subpanel load

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  #1  
Old 05-15-02, 09:32 AM
L
Libor
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subpanel load

I'm tying 7 kitchen circuits into a subpanel--a Square D 100 Amp 8 Space Load Center. Total calculated load on this subpanel will be 49 amps. 6/3 cable runs from the subpanel, along the bottom of the kitchen joists, to the main service panel and is connected to service panel at a 60 amp breaker.

Can I use the 6/3 with the 60 amp breaker? Should I step down to a 50 amp breaker?

Also, the subpanel has two lugs for hots and one bus bar that Square D indicates is neutral. But I've got this 6/3 cable with two hots, one neutral, one ground. How do I handle this? From reading old posts, I gather that you attach ground and neutral separately in subpanels, but don't know how to do in this particular panel. Thanks in advance.
 
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Old 05-15-02, 12:13 PM
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Wgoodrich
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You will have to buy a grounding bar that is an extra made available for that panel but bought as an extra. You may install a 60 amp breaker on a 6 awg copper conductor.

How did you calculate the demand load on this sub panel coming up with your 49 amps load applied to this sub panel? What does each of the 7 branch circuits serve. Are you aware that the small appliance branch circuits serving any receptacles in your kitchen must be rated 20 amps each?

Wg
 
  #3  
Old 05-16-02, 07:11 AM
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Libor
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Thanks, wgoodrich.
I bought the extra grounding bar last night and will install in panel tonight. Any preferred location for the grounding bar in this type of panel? Unfortunately, there are no pre-existing holes in the panel that conform to the holes in the grounding bar (though both are Square D products), so I'll have to drill my own holes.

Well, I realize my load calcuation is off-base and I have some circuits I don't know how to calculate. See table:

CIRCUIT/AMPS
1. Refrigerator / 7.2 amps
2. Disposer / 7 amps
3. Microwave / 13.3 amps
4. Dishwasher / 11 amps
5. Lighting (20 par lights at 50 watts each) / ? amps
6. Small-appliance branch circuit (3 GFCI receptacles serving counter) / ? amps
7. Small-applicance branch circuit (2 GFCI receptacles serving another counter) / ? amps
8. General purpose receptacles (3 non-GFCI receptacles, 20 amp each) / ? amps
 
  #4  
Old 05-16-02, 03:52 PM
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Wgoodrich
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YOU SAID;

CIRCUIT/AMPS
1. Refrigerator / 7.2 amps
2. Disposer / 7 amps
3. Microwave / 13.3 amps
4. Dishwasher / 11 amps
5. Lighting (20 par lights at 50 watts each) / ? amps
6. Small-appliance branch circuit (3 GFCI receptacles serving counter) / ? amps
7. Small-applicance branch circuit (2 GFCI receptacles serving another counter) / ? amps
8. General purpose receptacles (3 non-GFCI receptacles, 20 amp each) / ? amps

First your refrig would be considered as part of the 3000 va required for the two small appliance branch circuits reqruired in Chapter 2 of the NEC. Second the dishwasher, microwave if built in or in a microwave cabinet, and your diswasher would be considered fastened in place appliances allowing a reduction of 75% for 4 or more appliance. You only have three so you can't use the reduction. You will have to add the fastened In place appliances in at 100%. Then your gerneral lighiting would normally by at 3% per square feet but on the subpanel you would need to add them in at 100% again. 31.3 amps fastened in place plus 12.5 for the small appliance branch circuits then add in the 8.3 amps for general lighting would add up to 52.1 amps.

Sound like your 60 amp sub panel will carry the load. You don't have any room for adding anything in the future though.

You may install a 60 or 100 amp non fused main lug only panel and install a four wire 6 awg copper feeder with two hots, one neutral and one grounding conductor protected in the main panel with a 60 amp breaker.

I would install a four wire cable with 4 awg copper conductors and protect that feeder in the main panel with a 100 amp breaker using the 100 amp sub panel.

Actually I would run the 7 branch circuits from the main panel and forget any sub panel. This would be the mose economical and best loading in amps option to serve that kitchen. You can buy the 7 runs of 12/2wGrnd from the main panel to the kitchen area just as fast and with smaller holes and more flexibility with much less money invested doing the same thing as the sub panel would do. See no advantage of a sub panel installed in this project.

Hope this helps

Wg
 
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