What would U Do?

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You can carry out the AIC calculation as far as you want, so the down stream breakers could be less.

As for series ratings all of the panels and breakers would need to be of one manufacture. You can go fuse/breaker, but you would still need the book from the manufacture.
 
cowboyjwc said:
You can carry out the AIC calculation as far as you want, so the down stream breakers could be less.

As for series ratings all of the panels and breakers would need to be of one manufacture. You can go fuse/breaker, but you would still need the book from the manufacture.
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Thanks for your reply but I am unclear about the series rating. If all the panels are Sq. D what does that do for me in terms of the AIC rating? Does that mean that the main for the building would suffice and all downstream breakers could be 10K? I realize the calculation can go on to the end.
 
Dennis Alwon said:
The fault current calculator has 2 calculations, One is the fault current at the main disconnects for L-L at 41k and the other is L-N at 32K. Which one do I use???? I assume the higher?????

Also what does this all mean. I was told that if I had a breaker that had an aic rating higher than the fault current from the poco that I would not need to worry about the branch circuits downstream. The breaker feeds the MLO panel in the retail space. Then I had an inspector say that that was not true. He said all breakers had to be 56K???? I didn't even know they made 56K branch circuits for 120V panelboards. I thought they were all 10K.

The engineers also state that series rating is permissible. What does this mean.

Basically I need to know what I am required to do here. :-?:-? Totally.

The distribution panel is a Sq. D HCP model.
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To determine the AIC rating required of electrical equipment you calculate the 3 phase to ground fault. L-N means 1 phase fualt.

I have found this link useful to describe series ratings: http://www.geindustrial.com/Newsletter/application_considerations_for_series_connected_ocpd.pdf

series rated CB's have been determined by Test to be capable of interrupting the fault current available, where the upstream CB has a higher AIC rating than the downstream CB and the fault current available on the downstream CB is larger than the AIC rating of that CB, but the AIC rating of the upstream CB is greater the the Fault current it will see.

Did I say that right?
 
Dennis Alwon said:
Okay I have done a calculation based on all the info needed and I am still at 41k.

So I need understanding of some issues and I apologize for my ignorance as I never dealt with this before.

The fault current calculator has 2 calculations, One is the fault current at the main disconnects for L-L at 41k and the other is L-N at 32K. Which one do I use???? I assume the higher?????

Also what does this all mean. I was told that if I had a breaker that had an aic rating higher than the fault current from the poco that I would not need to worry about the branch circuits downstream. The breaker feeds the MLO panel in the retail space. Then I had an inspector say that that was not true. He said all breakers had to be 56K???? I didn't even know they made 56K branch circuits for 120V panelboards. I thought they were all 10K.

The engineers also state that series rating is permissible. What does this mean.

Basically I need to know what I am required to do here. :-?:-? Totally.

The distribution panel is a Sq. D HCP model.
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I just got done with a job where I had an AIC issue. My advice to you is give the POCO info to the engineer and have him provide the AIC info onto the drawings. If your inspector comes on the job and sees no AIC ratings on the drawings he could force you to add them and you'll be forced to go back to the engineer. When this happened to me the engineer billed me a sizable sum for the work he should've already done in performing the calculation. Don't own this, no good will come of it.
 
Thank you all for your help. I learned alot researching this and I am very thankful to you all. I did a fault calculation to the MLO panel in the retail store and it is 8K so I am good to go with standard breakersin that panel. If I get the job I will have to get a 65K breaker for the I-Line panel.

Thanks again
 
I would only use used equipment

1. On a very low budget job and be up front about it

2. If nothing new is available and be up front about it.

Careful about what customer says about saving $. The minute something goes wrong, his previous insistence on saving $ was just a suggestion. "I didn't want you to do anything unsafe or poor quality".

Be certain any used stuff is mentioned in writing and records kept.
 
How often do breakers go bad? Rarely. Who refurbed it? The manufacturer? I'd offer the customer the price with new and the price with refurb. Might be the difference between getting the bid or not getting it.
 
There is a difference between used and reconditioned. There is also a difference in companies that follow PEARL standards for MCCB's reconditioning or not, most do not, they just wipe it off and ship it.

You should always get a test report, in some ways reconditioned can be better than new because it was actually tested using ANSI test standards and calibrated equipment. New breakers are not tested, unless the installer tests them.

Another comment on this thread, be careful of those free calulators and doing your own fault current studies, many states require a PE to do them. Liability is on you when you do the analysis.

Last comment, offer pricing for both new and reconditioned. I would go with new in a new building but someone should test it.

OK, real last comment, I would get another price on those. And ask about the test report and certifications of the company that quoted you.
 
Dennis Alwon said:
Thank you all for your help. I learned alot researching this and I am very thankful to you all. I did a fault calculation to the MLO panel in the retail store and it is 8K so I am good to go with standard breakersin that panel.
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You account for motor contribution?
 
zog said:
You account for motor contribution?
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I did not-- there are 2 -3 phase geotherm units. One with a mca of 28 amps and the other 18 amps. The fault current to the MLO is about 8k. The big unit is about 75' from the panel with #10 wire while the other is about 50' with #12.

Would this change the results significantly? Or should I use a 25k breaker for those 2 units? I obviously don't know what I am doing and I am about ready to call the dang engineers and tell them what I think. I really don't think this is my job to do and I totally feel out of place here. I can handle all aspects of this job but this.
 
Dennis Alwon said:
I did not-- there are 2 -3 phase geotherm units. One with a mca of 28 amps and the other 18 amps. The fault current to the MLO is about 8k. The big unit is about 75' from the panel with #10 wire while the other is about 50' with #12.

Would this change the results significantly? Or should I use a 25k breaker for those 2 units? I obviously don't know what I am doing and I am about ready to call the dang engineers and tell them what I think. I really don't think this is my job to do and I totally feel out of place here. I can handle all aspects of this job but this.
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Dennis, take a breath. You're good enough to handle this too.;)
 
mcclary's electrical said:
Dennis, take a breath. You're good enough to handle this too.;)
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Thanks. I probably am the only one bidding this that is concerned. I bet all others use a 10K breaker at the main distribution panel and no one will ever know-- cept me , of course... If I don't get this job they better do it right cause I'll be watching. :grin:
 
Dennis Alwon said:
Thanks. I probably am the only one bidding this that is concerned. I bet all others use a 10K breaker at the main distribution panel and no one will ever know-- cept me , of course... If I don't get this job they better do it right cause I'll be watching. :grin:
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I do the same thing. If I get beat on a bid, I want to know how they did it. I'll be checking later to see the difference in what they did, and what I had planned.
 
mcclary's electrical said:
I do the same thing. If I get beat on a bid, I want to know how they did it. I'll be checking later to see the difference in what they did, and what I had planned.
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And use that info in the future, including how much the job went over bid in extras that we would have included.
 
LarryFine said:
And use that info in the future, including how much the job went over bid in extras that we would have included.
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The contractor I worked for in Kingston, NY did a lot of work at the IBM plant there. He would bid jobs below his cost to get his foot in the door because once you were in they always called on you to do small jobs all over the plant. The extras were his bread and butter.
 
Dennis Alwon said:
I did not-- there are 2 -3 phase geotherm units. One with a mca of 28 amps and the other 18 amps. The fault current to the MLO is about 8k. The big unit is about 75' from the panel with #10 wire while the other is about 50' with #12.

Would this change the results significantly?
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During a fault condition, motor contribution is approximately = FLA/"reactance" (looks like what we do for a transformer doesn't it?).
So you could "overestimate" the motor contribution as 20x FLA, so in your case they might add 920A.
 
jim dungar said:
During a fault condition, motor contribution is approximately = FLA/"reactance" (looks like what we do for a transformer doesn't it?).
So you could "overestimate" the motor contribution as 20x FLA, so in your case they might add 920A.
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Thanks Jim- that's what I needed. I am still good with 10k since I had 8354 amps without the motors. Thanks again
 
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