matching panels to breakers

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  #1  
Old 12-07-06, 06:45 AM
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matching breakers and panels

Is this acceptable: 60A Main (a 100A service drop protected with the double pole 60A main breaker) feeds via 60A breaker a 125A main lug subpanel 70' away?

To accommodate the future service upgrade to 200A, there is a 200A panel installed in between the main and the subpanel. The 200A panel recieves 60A from the main and passes it through to the 125A subpanel via 100A breaker. The 200A panel is > 10' away from the main (#6 romex cable w/four conductors, in 1.5" sch.40 PVC conduit), and 60' away from the 125A subpanel (three #1 Cu THHN conductors and one #4 EGC, in 1.5" sch.40 PVC conduit).

Some background: The 125A sub-panel is to service a small mother-in-law apt. that will have an electric W/D (each 240V, 15A), and some other light and kitchen circuits. I esimate the actual load demand to not exceed 50A (for now).

I do not have the load calculations, only an estimate. The whole area (a 2BR and the M-I-L - used to be a duplex) is now serviced by the 60A main with no problems.

Thanks, Al
 

Last edited by handyal; 12-07-06 at 09:15 AM. Reason: misspelling
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  #2  
Old 12-07-06, 08:37 AM
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> 60A Main feeds via 60A breaker a 125A main lug subpanel 70' away?

Yes, that's okay.

> three #1 Cu THHN conductors and one #4 EGC, in 1.5" sch.40 PVC

#1 Cu is good for 150A; you only need #2 Cu. for a 125A feeder. A typical copper feeder to a 125A panel would be 2-2-4-6 for hot-hot-neutral-ground respectively. In either case, the EGC only needs to be #6 Cu.
 

Last edited by ibpooks; 12-07-06 at 08:48 AM.
  #3  
Old 12-07-06, 02:14 PM
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Thanks, Ben.
Another question: both 125A and 200A (sub)panels are Square D QO and come with the neutral and ground buses bonded. So, I need to isolate the neutral bus from the ground (to prevent accidental energizing of the ground system?) using the ground bar kits in both panels. To these installed ground bar kits, mounted directly to the cabinet, I will secure the EGCs and the circuits' ground wires in both panels. Is that correct?

Thanks,

al
 

Last edited by handyal; 12-07-06 at 02:16 PM. Reason: misspelling
  #4  
Old 12-07-06, 02:22 PM
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> I need to isolate the neutral bus from the ground

In all subpanels, the neutral and ground buses must be isolated. The only place where neutral and ground are connected are in the main panel, which is the first panel after the meter. In the main panel only, the neutral and ground must be bonded.

This means that in the future, when your 200A panel becomes the main and the the 60A panel becomes a sub, you will need to seperate the grounds and neutrals in the 60A panel and bond the bars in the 200A panel. So when setting up the 200A panel, remove the bonding screw/strap but don't throw it away, because you'll need to re-install it when you upgrade to 200A service.

The 125A panel will always be a subpanel, so the grounds and neutrals should be isolated.

> I will secure the EGC and the circuits' ground wires in both panels. Is
> that correct?

The #6 EGC from the subpanel feeder and the circuit grounds (also called EGCs) all land on the subpanel's ground bar.
 
  #5  
Old 12-07-06, 04:20 PM
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Ben:

Thank you!

In the 200A panel there are four lugs: two separate for hots, and two bonded together for neutral and for the EGC. All will take the #1 and smaller (#6) wire. Since I am using the ground bar kit, the EGC lug is unused for now.

Is it acceptable to use this unused EGC lug for connecting the #1 neutral coming from the 200A panel? (It is awkward to fit the #1 THHN neutral to the neutral bus space).

When the service is upgraded to 200A, all conductors will re re-wired accordingly.

Thanks, al
 
  #6  
Old 12-08-06, 08:35 AM
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> Is it acceptable to use this unused EGC lug for connecting the #1
> neutral coming from the 200A panel? (It is awkward to fit the #1 THHN
> neutral to the neutral bus space).

Yes; you can also buy add-on lugs for connecting large wires to the bar. If you look closely at the panel label it should have a max wire gauge rating for the neutral bar (usually #4). Anything larger than that needs to be connected on one of the provided large lugs or with a lug kit.
 
  #7  
Old 12-08-06, 11:50 AM
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Ben:

Thank you!

Want to let you know that my project (adding a subpanel) is completed. The power is on. So far so good. Now I'll be connecting the existing and adding new curcits. One is for the 240v washer/dryer. So, you'll hear from me again soon.

I also want you to know that your kind guidance provided me with much comfort as I was moving along in unfamiliar territory. Thanks again and have a wonderful holiday season.

al
 
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