5 ms·
I think you may be right: Its actually IEEE and NFPA that recommend a maximum of 5 Ohms for the grounding system. NEC state less than 5 Ohms for sensitive equ
by supermatt 7y ago
I think you may be right:
Its actually IEEE and NFPA that recommend a maximum of 5 Ohms for the grounding system.
NEC state less than 5 Ohms for sensitive equipment, 25 Ohms otherwise. (NEC 250.56) - but as you mentioned, the measurement is only taken from first rod and a second can be inserted without testing (so it could be over 25 Ohms still, but based on the code it doesnt even matter....)
As an aside, its 200 Ohm in the UK (but it HAS to be measured - cant just blindly drive 2 electrodes and call it a day).
- sokoloff 7y agoThis discussion triggered in me the question, "Obviously, I can't just stick a meter probe in the ground [as I'd be measuring the dominant resistance of that probe rather than the grounding rod in series]. So, how would I reasonably measure the resistance of an earth connection?" I came up with the (mildly hazardous) solution of putting a 120VAC line from the power company supply down the ground rod and measuring the current flow back to the PoCo (grounded) neutral conductor and then went googling. There are a few other (safer) ways that might interest HN readers, so sharing this video: https://www.youtube.com/watch?v=Yg6G5VUSsWA https://www.youtube.com/watch?v=Yg6G5VUSsWA
- mcguire 7y agoThey have several hundred dollars of equipment there and have a stripped end of a piece of bell wire plugged into the 120VAC extension cord. I love electricians (and electrical engineers).