File = [PC#2] C:\Wordstrc\Wsc2\Scenario Discussion.doc
Topic: Electrical Installations Fictional Scenarios For Discussions.
The following items are fictional setups, posted to this forum for "What If" discussion purposes only. Although they are intended to be fictional [as in the listed methods being done], the fundamentals and theories will still apply to a normal systems' operation.
Please feel free to reply to the thread with any answers, questions, or comments you have. There are no "wrong" answers to these situations, only each persons' interpretation of what will happen and why. The combined responses from members will be the primary methods of determining an overall correct answer.
The member with the most in depth and conclusive replies wins the Grand Prize, which is the Coveted "Sparky Of The Year" award, in the field of Usenet replies
This message's fictional location will be a single family dwelling located in a Suburbial Residential Tract.
If this scenario type discussion message is of interest, and you want more, let me know.
This message will be posted to the following forums:
- ECN Discussion Forums / General Discussion Area / Fictional Scenario Discussion
- National Electrical Code Forum / NEC Message Forum / Fictional Scenario Discussion
System data: Pole mounted Transformer [supplied by local utility company] = 13.2KV x 240/120 VAC, 1 Phase 3 Wire, 25 KVA, Z = 2.0% [+/- 10%], Split-Coil Secondary. Ground wire included and mounted on pole for transformer grounding.
Service: 200 amp main distribution panel, 200/2 main, service feeders = 3 - 3/0 THHN cu. Main panel feeds one subpanel, plus branch circuits. Distance from transformer to main service = 200 feet. Soil = slightly damp, previously used for orange groves [non-rocky soil].
Grounding Electrode: Concrete-Encased reinforcement steel rods in building's foundation [AKA UFER ground], GEC = #4 cu. No cold water bonding or inclusion to electrode system.
This transformer feeds this house only. No other residences connected to the secondary circuit.
In your opinion, what would be the results to the system, connected equipment, and loads, if the grounding connection at the transformer was made to a terminal of one end of the coil's winding, instead of to the center tap [on X1 instead of at the X2/X3 jumper] and the grounding electrode conductor was also connected to the same line feeder?
- Would the system operate normally,
- Would the overcurrent devices function properly for line to line and ground faults,
- Would the transformer's maximum KVA need to be derated, or "double" the KVA rating for L-N loads,
- Would there be a ground fault path from the service to the source,
- Would there be a change in the voltage to ground,
- Would Multiwire branch circuits function properly,
- Would L-L loads function properly,
- Would GFCI devices work properly
On the same situation, what would happen if I decided to remove the ground connection at the transformer and disconnected the grounding electrode conductor from the service, leaving the enclosures and eq. grounds still bonded to the system?
- would the system still function normally,
- would OCPD work,
- would there be a ground fault path from a load to the transformer,
- would there be a voltage to ground,
- would GFCI devices work,
- would multiwire circuits work properly
If the transformer's ground was connected to the center tap and the service's grounded conductor was disconnected from the grounding electrode system, what would result from:
- ground faults [would this trip a OCPD],
- L-L loads,
- normal operation,
- will GFCI devices work,
- L-N loads,
- L-N currents
What would be the results of Lightning Discharges and related surges to the system under these listed conditions?
I'll end this one here and add more situations later after some input.
I hope this will be interesting for members and possibly help educate, or explain, certain areas to those that are new to the trade, or just beginning to study in depth theories and/or systems design.
Once again, there are no "wrong" or "bad" answers to these items. I have purposely "loaded" these questions to get variable responses. I'll reply with comments as they appear.
If you like this, let me know if you want more.
Thanks for your time!!