Usefullness of Isolated Ground Circuits
Usefullness of Isolated Ground Circuits
(OP)
Anyone know of any studies/papers that may have been written on the effectiveness of isolated ground circuits within office type buildings? I suspect that today's laptop and PC rectifiers are much better equipped to be immune to basic levels of common mode noise.
Thanks.
b
Thanks.
b






RE: Usefullness of Isolated Ground Circuits
The switching power supplies in the computers are creating most the noise in most offices anyway.
RE: Usefullness of Isolated Ground Circuits
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Usefullness of Isolated Ground Circuits
RE: Usefullness of Isolated Ground Circuits
SceneryDriver
RE: Usefullness of Isolated Ground Circuits
RE: Usefullness of Isolated Ground Circuits
SceneryDriver, in the not-too-distant past I had to design electrical for a couple of bowling alleys. There seems to be a major static discharge concern back in the pinsetter area. Think rubber balls sliding down a plastic-coated lane into plastic-coated pins. The auto scorekeeping manufacturer's engineer advised me that the power ground got mighty noisy from discharging all that static, and he didn't want it showing up on the signal cable shields or the chassis grounds. They pulled the IG directly from a ground bus on the service entrance bond with big fat wires, and apparently it did away with most all of the static discharge spikes.
So we had IG receptacles inside the scoring table, up above the approach area, at the cash registers, and in the video arcade. Supposedly it helped a lot... I hope it wasn't just a waste of money.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Usefullness of Isolated Ground Circuits
RE: Usefullness of Isolated Ground Circuits
EMT or thinwall conduit used indent type couplings. These were a straight sleeve type coupling that was indented into the conduit in four places by a special tool. It just took a little bending for the connections to become a little loose. Mechanically the couplings would hold even when loose but electrically, after a few years and a little surface corrosion, they were a disaster for electronic signals.
Most small commercial buildings housing supermarkets were wired with a combination of thinwall conduit and armoured cable.
Over the years grounding and bonding methods were improved to the point that they were the equal of isolated ground circuits.
The first problems that I was aware of came with the advent of Point Of Sale devices (Cash registers) with a data link to a computer.
The designers assumed that a ground connection was automatically a secure connection to the ground mass of the earth. Despite a clause in the North American codes of the time that no equipment may depend on a ground conductor for its operation except for grounding devices, data designers saved a wire by using the equipment ground as a signal return path.
Through code committees the data people lobbied for changes in the Codes to allow isolated grounds.
Concurrent with this code grounding methods were being upgraded. Although many data installations in older buildings needed upgrades to the grounding and bonding systems to function reliably, bonding methods in new construction was generally suitable for dependable data transfer.
I suspect that many data problems were blamed on grounding when the actual problem was elsewhere. When the problem was eventually located no-one jumped up and said;
"Hey! I made a mistake! The grounding was good all the time!!"
After a long career in construction I have a few anecdotes to support these assertions but no studies.
A good study or two may have saved us a lot of wasted time and money on isolated grounds.
I will be the first to admit that there are a very few exceptions where isolated grounds are a good thing, such as in operating theaters.
There have been studies years ago when explosive anesthetics were used when the combination of an explosive gas and a high frequency scalpel caused a patients lungs to explode on the operating table with concurrent injury and sometimes death of the operating team.
This was surely a case for small transformers with grounded inter-winding shields and isolated grounds.
For most data systems a well installed code ground has been the functional equal to an isolated ground for many years. (like 20 or 30 years).
Bill
--------------------
"Why not the best?"
Jimmy Carter