SWBD Short Circuit Rating
SWBD Short Circuit Rating
(OP)
480V, 3Ph, Paralleling SWBD rated at 100kAIC.
Using SKM the 3 phase bolted fault calculated at 91.8kA with x/r=15.4
L-G fault calculated at 121.8 with x/r=12
Does a normal 3 phase switchboard short circuit rating of 100kA have any associated L-G rating, or do I use the 3 phase rating?
Does this SWBD fail a short circuit evaluation?
I realize the breakers need to have a multiplier since the x/r is higher than the test value, but I'm trying to focus on the SWBD first.
Thanks
Using SKM the 3 phase bolted fault calculated at 91.8kA with x/r=15.4
L-G fault calculated at 121.8 with x/r=12
Does a normal 3 phase switchboard short circuit rating of 100kA have any associated L-G rating, or do I use the 3 phase rating?
Does this SWBD fail a short circuit evaluation?
I realize the breakers need to have a multiplier since the x/r is higher than the test value, but I'm trying to focus on the SWBD first.
Thanks






RE: SWBD Short Circuit Rating
Rafiq Bulsara
http://www.srengineersct.com
RE: SWBD Short Circuit Rating
RE: SWBD Short Circuit Rating
You might want to look at the data that was used in the model. It is true that the SLG fault current from a local generator can be greater than the 3-phase fault current, but most generators are only braced for the three-phase fault current, with the assumption that the ground fault current will somehow be limited externally to at most the three-phase fault current. If there is any external neutral grounding impedance, make sure that is included in the model that was used.
David Castor
www.cvoes.com
RE: SWBD Short Circuit Rating
Are there references out there of typical values for that type of normally ignored impedance?
RE: SWBD Short Circuit Rating
David Castor
www.cvoes.com
RE: SWBD Short Circuit Rating
RE: SWBD Short Circuit Rating
As stated above, don't attempt to include the breaker impedances. The results won't change much, unless you are using obsolete data.