I'm sure the best answer to my question is going to be "however the client wants you to do it." But I have to ask: for those of you who do Arc Flash Studies, where do you typically stop in your calculations and documentation? I can see a certain logic in starting at the utility and continuing down the distribution chain until you hit a PPE 0 level, rather than mapping out the entire system. Why go further?
Arc Flash Study
- Thread starter bcorbin
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What is the client willing to pay for? I have seen arc-flash studies down to the 208/120V panel boards, disc?s etc. even though if the transformer is small enough (less than 125kva I believe) everything downstream is a 0. I think the best approach would be to schedule a meeting and discuss the scope of the project with the owner or the owner?s rep, and define the limitations of the work involved so that way everyone has a clear understanding of what the deliverables will be. Also will it be performed based on NFPA or IEEE? Once all the scope is defined then a fee can be set and work can begin.
kingpb
Senior Member
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- SE USA as far as you can go
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- Engineer, Registered
If your trying to put a bid/scope of work together, typically, the level of choice is down to the MCC or 480V power panel level. Below that is not being typically proposed. You will also want to specifically state to do it according to IEEE. You also need to define who gathers data, who prints stickers, who applies stickers. Are you going to make recommendations for improvements if the level is higher than 4, 3, or what? Are you also going to check coordination on relays? How are they going to keep the system updated after the initial study? What form will the findings be presented in, e.g. program print out, summary report, detailed report, etc.
It is important to state what you are including, it is just as important to state what is additional service.
FYI: Data gathering is the most costly portion of the whole work. Options
are to have engineer do it (most expensive), have Contractor do it as a sub to engineer, have contractor do it as service paid by Owner, or have Owner do it himself. The best approach I've seen is to have the Owner hire an electrical contractor to do the data gathering; with data sheets and oversight provided by engineer. This helps keep the cost down.
It is important to state what you are including, it is just as important to state what is additional service.
FYI: Data gathering is the most costly portion of the whole work. Options
are to have engineer do it (most expensive), have Contractor do it as a sub to engineer, have contractor do it as service paid by Owner, or have Owner do it himself. The best approach I've seen is to have the Owner hire an electrical contractor to do the data gathering; with data sheets and oversight provided by engineer. This helps keep the cost down.
bcorbin said:
Because depending on your system configuration I have seen a 480 V panel that is CAT 0 feed a 480 V panel that is a class 4 hazard. Because the upstream panel is a class 0 panel doesn't mean that everything downstream is also class 0 so I would say to be safe and cover your people you need to do a study on the Entire system.
zog
Senior Member
- Location
- Charlotte, NC
bcorbin said:
Different clearing times?
Yes different clearing times. The length of the cable must also be considered since the cable impedance will limit the fault current. A fault at a downstream panel with long clearing times on the OC device and long cable lengths can have a higher PPE requirement. Like MJJBEE said, to be safe do the entire system
Limiting the scope of the analysis is the subject of:
Arc flash hazard calculations
Tinsley, H.W.; Hodder, M.; Graham, A.M.
Industry Applications Magazine, IEEE
Volume 13, Issue 1, Jan.-Feb. 2007 Page(s):58 - 64
Digital Object Identifier 10.1109/MIA.2007.265802
Summary:This article discusses a method for generalizing the arc flash calculations for select areas of a power distribution system. The method presented here helps to reduce the number of equipment locations and also calculations which are analyzed using a commercial software package. In an industrial example, this method reduced the number of small feeder locations that required a detailed analysis by 94%. This resulted in a large reduction of onsite data collection, detailed modeling, and arc flash warning labels
See http://ieeexplore.ieee.org/Xplore/l...Author=Tinsley,+H.W.;+Hodder,+M.;+Graham,+A.M.
Arc flash hazard calculations
Tinsley, H.W.; Hodder, M.; Graham, A.M.
Industry Applications Magazine, IEEE
Volume 13, Issue 1, Jan.-Feb. 2007 Page(s):58 - 64
Digital Object Identifier 10.1109/MIA.2007.265802
Summary:This article discusses a method for generalizing the arc flash calculations for select areas of a power distribution system. The method presented here helps to reduce the number of equipment locations and also calculations which are analyzed using a commercial software package. In an industrial example, this method reduced the number of small feeder locations that required a detailed analysis by 94%. This resulted in a large reduction of onsite data collection, detailed modeling, and arc flash warning labels
See http://ieeexplore.ieee.org/Xplore/l...Author=Tinsley,+H.W.;+Hodder,+M.;+Graham,+A.M.
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