Knightryder12
Senior Member
- Location
- Clearwater, FL - USA
- Occupation
- Sr. Electrical Designer/Project Manager
We call out the new or existing AFC and AIC. We have never called out the SCCR.
Electricians, responsibility or engineers
- Thread starter AC\DC
- Start date
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
And I'm not saying that I will always go with the absolute minimum. I would depend on all sorts of factors. In the case I mentioned in my previous post, the utility transformers were fairly new, had a very low %Z, were dedicated to our building, and were already sized 40% larger than the service rating. I am just saying, tell me what the ACTUAL available fault current is, not some made-up number.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Good luck in Wisconsin, Minnesota, and Illinois.
Actual, or realistic, available fault current is only provided to primary (MV) metered customers. Secondary metered customers are typically provided a worst case, not to exceed, value.
It makes Arc Flash Incident Energy studies complicated.
Some utilities will provide some assistance for arc flash studies, but my experience is many of them do not even know the actual nameplate data for which transformer until after it has been installed and the gear is being energized.
- Location
- Illinois
- Occupation
- retired electrician
Without any info from the utility how can you select the required AIC for the service equipment?
If you are calling out the available fault current, there is no need for the SCCR, and the people that select the equipment must select equipment that has an SCCR equal or greater than the available fault current.
This can be a huge issue for equipment like large air conditioners where the SCCR is often the default 5kA unless the specifications call for something that will match the available fault current at that point in the circuit. It can be costly when the inspector finds equipment with a SCCR of 5 kA and an available fault current of 20 kA at the final inspection.
- Location
- Illinois
- Occupation
- retired electrician
In that case I would be very tempted to do an infinite bus calculation based on the transformer kVA and impedance.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Yup, that's what I did. It got us down to under 65k which it would not have been using the utility number which was 60% higher than the nameplate infinite bus number. There may be times to use the conservation utility figure, but this was not one of them.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
I remember a job my company bid in a hospital. What a joke. Neither the "engineer" or the "PM" from our shop ever even looked in the ceiling. I looked in the ceiling. Because of the location the hospital made the workers get "TB" tested and suite up before we got in the space.
The TB testing and suiting up was probably the reason no one looked at the job.
Told my boss the job couldn't be done as drawn and probably couldn't be done at all. Not enough room behind the ceiling to pitch the steam lines and so many obstacles for the electrical you could barely get the tiles out. I told them it couldn't be done. Don't know if they did the job or not and don't care. Idiots.
The TB testing and suiting up was probably the reason no one looked at the job.
Told my boss the job couldn't be done as drawn and probably couldn't be done at all. Not enough room behind the ceiling to pitch the steam lines and so many obstacles for the electrical you could barely get the tiles out. I told them it couldn't be done. Don't know if they did the job or not and don't care. Idiots.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Are you looking at an all new build or are you dealing with existing equipment?
Either way the electrician isn't going to pass the inspection if the equipment isn't rated high enough. I always double check this kind of thing myself even if they have specified a particular figure just to make sure. I'd hate to purchase some gear and it can't be used, can't be returned and then try to get any reimbursement for it from the engineer. If I find something questionable it needs to be straightened out before ordering the gear. If still at bid stage, might want to bid for worst case if you don't know for certain but still better find out before ordering your gear if you get the job and are considering something lesser might be acceptable.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
We got it all figured out but my neck just curiosity. How does one count for the power company coming and changing their transformers and now your numbers are all screwed up. You could have a system that is either extremely low and could possibly cause issues if it’s not rated high enough for the new AIC
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
There are a million what ifs. Even if that were to happen, the chances of having a bolted fault where the fault current would reach that theoretical level that would result in an OCPD
fail catastrophically is extraordinarily small.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
Who responsible then? Someone always to blame
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Well, you shouldn't have to, because the requirement is that the SCCR has to be at or above the AFC, so that's a given...
Hopefully though, your specs clearly spell out that any packaged mechanical equipment and control panels shall have the proper SCCR to meet that. That's something that happens a LOT lately; low bidder packaged equipment suppliers pay no attention to it and use cheap control panels that come with the "courtesy" untested/unlisted 5kA SCCR, then expect the poor EC to come up with a way to connect it... That issue HAS TO BE dealt with in the specifications or procurement requirements.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Really, that's something that the utility has to consider when changing their equipment. I had that happen on a project once, where the utility changed out their primary transformers after the project started so my AFC went for 34kA to 49kA, and all my MCCs were rated 42kA. There was a lot of hand wringing and discussions about fault current limiting, but eventually the utility took care of it at their expense, because it was their problem.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
I had a job several years ago for a 200A 277/480 over head service. Utility specd 100 kva transformers (each) , which were already way oversized for a 200A service. There was a 30 horsepower motor so they said it was a power quality/flicker issue. Anyway, so utility guy calls me and said they were out of 100 kva pots so they did me a favor and put in 166's for no extra charge so it wouldn't delay the project. We did the math and it squeezed in (not saying there wasn't a little fudge, but it was infinite bus and using their bloated generic number) under the 14k of the equipment I had already installed.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
Seems like the issue can cause a lot of finger pointing
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Usually they are not changing transformers other than replacing with similar if there is a failure. Other than if additional load has been added and has gotten to point that the failure was because what was there is no longer sufficient.
Otherwise major load changes often result in reevaluating things, both by POCO and by engineer, electrician, etc and dealt with at the time of the change.
Often if they don't inform POCO of rather major load changes they might end up paying more in penalties on their electric bill than if they at least negotiated new billing contract based on the new expected demand, and the capacity of what is there will likely be evaluated in that process any changes will be known and won't be so much of an unannounced changing of transformer or other equipment.