Replacing Blown Fuse Prior to T/Sing Authorization
Replacing Blown Fuse Prior to T/Sing Authorization
(OP)
I am searching for the words, in the AEH, NEC, IEEE, etc., that give guidance that it is acceptable to replace a blown fuse once before commencing troubleshooting on the condition that the replaced fuse does not immediately blow following replacment.
I am being asked to show proof of this, and I know I read it before somewhere, I thought maybe in the American Electrician's Handbook, but now I am not finding it.
I am being asked to show proof of this, and I know I read it before somewhere, I thought maybe in the American Electrician's Handbook, but now I am not finding it.





RE: Replacing Blown Fuse Prior to T/Sing Authorization
RE: Replacing Blown Fuse Prior to T/Sing Authorization
OSHA 1910.334(b)(2)Re-closing circuits after protective device operation. After a circuit is de-energized by a circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual re-closing of circuit breakers or re-energizing circuits through replaced fuses is prohibited.
Note: When it can be determined from the design of the circuit and the over current devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
RE: Replacing Blown Fuse Prior to T/Sing Authorization
I was trying to capture the event that sometimes a fuse just blows out of the blue and there are no signs of symptoms for those who are questioning the cause of the fuse blowing. It is easy for me to understand this just happens occasionally (e.g., old/faulty fuse), but if I have supporting evidence (documentation) showing that this happens occasionally and that it is okay to replace one fuse in this event without extensive troubleshooting, I would have more of a case.
Although it does say, "the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized." Which, tells me that if there is no visible damage or simple ground fault check of circuit produces no ground fault present then I should be able to perform a one time replacment of the fuse before performing more further in depth troubleshooting.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
I would replace all three fuses.
Some of the "old" electricians around here may have better ideas.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
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RE: Replacing Blown Fuse Prior to T/Sing Authorization
It's not that I don't like/want to troubleshoot, but on the flip side, when production is shutdown due to downed equipment, sometimes you need to reproduce a blown fuse for those standerby lookyloos that have all the answers to prove that there really is a problem or all you hear is "maybe it's a bad fuse" type comments while you are trying to concentrate on troubleshooting something that is not readily apparent, if you know where I'm coming from.
As a troubleshooting engineer, I just would like to have the authorized lattitude is all.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
I blow a fuse in my car, I just replace it. Or at my last house, historic home, had a fuse box, replaced those too. A 600V fuse in a CAT III system, no way, bust out the megger and test the circuit first.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
Bill
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"Why not the best?"
Jimmy Carter
RE: Replacing Blown Fuse Prior to T/Sing Authorization
If it blew from a mild overload how would you troubleshoot that? Once you get running again you can measure the load.
If it blew from a short try to find the problem before re-energising.
Roy
RE: Replacing Blown Fuse Prior to T/Sing Authorization
RE: Replacing Blown Fuse Prior to T/Sing Authorization
It's better to test than get to the point that I've seen in the past. Customer wanting us to pay for 12 400A motor fuses because they just kept replacing them until they ran out of fuses even though the starter had an obvious problem.
You can cut apart the sand filled fuses such as a Ferraz AJT fuse and somewhat see what the problem was. You can see more element heat damage in the middle from an overload compared to a short circuit which is fairly uniform. But, it's not guaranteed.
RE: Replacing Blown Fuse Prior to T/Sing Authorization
No, my fuses are the same dumb fuses everyone else has. If you open it up it's quite obvious if it was a short (vapourized metal, nothing much left) as oposed to overload (small gap, discouloured element).
Try a test, using a couple of small fuses.
For the porcela1n fuses wrap in a piece of rag and wack it with a hammer
Roy
RE: Replacing Blown Fuse Prior to T/Sing Authorization
RE: Replacing Blown Fuse Prior to T/Sing Authorization
Used to be standard practice to refuse and often re-blow.
Did it for years. Now with the emphasis on anticipating and avoiding all any any possibilities, even if the net hazard is greater, I would at least require a quik ground tes and phase to phase test with a multi meter before refuseing.
When I see crews of scaffolders building 20 ft high structures to save an electrician two trips up a ladder, I have to wonder if the overall hazard has been reduced.
Bill
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"Why not the best?"
Jimmy Carter
RE: Replacing Blown Fuse Prior to T/Sing Authorization
RE: Replacing Blown Fuse Prior to T/Sing Authorization
The 'tourists' with all the answers mentioned by polareng, the scaffolding mentioned by Bill and the hours of discussions following the opening of a fuse are all too well-known.
One thing that I would like to add is that size matters.
The kind of fuses we use in Europe (Diazed aka "Poppenkorken") are used in low ampere circuits and the practice here is to replace a blown fuse without searching for the reason why it blew.
Above around 20 or 25 A. Cartridge fuses are used (even if there are Diazed fuses up to 63 A). A blown cartridge fuse is seldom/never replaced before the downstream circuits have been checked. And never with the circuit energized.
Gunnar Englund
www.gke.org
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