Splicing different sized wire for voltage drop

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Kg808

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Quick question that was brought up in a meeting yesterday.
We have an 800 foot run from a sub panel to feed a LV lighting transformer for small led lights.
We have 3 pull points along the way. Someone suggested why not run #10 to the first one #8 from 2nd to third and #6 from 3rd to end of run.

The plan is to pull #6 all the way. I’ve always pulled the same size wire from end to end with a small piece of smaller wire at the very end. However, I know just because “I’ve always done it this way!” Doesn’t make it correct...

So would this proposed way be acceptable? Why or why not.

Also. I am just generalizing the lengths and sizes. Just for a theoretical question we’re assuming the wire size is rated for the load to be delivered at each pull point.

Thanks!
 
The amount of voltage drop is proportional to the load, since the largest amount of load is at the beginning of the run that is where I would use the largest conductors.
 
You won't get same voltage drop at the end of the run both methods. You may still get something deemed acceptable with the multiple sizes in the run, really depends on the details. If you dropped some load at each junction point that would be different than having same load all the way through the circuit.

I too would suggest having the larger conductor at the beginning of the run, though it really should not matter much if all in series with no load being dropped at junction points, still same resistance from one end to the other.
 
kwired said:
I too would suggest having the larger conductor at the beginning of the run, though it really should not matter much if all in series with no load being dropped at junction points, still same resistance from one end to the other.
Click to expand...

Yes I assumed that based on the OP some load was being dropped along the way, if not I would figure out the amount of VD for the entire run and pull one size conductor to accommodate the load at the end. Pulling various conductor sizes and making splices is a waste of time and money.
 
cpinetree said:
This was posted in the past.
I find it very useful.
Segmented voltage drop calculator. http://forums.mikeholt.com/showthread.php?t=141401

If you don't get a response from the OP of that thread:
Send a PM if you would like me to email it to you, but it likely won't be until next year.
Click to expand...
OP doesn't seem to have a change in load as he changes conductor sizes. - makes sense to change conductor sizes as you go if that were the case. But to run three different conductor sizes leaves you with a fixed resistance from one end to the other and the drop at the end should be same whether you start large and end small or vice versa.
 
just so I understand the proposed... in the case of a fence line with lamps and the boxes in the fence where one taps for the light above... the suggestion is run largest wire to first position, drop down in size to next one, then drop to lowest size in last one... but if the lights were all grouped at one end of the run, like a soccer field, for instance, away from the locker rooms... then you would run the same wire the whole way...
 
Adamjamma said:
just so I understand the proposed... in the case of a fence line with lamps and the boxes in the fence where one taps for the light above... the suggestion is run largest wire to first position, drop down in size to next one, then drop to lowest size in last one... but if the lights were all grouped at one end of the run, like a soccer field, for instance, away from the locker rooms... then you would run the same wire the whole way...
Click to expand...
OP is suggesting using 10, 8 and then 6 AWG.

Now if there is no loads connecting along the way he may be about as effective using 8 for the entire run, would have to do some calculating to know for certain and would depend on how long each segment is.
 
kwired said:
OP is suggesting using 10, 8 and then 6 AWG.

Now if there is no loads connecting along the way he may be about as effective using 8 for the entire run, would have to do some calculating to know for certain and would depend on how long each segment is.
Click to expand...

Exactly, the KISS approach. :thumbsup:
 
K8MHZ said:
Wouldn't it make more sense to run 6, 8 and then 10?
Click to expand...
If dropping off some load at each transition makes perfect sense to start out larger and end up smaller. If no loads are connected along the way, and presuming same lengths no matter the order, don't you have same overall resistance from beginning to end?

If resistance and current are the same won't voltage drop be the same? Or did I miss something in Ohm's law?
 
cpinetree said:
This was posted in the past.
I find it very useful.
Segmented voltage drop calculator. http://forums.mikeholt.com/showthread.php?t=141401

If you don't get a response from the OP of that thread:
Send a PM if you would like me to email it to you, but it likely won't be until next year.
Click to expand...

Mike use to teach this in class using a parking lot lighting scheme. Start from the furthest point and the load will increase as you add lighting headed to the panel. I still use this system in my calculations. It can start as a #12 and end up as a number 6 to X breaker.

I have been doing this by hand. That excel sheet is nice!
 
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