russ_watters
Member
I would like to know more about the IEEE's 5 ohm recommendation for grounding systems for sensitive equipment.
For background, I'm a mechanical engineer in an MEP firm. We have an electrical engineer, but I do most of the field work here, so I've been tasked with this project. We received a call from a foreign-based pharmaceutical in our area that received a question from their corporate office about how good their grounding system is. No problems - they just want to know. My boss has a hands-on philosophy and the fee for the testing covered purchasing the equipment, so doing it was a no-brainer.
The NEC says little besides their 25 ohm requirement for a single electrode. There is an IEEE recommendation of 5 ohms and I bought the 700 page IEEE 1100 standard, but it makes only passing reference to this recommendation.
I'd like to know chapter and verse for this recommendation so I can cite it in my report. The biggest issue I'd like to clarify is where that 5 ohms is measured - is it at an electrode or in the system at the data center panel?
We used our new Fluke ground resistance tester to measure the resistance at various places in the system, matched it with the single line diagram, and came up with numbers that make sense (ie, for a point with two ground paths, the numbers exactly match the calculated resistance for resistors in parallel).
What we found is that at the panel that serves the data center, the resistance is 5.35 ohms. That's probably fine, but I'd like to be able to comment on the 5 ohm recommendation. The building lacks a ground connection to the incoming water service, so I'm going to make that recommendation regardless.
I have read THIS thread, and I understand that the whole procedure was probably unnecessary, but I'm being paid to "know" and paid to make recommendations.
For background, I'm a mechanical engineer in an MEP firm. We have an electrical engineer, but I do most of the field work here, so I've been tasked with this project. We received a call from a foreign-based pharmaceutical in our area that received a question from their corporate office about how good their grounding system is. No problems - they just want to know. My boss has a hands-on philosophy and the fee for the testing covered purchasing the equipment, so doing it was a no-brainer.
The NEC says little besides their 25 ohm requirement for a single electrode. There is an IEEE recommendation of 5 ohms and I bought the 700 page IEEE 1100 standard, but it makes only passing reference to this recommendation.
I'd like to know chapter and verse for this recommendation so I can cite it in my report. The biggest issue I'd like to clarify is where that 5 ohms is measured - is it at an electrode or in the system at the data center panel?
We used our new Fluke ground resistance tester to measure the resistance at various places in the system, matched it with the single line diagram, and came up with numbers that make sense (ie, for a point with two ground paths, the numbers exactly match the calculated resistance for resistors in parallel).
What we found is that at the panel that serves the data center, the resistance is 5.35 ohms. That's probably fine, but I'd like to be able to comment on the 5 ohm recommendation. The building lacks a ground connection to the incoming water service, so I'm going to make that recommendation regardless.
I have read THIS thread, and I understand that the whole procedure was probably unnecessary, but I'm being paid to "know" and paid to make recommendations.