service wire for sub panel

[cheechi]

First of all. I googled. GJ is the first result. Here is a thread with a lot of arguing and not a clear (to me) answer.

So the details I can provide.
125A sub 'room addition' panel.
125 amps breaker in the main panel.

Not stating the continuous or peak load is going to be there. But it could be and I want to approach this assuming the peak load could be 115-120A, possibly 124.999A so I want to do right by whatever measure, and not 'shortcut' the 125A breaker.

I don't know what the temperature ratings mean. However, this is going to be in an unfinished part of my basement that ranges from 40-80F with the seasons. Rarely is it at either extreme.

The total run is going to be 30-35 ft. The panels are about 20ft apart on the same wall. out, up, across, down, and in. simple.

I'm not moving the dryer or hot water to this sub. But I am moving everything else in the basement down there. Right now, the whole house is wired 115A outlets on 20A breakers and I don't have issues with 200A service as it is.

Realistically, I will be using at most 3-4 15A loads at most, at any given time, and 2 lighting circuits (for simplicity, the total load from the lights won't total anywhere near 30A; they will be the Feit Costco LED lights) so although I will have many circuits and outlets it won't all be used at once, not by a long shot.

I'm not an idiot but I'm not an expert either. I have some pages from a 2005 code book with the charts but don't really understand how to read them. Depending on who I trust from the internet I either need 1, 1/0, 2/0, or 3/0 for this.

This sub won't be adding any load so much as organizing and separating the basement from being intertwined from some of the upstairs rooms, rather than just adding more outlets where I need them.

Please help. Thank you.

 

[wyliesdiesels]

How will u have 120a of load when u say at most u will have 3-4 15a outlets?

Any 240v equipment going on this new subpanel?

Sounds like u need to calculate your load better before u go way overkill.

If theres nothing wrong with the current panel then why are u adding a sub?

For 125a, u will need #1 cu or 2/0 Al.

Wire is sized at the 75* c or 60* c column depending on termination temp ratings.

NM-b no matter the temp ratings is limited to 60* c column.

And 90* c is for derating purposes only.

So list all your loads and we can go from there...

 

[cheechi]

No 240v stuff is going in now. Possibly a compressor might run off this panel at some point. With the main being down here also, if it can't go in the sub it's not a tragedy.

This is a full basement. Part of it is finished, part unfinished. Out of the unfinished part, part is going to be a wood shop (or just general shop type area), part is a closet for the modem/router/server/etc, part is exercise area with planned TV, and part for electronics work. The unfinished will have 4 light switches, 2 each on 2 circuits, for simplicity of wiring rather than because of load. Of the finished part, home theater type stuff, my bass amp, very modest music studio.

The reason it's hard to estimate the load is right now, it's just a place that I'm storing stuff and improving. Once all the work is done, wife may decide to use it more. So with that in mind here's my theoretical 'max' load

dust collector, woodworking tools, we'll say maybe 40A. lights, server, switch internet all probably add up to 15A max. Maybe she will also be doing something, we'll say maybe 15-20A worth. Could be in different rooms down there though.

My point is that I wanted not to overkill, but I already have the 125A breaker (not yet installed) and didn't want to cause problems popping it all the time (or ever if I can help it). I understand without a load it's a hard question to answer. I don't want to underestimate it so I was hoping to assume the highest and be safe being below that.

So I will go with the #1 Cu or 2/0 Al. Is there a way I can tell if the sub should have one or the other type? If it were for copper only, for example, it would say so right?

My statement about the main panel being adequate was basically not enough information I guess. I don't plan to use more load than what I currently am using really, just moving things. There is nothing incorrect or illegal about the wiring or junctions. But there are several junctions that we plan to remove as we remove redundant or unwanted outlets. Basically, the panel is right there and 10ft away one of the lights is tapped from the room above. I want to undo dumb things like that.

 

[wyliesdiesels]

Gonna be way overkill....

Anyway, go with a main lug panel. U will need to make sure the neutral bar is isolated. U may need to buy a ground bar kit.

U will need 3 pieces of #1 CU or 2/0 AL and 1 piece of #6 CU or #4 al for the EGC.

Yes the panel should tell u what type of wire is acceptable.

What is the brand of the main service panel?

 

[cheechi]

Square D main panel and GE sub. it is a main lug sub.

Still looking for the book that came with the panel. Nowhere on the panel itself does it say to only use one type of wire or the other. Basically, things got moved all around, framing happened, things started moving back where they belong, and I'm running out of places it can hide. I won't make the purchase until I know for sure.

Thanks again. I know Lowe's near here very recently used to sell 2-2-2/0 but don't anymore. Do I assume that I wouldn't find a wire like I need all as one and I will need to buy it in pieces? Do I have to do anything to it to insulate the pieces as one wire?

edit: this is the sub. it says Feed: Either I assume that is referring to either Cu or Al wire.

 

[Norcal]

Square D main panel and GE sub. it is a main lug sub.
.............................................................................................................................................................................................................................................................................................................................................................................................

That is a mistake, unless it's a obsolete brand like FPE, Zinsco/Sylvania, ITE Pushmatic, or others, best practice is to keep them the same.

 

[cheechi]

Yeah I didn't realize until it was too late. The Square D panel has a GE breaker in it from before I moved in, I mixed up the brands of which was which when I bought the sub.

 

[Norcal]

Yeah I didn't realize until it was too late. The Square D panel has a GE breaker in it from before I moved in, I mixed up the brands of which was which when I bought the sub.

So you have a Homeline panel, you cannot use the HOM breakers in the GE panel or any panel other then a SQ D Homeline, and I doubt the GE is UL classified to be used in HOM panels.

 

[cheechi]

the Square D panel will have only Square D breakers. It doesn't now, but that is one of the circuits this is going to move and the proper breaker will be installed at that time.

The breaker for the sub that will be in the main box is Square D.

The GE panel will have only GE breakers. All of this will be made right it just was a mistake on my part at the time of purchase and wasn't revisited soon enough.

 

[wyliesdiesels]

Square D main panel and GE sub. it is a main lug sub.

Still looking for the book that came with the panel. Nowhere on the panel itself does it say to only use one type of wire or the other. Basically, things got moved all around, framing happened, things started moving back where they belong, and I'm running out of places it can hide. I won't make the purchase until I know for sure.

Thanks again. I know Lowe's near here very recently used to sell 2-2-2/0 but don't anymore. Do I assume that I wouldn't find a wire like I need all as one and I will need to buy it in pieces? Do I have to do anything to it to insulate the pieces as one wire?

edit: this is the sub. it says Feed: Either I assume that is referring to either Cu or Al wire.

If u dont want to use conduit and individual conductors then u can use SER which is a jacketed cable...

 

[cheechi]

Thanks. So if all I can source is individual wires, it's ok to run them in conduit, including the bare ground wire?

 

[wyliesdiesels]

Thanks. So if all I can source is individual wires, it's ok to run them in conduit, including the bare ground wire?

Ground wire should be insulated green or black if #4 or larger with taped green ends at points of termination.

 

[cheechi]

thanks. I must have assumed the ground could be bare. Thought I read it but after rereading I was mistaken.

 

[Norcal]

thanks. I must have assumed the ground could be bare. Thought I read it but after rereading I was mistaken.

It can be but #8 and larger conductors in conduit must be stranded, & most bare conductor is solid.

 

[theoldwizard1]

By trying so save a buck and use that 125A breaker, you could cost yourself a lot on the wire. If you put a 60A breaker in the main panel you could use #6 (or maybe #8) AWG wire and a 6 slot (12 circuit) sub.

 

[Norcal]

By trying so save a buck and use that 125A breaker, you could cost yourself a lot on the wire. If you put a 60A breaker in the main panel you could use #6 (or maybe #8) AWG wire and a 6 slot (12 circuit) sub.

With AFCI requirements, it's pure foolishness to use small loadcenters, they will fill up quick.

 

[cheechi]

First I want to say thanks to you both for getting me this far. There's a few changes since I last asked and want to make sure I'm still on the right track.

The sub is mostly wired. I have 5 circuits to move from the main to the sub, all of which are staying in place for now as they still need to be live. originally I said the hot water & dryer would not move to the sub. That plan has changed. As I have gone through and pulled down probably 200ft of old 12-2 and replaced rerun and now coming to the end, it is a straight line from the water heater and dryer, both in the same corner, to the panel. The holes are already drilled just haven't moved the wires yet. Those two, washer, lights & outlets 5 circuits total left to do, all going to move on or after the sub goes hot.
2 lights circuits, 2 outdoor GFI & 6 indoor outlet circuits are what's wired in so far.

Could I still do 2-2-2-4 SER given this change? What would be the equivalent Al and would it be acceptable in this case? Thanks again.

 

[benjamintmiller]

2-2-2-4 SER is aluminum wire, and will probably be the most economical cable to run.

If you are on the 2008 NEC, you can only use a 75 amp breaker on it because 338.10 and 334.80 tell you to use the 60 degree column.

If you are on the 2011 or newer NEC, you can use a 90 amp breaker as long as the cable is not buried in thermal insulation.

Be aware the this cable is really stiff and a giant PITA to route around tight bends. Also, as it is aluminum, you need to apply antioxidant grease to the wire and wire brush it in before making a connection. Use a torque wrench in the panels.

 

[Norcal]

2-2-2-4 SER is aluminum wire, and will probably be the most economical cable to run.

If you are on the 2008 NEC, you can only use a 75 amp breaker on it because 338.10 and 334.80 tell you to use the 60 degree column.

If you are on the 2011 or newer NEC, you can use a 90 amp breaker as long as the cable is not buried in thermal insulation.

Be aware the this cable is really stiff and a giant PITA to route around tight bends. Also, as it is aluminum, you need to apply antioxidant grease to the wire and wire brush it in before making a connection. Use a torque wrench in the panels.

A 75A breaker is not availible but 70 is.

 

[sberry]

The loads calculated in the beginning will be closer to 20 than 40 and closer to 5 than 15 and the wife wont be on the other wall with a 20A chop saw. I run 2 houses, 8 people from 100A and 2 alum, one has all electric appliances.

 

[cheechi]

ok sorry I was backwards. You're right 2-2-2-4 SER is Al. I got ahead of myself and tripped.

With regard to the changes from my original load, I still do not intend to exceed the 125A of the breaker. But in case different types of loads in the dryer outlet or water heater have changed the info I was given earlier, I thought it was prudent to ask.

I should have asked;
is 2-2-2-4 SER the right wire for 125A to run 30-35 ft between the panels? If not do I need to go to single conductors and if so what sizes Cu or Al should I get of so?

 

[sberry]

You need larger wire, single conductors, number 6 ground.

 

[cheechi]

ok so for the hots & neutral 2 AWG stranded copper, 3 conductors, and the ground 6 awg stranded copper. In an unfinished basement, is a conduit needed for these?

 

[sberry]

I think you need 1 for the ungrounded conductors, 2 for the grounded conductor and a 6 for the grounding conductor.

 

[cheechi]

are you saying 1 and 2 as in quantity? or as in wire size? From what you said before I thought you told me;
2 hots 2 awg
1 neutral 2 awg
1 ground 6 awg

3 conductors with ground

 

[pattenp]

For 125A you need to use 1/0-1/0-1/0-2 Al SER or 1-1-1-3 Cu SER. If the SER is run within thermal insulation those sizes need to increase.

 

[revamped]

Dude!!! Why are you insisting on using 125A breaker and buying some of the most expensive wire you can if you are not planning to use 125 amps... ever! I just wired a 2000SQft shop with a weld shop and 5 220 drops and used 2-2-2-4MHF with a 90amp breaker and 2 subs off of the main loadcenter which all feed off of the house 200A panel and a 90amp breaker.
I don't have a lot of experience, but it seems like you are ignoring some of the previous recommendations...

 

[bczygan]

Forget all the numbers above.

Get wire bigger in diameter than your bicep, and you should be safe....

 

[CNGsaves]

Forget all the numbers above.

Get wire bigger in diameter than your bicep, and you should be safe....

^ ^ ^ This. Drop in 4 (yep Quantity FOUR) conduits of 3" each.

Fill those UP with ONE CONDUCTOR each for the 3 (ie 2 hots & neutral), and for the 4th conduit with ground . . . . nearly all the conduit would be fine !! . .

 

[sberry]

The "hots" are ungrounded conductors, the neutral is actually a grounded conductor.

 

[Mwalke64]

If the panel is rated for 125A I would run cable rated for 125A. Nothing worse than someone loading up a sub panel with breakers and the feeder being undersized. Yes, it needs to 4 conductors with the bonding screw removed from the sub panel. If there is not a separate ground bar you need to add one.

http://www.generalcable.com/assets/documents/North%20America%20Documents/Information-Center/Catalogs/03$Copper_Building_Wire_Catalog.pdf

 

[Norcal]

A 125A breaker "may fit" but is it allowed by the manufacturer to be used in the panel? Some loadcenters have a 110A per bus stab limitation, which would not allow a 125A breaker to be used. The NEC does require that manufacturers instructions be followed.

 

[sberry]

Also this will really reguire 2 inch pipe moving all the equipment up a class. Really the people that build all this and do the codes have a good idea in the sense they know the real load demands and that 100A service will be well sufficient hence all the equipment made for,,,, 100A 2 inch is another pain for the diy, the knocks in the box are often smaller, not sized to leave or enter them in all directions, just did one in 1 1/2 that added an extra step. Replaced with this as the original had 2 few spaces for other equipment. It didn't need more power.