CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Forum > General Electrical Discussion

Reply
 
Thread Tools Search this Thread Display Modes
Old 12-15-2012, 12:28 PM   #1
Junior Member
 
Join Date: Feb 2012
Location: Louisiana
Posts: 14
Default Neutral to Ground Bonding

Hi fellas,

I am a first year apprentice and just helped install a 3 phase 208/480 service. And was wondering why the neutral and ground are bonded in panels, troughs, disconnects etc.

I have a problem understanding because I know the neutral is a current carrying conductor and if it is bonded at the panels wouldn't the grounds be current carrying also?

pmt8177 is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Old 12-15-2012, 01:13 PM   #2
Nothin' To Lose
 
Magnettica's Avatar
 
Join Date: Jan 2007
Location: Rahway, NJ
Posts: 14,083
Default

The bond is only at the main disconnect to facilitate circuit breakers and fault current.

Remember that electrons do work and return their source and this is why the bond at the main only is required.

Hope that helps you.

Btw, there's no such thing as a 208/480 volt service. It's either 120/208 or 277/480.

__________________
Be persistent, transparent, and more importantly, on time.
Magnettica is offline   Reply With Quote
Old 12-15-2012, 01:32 PM   #3
Senior Member
 
Vintage Sounds's Avatar
 
Join Date: Oct 2009
Location: Calgary, AB, Canada
Posts: 2,349
Default

I think you mean 277/480 service. The neutral and ground are only bonded in one place, generally in the first disconnect or the transformer where the supply originates.

The connection between N and G is there for, as I understand, a few reasons.

The biggest one is safety. People often (wrongly) think when something is "grounded" that they are going to send electricity "into the ground" so that it doesn't shock people in case of a fault. In reality in an AC system current wants to get back to the transformer it came from, not "into the ground". When we "ground" all our boxes and pieces of equipment and whatever we actually are bonding them but the terms are used interchangebly in the field which adds to the confusion.

So all of this equipment is bonded together all the way back to the panel and ultimately the disconnect. Suppose you have a ground fault, where an energised wire shorts to a bonded surface of a cabinet or box or something. Now electricity is flowing on the bond conductor which normally carries no electricity! It ultimately reaches the point at which the "ground"(again, actually bond) conductor meets the neutral. So now this electricity is getting back to where it wants to be. In the mean time, the circuit breaker or fuse supplying the faulted conductor will detect a short circuit condition and the high current flow will cause it to trip or pop the fuse.

If we didn't have the link between the bond and the neutral, the current from the shorted conductor would energise the bond, but it wouldn't have anywhere to go. Under these conditions the overcurrent protection wouldn't trip. Eventually if another phase shorted to bond, there would be a short across two phases and that would get pretty ugly. Or, if you touched this energised bond, and somehow came in contact with the neutral, you would be blown up by the fault current. There are systems designed to be ungrounded, and they have no neutral but they have detection apparatus that notifies of a fault condition.

Now, the system is not just bonded, but grounded. "Grounding" something strictly speaking refers to directly connecting it to the ACTUAL ground, i.e. a ground rod. So the ground rod or plate that you installed outside, gets connected to the same spot where the neutral and bond are joined. This means that the neutral now is at equal potential to the actual earth. If you measure between the now-grounded neutral and the dirt outside you will have 0 volts and this in turn means that no matter what flows on the neutral, its potential to ground isn't going anywhere. The point of that is that the voltage between the neutral and all of the phases becomes predictable. In your case approximately 277v from each phase to neutral. If the neutral was not grounded then the voltage from each phase to the neutral would depend on how much load was placed on each phase, with the most heavily loaded phase having the lowest voltage to neutral and the most lightly loaded phase having the highest. You would not be able to guarantee that a 277v load was really getting 277v and not 265v or 289v or whatever.

I hope that was clear.
Vintage Sounds is offline   Reply With Quote
The Following 3 Users Say Thank You to Vintage Sounds For This Useful Post:
Big John (12-15-2012), canaston (12-15-2012), stuiec (12-16-2012)
Old 12-15-2012, 01:55 PM   #4
Junior Member
 
Join Date: Feb 2012
Location: Louisiana
Posts: 14
Default

Yes I meant 277/480 I got it confused with our step down transformer 120/208 I believe so. Anyways, thank you for that explaination it helped a lot, but where does the electricity go after it goes back to the transformer after a short?
pmt8177 is offline   Reply With Quote
Old 12-15-2012, 05:59 PM   #5
Senior Member
 
220/221's Avatar
 
Join Date: Sep 2007
Location: Phoenix, AZ
Posts: 6,484
Default

Quote:
Originally Posted by pmt8177 View Post
Hi fellas,

I am a first year apprentice and just helped install a 3 phase 208/480 service. And was wondering why the neutral and ground are bonded in panels, troughs, disconnects etc.

I have a problem understanding because I know the neutral is a current carrying conductor and if it is bonded at the panels wouldn't the grounds be current carrying also?
It may take a while for this to sink in. It did for me.

The neutral is only bonded at the service or service panel (the first point of disconnect) so, as long as there is a proper neutral service conductor intact, the grounds aren't carrying current.

At any other place in the system, the neutrals and grounds are isolated. The reason behind this is, if a neutral feeder fails, the current would "go back" thru the grounds/bonds and potentially energize any metallic things that were grounded. This could happen on the service conductor also but there are fewer splices therefore less chance.
220/221 is offline   Reply With Quote
Old 12-15-2012, 06:05 PM   #6
Registered Member
 
Join Date: Aug 2010
Location: georgia
Posts: 10,305
Default

Quote:
Originally Posted by 220/221 View Post
It may take a while for this to sink in. It did for me.

The neutral is only bonded at the service or service panel (the first point of disconnect) so, as long as there is a proper neutral service conductor intact, the grounds aren't carrying current.

At any other place in the system, the neutrals and grounds are isolated. The reason behind this is, if a neutral feeder fails, the current would "go back" thru the grounds/bonds and potentially energize any metallic things that were grounded. This could happen on the service conductor also but there are fewer splices therefore less chance.
First point of disconnect OR at service or service panel ?? or both? Any execeptions to this rule at all or 100% of time ? Just askin
Cletis is offline   Reply With Quote
Old 12-15-2012, 06:07 PM   #7
Registered Member
 
Join Date: Aug 2010
Location: georgia
Posts: 10,305
Default

What I mean is how to you classify First point of Disconnect ??
Cletis is offline   Reply With Quote
Old 12-15-2012, 06:52 PM   #8
Nothin' To Lose
 
Magnettica's Avatar
 
Join Date: Jan 2007
Location: Rahway, NJ
Posts: 14,083
Default

Great question by the OP by the way...

He should read this for a broader explanation:
__________________
Be persistent, transparent, and more importantly, on time.
Magnettica is offline   Reply With Quote
The Following User Says Thank You to Magnettica For This Useful Post:
BuzzKill (12-15-2012)
Old 12-15-2012, 10:39 PM   #9
Senior Member
 
Join Date: May 2008
Location: Texas
Posts: 942
Default

The OP made mention of a 480 / 208 step down transformer which constitutes a seperate derived source. Bonding jumper at the secondary of that transformer or first disconnect means as well.
ohmontherange is offline   Reply With Quote
The Following User Says Thank You to ohmontherange For This Useful Post:
denny3992 (12-16-2012)
Old 12-16-2012, 07:51 AM   #10
Senior Member
 
Dash Dingo's Avatar
 
Join Date: Mar 2012
Location: Minnesota
Posts: 366
Default

Quote:
Originally Posted by 220/221

It may take a while for this to sink in. It did for me.

The neutral is only bonded at the service or service panel (the first point of disconnect) so, as long as there is a proper neutral service conductor intact, the grounds aren't carrying current.

At any other place in the system, the neutrals and grounds are isolated. The reason behind this is, if a neutral feeder fails, the current would "go back" thru the grounds/bonds and potentially energize any metallic things that were grounded. This could happen on the service conductor also but there are fewer splices therefore less chance.
So if the neutral at the transformer is bonded to the ground via a ground rod and the neutral at the service is bonded to the ground via ground rod or water pipe.... Then why doesn't some current flow on the grounding electrodes and grounding electrode conductors back to the transformer?
Dash Dingo is offline   Reply With Quote
Old 12-16-2012, 07:58 AM   #11
Moderator
 
Dennis Alwon's Avatar
 
Join Date: May 2009
Location: Chapel Hill, NC
Posts: 14,901
Default

Quote:
Originally Posted by Dash Dingo View Post
So if the neutral at the transformer is bonded to the ground via a ground rod and the neutral at the service is bonded to the ground via ground rod or water pipe.... Then why doesn't some current flow on the grounding electrodes and grounding electrode conductors back to the transformer?
Depending on soil conditions, distance etc there can be some flow but the impedance of the earth is great and not much will go back thru the earth.
Dennis Alwon is online now   Reply With Quote
Old 12-16-2012, 08:40 AM   #12
Senior Member
 
Dash Dingo's Avatar
 
Join Date: Mar 2012
Location: Minnesota
Posts: 366
Default

Quote:
Originally Posted by Dennis Alwon

Depending on soil conditions, distance etc there can be some flow but the impedance of the earth is great and not much will go back thru the earth.
What are the reason(s) for the poco bonding the neutral to the soil? For Faults?
Dash Dingo is offline   Reply With Quote
Old 12-16-2012, 08:48 AM   #13
BBQ
Salty Member
 
BBQ's Avatar
 
Join Date: Nov 2010
Location: New England
Posts: 31,028
Default

Quote:
Originally Posted by Dash Dingo View Post
What are the reason(s) for the poco bonding the neutral to the soil? For Faults?
Mostly lightning.

But now we get into the confusing part, while the earth has to much impedance to clear a fault at say 120 volts to ground, once you raise the voltage to say 7000 volts to ground things change.

Let's say you have a grounding electrode with 25 ohms of resistance.

120 volts / 25 ohms = 4.8 amps of current, far to low to trip any breaker on a typical 120 volt circuit

On the other hand

7000 / 25 ohms = 280 amps of current more than enough to open the cut out of a 7000 volt circuit.
BBQ is offline   Reply With Quote
The Following User Says Thank You to BBQ For This Useful Post:
Big John (12-16-2012)
Old 12-16-2012, 01:10 PM   #14
Registered Member
 
Join Date: Aug 2010
Location: georgia
Posts: 10,305
Default

Quote:
Originally Posted by Magnettica
Great question by the OP by the way...

He should read this for a broader explanation:
Is a meter with a handle disconnect considered the first point of disconnect?
Cletis is offline   Reply With Quote
Old 12-16-2012, 02:42 PM   #15
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Cape Breton, Nova Scotia, Canada
Posts: 3,633
Default

Quote:
Originally Posted by Cletis View Post
Is a meter with a handle disconnect considered the first point of disconnect?
Is it the "first" disconnect after the POCO's transformer???? That's the easiest way to explain it. Regardless of wether its a meter can with a disconnect, a panel with a main breaker installed, a 100 or 200 amp disconnect switch feeding a distribution panel...........if its the first one after the transformer......bond the neutral.
Rollie73 is offline   Reply With Quote
Old 12-16-2012, 02:46 PM   #16
Registered Member
 
Join Date: Aug 2010
Location: georgia
Posts: 10,305
Default

Quote:
Originally Posted by Rollie73

Is it the "first" disconnect after the POCO's transformer???? That's the easiest way to explain it. Regardless of wether its a meter can with a disconnect, a panel with a main breaker installed, a 100 or 200 amp disconnect switch feeding a distribution panel...........if its the first one after the transformer......bond the neutral.
Ok then. Now, can you run a 3 wire from that through a 10" nipple to a 200 amp main breaker panel and wire it like a main???????
Cletis is offline   Reply With Quote
Old 12-16-2012, 02:54 PM   #17
IBEW L.U. 1852
 
Rollie73's Avatar
 
Join Date: Sep 2010
Location: Cape Breton, Nova Scotia, Canada
Posts: 3,633
Default

Quote:
Originally Posted by Cletis View Post
Ok then. Now, can you run a 3 wire from that through a 10" nipple to a 200 amp main breaker panel and wire it like a main???????
Sorry....you'll have to wait for someone with more knowledge of the NEC to answer that for you. If I understand what the scenario that you are laying out there......I don't see why not.
Rollie73 is offline   Reply With Quote
Old 12-16-2012, 05:01 PM   #18
Senior Member
 
220/221's Avatar
 
Join Date: Sep 2007
Location: Phoenix, AZ
Posts: 6,484
Default

Quote:
Originally Posted by Rollie73 View Post
Is it the "first" disconnect after the POCO's transformer???? That's the easiest way to explain it. Regardless of wether its a meter can with a disconnect, a panel with a main breaker installed, a 100 or 200 amp disconnect switch feeding a distribution panel...........if its the first one after the transformer......bond the neutral.
I have gotten very confused but, Yes
220/221 is offline   Reply With Quote
Old 12-16-2012, 07:09 PM   #19
Registered Member
 
Join Date: Aug 2010
Location: georgia
Posts: 10,305
Default

Quote:
Originally Posted by Rollie73 View Post
Is it the "first" disconnect after the POCO's transformer???? That's the easiest way to explain it. Regardless of wether its a meter can with a disconnect, a panel with a main breaker installed, a 100 or 200 amp disconnect switch feeding a distribution panel...........if its the first one after the transformer......bond the neutral.
If that's the case then, when you have a meter with by pass lever do you run a 4 wire through a 12" or less nipple to main breaker panel and make a sub??? How do add an insulated neutral bar to a meter base ?
Cletis is offline   Reply With Quote
Old 12-16-2012, 07:18 PM   #20
BBQ
Salty Member
 
BBQ's Avatar
 
Join Date: Nov 2010
Location: New England
Posts: 31,028
Default

Quote:
Originally Posted by Cletis View Post
If that's the case then, when you have a meter with by pass lever do you run a 4 wire through a 12" or less nipple to main breaker panel and make a sub??? How do add an insulated neutral bar to a meter base ?
What be the crap yoz is axeking about?

BBQ is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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
Determining wire size for bonding bonding bushings to ground. God man Services and Service Equipment 1 11-17-2012 06:33 PM
Neutral and Ground bonding??? Elephante Alternative Energy Forum 2 01-19-2012 12:09 AM
Neutral to ground bonding jayare General Electrical Discussion 23 10-18-2011 09:39 AM
Bonding GEC to neutral nitro71 NEC Code Forum 5 09-22-2010 01:17 PM
50 Volts Neutral to Ground and 50 Volt Hot to Ground... DarkDune Residential Electrical Forum 6 06-25-2009 09:56 PM


All times are GMT -4. The time now is 09:24 AM.


Copyright 2006-2014 Escalate Media LP. All Rights Reserved
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com