Indirect problems with the instrument cabinet
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There has been a problem that has been bothering me since I started working. During the construction of the instrument cabinet room at the beginning of my employment, it was required that the protective ground and the working ground for the instruments be separated, with a separate set of grounding electrodes needed for outdoor areas. Design drawings that I have been working with for about 10 years now generally involve the common grounding for instruments and electrical systems; the protective ground and the working ground are connected to two separate busbars, which in turn are connected to the electrical grounding grid. So hasn’t another one been received?
The new standard requires connection to the electrical ground, whereas previously they were grounded separately.
From the beginning to now and even in the future, it’s all connected; no one said it needed to be grounded separately.
It was designed this way during construction in 2009; later, I asked other designers and was told that it had changed, and now it is specified that a separate set of grounding electrodes should be used when the grounding resistance does not meet the requirements. It was also mentioned in the early construction specifications
That’s indeed the case; we’re doing the same thing.
Even separate grounding must be connected to the factory grounding grid; there is no such thing as separate grounding at all. The so-called separate grounding is nothing but paralleling the factory grounding grid.
The function of grounding is to protect electrical equipment; whether to use common grounding or separate grounding, the most important thing is to determine the value of the grounding resistance. If the common ground resistance is <10 ohms (I think so; I’m not very sure as I’m not an electrical engineer), then a common ground can be used, but if it’s greater than that, a separate ground is required.
The electrical grounding resistance is generally designed to be no more than 4 ohms, and instruments are usually connected to the electrical system as well
The protective ground is the metal casing of the enclosure that is grounded. The working ground is provided to ensure the reliable operation of the system as well as the instruments connected to it, and to maintain accuracy in measurements and control. The voltages at the working site and the protection area are different, so they are grounded separately to prevent high voltage from reaching the low voltage area. As for the part where it ends up converging again, it’s not quite clear to me.