Wire splicing question

[Philip]

I'm putting 20KW on my front hill and have a slight problem. The buried conduit is 3/4" which means I can only get 8-2 UFB to run through it. Since it's 60 feet under ground plus 75 feet through the attic to get to the inverters I could split the run with a splice and go 60' 8-2 and 75' 6-2.

From the sticky spreadsheet on cable losses the all 8-2 run would result in .46% loss while the split would result in .37%. Is that extra 0.09% worth it? My guess is the splice loss would be negligible but it doesn't seem worth the hassle and expense. I could go 75' 4-3 to get down to .31% loss or a .15% differential but I would think at that point, the cost of the wire would make any gains negligible.

Doing the math, simulated yearly yield would be 21770KWH at $0.067/KWH or about $1460/yr. If my logic is correct that means a .09% loss would translate to $1.30/yr. while a .15% loss would translate to $2.20/yr. Extra copper cost would be $165 for 6-2, (+ cost of splices 20 yr. payback), and $515 for 4-3, (never payback).

Am I missing something? If my math is correct the splice just doesn't pay.

[Naptown]

You cannot put UF cable in a conduit of that length. A short sleeve out of the ground would be about the limit.

[inetdog]

Why spend money on direct burial cable and then not bury it?
If you put in PVC, you can use wet rated individual wires, possibly aluminum, and save some space in the pipe and some money potentially wasted on copper.

[Philip]

Naptown,

Is that code? Unfortunately I have 10' in the wall and another 10' under concrete. I could dig up the rest though it would be a pain.

Inetdog, What code wire would I look for? The only thing I knew of was UF type romex. I found THWN on the net, will that do? I could run he conduit within the attic all the way to the inverters and get down to two #6 with a #10 ground.

[inetdog]

Inetdog, What code wire would I look for? The only thing I knew of was UF type romex. I found THWN on the net, will that do? I could run he conduit within the attic all the way to the inverters and get down to two #6 with a #10 ground.

THWN will do the job. THWN-2 has better high temperature properties which may allow you to use smaller wire in areas of high ambient temperature, like on top of the roof or in the attic.

Basically any type that starts with T and includes a W is rated for wet conditions, just not for direct burial without conduit.
The N in the type refers to a thin nylon outer jacket that can make the wire easier to pull. But for long runs that may be hard to pull, Simpull (TM) wire does not require lubricant. You may not find that readily available in small quantities except at an electrical supply house.

At Big Orange (Home Despot), as far as I have seen, all of the wire with W rating is on the carousel rather than on the shelf in rolls.

[Philip]

Sweet! That may be the way to go since I could likely pull two #6's as individuals vs. flat 6-2.

[inetdog]

Sweet! That may be the way to go since I could likely pull two #6's as individuals vs. flat 6-2.

Don't forget that you probably also need an Equipment Grounding Conductor (EGC). That is separate from any ground electrode connection at the panels and racking.
Figure that will be #6 also, but three #6 should still be easier to pull than the UF.

[Philip]

Yes, I was thinking of that. Funny thing, it appears Home Depot may be the lowest cost source. Everywhere I checked on the internet is more expensive and that doesn't include shipping!

I tried pulling two 6's through back to back 3/4 in 90's and it was a breeze so it's looking like a winner.

[Sunking]

Yes, I was thinking of that. Funny thing, it appears Home Depot may be the lowest cost source. Everywhere I checked on the internet is more expensive and that doesn't include shipping!

I tried pulling two 6's through back to back 3/4 in 90's and it was a breeze so it's looking like a winner.

For a HO Agent Orange maybe the best price in town, but generally local electric supply houses are less expensive and have higher quality supplies. Additionally Blue Box tends to be less expensive than Agent Orange. Shop around locally.

[Philip]

Unfortunately the locals thumb their noses on retail and will stick it to you unless you are a contractor. One plumbing supply place wouldn't even give me the time of day. Even at that I see a lot of contractor trucks at HD every time I go there. I ended up building most of my house thorough HD, the local lumber companies could only beat them on a couple of items, (lumber not being one of them!).

The nearest HD is 15 mi., the nearest big blue is 50 miles and the same price.

Isn't the Internet great! Great advice via places like this, shopping for best price without burning gas and time, etc., it's all good!

[russ]

Even at that I see a lot of contractor trucks at HD every time I go there.

Right - for many contractors costs are a pass through so they don't care what a part costs. Others are too lazy to shop for decent deals. That is like the old saying about truckers knowing where the good food is served while in reality they often only know of a place with adequate parking.

[inetdog]

For a HO Agent Orange maybe the best price in town, but generally local electric supply houses are less expensive and have higher quality supplies. Additionally Blue Box tends to be less expensive than Agent Orange. Shop around locally.

Based on anecdotal figures on another forum we visit, I would qualify that to say that the package deals at HD and the cost of high volume items may well be lower than what an electrician with a business license would pay at a local supply house.

HD tends to skim the cream of the business and offer occasional loss leaders, so their prices can be lower than a supply house that has to stock or special order a wider variety of goods. It is true that if you want higher quality items, even from the same manufacturer, you may do better at a supply house.

One of the best examples of this is the load center (breaker panel). A package deal from HD including the main and a fixed assortment of branch breakers can cost less than the same package from a supply house, and that in turn costs far less than the price of the panel and breakers individually.

If you want exactly what HD or Blue has and can pay up front, you can get a good deal. If you want (or need) something that they do not have, you are SOL.
If you mix and match, you will end up somewhere in between.

Just do not count on getting accurate information about the product at Orange or Blue (or for that matter at some supply houses). But if you buy through the supply house you probably have a better chance of getting through to an engineer at the manufacturer for those really tough questions.

[Naptown]

Here is an example
Bought 2 combiner AC weatherproof 200 amp panels from Orange.
Cost for panel and main breaker $150.00
Electric inspector who was inspecting his first solar system wanted the wires upgraded to 250MCM or main dropped down to 175 amp.
Replace wire $100
Replace breaker ( main only without panel $225.00
Guess what happened

[russ]

The big box stores also can buy much cheaper - they are buying thousands whereas the local supply house is buying ten or a hundred - volume discount.

Normally the big box pockets the difference but when there is a big sale -

[Philip]

Actually, two of my neighbors are contractors, HD does best on many items around here, the locals do better on some items so they tend to shop both. At least around here they don't do cost plus materials, the current market is very depressed and won't support it. The one next to me was smart and didn't rip off people when the market was strong. As a result he's been able to keep working through the entire downturn. A couple of other contractors I'm familiar with did gouge people when they could and when the downturn hit they were SOL. Both had to leave the state to find work.

Probably not the norm but up here the local shops were really ripping off people before HD moved in. There was a stone supply house that was charging double what HD did. After HD moved in, they dropped their prices on most items to match HD and are still in business. What really amazes me is they still charge double for some things and get away with it.