Conductive paths thru the EGC for a Fault-Current

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  #1  
Old 10-27-14, 07:50 AM
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Conductive paths thru the EGC for a Fault-Current

AN Emergency sub-panel can be supplied with utility power or emergency generator power. A Ground-Fault occurs on a 20 amp circuit when operating on utility power. The path for Ground-fault current is thru the #12 EGC, thru the #8 Feeder EGC ,then to the Neutral Service Conductor. The purpose of the EGC connections is to form a low-impedance path to the "Source" , the Neutral Service Conductor.

When operating on "Emergency Power" , the "Source" is the Neutral connection at the generator stator winding. The Ground-Fault current-path is now the #12 EGC , the #8 Feeder EGC , the Neutral Feeder termination at the Service , the #6 Feeder Neutral Conductor, the Neutral sub-panel termination , and the Neutral Conductor to the generator winding.

??? ; have I correctly described the fault-current paths for both utility and generator power?.
 
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Old 10-27-14, 09:00 AM
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What do you mean by an emergency sub panel?

Your paths sound correct but you left out the transfer switch. With separately derived systems you need to switch the neutral as well.
 
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Old 10-27-14, 10:22 AM
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Best I remember , there are 2 ways to deal with this , depending on whether the generator neutral is bonder to the frame and / or earth ground . In one case the transfer switch switches the neutral , in the other case it does not . Most of the generators we deal with do not groind / bond the generator neutral , at the generator & do not switch the neutral . But it depends on gow the engineer drew the plans .

Draw up the power riser and post a scan .

God bless
Wyr
 
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Old 10-27-14, 11:37 AM
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What is to be avoided when making the necessary Grounding connections for a "Stand-By" system is a Grounding connection that Ground-connects any Neutral conductor that extends from the Service panel, Art 250.24 , (A), 5.

As to whether or not the stand-by generator is a "separately derived " system , it depends on the switching-action of the transfer-switch; if the transfer-switch does not open the generator Neutral Conductor , the stand-by generator is not a "separately derived" system.

Given this is a "Optional Standby System" powered by a portable generator , and not a "separately derived" system , the EGC must be bonded to the system Grounding Electrode , Art 702.11 , B.
 
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Old 10-27-14, 01:57 PM
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What matters is where the system bonding jumper is located. From your original post it should be described when talking about the fault current paths. Depending on who your audience is you could also list the panel grounding bars. Wiring methods also play into this as any conduits and metal enclosures could be included for parallel grounding paths.
 
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Old 10-27-14, 03:16 PM
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The Main / System Bonding Jumper is required to be in the enclosure that contains the Service Disconnecting Means , Art 250.24 , B.
 
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