Many fused switches are still energized with exposed parts on the line side when the switch is open. This week's question is about replacing fuses and whether it is done with just the fused switch open and still energized/exposed on the line side, or opening the next device upstream.

Do you open the next device upstream when replacing fuses and the line side is energized/exposed?
Yes
No
No fused switches/I don't do this

Comments are certainly welcome!

If the fused switch is designed to open up immediately upstream of the fuses, than that is acceptable. Otherwise, we open up an upstream device before replacing fuses. If there are any current practices that don't follow this I will have to talk to them.

I started my electrical apprenticeship in 1963 giving me 53 years (48 as a journeyman) of exposure to all sorts of electrical devices mostly good some bad, it appears to me that we are trying to legislate good well founded and safe work practises out of existence not to mention common sense by implementing one size fits all rules. Having said that correctly working well maintained fused disconnect switches are designed in such a way as to allow the safe removal of fuses when open, this of course is after the qualified individual removing the fuses has visually checked for correct operation of knife blades and tested all three test points for voltage with known certified testers.
As a safety conscious tradesman I have developed a routine when working in on and around electrical equipment alive or dead, best trade practises dictates you test every thing and take the word of no one.

I think this needs to be qualified. If this is a fused disconnect that is designed for this purpose then no, the switch must opened to open the box. If this is fuse blocks with in an industrial panel where the disconnect is not integral to the fuses, then yes.

It depends!

Light poles along highways typically have fuses only with no disconnects. Think of the consequences of having a fused disconnect and Joe Q Public Enemy #1 goes along and opens all the disconnects. So whether it seems like a good idea or not they have just fuses and you have to pull/insert them with a fuse puller tool.

In a similar way some cutouts are basically nothing more than clips on the ends of a boric acid fuse. So is the metal clip attached to the end of the fuse an "upstream device" or is it part of the fuse assembly at that point?

I think this needs to be qualified. If this is a fused disconnect that is designed for this purpose then no, the switch must opened to open the box. If this is fuse blocks with in an industrial panel where the disconnect is not integral to the fuses, then yes.

To qualify the above posted statement, if it's a fused 3 phase disconnect switch North American/Canadian standard with interlocking mechanisms you can open the door to exposed parts without opening the knife blades as you can also re-establish the knife blades with the door open, this is not a safety issue it's a due diligence and good work safe practice procedure implemented by an experienced qualified Journeyman, fuse blocks within a panel inherently have some isolating mechanism up stream of fuse holders, many industrial panels and disconnects have these interlock devices to facilitate trouble shooting circuits and equipment faults. In essence it amounts to having Fully Qualified Journeymen working on the piece of equipment deemed to be at fault this all goes back to having well trained and situational aware personnel on duty, standardized electrical trouble shooting procedure 101 is a good place to start.

While I don't agree with our policy "we open the upstream device if an electrically safe working condition does not exist" I'm too black and white and work in an environment that does not deal well with not following the rules. Until the rule changes I don't see us changing.

After witnessing a "slip" when putting in a 5A fuse into a 30A busman fuse holder and seeing the effects of the short arc welding experiment across phase 1 and phase 2, I've always preached opening the upstream safety device before doing anything with fuses. I still have the same reservations with the finger safe blocks. 1st problem is closing the block toward the energized side. 2nd problem is how do I know the person that constructed the block wasn't having a bad day.

Hi Jim,

I have to agree with Buschwackers comments above. Myself I do not teach the practice of opening the upstream disconnecting means. However we have to ensure verification on the absence of voltage on the line side of the fuse block to ensure for worker safety. Someone did an excellent paper at this years ESW illustrating a blade failure on one phase of a 3 phase fusible disconnect switch. One of the blades stuck in, enabling power one one phase to the line side of the fuse block. I would be more interested in empasizing to the worker, particularly a Millwright who may not have the electrical knowledge of an electrician, that equipment failure can occur particularly on aging equipment or electrical equipment that has not been maintained