Sub Panel Grounding

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Old 01-21-18, 08:42 PM
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Sub Panel Grounding

While researching posts for my sub-panel installation, I seem to recall that your resistance to ground should be less than 25 ohms. Is that literally checking resistance from your sub-panel grounding lug to the earth with an ohm meter, or is a special meter used or some other process?
 
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Old 01-21-18, 08:50 PM
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Sub Panel Grounding

For my sub-panel installation I know that neutral and ground have to be isolated. I discarded the green ground screw that came with the panel and bought a ground lug terminal kit and installed it for my grounds. But while looking for some other material, I now see there are isolated ground terminal kits. Should I have purchased and installed an isolated ground terminal instead?

I'm thinking that if I disconnect my neutral wire from my feed at my sub panel and check the resistance from the neutral bar to my ground bar that would be good enough to verify my ground is isolated- correct?
 
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Old 01-21-18, 09:25 PM
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I combined your similar threads.

The ground block gets connected directly to the metal panel.
Only the neutral remains isolated.
 
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Old 01-22-18, 05:17 AM
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The first panel (typically a subpanel for an outbuilding) needs ground rods (8 foot driven in all the way). After 2 ground rods are installed, no 25 ohm or less resistance check (requires special equipment rarely possessed by a homeowner) is needed.

A grounding terminal strip (bus bar) sold separately must be installed according to instructions which usually include scraping the paint from the panel back where the strip is attached or adding a jumper strip or wire to the panel back.
 
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Old 01-22-18, 06:35 PM
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PJmax- thanks for the clarification.
Allanj- that's good to know, thanks. Per previous input I've already driven the two rods in, but after reading the 25 ohms comment somewhere I was starting to wonder if I had missed something.
 
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Old 01-23-18, 06:32 AM
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If there is only a single driven electrode you need to be less than 25 ohms. The test is requires expensive equipment. It is easier to drive a second rod and be done with it.
 
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