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Does wiring Meter/Main Combo to Load center make load center a sub-panel?

Does wiring Meter/Main Combo to Load center make load center a sub-panel?

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  #1  
Old 03-15-13, 12:09 PM
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Does wiring Meter/Main Combo to Load center make load center a sub-panel?

I have a 200 A service to a meter socket which feeds a 200 A load center through a 2" nipple. There is no "main" breaker at either side (socket or load center). The load center doesn't have room for the number of circuits I need.
My proposed upgrade will give me two main breakers so that I can disconnect either the load center or both panels. The new meter/main has 8/16 spaces/circuits and will be located outside (surface mounted) as underground feed in 3" conduit. The new load center will be flush mounted inside.

I am changing out a 200 A meter socket to a 200 A Siemens meter/main (M/M) combo, w/ feed thru lugs, (feed thru lugs at bottom of Buss controlled by the 200 A main). I intend to wire from fd. thru lugs to a Sq D load center with its own 200 A main breaker. There is no seperat breaker (disconnect) feeding this new load center other than the meter/main. Does this make the load center a sub-panel or since it is wired in series with the meter/main is it just an extension of the meter main as regards bonding neutrals and grounds. The installation of these two new panels will be back to back with a 2" nipple with 3/0 Cu hots and 1/0 neutral. This M/M will have a #4 Cu solid or braided wire to two grnd. rods. No attachment to water pipes as service is in PVC. I do have an CEE (concrete encased electrode) currently attached to my existing load center though I am uncertain of its integrity. My existing load center has the grnd , neutral and enclosure bonded together and an additional #6 solid Cu wire to a questionable grnd. rod outside below the meter socket. The existing meter socket has no dedicated ground wire, and relies on the nipple/nut for bonding to the load center and its grounds.

My confusion is regarding the proper grnding of the load center

The new Sq D (QO) load center has 4 bars attached by a screw to the neutral buss, but there is no screw attaching the neutral to the enclosure (there is provision for a bonding screw to attach to these neutral and ground bars to the enclosure though I don't have the screw). The label indicates that as service equipment I can attach grnd wires to unused openings in these bars, but it doesn't address whether to bond these busses to the enclosure). It seems I could remove two of these bars and attach them directly to the enclosure for grounding my circuits separate from the neutrals if that is the proper way to set this up (there are three locations in the enclosure with a single screw hole and two tits that would index with these bars presumably for attaching two of the four bars directly to the enclosure, and separate from he neutrals <or I could purchase two new grnd. bars and install there>.

Questions: For purposes of clarity; when I am talking of neutrals and neutral buss bars I am talking of attachment points for the white commons and bare ground wires for my circuits. NOT the 3/0 neutral attaching from the pole to the meter/main to the load center.

1) Treat new load center as a sub-panel, an I believe that would mean I need to either install new grnd. bars attached to the enclosure or steal two of the four grnd. bars from the neutral/grnd bar configuration that exists?

2) Treat the new load center as an (series) extension of the meter/main combo and find a bonding screw to bond the neutral, grnd. and enclosure?

3) Can I/should I, run a #4 bare Cu wire through the nipple from the meter/main into the load center and what do I do with it (a four wire set-up)?

4) If the load center needs the neutral/grnd busses attached to the enclosure where might I find such a bonding screw (it looks to be about 1/4 inch fine thread hole in the buss bar with the hole in the enclosure not threaded, like the screw would be self-tapping)? This would presume the load center is to be treated as an extension of the service entrance.

5) If the load center is to be treated as a sub-panel, am I correct that the ground bars need to be separate from the neutrals and attached to the enclosure?

6) When is it necessary to actually isolate the ground wires with an insulator?

7) Where/how do I attach the CEE grnd. to this system?

8) Please provide any other questions and answers to other aspects of my proposed situation that I have missed.

Time is of the essence for me, but others have lives too! So I thank all that can assist me and my compulsive nature.

Thank You for any/all input?
 
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  #2  
Old 03-15-13, 12:25 PM
ray2047's Avatar
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Any panel after the first panel with a (main) over current protection device (OCPD) is a subpanel. Only the first panel of multiple panels in the same structure require a main disconnect.
 
  #3  
Old 03-15-13, 05:35 PM
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Welcome to the forums!

I am changing out a 200 A meter socket to a 200 A Siemens meter/main (M/M) combo, w/ feed thru lugs, (feed thru lugs at bottom of Buss controlled by the 200 A main). I intend to wire from fd. thru lugs to a Sq D load center with its own 200 A main breaker. There is no seperat breaker (disconnect) feeding this new load center other than the meter/main. Does this make the load center a sub-panel
Yes. Because the 200A MOPD in the M/M combo disconnects the power feeding the interior panel, that interior panel is a subpanel.

It must have the grounds together and bonded to the box. It must have the neutrals together and isolated from any path to ground, including the box. It can have a 200A main breaker, as you propose, a 100A main breaker or no main breaker. It doesn't matter, since that "main" breaker only serves as a convenient means of disconnect.
 
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Old 03-15-13, 08:12 PM
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You have a lot of questions and some have been answered. Here's a couple more. Your Ufer ground (CEE) and ground rods get attached via the ground wires to the neutral at the main which is the MM combo. You need 4 wires to the subpanel (2 hots, 1 neutral and 1 #6 ground). All you need is a #6 copper to ground rods and #4 copper to ufer ground (CEE). You state you are using 3/0 copper for the 200 amp service. The NEC residential requirement is 2/0, but 3/0 is fine. The metal nipple between the MM combo and subpanel should have bonding bushings at each end. The lug on each bushing to be bonded to ground bar at each end.
 
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