100 Amp Garage Sub Panel - Electrical - Page 2 - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 12-31-2011, 10:30 PM   #16
Newbie
 
Join Date: Jul 2011
Posts: 11
Rewards Points: 10
Default

100 amp garage sub panel


Ok,so school me ,why are the neutral ,and ground bonded in the main ,but not in the sub.Has the code always been this way? Thanks

Advertisement

Scott7 is offline   Reply With Quote
Old 12-31-2011, 10:35 PM   #17
Licensed electrician
 
Join Date: Sep 2007
Location: Maryland
Posts: 8,056
Rewards Points: 2,910
Default

100 amp garage sub panel


Quote:
Originally Posted by Scott7 View Post
Ok,so school me ,why are the neutral ,and ground bonded in the main ,but not in the sub.Has the code always been this way? Thanks
Stuubies diagram should have this explained, but if the two are not isolated after the service you will have current flowing on the metal parts of the system that should not. You would be creating a shock hazard.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
Jim Port is online now   Reply With Quote
Old 12-31-2011, 10:40 PM   #18
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,248
Rewards Points: 2,466
Default

100 amp garage sub panel


Quote:
Originally Posted by Scott7 View Post
Thanks Stubbie for the input.I see you are located in Kansas also(hicksville)my box in the garage does have a 100 amp main.Ill have to get another bar for the ground.The one that's in there is not bonded.So you guys think 3-3-3-8 would be ok ,or should I just stick with 2-2-2-6.thanks
I'd rather hang out with 'Hicks' than shirts and ties ....

#2 copper is fine so is #3. Since you mentioned conduit I assumed your going underground and your garage is detached from your home.

The single bar that is factory is on insulated standoffs. There should have been a bonding screw or an attached bonding device that came with the panel. You will not use them.

There will be pre-drilled and swaged holes in the panel back which the ground bar will use for mounting. You need to get one that is made for your panel.

What panel do you have for the garage?
__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie
Stubbie is offline   Reply With Quote
Old 12-31-2011, 10:44 PM   #19
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,248
Rewards Points: 2,466
Default

100 amp garage sub panel


Easier to show why with a different diagram. Objectionable neutral current is energizing the metal of the sub-panel and using the egc along with neural of the feeder to return to the transformer. You never want neutral current on the bonded metal or the egc where it is not expected.
Attached Thumbnails
100 amp garage sub panel-4-wire-improper-bonding.jpg  
__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie

Last edited by Stubbie; 12-31-2011 at 10:50 PM.
Stubbie is offline   Reply With Quote
Old 12-31-2011, 10:55 PM   #20
Newbie
 
Join Date: Jul 2011
Posts: 11
Rewards Points: 10
Default

100 amp garage sub panel


Thanks Jim, I understand now on the bonding issue.Yes Stubbie my garage is detached.Cutler Hammer is my sub panel .Should I use 2 ground rods at the sub,and do they need to be at least 10' apart. Thanks again
Scott7 is offline   Reply With Quote
Old 12-31-2011, 10:56 PM   #21
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,248
Rewards Points: 2,466
Default

100 amp garage sub panel


And proper bonding ... The ground rod at the added panel is not required if the panel is installed in same structure/building/dwelling as the service panel
Attached Thumbnails
100 amp garage sub panel-4-wire-proper-bonding.jpg  
__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie
Stubbie is offline   Reply With Quote
Old 12-31-2011, 11:04 PM   #22
Licensed electrician
 
Join Date: Sep 2007
Location: Maryland
Posts: 8,056
Rewards Points: 2,910
Default

100 amp garage sub panel


The rods need to be a minimum of 6' apart.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
Jim Port is online now   Reply With Quote
Old 12-31-2011, 11:18 PM   #23
Newbie
 
Join Date: Jul 2011
Posts: 11
Rewards Points: 10
Default

100 amp garage sub panel


I hate to ask stupid questions but,why is there not current flowing on metal parts where you don't want it in the main panel where the neutral ,and ground are bonded.
Scott7 is offline   Reply With Quote
Old 12-31-2011, 11:54 PM   #24
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,248
Rewards Points: 2,466
Default

100 amp garage sub panel


All current seeks the source where it was created and it will take all paths given to it to get there. However the lower the impedance/resistance the more current that will use those paths. This is why we intentionally construct only one low impedance path back to the transformer. At the service (main) panel the service neutral is the only path back to the transformer that is low impedance/resistance. All other paths lead to earth (dirt) which is rather high in impedance/resistance. So nearly all neutral current uses it to return to the source/transformer. Some will use earth but it is negligible due to resistance to current flow. By bonding the neutral and ground to the service neutral at the neutral buss we insure that the current doesn't energize metal parts. This will only happen if the service neutral were to open or break and we would lose that low impedance path to the transformer. In that situation neutral current would seek the transformer through bonded metal, water pipes and earth as this would then be the only way to return to the transformer.

Note that the equipment grounding conductor runs essentially parallel to the neutral (grounded conductors) of your branch circuits. It is only there to carry fault current and to bond metal. This bonding system is called "the effective ground fault path". Without it circuit breakers cannot trip and clear ground faults like hot wires touching metal boxes. The egc is primarily for human safety from electrocution whereas the grounding at the service panel to earth is primarily equipment and property protection.
__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie
Stubbie is offline   Reply With Quote
The Following User Says Thank You to Stubbie For This Useful Post:
Jim Port (01-01-2012)
Old 01-01-2012, 12:12 AM   #25
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,248
Rewards Points: 2,466
Default

100 amp garage sub panel


This is a diagram of mine showing the effective ground fault path necessary for enough current to flow through the circuit breaker to cause it to trip open and clear the fault. If this path is broken the the fault circuit is not complete and all metal exposed to the fault will come to line voltage and pose an electrocution hazard because the breaker will not open/trip. Remember this type fault has no load restriction and massive amps of current will flow in the fault circuit ... those amps must flow through the circuit breaker. So if 175 amps are are imposed on the fault circuit and that circuit is protected by a 15 amp breaker will trip instantly de-energizing the circuit. It will not reset till you correct the fault.
Attached Thumbnails
100 amp garage sub panel-bonding-diagram-1.jpg  

Advertisement

__________________
" One nice thing about the NEC articles ... you have lots of choices"

Stubbie
Stubbie is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
new sub panel BlueBSH Electrical 11 01-22-2012 09:28 AM
Grounding/Replacing a Garage Sub Panel wmjp Electrical 12 07-15-2011 11:12 AM
adding 2nd panel (detached garage) SigZac Electrical 8 04-09-2011 05:05 PM
Next Question, Sub panel in detached garage... OmegaBunny Electrical 5 09-16-2008 12:37 AM
Detached Garage Sub Panel MainePainter Electrical 6 08-25-2006 10:58 AM




Top of Page | View New Posts