# 70E & Buss Plug Fuses



## AtomicDeathRay (Jun 10, 2021)

If a buss has an incident energy level that would rate it "dangerous" (>40cal/cm2) then the plugs are also rated as such. Are there steps to follow which allow changing a fuse without de-energizing the entire buss? We understand the potential hazard of the possible blast should something internal fail but with each step of the below procedure the chances of a failure are reduced. These are the steps we follow, always standing to the side of the plug to stay out of the "line of fire":

1. Move disconnect handle to the off position standing to the side away from the front panel of the plug, preferably with a hot stick.
2. Open the cover from the side away from the front of the enclosure and allow it to swing open
3. inspect that the knives are fully disengaged and the energized sockets are behind intact insulators - if not, close and schedule to shut buss down
4. Using a cat4 non contact voltage detector check that fuses are not energized.
5. If tools are required to change the fuses, they must be insulated 

What are your thoughts?


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## just the cowboy (Sep 4, 2013)

AtomicDeathRay said:


> If a buss has an incident energy level that would rate it "dangerous" (>40cal/cm2) then the plugs are also rated as such. Are there steps to follow which allow changing a fuse without de-energizing the entire buss? We understand the potential hazard of the possible blast should something internal fail but with each step of the below procedure the chances of a failure are reduced. These are the steps we follow, always standing to the side of the plug to stay out of the "line of fire":
> 
> 1. Move disconnect handle to the off position standing to the side away from the front panel of the plug, preferably with a hot stick.
> 2. Open the cover from the side away from the front of the enclosure and allow it to swing open
> ...


Questionable area because of buss duct.
AFAIK you don't *need* to shut buss down to change fuse but suit up.
You do need to shut down to replace plug in buss switch, due to the way they get plugged in.
I have seen faults in buss duct you don't want to do much near them, they bend twist and are full of dust. Years ago I remember it was common to grab the buss frame with both hands and use your chest to push the switch in with the buss hot. Young and stupid back then never saw arc flash videos',


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## mayanees (Jan 12, 2009)

NFPA 70E does require that the bus be deenergized to replace the fuse, unless it's more dangerous to turn it off. And I think your procedure is legitimate. You do need to be suited to the level of incident energy to do your opening and testing operations. You made reference to the area being considered Dangerous because it's above 40 calories and that's a holdover from the 2009 70E edition. There is PPE to cover up to 140 calories, if not higher. And the Dangerous classification is in conflict with ANSI Z535 for labelling. Red and Danger should not be used for arc flash listings, but instead Warning in Orange. 
The 40+ cals couldn't have been determined by the 70E categories method because that only goes up to 40 calories.
I was in an NFPA 70E class given by NFPA just last week. I asked the question if the installation of Power Quality metering could ever be done without an Energized Electrical Work Permit and the response was no. Apparently touching the cables with a CT is considered energized work, and it's only allowed if it's more dangerous to turn it off, like maybe for a hospital.
I think things are too restrictive and work should be permitted if it can be done safely, with the correct PPE, etc. But 70E has evolved into what it is and if you're going to be in compliance with OSHA you need to adhere to it. To that end, I think your procedure is legit.


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