step down transformer

[vandasboy]

I am a journeyman electrician, recently was on a job where a new 13.8kv to 208 volt step dowm tx was being installed I have never seen this big of a stepdown before. Does anyone know what kind of arc flash issuses this might have and wouldn't there be a considerable secondary fault current

 

[dpc]

The primary voltage is not the main issue - it is the kVA rating and impedance of the transformer that determines that fault current and to a large degree the arc-flash hazard.

Per IEEE 1584, arc-flash calculations are not even required for 208 V systems fed from transformer smaller than 125 kVA.

480 V systems create much bigger arc-flash hazards than 208 V systems.

David Castor

http://www.cvoes.com

 

[cuky2000]

The length of the low voltage and cable produce considerable impedance damping the short circuit significantly and impacting the arc flash energy..

 

[PHovnanian]

Are you working in the transformer's secondary compartment itself? Or just at the other end of the service drop? Either way, the engineer responsible for the system should be able to calculate the available fault current at the various service entry equipment and panelboards and establish the associated arc flash boundary and PPE requirements.

By 'big stepdown' are you referring to the voltage or KVA rating? Its a large KVA rating (and associated low impedance) that will result in high arc flash hazards. The 13.8 kV isn't a big issue by itself unless you've got to work on it. Odds are that every 120/208V system you've encountered comes from the 13.8 kV system through just such a transformer somewhere.