subpanel feeder

Currently have a main panel and subpanel sided by side. From the subpanel feeds another subpanel in a detached garage. The feed between the two subpanels inside the house is armored cable with a black red and white wire with what looks like a bonding strip. There is a junction box on the inside of the house where armored cable spilces with the cable going to the detached garage. There is no ground wire from the armored cable. The jbox hookup has the ground from the garage wire bonded to the metal jbox and the armored cable looks like the strip is connected to the connector on the jbox making the ground between the two wires.

Some questions. The ground wire coming from the garage seems to have a smaller gauge wire than the rest of cable? Is this sufficient for ground? Can the bonding strip from the armored cable be used as the ground? Lastly, if the bonding strip is providing the ground how can it provide a ground if the inside subpanel that it is connected to is not bonded to the subpanel? If neutrals and grounds are to be separated in a subpanel and not bonded to it, where is the ground coming from? Neutral wire hookup from the armored cable on the inside subpanel? The receptacles in the garage show a ground. Thanks.

 

Welcome to the forums! Just a few observations and questions so you can get better answers. How are the armoured cable grounding strip and the grounding wire in the junction box connected? Is the grounding wire in the j box connected to the jbox with a green screw?

The smaller ground wire is normal except in certain situations. You have not stated the size of wire nor the ampacity of the breaker controlling the circuit to the garage.

In a subpanel for a detached building, you must run a grounding conductor to a ground rod outside the building. Some localities require two rods spaced apart and interconnected. The grounds in the subpanel are segregated from the neutrals and are not touching the panel casing. The neutrals will travel back to the original panel. Do you have ground rod(s) in place now? Grounds and neutrals are not combined in a sub panel. Once everyone wakes up, you will get more answers and possibly more questions, so hang in there.

 

This might be OK depending on the size of the wires.

Yes and no. The bonding strip in combination with the armor jacket is the grounding path. Not just the bonding strip alone.

It is (or should be) connected to the steel case of the sub panel and metal junction box with a proper connector. This bonds it to the sub panel.

Again, the armor jacket, bonding strip, and connector.

Neutral wire connects to the neutral bus, which is separated from the steel case of the sub panel. The steel case is the ground and should have a ground bar installed.

Note: The requirement for a feeder to detached structure to have 4 wires did not go into effect until 2002(?). If this is an existing installation is may be grandfathered in.

 

As Chandler suggested some additional info should be provided. This is an existing installation. The subpanel feeder wires are both 10gauge with a 30 amp breaker at the inside panel. The metal jbox 4x4x1.5 where the splice occurs is mounted to the wood plate of the house. There are no threads on the metal jbox for a green ground screw. The ground wire from the garage is attached to the metal jbox with a sheet metal screw through the jbox into the wood plate. The armored cable has a connector to the jbox. The detached structure subpanel has no ground rods. The inside subpanel does not have ground rods. The inside subpanel is right next to the main panel which has two ground rods. After reading numerous threads, I thought since the subpanel is inside and next to the main panel it does not need ground rods?

The inside subpanel does not have a separate ground bar directly contacting the metal of the sub panel. The subpanel has two bars one on the left and one on the right that are on plastic separating it from touching the metal of the subpanel. The grounds are on 1 bar and the neutrals are another bar and the bars are not connected together. I looked for a green bonding screw for these bars that would bond the panel. Read in a subpanel the green/bond screw must be taken out. The armored cable black and red wires go to the 30 amp breaker and the white goes to the separated neutral bar. I dont understand how the armored cable is providing a ground at the inside subpanel if it is only bonded to the subpanel by the metal knockout connector and not connected to any type of ground? Is the armored cable neutral wire providing the ground reading for the receptacles at the detached structure? Thanks for your help.

 

That is correct.

No. It is connected to a ground, the metal case of the sub panel. The metal case is connected to the main panel via a nipple/conduit/cable. The main panel case is connected to the grounded conductor (the neutral) via the bonding screw (main bonding jumper). In electrical installations, anything that is conductive, and is not intended to carry current, is bonded together to create a grounding path back to the source.

The path from the garage receptacle back to the main panel is:
Garage receptacle connected to ground wire of branch circuit
Ground wire of branch circuit connected to ground bus of sub panel
Ground bus connected to ground wire of feeder from house
ground wire feeder from house connected to steel junction box inside house
Steel junction box inside house connected to cable armor via connector
Cable armor connected to inside subpanel via connector
Subpanel connected to the main panel via conduit/cable.

A grounding path does not need to be a wire. It can be any NEC approved grounding path.

As long as the neutral bus is not connected to the steel case, and floats, it is OK. The ground bar must be connected to the steel case of the panel. This is commonly done with a bonding jumper or bonding strap.

Unless the box is VERY old, there will be a threaded 10-32 hole in the back of the box for a ground screw.

 

The green screw in subpanel is removed for the Neutral bus bar, but for the other bus bar in which you will have ALL and ONLY the grounding wires connected for that one you need the green screw to make those grounding wires bonded to the metal enclosure of the subpanel and therefore provide grounding for those circuits. This is true for both of the two subpanels you have. What you want to avoid is to mix grounding wires with neutrals or to use the green screw in the neutral bus bar, so those bus bar need to be isolated from themselves, the neutral bus bar WILL NOT use the green screw, but the grounding bus bar WILL USE IT.

Now, regarding the grounding electrode system, you have two subpanels the first one that is close in the same building than the main service panel DOES NOT need separate ground rods, HOWEVER, your second subpanel doesn't matter if is inside, but if is on a DETACHED BUILDING as it is, you NEED to install the separate ground rods for this subpanel. Use a #6 wire that will go to the ground rod clamp and will terminate in the grounding bus bar of the subpanel with the green screw installed only at the grounding bus bar... that will be completing your grounding electrode system for that detached building.

 

!!! The way you have it right now with the green screw removed from the grounding bus bar, means that you are using your grounds like neutrals, therefore the grounding path for your subpanels is incomplete. !!!

Neutral bus bas in subpanel = Always must have GREEN screw removed.

Grounding bus bar in subpanel = Will have only grounding wires and will have GREEN screw installed.

 

Many ground bars do not use or have green screws. It is true it must be screwed to the enclosure.

 

Thanks for the detailed explanation. Understand how the subpanel is conducting with the armored cable or anything bonded to it. I looked for a nipple conduit etc to the main panel or anywhere else and there is none. The question I have is why when I test for continuity on the neutral bar of the subpanel by touching the bar and bare metal on the subpanel, it shows continuity. Not sure if I am testing correctly. Using an Ideal vol con 67076 that has two lights on the bottom portion of the tester. One red light lights up that says DC+ continuity. I have done this test with the ground wire removed from the subpanel bar and it still shows continuity. Also, removed neutral wire from subpanel and still shows continuity. The neutral bars look to sit on a plastic shield. I do not see anything that is bonding the bars to the subpanel. Proper way to test to see if neutral and ground bar are unbonded and bonded? Panels is a Siemens G1224MB1100 appears to be somewhat old. Is it possible this panel is only to be used for a main/service equipment? Thanks for your help.

 

Are you sure there is not a screw going through the neutral bar into the case?

 

Can you post a picture of the subpanel? Please take a clear picture of the Neutral and Grounding bus bars as well.


Ideally I will use a Multimeter that beeps when checking for continuity.

 

Another important question: Does the neutral and grounding bus bar have for any chance a jumper between them? Some panels have those bus bars bonded together.

 

I have looked several times and still cant find a screw,strap etc... that would be bonding the neutral bar.

 

I would post a pic if I knew how.

 

There is not a jumper between them now. But there are two screws at the bottom of the bars that would connect a jumper. The panel was like this without the jumper.

 

To post a picture, find the small icon that have a tree inside a picture frame in the tools section, it's just right below the undo arrow in the tools section, click on it and then click on search file from computer, then select file in the windows that will open, click on it and then press Upload button, wait a few seconds until it will insert the picture into the reply, you will see a text like coding not the actual picture in your message. Then press Submit reply.

 

To insert pictures

http://www.doityourself.com/forum/el...-pictures.html

 

picture of subpanel At the bottom of each of the bars there are two different screws on the bars where a jumper bar could be attached to connect the the bars.

 

another picture of subpanel

 

Update on sub panel. Removed several neutral wires from the neutral bar. 1 neutral wire was bonding to the sub panel through a Gfci outlet. No continuity now between neutral bar and sub panel. This panel needs a strap, screw etc... For it to be bonded to the sub panel. However the ground bar is showing continuity to the sub panel when it should not. Removed all ground wires from the ground side and the last grd wire removed the contunuity. A ground bar or strap needs to be installed? I have the ground wire from the main panel to the sub panel disconnected as well as the neutral. Why or how is the last gird wire making the sub panel bonded? Also, the neutral wire in the main panel has been cut to fit into the neutral bar. Is this ok? In the sub panel a breaker is pigtailed to allow 2 circuits is this ok? Thanks for your help.

 

I must be missing something. In a sub-panel the ground bar is bonded to the panel. The neutral bar is not to be bonded to the ground/panel. Stranded wire is not to be trimmed the fit in the bar. Buy a correct sized lug. It's ok to pigtail to a breaker.

 

The thread is long and hard to follow. The issue began when I tested to see if the neutral bar on the subpanel did not have continuity with the subpanel itself. It did. There was no screw, strap etc... bonding it to the panel. Removed some neutral wires from the neutral bar and found one that was causing the continuity. Also, the ground bar that was on a plastic shield showed continuity but the bar was not bonded to the subpanel. Removed ground and neutral feeder wires to each bar from the main panel to the subpanel while testing. Started to remove the ground wires and there was one that was causing continuity. Need to install a ground bar that is bonded to panel.

 

Indeed. ASAP!

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This is your statement that threw me a curve because the ground bar should have continuity to the panel.