NEC is designed for electrical safety. It's based on the size of the conductor necessary to permit a breaker to trip when you have a ground fault.
R56 is designed to improve survivability of lightning strike or other EMP event. The wires are sized large enough to ensure a low impedance (resistance) path interconnecting all parts of the grounding system. These oversized conductors minimize voltage differences when carrying the significant current caused by a strike. These will generally be larger than the NEC sizes. And, in the case of vendor specs, it's hard to know the motivation. On Tue, Jan 7, 2025, 9:15 AM Adam Moffett <dmmoff...@gmail.com> wrote: > 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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