Selective Coordination vs design-bid-build

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sceepe

Senior Member
Has anyone figured out a way to perform a selective coordination study (say for a NEC 701 system) before the project bids. How do you do the study when you don't know the manufacturer until after bid. Also, if you waited until after the bid, any change to the selected OCPDs will result in additional $.

So, do you just put in a bid day allowance for additional costs? Or maybe put all the info the manufacturer's would need in the contract docs and make them do the study as part of the bid price they give the contractors?

Thanks in advance.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
I believe you are speaking from the design engineer’s point of view. I handle it by doing two things.

First, we base our design on a particular brand of equipment. We perform the selective coordination study (and other calculations) on the basis of that equipment manufacturer’s published documents. In essence, this is to prove that “it can be done,” or that “a solution exists.” Thus, if the contractor chooses to buy the type of equipment we used as a design basis, and if they select the very same breaker types and ratings as we show on the drawings, there is a basis for asserting that the system will be coordinated.

We also state, for the record, the brands and types of equipment that we used as a design basis. We then call upon the contractor to provide (or more to the point, to purchase from the equipment manufacturer) a set of calculations that proves that the actual brands and types they buy will meet the selective coordination (and other) requirements. Thus, if the contractor chooses to buy a different brand, it becomes incumbent on the contractor to prove that that set of equipment satisfies the same requirements as would have been satisfied, if they bought the design basis brands and types instead.
 

VUGear

Member
Location
I-40, TN
We then call upon the contractor to provide (or more to the point, to purchase from the equipment manufacturer) a set of calculations that proves that the actual brands and types they buy will meet the selective coordination (and other) requirements. Thus, if the contractor chooses to buy a different brand, it becomes incumbent on the contractor to prove that that set of equipment satisfies the same requirements as would have been satisfied, if they bought the design basis brands and types instead.
So if the EC chooses a different brand, then you require a coordination study using that equipment to be submitted along with the gear submittal?
 

charlie b

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Location
Lockport, IL
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Correct. That requirement is included in the specifications section related to the gear. The requirement is there, even if the EC buys the exact same brand and types and models that I used as a design basis. I don't publish my own calculation, although I will show it to the inspector or give a copy to the owner, if asked. The point being that I, as the design engineer, am responsible for proving that a solution exists, and the EC is responsible for proving that a solution has been implemented.
 
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sceepe

Senior Member
Thanks for reply. Just a couple more questions

and if they select the very same breaker types and ratings as we show on the drawings
So for your basis of design system you are showing breaker model #'s. I have not been doing that but I guess I could.

We then call upon the contractor to provide (or more to the point, to purchase from the equipment manufacturer) a set of calculations that proves that the actual brands and types they buy will meet the selective coordination (and other) requirements

So in the contract documents, do you include the available fault current at each device or just specify a fault current rating for the panel and let the manufacturer use that in their coordination study?
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
So for your basis of design system you are showing breaker model #'s. I have not been doing that but I guess I could.
That information goes into the "Basis of Design Document," published in report form at the beginning of the job, and revised as need arises.

So in the contract documents, do you include the available fault current at each device or just specify a fault current rating for the panel and let the manufacturer use that in their coordination study?
I show the fault current that is available at various places on the riser diagram. The places include the main switchgear or switchboard, at least one spot on each floor level, and downstream of any transformer. The minimum fault current rating of any given panel is shown on the panel schedule.
 
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