subpanel size?

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  #1  
Old 06-21-01, 02:03 PM
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I am adding a family room a half bath and remodeling my kitchen. My current breaker panel is 100-amp. I have been told by a residential electrician that I can install a subpanel off one of the 50-amp breakers in my current panel that is not being used. The breaker has 6 awg wire and was for the electric dryer in the garage. I now have a gas dryer and want to know what size panel I can put in the garage to feed my addition and part of the kitchen?
 
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  #2  
Old 06-21-01, 02:29 PM
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By "size of panel" do you mean the number of circuits? The important consideration is the load on the 50 amp feeder. You could install a 12 circuit or a 20 circuit panel if the 50 amp feeder is adequate.Will the feeder supply air-conditioning compressor motors, and what's the kitchen load?
 
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Old 06-21-01, 02:41 PM
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There will be no air conditioner or motors. I am looking at a lighting circuit with maybe 10 lights, a receptacle circuit with maybe 10-12 receptacles, a dishwasher, a microwave, gas stove, garbage disposal, and maybe a refrigerator? Or some of the above if this is too much.
 
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Old 06-21-01, 03:23 PM
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50 amps at 240 volts is plenty to power everything you've listed, with room to spare.
 
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Old 06-22-01, 07:01 AM
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That sounds great! So what size panel (how many breakers?) can i put in?
 
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Old 06-22-01, 02:50 PM
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John has correctly assesed the feeder power.I estimate you'll need 8 CB's for the proposed load and if this is correct a 12 circuit LC leaves 4 spares.If the wiring method is Romex you will need a ground terminal stip bonded to the metal of the cabinet-don't connect the cable ground wires to the neutral.
 
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Old 06-23-01, 12:18 PM
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modaddy, you can put in a panel with 600 breaker positions if you can find one (not likely!). You could even put 600 breakers in that panel. This is not the way the service is limited. There's no harm in buying a big box.
 
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Old 06-25-01, 07:27 AM
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Thanks to all that answered. You guys are great! One last question though, how far away can the grounding rod be from the subpanel? I bought a grounding rod and it can be installed around 40' from the subpanel, is that okay?
 
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Old 06-25-01, 07:48 AM
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Take the grounding rod back and get your money back. Do not use it.
 
  #10  
Old 06-25-01, 08:35 AM
resqcapt19
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Modaddy38,
How many wires are feeding the dryer recptacle? This sub-panel installation will require 4.

John,
384-15 limits the number of breaker poles in a lighting and appliance branch circuit panel to 42.

Don(resqcapt19)
 
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Old 06-25-01, 08:40 AM
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The subpanel is being fed by only 3 wires, Red, Black, and White. There is no ground wire, that is why I asked about the grounding rod.
 
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Old 06-25-01, 08:59 AM
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Probably the wiring method is flexible armored cable(BX) so the metallic armor is the equiptment ground.Avoid using reducing washers where the cable connector enters the cabinet.Use a 1" 2-screw connector for the cable and a 1" KO in the box.Use a 1" conduit loknut that will bite into the metal and a 1" plastic bushing.
 
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Old 06-25-01, 10:17 AM
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But do I still need to ground the panel to a grounding rod? Does it hurt anything to go ahead and ground the panel itself?
 
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Old 06-25-01, 10:18 AM
resqcapt19
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A ground rod will not do the job. You must have an approved equipment grounding conductor from the main panel to the subpanel. The cable armour may or may not be an approved equipment grounding path.
Don(resqcapt19)
 
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Old 06-25-01, 10:35 AM
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Okay, let me get this straight. I do not need a grounding rod for the subpanel but instead I need a ground path to the existing panel, even though the main panel does not have a grounding bar. If this is true, can I tap into a ground from another circuit off the main panel that has a ground wire that connects to the neutral bus on the main panel. The reason I ask is that there is a circuit that runs near the subpanel that has a ground wire.
 
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Old 06-25-01, 01:45 PM
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NEC Article 250-91(b),Types of equiptment grounding conductors lists (6) "armor of type AC cable". It's important that the armor be bonded to the metal of the box via the connector.Possibly you could add a bonding jumper clamped to the armor and lugged to the bare metal of the box. Art. 250-70 states "Bonding shall---conduct safely any fault current". If you bonded to a #14 ground wire in an adjacent box it would be too small for the fault current if one of the feeders grounded and would be a hi-resistance path to ground for a feeder circuit.Suggest you use the cable armor well-bonded at both ends.
 
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Old 06-25-01, 03:27 PM
Matt Marsh
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Switchman,

I don't mean to harp on you buddy, but you need a new code book. Article 250 was completely rewritten in 1999. Article 250-91 of the 1996 NEC is now spread throughout articles 250-54, 62, 64, and 118 (118 pertaining to your quote). Article 250-70 of the 1996 NEC is now article 250-90.

Matt
 
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Old 06-25-01, 06:54 PM
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Arrow sub panel install. summary

Hello to all, I decided to stop into the forum which I have not done in several months.
It sounds like most of the important information has been covered more or less, but lacks some organization at this time. I note the number of people who read postings made about sizing subpanels.
The feeder going between the main panel and the subpanel must have four (4) wires, (Bk, Rd, Wh, Gr/Bare). The Neutral wires/bus is isolated from the frame of the subpanel. A seperate grounding bus is installed for the grounding conductors. If thee cable that is there does not meet this requirement, leave it. Install a new cable of the appropiate length and size. It never hurts to oversize.
A 50A 120/240V circuit for the subpanel should be adaquate for the particular installation described that is mostly if not all 120V circuits. I would recomend generally no more than 6-8 items on a circuit. Ltg depends on the max. wattage of the fixtures, and receptacles are calculated at 180W (VA) each (I beleive). Kitchen counter circuits need to be well balanced. Min. of two (2), and GFCI protected, but never the refrigerator. Nothing other than small aplliance area receptacles are allowed to be on the sm. app. ckts. Try to install 20A receptacle circuits for most circuits, 12 AWG min., the recep. with 20A faces. Any swithced receps. must have 20A switches supplying them.

back to the panel...
Some people prefer to have a shutoff for the subpanel at the subpanel as well even IF it is not required by code. Since the supanel is within the same building and supplies general circuits, it is not nesesary. Use at least 6AWG copper cable or in conduit.
 
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