# J fuses installed ahead of service panels



## KAD (Mar 11, 2011)

My bosses boss talked to an "engineer" about arc flash and ways to lower the arc flash rating of the service panels in this plant. He is all hepped up about installing "J" fuses before each panel. I'm no engineer so I talked to a local one at another plant. He thought that doing this with the panels would violate the tap rule in the NEC but he wasn't sure. I would sure like to put the kabash to this idea mainly because we have about 20 panels in the plant but also to tell my bosses boss he is all wet.

THK
mrelectrode


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## Big John (May 23, 2010)

I'm not seeing how the addition of fuses would violate a tap rule. How are these panels currently connected, are they MPBs that are fed by feeder taps? 

And to clarify, are these all actually service panels, or was that a mistype?


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## BBQ (Nov 16, 2010)

To put fuses ahead of existing service panels would require a new disconnecting means that would have to become the new service disconnecting means and the existing service gear would have to be reconfigured as 'sub-panels' meaning isolated neutrals, removal of the bonding jumpers and moving any GECs to the new disconnects.


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## KAD (Mar 11, 2011)

Big John, thanks and yes, I'm talking about 20 plus service panels. I guess "J" fuses are quick acting to minimize arc flash.

BBQ thanks, I would have the "J" fuses in lockable disconects, so I would have to reclasify these service panels.


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## JRaef (Mar 23, 2009)

KAD said:


> Big John, thanks and yes, I'm talking about 20 plus service panels. I guess "J" fuses are quick acting to minimize arc flash.
> 
> BBQ thanks, I would have the "J" fuses in lockable disconects, so I would have to reclasify these service panels.


It's a legitimate strategy for reducing the Available Fault Current going into the panels, IF it is done by *and stamped by a PE* that knows what all the issues and ramifications are. The only other way would be to change out the transformers feeding them to have a higher impedance.


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## 99cents (Aug 20, 2012)

KAD said:


> My bosses boss talked to an "engineer" about arc flash and ways to lower the arc flash rating of the service panels in this plant. He is all hepped up about installing "J" fuses before each panel. I'm no engineer so I talked to a local one at another plant. He thought that doing this with the panels would violate the tap rule in the NEC but he wasn't sure. I would sure like to put the kabash to this idea mainly because we have about 20 panels in the plant but also to tell my bosses boss he is all wet.
> 
> THK
> mrelectrode


Great attitude. Somebody comes up with an idea to make your system safer and you want to "kabash" it. Why does the number of panels matter? Would it be okay if there was one? Three? Ten? Fifty? I don't get it. Are you scared of work? 

Current limiting fuses might just save your face when you stick it inside one of those panels. Of course it has to be engineered properly. That should include a little bit of a coordination study. But open up your mind, man.


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## KAD (Mar 11, 2011)

*Defending myself*

I might have come off as being "lazy" but if this is a good fix I'm all for it. You don"t know my bosses boss. He tends to throw money at problems. This whole deal started off with a 10 minute phone conversation between him and the engineer. I just don't want to be excersized for nothing. I got enough work to do. Last year it was historesis mitigating transformers, this year it J fuses


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## Big John (May 23, 2010)

KAD said:


> ...Last year it was historesis mitigating transformers, this year it J fuses


 One of _those_ guys. Yeah, I know the type: Everything is a fantastic idea for 5 minutes, but the hell with the details, and it quickly becomes someone else's problem to implement. 

While I'm all for making an environment safer for guys doing work, and I agree, current limiting fused may may well solve the problem, do you even have a problem to begin with? What's the existing incident energy available at these panels? What are the guys doing that is exposing them to a flash hazard?

All the current-limiting in the world doesn't count worth a hill-of-beans if guys are doing unnecessary live work. A much safer solution would be to figure out how to reduce the interaction with the equipment, regardless of the flash hazard.


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## bobelectric (Feb 24, 2007)

Did your plant go through the NFPA 70 E arc flash study.THe new fusing might change the panel ratings.


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## KAD (Mar 11, 2011)

*Arc flash ratings*

Yes, that is how the whole thing started. I know nothing about ratings but my boss thinks the engineering co. who rated our plant rated it too conservativly( 3's and 4's for every panel. I have to dress up fully to change a c.b. We were told that if we add "J" fuses before each panel, it would lower the arc flash ratings.


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## Big John (May 23, 2010)

The current-limited fuses will lower the incident energy you are exposed to. The problem is, the work you're doing changing breakers is very likely an 70E and OSHA violation. So while these upgrades would make you technically safer, and that's great, it doesn't make a lot of sense to me to invest significant money towards a goal that is not legal or compliant.

How many services feed this plant that you have so many service panels?


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## KAD (Mar 11, 2011)

Thank you. That was what I thought. If adding fuses before the panel was a good fix, we would not be the first place to do it. 
We have six 2500 KVA transformers feeding 6 switchboards, 4 MCC's and about 20 service panels. Am I getting the description wrong about the equipment? (Circuit breaker panels)

Thanks again


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## Jlarson (Jun 28, 2009)

Big John said:


> What are the guys doing that is exposing them to a flash hazard?


We get a few of these hair brained engineering schemes every few months. The answer to that is always nothing that they should be doing. :laughing:


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## Ultrafault (Dec 16, 2012)

Do you know the impedance of the transformers? The voltage? Or the wire length and size of service conductors?


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## Ultrafault (Dec 16, 2012)

Hey where did you go.


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## wendon (Sep 27, 2010)

BBQ said:


> To put fuses ahead of existing service panels would require a new disconnecting means that would have to become the new service disconnecting means and the existing service gear would have to be reconfigured as 'sub-panels' meaning isolated neutrals, removal of the bonding jumpers and moving any GECs to the new disconnects.


I've used the fused transfer switches. If your MDP isn't rated for the available fault current it takes care of that problem. When you have a pad mounted transformer next to the CT, MDP etc. the fault current will be pretty high.


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## erics37 (May 7, 2009)

KAD said:


> You don"t know my bosses boss. He tends to throw money at problems.


That's not a bad problem to have. Most places are the opposite.


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## BBQ (Nov 16, 2010)

wendon said:


> I've used the fused transfer switches. If your MDP isn't rated for the available fault current it takes care of that problem.


It can, or it may not, each installation is different and has to be engineered. Please see post 5, it is the same thing.


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## Jlarson (Jun 28, 2009)

erics37 said:


> That's not a bad problem to have. Most places are the opposite.


Yeah but most often the money gets thrown at "problems" then when a real problem comes around management just stands there with the dumb "why do we have no more money" look on their faces. :laughing:


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## Inspecluso851 (Jun 1, 2013)

Jlarson said:


> Yeah but most often the money gets thrown at "problems" then when a real problem comes around management just stands there with the dumb "why do we have no more money" look on their faces. :laughing:


Some utility's don't trust thy inrush available at service point


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