Add Sub-panel to existing service panel?

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  #1  
Old 10-19-06, 09:35 AM
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Add Sub-panel to existing service panel?

My home's 200A main service panel appears to be stuffed to the gills and for the moment I need to add a 240v 50A 6/3wg UF cable feed to my dock service panel where I will need both 240 and 120 circuits (boatlift, outlets, pole-light, etc.).

Instead of replacing my current house service panel with a larger one ($$), it's been suggested I simply add a subpanel adjacent to, or in my case, below the current one for the extra circuit space/capacity.

Question is how do I connect/feed a set of wires supplying juice from the old service panel to the new sub (connect it where in the old, and what size wire)? Will it make a difference whether I will only be using maybe 50-100amps, or is it best to go ahead and set it up for the full 200amps?
 
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  #2  
Old 10-19-06, 09:58 AM
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In my opionion you would be best served to call an electrician. You have much to learn and I gather you want something done sooner rather than later.

If you want to learn, buy at least two or three books on hiome wiring and read them. The books will tell you how to do this project. You can then post back with specific questions.

Installing a sub panel is not for the novice.
 
  #3  
Old 10-19-06, 10:27 AM
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Panels can never be fully turned off, even when you kill the main breaker, there are still hot wires, remeber that when your hands are in the box! And I second racraft that hiring an electrician is not a bad idea for this. If you're going to be doing all the dock work yourself, I don't imagine a small bit of difficulty will dissuade you, though For the amount of work you'll be doing, I highly recommend you buy a copy of the NEC, as it will save you a LOT of rework when the inspector fails your dock- working around water is VERY tricky and requires a lot of special wiring techniques.

Do you have ANY breakers free in your panel? You'll need two side-by-side so you can get a 240A double breaker in there. You can move the other breakers if you need to; if there's no room, you'll need to pick a circuit or two to bump to the new panel. Look at the placard inside the door- it should give a ton of information regarding the ratings of the bus and the maximum size and type of breakers. It will probably allow you to put on a 100A or 125A breaker, but might not allow you a full 200A (In reality, you would never be drawing 200A on your subpanel or your main would trip so it's kinda moot.) It will also tell you if your panel is rated for 60C, 75C or 90C which is important when sizing cable.

You can install the new 125A (or whatever) breaker in the empty slot. The subpanel won't need a main breaker, so you can buy a simple Main Lug Only panel- it must have a ground bar and isolated neutral bar. It can be any size- 100, 120, 150 or 200A, depending on what's on sale at the big box. (It's OK to buy a 200A panel and only use it for 50A or 100A) Brand doesn't matter, although it's easier buying breakers if it's the same brand as your main panel, as the breakers have to match the panel's UL listing.

Then you'll need to put in conduit between the two panels and you're finally ready to wire it up. The type of wire you need will depend on what amperage panel and circuit you choose, and whether you want to oversize it or not; will probably be somewhere around #1 or #2 THHN for the hots and neutral, and #6 for the ground, but this is again dependant on the rating of the circuit breaker and the temperature rating of the panel.
 
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Old 10-19-06, 03:33 PM
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"Panels can never be fully turned off, even when you kill the main breaker, there are still hot wires, remember that when your hands are in the box! And I second racraft that hiring an electrician is not a bad idea for this. If you're going to be doing all the dock work yourself, I don't imagine a small bit of difficulty will dissuade you, though. For the amount of work you'll be doing, I highly recommend you buy a copy of the NEC"

I hear ya. Been reading up via several "How-To" wiring books including one based on the NEC. "Wiring Simplified". Everything is basically been run and setup except the actual connections at the dock panel, and the install/connection of the possible subpanel below the current one.

I actually have two docks (only one with lift) with each having gotten it's own dedicated run of UF 6/3wg buried in PVC. So I will need two runs of 50amp feed from the proposed in-house subpanel. For right now I don't care about the 2nd dock connection. That can be done later after more improvements to my panel situation. For now I just want the lift and an outlet set working.

So if space allows, install a 100-125A breaker in the main panel, then feed the appropriate sized wire from there thru conduit to the subpanel lugs (I would mount right below the other). From there (for now) a single 50-60amp breaker giving feed thru the UF down to the dock subpanel. Install a GFCI shutoff breaker of 50-60amps and whatever other breakers from there.

At the dock subpanel, what should the ground setup be? Separate ground bar with copper wire to a driven pipe in the ground? or no?

Worst case scenario. What if I "don't" have space for another 100-125amp breaker in the main panel? What to do for a temp setup with only one 50amp feed needed just to get the lift runningin the interim and tackle the bigger problem via professional means?
 
  #5  
Old 10-20-06, 10:13 AM
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> Worst case scenario.

If you really don't have space and can't add tandem breakers, I would find the four most lightly loaded circuits in the main panel. Combine the four circuits into two circuits by wirenutting the hot wires into pairs with a short pigtail of wire to the smaller of the two existing breakers. If your breaker lugs are rated for multiple wires, then you can avoid the wirenut and pigtail and just land two wires on one breaker. Do not do this with circuits that serve the kitchen or bath. Also, this should only be done as a stop-gap as it reduces the available power to the circuits in the home and, you should remember to undo when the service upgrade or subpanel install happens.

This should free up two spaces in the main panel for the 50A dock panel feeder breaker.
 
  #6  
Old 10-20-06, 11:28 AM
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Your other option is to find 2 circuits to re-route to the new panel, and move their breakers to the new panel. You're putting the new panel right below the old panel, right?If there are any wires coming up from below, you'd probably have to move them anyhow, and it's likely easier just to move them to the new panel instead of trying to stretch them. You can get a pack of plastic blanks at the big box to cover up any holes left over.
 
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Old 10-20-06, 12:26 PM
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grover & ibpooks

That's some real good out of the box suggestions, again as a temp solution pending a professional upgrade of the mian service panel situation.

How about thoughts concerning the subpaenl at the dock with regards to the grounding thereof? Is the equipment ground from the house good enough, or do I need to do the pipe in the ground and separate ground bar in the panel setup?
 
  #8  
Old 10-20-06, 01:38 PM
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You do not need to pound in a new grounding electrode at the dock- bring a separate ground and neutral wire from your house, and that will provide grounding. The neutral bar should be isolated from ground at the dock panel, don't ground it.

Also, if you run steel conduit (RMC, etc), then the conduit itself will also act as a ground, soo. So long as this is greater than 20' (I think it's 20' but don't quote me on that), then it could legally take the place of a ground rod even if one was required. Just make sure everything is grounded and bonded together, and there shouldn't be any issues.
 
  #9  
Old 10-20-06, 01:51 PM
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Well no metal conduit. I ran everything in PVC at approx. 24" down to the bulkhead where it comes up thru flexible conduit to the subpanel.


grover...When you say "separate ground/neutral" from the house, do you mean in addition to the neutral and ground contained in the UF 6/3 I ran? or those ARE what you're talking about?

As I mentioned before, I will be installing a GFCI shutoff breaker in the subpanel as well, if this means anything grounding-wise.
 
  #10  
Old 10-20-06, 02:57 PM
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If you ran 6/3, you're good, the white and copper in the UF are what I meant I had forgotten you ran UF through the conduit.
 
  #11  
Old 10-24-06, 12:11 PM
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Read in one of those DIY wiring books that another way to make room in the main service panel is to utilize "Slim-Line" replacement breakers that in essence put two single pole breakkers worth into one slot making room for additional breakers like I need for either a service subpanel add-on in the house, or to run direct out to the dock subpanel?

Thoughts, suggestions?

My house service panel is a Westinghouse CAT# B24-40 BFN, BSN if that makes any difference in using the Slim-Line's?
 
  #12  
Old 10-24-06, 02:05 PM
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The panel has to be rated for slim-lines- normally it will be something like 20/20 or 20/40, for the # of slots and # of breakers it can support. I can't find anything on your panel on Westinghouse's website, but 24-40 sounds like it's 24 slots and supports 40 breakers? If so, you can just use pony breakers and save yourself putting in a new panel!

You might have problems finding Westinghouse breakers, though. Look on the sticker, see if it's listed for other brand breakers that might be easier to find.
 
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