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Greetings, I have received available fault current data from the utility in the form of L-L instead of Three phase. I have not seen this before from my local utility. I am wondering if this is a mis-speak because I was given this data third hand. I have not been successful reaching the utilty...

Thanks for the response. Any tips on good sources for MV substation design and review? Thank You!

Greetings - I need to select coordination settings for a Basler BE1-51 between the PG&E SEL-251 and the (5) Cutler Hammer RBA-400 125E fuses for the 5 substation feeds. I am confused by the info from the utility. Here is what I was given: Relay = SEL-251 CTR = 1200/5 Ground: curve = VI, T = 1...

OK I had a corrupted SKM project... I "merged" the existing project into a "blank" one and the new results look great! thanks for the advice. This actually got me revisisting transformer technology and conceps which should happen every once in a while! (There are some interesting transformer...

Looks like some glitch - If I first add a new 208V bus, the Isc is reasonable -5k ish. When I rerun, it drops to .5 ish. Hmmm Can't revert.

Hello and help. My sc report results don't make sense. I have a 3000A 480/277V building with utiltiy reporting 51k AIC. For some reason all the 208V fault currents are calcuulated in the 500A range. When I model the 208 v portion separately, the results are in the 5000A range. Any ideas whate my...

This is sort of after the fact but here are three pieces of info I include in reports: Source of Data: Often I am working on an existing building with data provided to me from bill of materials or other's field data. Stating this here can protect you if there are errors in data that was...

Perfect clear answer. It seems so obvious now! Thank you very much.

Greetings! I am performing a short circuit and arc flash for a multi-story building with 4000A 480V busduct risers. Each floor has several plug-in breakers. Do I model this busduct as one long bus or each "floor" is it's own bus? I just need to err on the conservative side for a preliminary...

I spoke with the AHJ to confirm the requirements. I was trying to figure out if I needed to use NEC 220-35 to look at existing vs new loads. I decided not to go this route since the existing to remain are so few. I am just showing all the loads and doing load calcs for everything. thanks, everyone!

(E)400A-1P service. Office bldg being "mostly gutted". (E) and (N) lighting and rcpts to be added to 2 new panels. 2 (E)panels to remain have HVAC & misc. Do I treat this as "new" or "addition"? Any guidance is so appreciated!

Sometimes it's a matter of finding the correct person to ask at a small or even large utiltiy... Someone knows! For "maximum" you can always use the infinite bus as a conservative back-up. "Minimum" is trickier. I use it for arc flash calcs. I have had a more difficult time obtaining this value...

I'm trying to coordinate breakers using SKM software. I don't understand how the cable damage curves come in. Aren't cables damaged in more of an long-term heating "overload" situation and not in the .1 or 1.0 second range? I actually have not considered cable damage before so I would love some...

Thanks peebee! After reading your post 430 and 440 were a breeze. While you are on a roll... There is also a condenser made up of three 1 hp fans, 3.3 amps each (480V) 4.53kW MCA=10.74 MOCP=15 This makes sense except isn't 1 hp 1.8 amps?? I am happy to use my manufacturers recommendations but...

It's been a while so I'd appreciate some help. What is the difference between and the significance of MCA (minimum current ampacity) MOCP (maximum overcurrent protection) FLA (full load amps) and LRA (locked rotor amps)? I've got a chiller with MCA, MOCP, and RLA and a ac unit eith FLA and...

Hang On- I was following this thread in full agreement until that last statement about smaller transformers causing more arc flash problems. Can you explain? SKM has the option to not include smaller transformers based on actuals. That is for 480-208/120V. Maybe you are talking about higher...

Thanks everyone for the helpful discussion. (I now realize that I am supposed to be judicious with the star ratings. I truly appreciate everyone's feedback. I could star you all....) The bottom line, as it was so succinctly stated, is that that by design neither the KVA nor the kW rating should...

How many amps can I put on this 750kW cat? Manufacturer uses 0.8 as power factor. My 480V building is at 0.95 power factor. 750kW/0.8 = 937kVA 750kW/0.95 = 789kVA Building Load is 1020A. 1020 X 480V X root3 x 0.95 = 806kVA So, one guy says use the 937kVA rating because the bldg pf is .95...