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#112492 06/29/01 11:02 PM
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[Linked Image]
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While getting some info for a single-line diagram I found this. Service is 277/480V, 1600A, with a number of 200A &1-400A Fusible Switches. The 400A was fused at 225A. OK. The first 200A Switch was fused at 225A . Huh? I really did a double take on this. The remaining 5- 200A were the same way.
Can you see how they managed this? What would/could happen if these units were called upon to "do their duty?"

Electure

#112493 06/30/01 05:35 AM
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So U have 225A fuses in many 200A disco's. The result of a 'dead short' and subseqent AIC may see the disco, not the fuses, as the weak link.

#112494 06/30/01 07:16 AM
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But the 225A 600V fuses in the 400A disco are way too large to fit in the 200A switch. [Linked Image]

#112495 06/30/01 10:00 AM
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yes they are, do you suppose there would also be more of a 'flashover' possibility???

#112496 06/30/01 10:56 AM
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I SURE DO see flashover as a problem. There was a hint in my last post, here's another, a little more obvious 110-4. [Linked Image]

#112497 06/30/01 01:55 PM
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no aurgement from me, we could list a few more codes on top of this. my post was stictly speculation, supposing a 'short', not G-fault across two phases fused side by side. they look close!
as a contractor, i find exercising that 'liability node' part of my grey matter to the worst case scenario essential to my survival it's a jungle out there!

[Linked Image]

#112498 06/30/01 03:43 PM
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FRS>FRN, 480>250,(OK, I'll stop this secretive business). These are 250V rated fuses used on a 480V system. They actually fit sickeningly well into the fuse clips. We've included replacing these fuses with 200A, 600V fuses in our bid for the owners' work. If they don't want the work performed, they can't care much about their beautiful 4 story office building.

#112499 06/30/01 04:41 PM
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pardon my ingnorance, now that U mention the obvious, they do look a tad short....

[Linked Image]

#112500 07/01/01 09:32 AM
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I sure hope you're not ignorant, Sparky, because I stood gawking, scratching my head, gawking some more for an awfully long time before I realized what was going on...and I could read the writing on the fuses!! We get so used to seeing things in a certain way that when something looks almost right, it almost passes us by. If you're ignorant, then I'm an absolute moron!

#112501 07/01/01 10:02 AM
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Ok, now that we have established the obvious, as applied to the original Q, what would happen if these fuses were called to duty?
In a worst case scenario ( all i can think of is a dead short), would we have the equivalent of 3 grenades?
[Linked Image]

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