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Looking at the actual text of the code I see why there was some confusion in my Google results. Yeah you size the equipment ground based on the ampacity of the protection device, but if you install larger than necessary power conductors you have to proportionately upsize the ground. I’ve got an installation guide from Nokia calling for a 4 gauge ground and that didn’t make sense to me, but I think I got to the bottom of it. They call for 2-gauge power conductors, which would be stupid overkill for 70A unless you consider an installation in a CO where you might connect to a power plant 40ft across the room. Then you DO need 2 gauge power wires, and if you upsized the power cable that much then you have to upsize the ground. So if they have to give an installer one number they’re giving them a safe number. With a 4ft power run to a rectifier in the same rack I think I could drop all of those power and ground conductors to 6-ga rather than fight a bundle of 2-ga anacondas through the rack. Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: AF <af-boun...@af.afmug.com> on behalf of ch...@go-mtc.com <ch...@go-mtc.com> Sent: Tuesday, January 7, 2025 12:08:34 PM To: AnimalFarm Microwave Users Group <af@af.afmug.com> Subject: Re: [AFMUG] Equipment Ground Wire Sizes Depends on if you are grounding for safety and circuit breaker blowing, like for a receptacle, or grounding for surges etc. They keep trying to convince the world that a small surge suppressor needs a #6 wire, but that is almost impossible. #10 works well for surge suppressors. As far as the NEC is concerned, you can go smaller than the current carrying conductors for the grounds. 120.122 has the rules but for example a 60 amp circuit can use a #10 wire. It has to do with what the circuit breaker needs in order to properly interrupt the current during a fault. For 15 and 20 amp circuits you normally would use a #14 and #12 ground respectively. From: Adam Moffett Sent: Tuesday, January 7, 2025 9:14 AM To: AnimalFarm Microwave Users Group Subject: [AFMUG] Equipment Ground Wire Sizes I found some code references saying that an equipment ground wire should be either equal in size to the power conductor to the equipment or based on the amperage of the circuit protection device. For example, a device on a 20A breaker would use the larger of 12ga or the size of the power conductor to the device. But then you have things like R56 calling for nothing smaller than 6 gauge. And then I have manufacturer installation guides which may go a step further and call for 4 gauge or 2 gauge. So why the apparent overkill? Is it for mechanical robustness? Performance even if connections are corroded or incorrectly torqued? I'm ok with all of that, I'm just wondering if they just want a big safety margin or if there's some electrical reason why I'd need a 2 gauge ground for a piece of equipment with 70A @ -48VDC breakers. -Adam ________________________________ -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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