# AIC rating



## 99cents (Aug 20, 2012)

I don’t know how you can go wrong if you were able to fill in all the blanks in the Bussmann app. Was the utility able to give you any help?

Fuses upstream of your breakers will get it below 10k and could save you some $ .


----------



## blueheels2 (Apr 22, 2009)

Utility gave me their fault current at 120/240 and I was able to punch it all in. Problem is I’m not sure any ats is rated that high. I’ve never used current limiting fuses to bring the current down but that might make the job easy. 600 amp fusible disconnect right after the CT and then to the transfer switch which would no longer have to be service rated correct? Another problem is I don’t think the ATS will be available for 3-4 weeks unless anyone knows where I can get a 600 amp ats quicker than that. Customer seems to want this done 2 weeks ago.


----------



## blueheels2 (Apr 22, 2009)

99cents said:


> I don’t know how you can go wrong if you were able to fill in all the blanks in the Bussmann app. Was the utility able to give you any help?
> 
> Fuses upstream of your breakers will get it below 10k and could save you some $ .



So if I set a service disconnect with current limiting fuses that would reduce the fault current to a lower level wouldn’t the fuses have to be series rated with the breakers downstream? I can’t just decide to do it. It has to have been tested together or an engineer has to design it correct?


----------



## Dennis Alwon (May 9, 2009)

I have done a few 600 amp services and have never even checked the tranies fault current. Never seen anyone do that for a residence. 

I am sure they make an ats rated at more than 10,000 aic however it may be a 3 phase setup and quite pricey.


----------



## blueheels2 (Apr 22, 2009)

Hey Dennis, so I'm just overthinking it? Never had to do anything really on the design side and this job has been a pita to figure out. Apparently the ats breakers are rated over 15k to begin with but still waiting on the quote.


----------



## 99cents (Aug 20, 2012)

blueheels2 said:


> Hey Dennis, so I'm just overthinking it? Never had to do anything really on the design side and this job has been a pita to figure out. Apparently the ats breakers are rated over 15k to begin with but still waiting on the quote.


Maybe you’re overthinking it but you did the calc and you’re over 10k. Maybe overthinking isn’t a bad thing from a safety point of view.

I would never get over 10k on a residence here but I would never do a 600 amp house either. That must be a monster house.


----------



## blueheels2 (Apr 22, 2009)

It's really not that big. We just have an impatient owner who would rather pay for a 600 amp service than wait for proper load calculations. It's about 5,000 square feet with a pool/plunge pool gas heat for now, 5 to 6 HVAC units with emergency heat, indoor and outdoor kitchen but the interior kitchen has a gas stove and nobody knows the equipment on the outside. If I had time I would use a service rated ats outside then hit a trough and penetrate into the garage and mount 3 200 amp main breaker panels. However, 1 of the panels is essentially a refeed of the existing main which is 125 feet away so I would need feed through lugs on of the panels. 

Because of impatience current plan is meter/ct can to fused disconnect outside, then disconnect to gutter that feeds a 600 amp I line panel in the garage. A 200 amp panel will be set beside it and I will have a 200 amp breaker installed in the I line to refeed the basement main. When ATS arrives I will rework the ATS in outside and feed the ILine off of that. Should mention that I have limited wall space outside to mount equipment. I have 134 inches and most of that is taken by the ct,meter, disconnect, and ats. Anyone see any easier options for design?


----------



## Dennis Alwon (May 9, 2009)

99cents said:


> Maybe you’re overthinking it but you did the calc and you’re over 10k. Maybe overthinking isn’t a bad thing from a safety point of view.
> 
> I would never get over 10k on a residence here but I would never do a 600 amp house either. That must be a monster house.


My worker has a license and his first side job was an 800 amp service for a residence. Internet currency such as bit coins can increase the demand on electricity tremendously. 

The servers put out alot of heat so a/c must be sized larger, etc. That job-- my guess- was overkill but the owner swore he was expanding with 20-40 more servers


----------



## Dennis Alwon (May 9, 2009)

I wish Duke would use what Piedmont electric uses. It is a 600 amp meter base with the CT's in it and it is not much bigger than the 400 amp meter base.


----------



## MDShunk (Jan 7, 2007)

blueheels2 said:


> Utility gave me their fault current at 120/240 and I was able to punch it all in. Problem is I’m not sure any ats is rated that high. I’ve never used current limiting fuses to bring the current down but that might make the job easy. 600 amp fusible disconnect right after the CT and then to the transfer switch which would no longer have to be service rated correct? Another problem is I don’t think the ATS will be available for 3-4 weeks unless anyone knows where I can get a 600 amp ats quicker than that. Customer seems to want this done 2 weeks ago.


Now wait a minute. They gave you the fault current. What did you "punch in" and why? Fault current is fault current. There's no more math massaging you need to do with the number.


----------



## sbrn33 (Mar 15, 2007)

MDShunk said:


> Now wait a minute. They gave you the fault current. What did you "punch in" and why? Fault current is fault current. There's no more math massaging you need to do with the number.


Size and length off wire come into this big time. 
I have never seen any resi over 10K.
If it is overhead I will bet a ton of money that it is under.


----------



## blueheels2 (Apr 22, 2009)

Used the Bussman app. Transformer is 4160 volt 100kva 240v secondary. Impedance is 1.5. 240 fault is 27800 120 fault is 41700. Transformer is around 100’ from the house. 100' of parallel 350MCM aluminum in PVC results in 15,908A L-L and 13,343 L-N.


----------



## blueheels2 (Apr 22, 2009)

Dennis Alwon said:


> I wish Duke would use what Piedmont electric uses. It is a 600 amp meter base with the CT's in it and it is not much bigger than the 400 amp meter base.



THis would save a lot of room.


----------



## mbednarik (Oct 10, 2011)

blueheels2 said:


> Used the Bussman app. Transformer is 4160 volt 100kva 240v secondary. Impedance is 1.5. 240 fault is 27800 120 fault is 41700. Transformer is around 100’ from the house. 100' of parallel 350MCM aluminum in PVC results in 15,908A L-L and 13,343 L-N.


That fault current will drop through the main and each feeder breaker as well.


----------



## 99cents (Aug 20, 2012)

MDShunk said:


> Now wait a minute. They gave you the fault current. What did you "punch in" and why? Fault current is fault current. There's no more math massaging you need to do with the number.


Actually no. There are a number of variables (transformer resistance, conductor resistance, conductors in conduit, etc.) that will determine fault current at any given location. If it was simply a matter of getting the available fault current from the utility at the pole, there wouldn’t be a need for system analysis (or the Bussmann app).


----------



## mbednarik (Oct 10, 2011)

Some utilities will produce a load side fault current number, all depends on the utility.


----------



## 99cents (Aug 20, 2012)

blueheels, the Bussmann SPD is available for free download. It’s worth a read (not the whole thing, it’s about 300 pages) but it’s reference material every electrician should have. It’s even written in language that a dummy like me can understand  .

Bussmann used to charge for the document and for good reason.


----------



## frenchelectrican (Mar 15, 2007)

blueheels2 said:


> So I’m building a 600 amp service for a house I’m doing and saw it suggested on other threads to run the short circuit current calculation to make sure the equipment can handle the fault. I downloaded the Bussman fault current app and I have available faults of L-L=15,908 and L-N=13,343. So I assume any breakers and paneleboards that are part of the service need to be able to handle a fault current of 15,908A? It is possible there would be a 600a ats in the mix as well. Am I understanding this correctly?


For the 600 amp main breaker ? I know they are typically rated for both 10/22 AIC rating but anything higher than 22K will charge more and check the specs on the main breaker when you plan to install it and I am sure they are dual rated so it can take either 10 or 22 K but for branch breakers they are typically at 10K so just be aware of the rating on them. 

Most resdentails I have ran into typically use 10 K if the transformer is small or very long run of latheral or overhead drop ( most POCO undersized the drop on purpose) so it will act like light choke with hard short. 

The only time I use the higher AIC if it was feeded off from much larger transformer like 300 KVA or larger single phase or 150 or larger kva triphase. that typically used on larger commercial location or industrial location that is typical to be expected on that. 

again check the specs before you get too far on that.


----------



## blueheels2 (Apr 22, 2009)

Appreciate it everyone. No specs on this job. Available fault current I got from the white book given to me by the power company. I was asked to design this service which is a pain in the neck by the way. At least it is for someone who has spent the last 17 years installing someone else’s design. I’ve gotten a price with just 10 k equipment but thinking I may change it tomorrow to 22k. By NEC it is right but probably overkill but that is cya. Honestly the only real change would be the subpanels although the Square D quote sheet lists the panel at 10k. All QO so I’m pretty sure it’s just the difference in bolt on vs. plug in.


----------



## blueheels2 (Apr 22, 2009)

This is the plan as it now sits. Fused service disconnect to MLO Iline panel with 3 200 amp breakers and a 125a breaker. ILine to 2 MLO 200 amp panels mounted on either side of it. 3rd panel is 125' away so probably ok. 125 a breaker feeds a future omni pool controller that will be 50-75' away from the MDP.


----------

