Neutral and ground in service panel

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  #1  
Old 07-25-02, 01:00 PM
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ksorce
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Question Neutral and ground in service panel

I am reviewing my current electric service panels and considering adding a sub panel to my electrical service and have a few questions concerning grounding.

Existing service - 2 panels with a 150 amp main breaker on each are on one side of my garage on the inside wall of where my electric service enters my house.

On the far side of my garage are my breaker panels (load centers?). There are two panels (each is connected to one of the 150 amp main breakers where the service comes in) with approximately 32 single pole slots in each panel.

Inside of each load center there are the two black feeder wires, a gray neutral and a bare wire. The two black feeders are obviously connected to the main power bus bars. The neutral to the bus bar and the bare wire (ground) is ALSO connected to the neutral bar.

There is also a grounding block screwed to the back of the panel opposite the neutral bar for all the bare ground wire connections.

Since the ground block is connected to the back of the panel how is ground established in a fault situation since the neutral bar is isolated from the metal of the cabinet? Should a blocking lug be present that connects the neutral bar to the cabinet itself? If I add a new 220 breaker on a 2 wire application, would just 2 wires of the circuit be connected to the breaker and the ground to the ground block or to the neutral bar lugs?
 
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  #2  
Old 07-25-02, 04:13 PM
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Wgoodrich
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The panels that contain the first main breaker after the meter base is your main service rated panel requiring the neutral and grounding bars to be made as one entity married together with both bars electrically one with the metal casing of that main service rated panel.

Teh panels that are slaves of that main service rated panel is a sub panel or non service rated panel. Sub panels or non service rated panels that can be shut off and are slaves of another panel must have the neutral bar isolated from both the metal case of that panel and the grounding bar. The grounding bar must be bonded to the metal case of the panel but not be in contact with the neutral bar.

The neutral bar in a nonservice rated [aka sub panel] must be separate from non current carrying metal parts and the grounding bar.

Sound like you need to move the bare wire of the feeder serving that nonservice rated panel [aka sub panel] to the grounding bar. The groudning bar and the neutral bar must be two different unrelated parts of that circuit not electrically connected.

Sound like to correct you problem and concern which is valid is to move the bare feeder wire to the grounding bar in each nonservice rated panel [aka sub panel]

Hope this helps

Wg
 
  #3  
Old 07-26-02, 08:00 AM
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ksorce
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Smile Follow-up on neutral and grounding

Thanks for the informative reply. I follow you exactly in that my sub-panels should have the bare feeder wire attached to ground, not neutral.

Just to confirm, all my breaker / service panels do NOT have a main breaker. There are two boxes on the inside wall of my garage where the service comes in that have one 150 AMP breaker each, that are the mains, and they are SEPERATE from the service panels. There are no individual service breakers located with the mains.

In that case do I have to ensure that the two main boxes with the 150 amp breakers have the neutral to ground bonding and setup my serivce panels as you described? Or, do my actual service panels need to have the neutral to ground bonded with this setup?

This is difficult to describe exactly what is there. I could easily send a digital pic or two of the setup..a picture may speak a thousand words in this case.
 
  #4  
Old 07-26-02, 08:09 AM
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Sparksone42
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I think what Wg was trying to get across to you is the fact that a service may only have it's neutral bonded to the grounding electrode conductor at one point. This occurs in your first means of disconnect. Usually the first means of disconnect is the main breaker. However, some localities consider the meter to be the first means of disconnect.

If I understand things right you are saying that this takes place in the sub-panels, the ones with the 32 breaker spaces in them. This would be incorrect. The neutral bonding must occur in that first means of disconnect where your main breakers are located inside of your garage on the wall right behind the meter.
Hope this helps and I hope I got Wg's interpretation right!
 
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Old 07-26-02, 10:37 AM
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Each Branch-Circuit from the circuit-breakers in the sub-panels must have an Equippment Grounding Conductor. If the Branch-Circuit wiring is armored metallic cable,the cable metal is the EGC.If the wiring is Non-Metallic cable then a bare un-insulated wire is the EGC. These bare EGC's cannot be terminated on the Neutral terminal bar where the White Branch-Circuit wires terminate. The branch-circuit EGC's and the Feeder EGC ( the feeder is the 150 amp cable) must terminate on a Grounding terminal bar that is "bonded" to the metal enclosure.---The Branch-Circuit EGC connected to the Feeder EGC froms a path back to the Service Neutral for conducting Ground-Fault currents.-----Good Luck!!
 
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Old 07-26-02, 12:46 PM
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ksorce
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Smile Thanks!

Thanks sparksone42 pattbaa for your replies.

Based on spark's comments, I will pull the covers off the main breaker service panels to see if the neutral to ground bond is present. If it is then that verifies that my service panels are not setup right, and the bare ground wire off the feeder cable to those panels should be connected to the ground bar, not the neutral bar.
 
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Old 07-26-02, 01:22 PM
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Ksorce: you state----"to see if the the Neutral to Ground Bond is present.If it is then that verifies that the Service panels are not set up right"-----The Code reads (Art 250-28)-----"A Main Bonding Jumper shall connect the Equipment Grounding Conductors and the Service Dis-connect enclosure to the Grounded Conductor of the system (the Neutral) with-in the enclosure of each Service Dis-connect"
 
  #8  
Old 07-26-02, 06:58 PM
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Wgoodrich
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IN laymen's terms the panel that has the one breaker or disconnect switch that shuts off the entire house is the panel that all bares and white nuetrals must be connected to each other. This includes all branch circuits and feeders that are about to leave that main panel. Then once and feeder or branch circuit leaves that man panel the white nuetral conductors nor any neutral bar where those white nuetural conductors are connected to inside any panel connected after the first main panel must never touch the bare or green wires again clear to end of circuit.

All whites neutrals and bare or green grounds must be electrically connected inside that first main panel that contains the one switch or breaker that will shut off the entire house. Nowhere else in the house is the bare or greens supposed to touch the white neutral conductors not even in any panels that appear after any wire leaves the interior of the first main panel where the main shut off or breaker is located that will shut off the entire house.

Hope this helps

Wg
 
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Old 07-27-02, 08:11 AM
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ksorce
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Talking Thanks!

Thanks guys for the very descriptive information. After pulling off the cover of the main panels where my 150 amp breaker is I have now verified that they are correct - the neutral and ground are bonded together on a (neutral?) bar.

BUT!!!!!! In each of my service panels the neutral and ground are also bonded together on the neutral bar so this is INCORRECT according to your information. ANd everything you stated makes absolute sense. I see I have to change the way each service panel is setup so that the bare ground feeder wire is directly attached to the ground bar NOT the neutral.

I'm glad I investigated this and received your very helpful information. Not just becasue I wanted to add the small sub panel, but that I now know the existing service panels are not setup right and that could certainly be a big problem if there ever was a short! Also, it appears that a lot of the average electricians out there have this very confused and are wrong because I have seen several panels setup this way - incorrectly - especially many where the grounds and neutral branch circuits are together on the neutral bar. Also in asking some supposed electricians - especially the guy who works in the electricial department at home depot - he stated " the ground and the neutral is the same thing" !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
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Old 07-27-02, 09:01 PM
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Re: Thanks!

Originally posted by ksorce
Thanks guys for the very descriptive information. After pulling off the cover of the main panels where my 150 amp breaker is I have now verified that they are correct - the neutral and ground are bonded together on a (neutral?) bar.

BUT!!!!!! In each of my service panels the neutral and ground are also bonded together on the neutral bar so this is INCORRECT according to your information. ANd everything you stated makes absolute sense. I see I have to change the way each service panel is setup so that the bare ground feeder wire is directly attached to the ground bar NOT the neutral.

I'm glad I investigated this and received your very helpful information. Not just because I wanted to add the small sub panel, but that I now know the existing service panels are not setup right and that could certainly be a big problem if there ever was a short! Also, it appears that a lot of the average electricians out there have this very confused and are wrong because I have seen several panels setup this way - incorrectly - especially many where the grounds and neutral branch circuits are together on the neutral bar. Also in asking some supposed electricians - especially the guy who works in the electrical department at home depot - he stated " the ground and the neutral is the same thing" !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
If I understand you correctly the feeder cables Bare Equipment Grounding Conductor and its gray insulated grounded (neutral) conductor both terminate on the neutral buss bar. You plan to move the bare EGC to the equipment grounding buss bar. So far so good but there is a likelihood that the Grounded Conductor (neutral) buss bar is bonded to the cabinet that encloses these panels. Look for a green screw or a metal strap that connects the grounded conductor buss bar to the metallic case of the cabinets in which your lighting and appliance panel boards are mounted. If there is such a connection it will have to be removed in order to render the installation safe. In order to test for proper isolation of the two buss bars in your panels you will need to deenergize the feeder cable by opening the breaker on the other side of the garage and remove both the ground and neutral wires from the grounded conductor (neutral) buss. Since these cable are probably aluminum you might want to have an electrician in to make the changes. The aluminum conductors need to be wire brushed, coated with anti oxidation paste, and terminated using a torque wrench or torque screw driver. These aluminum connections can and indeed will go bad if they are not done with considerable care.
--
Tom
 
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