Missing SBJ

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
2E57FE3A-3A0A-49E4-BE54-F5599D03B395.jpeg In this graphic it shows the SBJ missing. And says parts can remain-energized.

Am I thinking of this wrong? if you had a 120volt ground fault (line1) with a missing SBJ. The secondary WYE is left ungrounded. Therefore like a ungrounded 3wire delta. So wouldn’t the first line fault to ground just than be the grounded conductor of the system and not energize metal parts? Than the 2nd fault (line2) from opposing leg (phase) would be 240volt to ground?
 
Last edited:

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
As the metallic parts are bonded back to the premises electrode system, I agree with you.

It would merely fix various voltages to ground among the other conductors.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
You are correct that this would be exactly the same as an ungrounded delta system, but there will be capacitive voltage to earth from the metal parts that have been accidentally connected to one of the ungrounded phase conductors.

If the transformer and system is large enough, that capacitive voltage can have enough current behind it to be dangerous. This only happens on large transformers and systems. Large systems can have capacitive voltages that can source currents greater than one amp. Small systems cannot source enough current that you could even feel that shock.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
You are correct that this would be exactly the same as an ungrounded delta system, but there will be capacitive voltage to earth from the metal parts that have been accidentally connected to one of the ungrounded phase conductors.

If the transformer and system is large enough, that capacitive voltage can have enough current behind it to be dangerous. This only happens on large transformers and systems. Large systems can have capacitive voltages that can source currents greater than one amp. Small systems cannot source enough current that you could even feel that shock.
But, the bonding of the EGC/GEC system is shown as intact in the drawing in the OP. The only thing missing is a bond between the neutral and the EGC/GEC system, rendering it a floating SDS.

While the floating system will develop capacitive voltages relative to earth/ground, and prevent operation of OCPD, there's nothing that would cause voltage between metallic parts and earth.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
But, the bonding of the EGC/GEC system is shown as intact in the drawing in the OP. The only thing missing is a bond between the neutral and the EGC/GEC system, rendering it a floating SDS.

While the floating system will develop capacitive voltages relative to earth/ground, and prevent operation of OCPD, there's nothing that would cause voltage between metallic parts and earth.
Yes, I missed the connection to earth.
 
Top