment ground or
a person), it trips instantly.29 An artificial N-G bond can create parallel paths for
neutral current that can blind the GFCI to a real fault. Safety for the AC system is
achieved through the combination of the equipment ground connection and the
proper functioning of the inverter's built-in protection mechanisms.


THIS WAS A PAIN TO COPY AND PASTE!!!

 

I read that attachment. It is a publication relating to robots in general.

You are probably correct. I thought it was the spec for the TS's robot.
Certainly, any robot built to that spec would not be legal in Britain.

 

One more piece of information: I have three small inverters, all 120 volts output (modified sine wave), with 12 volts DC input.
Two of them have a very explicit warning: DO NOT CONNECT EITHER SIDE OF THE AC OUTPUT TO THE GROUND PIN !!! One instruction sheet explains that will cause immediate damage to the inverter.
Elsewhere in the manual it mentions that the third pin (ground) is tied to the DC input negative input.
The wise choice will be to read the inverter manual and see what is recommended.