Hello, I'm wondering if someone can help me with this. I've always understood 240.60(A) to not allow a 300V fuse on a 480Y/277V system unless it's protecting a single-phase (L-N) circuit, per 240.60(A)(2). Today one of my foremen (who was performing documentation fin order for us to produce single line diagrams) sent me some pictures and I encountered something I hadn't seen before. Most of the blocks in the fusible 3-phase meter mains (200A to 600A) have 300VAC Class T fuses. I consider this a code violation. However, what I found interesting is that many of the fuses do not say, "300 VAC" and instead say, "300 VAC to Ground." This is interesting as a 480Y/277V system IS less than 300VAC to Ground. I noted that this particular manufacturer still produces fuses using the exact same part number but they now say, "300VAC" which sync's up with the current NEC.
Does anyone know if the NEC has changed with respect to this situation? I was going to ask the MFG on Monday, but I also thought perhaps someone here would know. I can't really advise replacement of dozens of fuses if they were code compliant when they were originally installed. Thanks in advance.
Does anyone know if the NEC has changed with respect to this situation? I was going to ask the MFG on Monday, but I also thought perhaps someone here would know. I can't really advise replacement of dozens of fuses if they were code compliant when they were originally installed. Thanks in advance.