Busbar Clearances

[nonsinusoidal]

Does anyone know where to find the miniumum allow outdoor and indoor clearances for 5k to 35kV Bus bar systems in switchgear and vaults? I do not seem to find anything in the NESC.

 

[PHovnanian]

The NESC clearances deal more with minimum safe clearances required for working around energized equipment.

If the switchgear or bus section can be taken out of service and grounded as a unit, then the clearance between its individual phases is an engineering decision*. The clearances between the components being worked on and the adjacent equipment, which may still be energized, should be addreesd by the working clearances.

*These clearances are determined by the equipment's BIL, breakdown potentials of air, contaminants, how far a rat can step when standing on one energized bus bar (I've seen this failure mode numerous times), etc.

 

[nonsinusoidal]

In particular, I am in need of the minimum clearances for in field-fabricated(such as vaults, switch gears, etc.) installations; that is, the minimum air separation between bare live conductors and bus bars and adjacent grounded surfaces. This came about when an existing bus bar configured system was going to be converter from three phase 7200/12470 to 14.4/24.4K volt system. Any further feedback to assist me with the above mentioned will be appreciated.

 

[kh2]

You may consider the minimum clearances given on the National Electrical Code (NEC) table 490-24. This table provides the phase-to-phase and phase-to-ground minimum clearances of live parts for indoor and outdoor applications. For example the clearance for 7.2 kV ph-grnd is 4.0 inches and for 14.4 kV ph-grnd is 6.5 inches indoor. The table also provides the BIL kV for each voltage rating. I have the 2005 NEC edition. You will find the same table on the new edition too.

NEC article 490-24 titled Minimum space separation states, "In field-fabricated installations, the minimum air separation between bare live conductors and between such conductors and adjacent grounded surfaces shall not be less than the values given in Table 490-24. These values shall not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards".

Hope this will help.

 

[nonsinusoidal]

Thank you very much for valuable information. Does anyone has any other references to other information such as NEMA or IEEE documents. Please advice......