fault current calculation

[JoeStillman]

it isn't an unreasonable burden-they have to do the study anyway.

my calc is for the building department. their calc is for me to confirm everything meets design criteria.

making a preliminary submission is a precaution-like requiring a conduit plan for electric rooms, instead of just letting the journeyman wing it. it is intended to have them demonstrate they've thought it through from top to bottom and equipment complies with the design requirements. we are all human, mistakes happen-maybe the wrong transformer was submitted, with lower impedance than a generic transformer? Maybe a breaker with the wrong pick-up unit? Maybe wrong duty rating? that said-it is far cheaper to fix a problem that hasn't been installed yet.

Also, the most important piece of information needed to do a study - the available fault current from the utility company - is usually not available at the time the engineers are designing a new building. Anything we put on the drawings for bidding purposes is just an assumption.

Once a job is underway and there is a contract with an electrician, the utility will finally get serious about doing their part and only then can you do a calculation with any certainty.

 

[MBWagner]

I recently viewed a webinar where a NFPA representative and Mike Holt reviewed proposed changes to the NEC for 2023. I know the proposed changes have not yet been adopted by the NEC much less by state/local jurisdiction however, my question is, 'IF the proposed changes regarding fault calculation are adopted by NEC & state/local jurisdiction, thus making it code, will the A/E firm be responsible for the fault calculations or will the EC (in some cases) continue to provide the arc flash labels?

 

[kwired]

I recently viewed a webinar where a NFPA representative and Mike Holt reviewed proposed changes to the NEC for 2023. I know the proposed changes have not yet been adopted by the NEC much less by state/local jurisdiction however, my question is, 'IF the proposed changes regarding fault calculation are adopted by NEC & state/local jurisdiction, thus making it code, will the A/E firm be responsible for the fault calculations or will the EC (in some cases) continue to provide the arc flash labels?

Couple things, 2023 NEC content should be done deal by now, actual printed copies will be available probably within two or three months from now. You should be able to comb through content on NFPA site to have pretty good idea of what final copy will be say for any particular section.

JMO but NEC should not require any more than a fairly generic arc flash warning label. Marking available fault current is even somewhat questionable requirement from NEC. Yes one does need to have equipment rated for what is available, but said information is important at equipment selection stages not after it is installed. Should the supply be changed at a later time and that effects available fault current, that is a new design stage and fault current topic needs revisited to see if existing equipment still usable with the new conditions.

Arc flash incident energy labeling and such - does not belong in NEC, it belongs in 70E or other safety policy related content. Available fault current is only a part of incident energy calculations and posting that alone on a piece of equipment doesn't tell a worker what any danger level really is when it comes to arc flash possibilities.

Many the available fault current labels we have been required to place in recent years by NEC end up being worst case fault current, are potentially inflated values from what actual current is, and are good for nothing other than to verify the equipment itself was designed to withstand what might be available.