Upgrading during large addition


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Old 05-27-06, 12:12 PM
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Upgrading during large addition

I need to upgrade my panel during doubling the size of my house. From 100 to 200 amps. Wires run overhead now, but I am allowed to put them underground, and want to do so; the pole is in my backyard, so that's easy. Power company says to give them 30 feet of wire at bottom of pole and they'll finish that part.

I have 120' total feet from top of pole to inside new panel location. This will just be for the meter and main breaker.

I will then take the full 200 amps to the existing panel location and turn that into a 200 amp subpanel that feeds the existing wiring and the new wiring for the addition. This run will also be underground in conduit, another 100'.

So, what size wires do I need and what size conduit? From the codebook in the library, it looks like 3/0 wire, but what will be the likely temp rating of the wire they give me at the electrical store? It's 120 degrees here in the summer, does that matter?
 
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Old 05-27-06, 08:30 PM
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The rating will be 75C.
 
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Old 05-27-06, 10:57 PM
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So that gives 200 amps for 3/0 wire on that chart. But is it that easy? There's another section about services, but it just jumps you around.

An electrician friend is helping me; the permit is in my name as homeowner. He's explained to me how to do the work and safely, but doesn't have the experience in choosing the materials.
 
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Old 05-28-06, 06:32 AM
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use table 310.15 (B) (6)

For a 200 amp service it is 4/0 aluminum or 2/0 copper.
For the 100 sub feed it is #2 aluminum or #4 copper.

The service should have 3 wires in it, one may be stranded and wrapp all arround the other two so that you will have to twist it together to land it.

The sub feed should have two hots one neutral and a fourth ground.

Bring all your grounding electrodes and water pipe ground to the main panel. Bond the ground and neutral at that panel. Also bond these to the panel enclosure.

Seperate the grounds and neutrals in the sub panel. Bond the ground bar in this panel to the panel enclosure not the neutral.
 
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Old 05-28-06, 07:15 AM
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There is absolutely no way that this discussion board can provide you with all of the information that you need to do this job correctly. There are far to many details, all of which need to be correct for a code compliant and safe installation. The best that we can hope to accomplish on this board is to answer your specific questions, and to make a few guesses about the things that you don't even know to ask about. But in a job this complex we will certainly leave _essential_ steps out.

Installing a complete new service is a job that requires considerable knowledge and planning. You need to start by reading several books on the process, starting with something like 'Wiring Simplified' (green book at home depot) and graduating up to something like 'Wiring a House' by Rex Cauldwell. Then get and read the relevant sections of the National Electrical Code. Then find out from your local permitting / inspection department what _local_ code variations exist.

If you buy any materials prior to having a complete plan, then you are setting yourself up to waste lots of money.

We can help you by answering specific questions, and by reviewing your plans for obvious errors. But to tell you how to install a service would require a complete _book_, and we will not write for free books that have already been written. Reading these books will also help with a significant issue: the advice you get here is worth something more than you pay for it, but you need to know enough to separate good advice from bad advice.

For wire sizes: The tables in the code book give you the _minimum_ wire size that can safely carry a given amount of current. If you look at the bottom of table 310.16 you will see adjustments for _temperature_, so in the detailed examination the ambient temperature does matter. However for residential services the load is usually so much less than the maximum service capability that for practical purposes so called thermal derating does not matter. Because you are in a warm climate, you should ask your local electrical inspectors if they have any local requirements or recommendations on this topic.

Additionally, for residential services the code permits the use of reduced size conductors (table 310.15(B)(6) for your _main_ power feed). Some localities will permit 310.15(B)(6) to be used for subpanels, others will permit it for subpanels that are the same rating as the main service, and others won't permit it for subpanels. You need to check this locally.

On top of this, wire size is related to _voltage drop_, which is not a safety issue addressed by code, but which is a 'power quality' issue. You have very long runs (220 feet plus whatever feeds to the pole). If you use the minimum size wire, and have large loads such as a big heat pump, then you might have issues with lights flickering or voltage sags every time the big load starts up. Prior to buying any wire, you need to plan this out; you clearly don't want to spend money on what might be $1000-$2000 of wire (wire prices have spiked recently, and I don't have any idea how much it will cost right now) and then realize that you need to pull it out and replace it with something larger.

Best luck,
Jon
 
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Old 05-28-06, 08:57 AM
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So far, so good...

Ah, okay, I was looking at the wrong chart. Thanks.

Winnie's point seems valid, too, and this chart doesn't take voltage drop into account. After getting to the top of the pole, the power company's transformer is the next pole over.

Okay, while I take those under advisement, and will look for those books, thanks, if I have 3 2/0 cables, what size PVC will I need? What if I upgrade and use 3 3/0 cables?

This is copper, of course. Would properly-terminated aluminum be okay and less expensive? Which is easier to pull into the conduit? The long run will have 2 full bends and maybe a 45. The subpanel run will have two full bends and 2 45s, both of which I understand are to code.

What do the appropriate aluminum wires do to the needed conduit size?

Thanks again, guys; this is an awesome board. I won't do any work I don't fully understand, but do have some experienced electrical help also, and will be a better homeowner because of it.
 
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Old 05-28-06, 09:24 AM
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Copper prices have gone through the roof. Properly terminated aluminum wires will be fine for the main feed to the house and the sub feed to the next panel. I would not use aluminum beyond that point.

4/0 aluminum is good to 200 amps on a service that would be a 2 conduit min I would use 2 1/2.

I can't find anything that says that the Service conductors need to be de-rated for temperature but the feeders to the sub panel will need to be. Check with your local building dept to find out for sure if they require this de-rating and what the factors need to be for the main feed and the sub-panel feed.

At 125 ambient 3/0 aluminum is needed for a 100 amp sub panel feed. if this will be in emt the conduit size would have to be 2 inch also. Again I would use 2 1/2. (I like to bump conduit sizes by one always to make pulling the wire easier.)

You are not likely to find a 200 amp main panel that lets you feed 200 amps back out. Your existing panel is also not rated 200 amps so you need to feed this with 100 amps or replace that panel also.

Total computed load is a difficult calculation and will need to be done by an electrician or EE to determine if voltage drop will be a problem. My initial guess is no, but I do not have enough information to make an informed conclusion.
 
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Old 05-28-06, 09:35 AM
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Copper prices have gone through the roof.
Boy is that an understatement. I think in more of astronomical terms.
Your existing panel is also not rated 200 amps so you need to feed this with 100 amps or replace that panel also
.Nice catch. The OP wasn't real clear on the point of actually replacing the 100 amp panel.

Just so the OP understands. You cannot just turn a 100 amp panel into a 200 amp panel by just feeding it with the correct conductor and breaker. The buss is only designed as a 100 amp panel and therefore the entire panel would need to be replaced with one rated for 200 amps. Maybe you were already doing this and aware, it was just unclear from my perspective.

as to the 200 amp in/out thing. There is a 200amp outside rated and rated as service disconnect available through square d (and I'm sure others). Not cheap, not pretty, but you get what you have to get.
 
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Old 05-28-06, 09:55 AM
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Cool

I am pretty much into using one brand of equipment so I'm not as familiar as I could be with other makes but I would assume all manufacturers supply this type of panel, but it'll come from a supply house - Homer's won't have it.

Typically, where I have a situation like yours I use a 200 AMP panel in a 8/16 configuration with feed through lugs as the main service disconnect. (Cutler Hammer P/N BR816B200RF) I run a 200 AMP feeder to the sub panel which can have but doesn't need (as long as it's on the same structure) a main breaker.

The panel with a main breaker is cheaper than a box with a breaker only. In most instances it proves convenient to use a couple of spaces in the smaller panel for feeds to an outbuilding or AC, hot tub, etc.

Use aluminum wire for the service and feeder. You'll need another loan to buy copper.
 
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Old 05-28-06, 09:56 AM
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See the Chapter 9 'Tables' section of the code book; this is filled with charts of various wire sizes and conduit sizes.
.
The minimum rule for conduit sizing is that the area taken up by the wires must be no more than 40% of the internal area of the conduit.

Different wire insulation types have different thickness, and thus have different area. But for a couple of wire types:
2/0 THWN 143.4 mm^2
2/0 XHHW 141.3 mm^2
Remember that you need an 'equipment grounding wire' run to your subpanel, which will add some area usage.
#6 THWN 32.71 mm^2
#6 XHHW 38.06 mm^2
(No, I don't know why the big XHHW is smaller and the small THWN is smaller; perhaps an error in the table)
So for 3 #2/0 plus 1#6 you get:
463mm^2, and need 1.5" SCH 40 or 2" SCH 80 rigid PVC conduit. Without the equipment ground, the conductors would just fit in 1.5" SCH 80.

Warning: Some of these combinations fall right into the 'jamming range' described in Chapter 9, Table 1, FPN 2. I _strongly_ recommend that you exceed code minimum for the conduit size. I would use 3" or 4" PVC to provide more room for the wire and prevent the chance of jamming.

Aluminium wire of the same ampacity and resistance is 2 wire gauges larger, or about 26% larger in diameter than the corresponding copper wire. You can get 'compact stranded' aluminium wire that is a bit smaller than normal aluminium wire, but as an approximation, if you use aluminium, then use a conduit 25% bigger in diameter.

Aluminium wire, when properly terminated is perfectly safe and less expensive than copper. Proper termination requires using terminals rated for aluminium, using anti-oxidant, and tightening the terminals to the recommended torque using a torque wrench. You _don't_ want to make the terminals 'as tight as possible', because this can distort the wire too much and make a bad joint; you want to use the torque values recommended by the terminal manufacturer.

Aluminium does have the issue that if there is a slight pinhole in the insulation anywhere, the aluminium can corrode and break. But that is why you use conduit; so that you can replace the conductors if needed.

Code permits a maximum of 360 degrees of bend in any conduit run. So you meet the code requirements in both cases. However the friction caused by bends in conduit is exponential with the angle of the bend and this friction multiplies any tension on the wire going into the bend. This means that pulling through 180 degrees of bend is roughly 7x harder than pulling through 90 degrees of bend, and bends near the 'feed' end of the conduit (where a helper can _push_ the wires in) are less of a strain than bends near the 'exit' end of the conduit. I have never had to do a long run in underground conduit, but I've picked the following suggestions up:

1) Use metal rather than PVC for the bends or the bend on the 'exit' end (note that this may require deeper burial because of ground bonding requirements). This prevents the pulling rope from cutting through the PVC.

2) Use lots of lube on the wire.

3) Have someone to feed the wire in, and pick the direction that will result in lowest pulling forces (feed end closest to the most bends)

-Jon
 
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Old 05-28-06, 10:04 AM
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Sorry about the confusion, yes I will be replacing the existing panel completely to a new 200A subpanel. More later, lots to do today...
 
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Old 05-28-06, 10:24 AM
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One thing I just remembered.

Because I don't do resi as a regular thing, I just remembered some of the pocos in my area are requireing a 3 inch conduit for an underground feed for anything 200 amps or less.

check with your poco to be sure they do not have a regulation concerning this.
 
 

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