Confused About SEC Cable Size

[pat32rf]

I get the feeling that the whole problem was caused by not realizing the difference between #2 and 2/0....?
The usage and type of insulation, as well as copper versus aluminium all make a difference in current capacity (rating)
I used to use a #10 that was rated to carry my 42 amps electrical heating load....special cable for a special use. Normally it would require #6 wire

 

[_RaT_]

I get the feeling that the whole problem was caused by not realizing the difference between #2 and 2/0....?
The usage and type of insulation, as well as copper versus aluminium all make a difference in current capacity (rating)
I used to use a #10 that was rated to carry my 42 amps electrical heating load....special cable for a special use. Normally it would require #6 wire

other things make differences as well, in free air versus Nm (romex), in conduit (de-rated when over X number of conductors), direct burial, believe it or not, even attic temperatures should be considered when sizing a wire.

 

[lostcause]

other things make differences as well, in free air versus Nm (romex), in conduit (de-rated when over X number of conductors), direct burial, believe it or not, even attic temperatures should be considered when sizing a wire.

i think there's more exceptions than rules. i've even read of cases where you can use a #10 wire with a 50a breaker for a welder, provided the duty cycle of the welder is low enough so that the wire will not carry current for a long enough period to overheat. i think there was a calculation along with that tidbit, but i dunno where i found it, lol. it's probably easier to just run #6 and not have to think about it.

 

[_RaT_]

i think there's more exceptions than rules. i've even read of cases where you can use a #10 wire with a 50a breaker for a welder, provided the duty cycle of the welder is low enough so that the wire will not carry current for a long enough period to overheat. i think there was a calculation along with that tidbit, but i dunno where i found it, lol. it's probably easier to just run #6 and not have to think about it.

You are correct. You can run a much larger breaker than the wire size can handle under typical amperage charts. The exceptions that are used all the time are with HVAC. Maximum fuse size and minimum circuit size come into play. The high start-up current versus the continuous current draw. For welders it comes down to duty cycle. If you are overly concerned, get some big wire in there. If you decide to upgrade your welder to a higher duty cycle or higher demand, you are prepared. Conduit makes all these decisions really easy.

 

[Mace Canute]

I was referring to paccorti's post. He said that he had 2 neutrals that he twisted together.

I have not run a separate ground for the sub panel, but I will eventually. The hot tub is currently out of commission anyway. Even my main breaker panel has the grounds and neutrals on the same bar though. Don't know if I've ever seen a panel that had a separate ground, other than when I specifically requested an isolated ground.

OOPS! Sorry, Brent. I thought you were referring to lostcause`s post. As far as neutral and grounds being on the same bar, they can be IF that is the main panel. Any subpanel fed from that main panel is suppose to have the neutral isolated from the ground.

 

[Mace Canute]

Thanks everyone. I think I'll get either the 1/0 or the #1 SEC in copper. That seems well above code (and is the max or close to the max this panel can take anyway). The #2/0 was $8/foot so at least it will be cheaper!



Peter

paccorti, you would be better off using the no. 2 copper. It is more than ample for the load and much easier to work with. You might also want to check with the Electrical Inspectors about using SEC (the concentric neutral stuff) between the meter socket and the panel. Here in Saskatchewan, they only allow SEC IF it actually is direct buried for part of the way, but they won`t allow it if going through conduit all the way...in that case they want to see individual runs of conductor. (I know..stupid as all get out, but they interrupt the rules).

 

[hilltopper34w]

For your application, I would use 2 hots (red & black) each should be #3AWG or larger. Since the distance is so Short, you won't save any cost by using a smaller neutral, so mark some #3AWG white and you're done. Get your inspector or an electrician to check your work before you make it hot.

Ok let me add a couple of things here. The meter and main panel are back to back (meter is outside). The SEC cable only needs to move the power from the meter to the panel (which is about 3 feet or less total distance lug to lug). The electric company will take care of transformer to meter.

The 2/0 wire also seems to big to fit into the main breakers (which power the panel) so I'm pretty sure that this wire is too big for the panel.

In my panel I have:

1. Main breakers (2 x 50amps came with panel these are fixed)
2. Neutral bus with 1 large lug
3. Ground bar

I don't have two neutrals, but the SEC wire has:

1 insulated black hot wire
1 insulated red hot wire
a bunch of uninsulated copper wires (braid?) surrounding the two hot wires
insulation around the whole thing (including braid)

So when I say I'm wrapping the neutrals together I'm referring to the collection of copper wires surrounding the two hots: those need to connect to the neutral lug (but twisted together they are simply too big). Note the hots are too big for the main breakers too.

For clarity the the ground bar in the panel will be grounded to a grounding rod using a separate copper cable (not using anything in the SEC cable for the grounding bar).

Also note: I'm not trying to cut any corners or do anything unusual, I want this to be a plain jane vanilla setup.

hilltopper34w

I guess ultimately I'm confused about the SEC cable size designation. If a 2/0 is too big then what wire size do I want for 100 amp service (remember I'm only going 3 feet lug to lug from the meter). I need two hots with the braid.

Peter

 

[paccorti]

I would like to just use individual copper #2's and connect from the meter to the panel (no SEC) but running the conduit is tricky. The meter has a knockout in the back which (if I punch thru) will come out about 3 inches below the bottom knockout of the panel. So if I did that I'd have to make a tight 90 turn upward (maybe that's do-able with individual wires vs SEC). Do they make conduit that makes turns that sharp? Maybe a condulet (say 1.5") would work. The big box stores have plenty of schedule 40 conduit...

If I move the meter up higher so that it's knockout corresponds to the panel's rear knockout (my preferred solution) then the meter is too high to read for the electric company. About 4" below the main panel is a major horizontal oak framing member of the barn. I don't want to cut huge holes in the oak for conduit.

My house just uses SEC from meter to panel (no conduit). I guess I'll go look at the conduit and see what they have to make this sharp turn. That would be a nice solution and I wouldn't have to mess with the SEC.

Peter

 

[_RaT_]

I would like to just use individual copper #2's and connect from the meter to the panel (no SEC) but running the conduit is tricky. The meter has a knockout in the back which (if I punch thru) will come out about 3 inches below the bottom knockout of the panel. So if I did that I'd have to make a tight 90 turn upward (maybe that's do-able with individual wires vs SEC). Do they make conduit that makes turns that sharp? Maybe a condulet (say 1.5") would work. The big box stores have plenty of schedule 40 conduit...

If I move the meter up higher so that it's knockout corresponds to the panel's rear knockout (my preferred solution) then the meter is too high to read for the electric company. About 4" below the main panel is a major horizontal oak framing member of the barn. I don't want to cut huge holes in the oak for conduit.

My house just uses SEC from meter to panel (no conduit). I guess I'll go look at the conduit and see what they have to make this sharp turn. That would be a nice solution and I wouldn't have to mess with the SEC.

Peter

I like conduit. Use a condulet in the configuration needed (LB, LLB etc.) I also warm conduit and flex it in many times. All conduits have minimum radius turns. If I had my book with me right now I could tell you the conduit size for 3 #2's and a ground. I think 1 1/4" would be plenty, I'm thinking 1" may handle it but I always check my book. The smaller conduit sure makes it easier to work with.

 

[mustangsallysdad]

I would like to just use individual copper #2's and connect from the meter to the panel (no SEC) but running the conduit is tricky. The meter has a knockout in the back which (if I punch thru) will come out about 3 inches below the bottom knockout of the panel. So if I did that I'd have to make a tight 90 turn upward (maybe that's do-able with individual wires vs SEC). Do they make conduit that makes turns that sharp? Maybe a condulet (say 1.5") would work. The big box stores have plenty of schedule 40 conduit...

If I move the meter up higher so that it's knockout corresponds to the panel's rear knockout (my preferred solution) then the meter is too high to read for the electric company. About 4" below the main panel is a major horizontal oak framing member of the barn. I don't want to cut huge holes in the oak for conduit.

My house just uses SEC from meter to panel (no conduit). I guess I'll go look at the conduit and see what they have to make this sharp turn. That would be a nice solution and I wouldn't have to mess with the SEC.

Peter

AEP will put in an RFID meter free of charge if you request it (if you have a mean dog, they'll insist on it. Ask me how I know!)...they would no longer need to physically read it...if you are close enough to the highway they may be able to read from there...I think they have about a 3/8 mile line of sight range.