Ask Me Help Desk - Wire Size

As I sit here and read the forum, and look up cable pricing on the net I came across something. Im reading about the #1 #2 wire etc. My question is, does this wire only come in single strands? Do they not make it so you can buy all the cable as one? So if I wanted to run #1 wire, do I have to buy each strand/color separate? Im just curious about this. I may want to run #1 wire to my sub out in my new shed. Its only about 30 ft, so won't be too bad. Do I have to buy all the wire the same gage? Can I use a smaller gage for say the grounding rod etc..? Any help will be appreciated!! ~~200 amp over to a 125 amp 30 feet away.~~

Wire size is one thing, what size ampacity feeder are you planning?

Both hots and the one neutral are the same size. Some may advice that the neutral can be smaller, however, that is allowed ONLY if load calculations are done to determine the size neutral, and cannot be smaller that 70 % of the wire size for the feeder.

At this stage for this small a job, and considering your beginner's abilities, doing load calcs are not recommended to save a bit of money to run a reduced neutral.

The equipment ground size is determine by the rating of the circuit breaker for the feeder. If it will be a 60 amp feeder, then it can be a #10 copper.

If, because you have a 125 amp rated panel, and will be using #1 with a 125 amp circuit breaker, then a #6 copper is needed for the equipment ground.

This is from Table 250.122 Equipment Grounding Conductor Sizes of the NEC.

Keep in mind, for every action there is a reaction.

So, need to decide exactly what you want to do, as changing wire sizes, for instance, affects other aspects of related materials.

The equipment ground wire is the fourth wire that will go along with the feeder from main panel to subpanel.

You mention the wire size to the ground rod. This is sized differently, according to NEC Table 250.66 Grounding Electrode Conductor

The smallest allowed is #8 and applies to the feeder wire sizes up to #1/0. So, your wire from subpanel equipment ground bar to the ground rod(s) cannot be smaller than #8 copper.

As far as the type of wire installed, yes, some, but not all, wire sizes come in cable assemblies. First decide on the wire size, then determine the type of cable needed. In this case I believe direct burial is desired.

I am not familiar with any 4 wire cable containing #1 copper wire that is rated direct burial. There is USE individual wire, 4 separate wires need to be pulled off a reel and laid in a trench.

Typical underground wiring is done using 4 wire aluminum cable called URD, 4 wires twisted into a cable assembly. Not available in copper. So if you want a 125 amp feeder, and using aluminum wire, then #1 Al is not allowed, must use min #1/0 Al wire.

Laying wires in trenches calls for certain depth, local conditions and codes may require a sand base below and above the wire, etc.

You may have no choice but to install a complete conduit system from box to box and pull individual wires, either THHN/THWN or XHHW insulation.

You really need to decide what you want to do, what your abilities are, what materials are available and allowed in your area, etc.

Somewhere you got the idea to use #1 copper for a125 amp feeder, I think is what you want. Again what size feeder and circuit breaker are you planning?

For a 125 amp feeder, then you can use #2 copper.

This is all listed in the NEC Table 310.15(B)(6) Residential Feeder Sizes.

So, you have asked a few piece meal questions, and I think I now have unloaded enough info to get you to understand how a system needs to be planned out, decied upon, and designed.

My intention is to not to confuse, but to help you, and others, understand the process, and the amount of detail involved.

Well you most deff threw some great information my way that's for sure. When I started this venture, I was actually going to run a 50 amp breaker out of my main box using 6-3 w/ gnd. NOW I am thinking, since I have a 125 sub panel, to just drop the #1 in the ground and that way I can get all the amps I can from the sub panel. Probably cost me more NOW, but in the long run I'll have the power I need for future use. I think that's the best way do it and get it over with. Only money and we can't take it with us lol.

Thanks for all the ideas and advice on this subject. I might be back if I run into a road block, but I think I have way more knowledge on what I want to buy and how to install it. Where I live, the codes are not a factor (Im way out in God's country) BUT I want to do it right and SAFE so I don't lose all the stuff I got over the years. And you guys have helped me do that.

Again thanks a LOT.

Mike

Quote:

Originally Posted by tkrussell

Both hots and the one neutral are the same size. Some may advice that the neutral can be smaller, however, that is allowed ONLY if load calculations are done to determine the size neutral, and cannot be smaller that 70 % of the wire size for the feeder.

If, because you have a 125 amp rated panel, and will be using #1 with a 125 amp circuit breaker, then a #6 copper is needed for the equipment ground.

You mention the wire size to the ground rod. This is sized differently, according to NEC Table 250.66 Grounding Electrode Conductor
The smallest allowed is #8 and applies to the feeder wire sizes up to #1/0. So, your wire from subpanel equipment ground bar to the ground rod(s) cannot be smaller than #8 copper.

OK! Little clarification on MY part please.. So, if I read this correct, with my 125amp service on my new shed, I run #1 wire for hots AND neutral and then #6 for my equipment ground from the main panel out to the sub, and #8 from the sub out to the ground rod. Did I get that all corect? So sorry to sound redundant BUT I want to do this the correct way. You know how us newbies can be!