We're running power for medical equipment. The equipment comes with a service manual. In the service manual it mentions "D type grounding". Here is all the information as it is stated in the manual:
"Ground Terminal
Grounding resistance should be less than 100 ohms (D type grounding) ground terminal. Use a single ground to earth. Do not share with other electrical apparatus."
Never heard of "D type grounding". Based on the description it sounds like an "isolated ground" but since it's referring to the "ground terminal" I'm not certain. Anybody familiar with the term "D type grounding"?
Could it by chance mean "dedicated ground"?
The instructions appear to call for a ground that violates our code. Better have a chat with the inspector.
Never heard of that term either but looking at Google shows referenced to class A thru D grounding.
Some installation manuals that are in the search seem to be from Europe / Asia and have the line:
D type Grounding (grounding resistance is lower than 100 ohms)
They mean isolated ground. You run a dedicated, insulated conductor way the way back to the grounding electrode. You don't share "that conductor" with any other apparatus.
That commonly gets misunderstood to mean you drive a separate rod. That is not right.
All grounding conductors have to be bonded to the neutral back at the SERVICE.
Truly isolated grounds have been tried -- and they ended up causing the whole dang structure to burn down to the ground during lightning strikes. (Florida)
It's essential to establish an equapotential voltage plane. That stops instantaneous arcs from jumping during lightning events -- or other weird transients -- such as a nearby transformer fault. (traffic collision)
At some point I will meet the tech from the company who is supplying the equipment and he will likely confirm that "D type grounding" is in fact an "isolated ground". Until then, thank-you for the replies.
I have run into quite a few cases where the terminology ended up being the enemy.
I would suggest that you draw up what you want to provide and ask the tech to look at it. That works out better than agreeing on what to call it...only to find out later on that your definition differs from his.
Case in point; I have run across at least 3 meanings of the term 'dedicated circuit'. All of them being equally right (or equally wrong) since NEC does not define the term.
I have run into quite a few cases where the terminology ended up being the enemy.
I would suggest that you draw up what you want to provide and ask the tech to look at it. That works out better than agreeing on what to call it...only to find out later on that your definition differs from his.
Case in point; I have run across at least 3 meanings of the term 'dedicated circuit'. All of them being equally right (or equally wrong) since NEC does not define the term.
Excellent advice. Thank-you.
Ghost307:
I agree that your suggestion is excellent, and well said.
My opinion of the OPs question, I would lean toward a EGC straight back to the source panel.
More details...
This installation is taking place in a hospital. The room with the equipment will be fed from a newly installed panel. There will be a step down transformer with an electrostatic shield installed between the panel and the equipment. The primary will be supplied with 208V and the secondary will be 100V. A 3 meter cord will supply power from the secondary to the equipment. The tech told my boss to bring the "isolated ground" (term my boss used although he's called it a "dedicated ground" as well) off the secondary. My boss then plans to run the ground all the way back to the building ground which is a few floors down. I believe he's going to use insulated #6 CU. Thoughts?