Another wiring/subpanel/compressor question

[Rickster55]

I am going to add a subpanel in my attached garage. The run from main panel to the new sub will be about 40'. I will need circuits for: a 5hp 80 gallon IR compressor, thinking a separate circuit for vacuum on the sandblaster, a couple lighting circuits, and room to add on in the future.

Now for the questions! What size wire for run from panel to subpanel? Subpanel to compressor? Copper vs. Alum besides $ factor? Is there a fav subpanel I should be looking for? I might have a few more questions before I'm done.

TIA!

 

[930dreamer]

What amp sub panel are you installing? If it's a 125 amp panel, that's what your sizing the wire for.

 

[pattenp]

IMHO a 100A sub panel fed with #2 aluminum SER cable will be all you need. SER is installed the same as NM but if very little to none of the SER is run within insulation you can overcurrent protect it to 90A. If a certain amount of the SER is run within insulation then you should over current protect it to no more than 75A. As far as the compressor goes usually a 30A 240V circuit using #10 copper is all you need, but you should look at compressors to make sure of what circuit size you need.

Edit: You can use a Main lug or a Main breaker panel since this will be in an attached garage. I'd get at least a 20 to 24 circuit panel.

Oh.. if you need to max it at 75A because of insulation you can use a 80A breaker because that's the next standard size breaker. You can always use a smaller feeding breaker such as a 60A if you want to.

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[scarpozzi]

I'd be nervous about running aluminum in an indoor application since it's an attached garage. Aluminum is typically used for service connections like mobile home feed simply because it's rated for direct bury and is much cheaper than copper. There is some extra fire risk with aluminum.

I'd check with your local electric supply rather than going through Lowe's or Home Depot and get some #4 copper....which can handle 90A. I'm assuming you have 200A service to your main panel. Be aware of how many circuits you add to the sub and don't overdraw your main panel. You can always start with 50A-60A and split that into 3 20A circuits or a 30A for heat and your compressor and 2, 15A circuits, etc...for lights and incidentals.

 

[aandpdan]

I'd be nervous about running aluminum in an indoor application since it's an attached garage. Aluminum is typically used for service connections like mobile home feed simply because it's rated for direct bury and is much cheaper than copper. There is some extra fire risk with aluminum.

Aluminum is perfectly acceptable for use indoors and is commonly used for subpanel feeds. There is no extra risk when installed properly.

 

[pattenp]

You are giving false information. Besides feeds to sub-panels aluminum SER cable is also used quite often for circuits to Ranges, Electric heating strips in HVAC and such. If you are basing your comments on the problems from the 60's to early 70's with aluminum wiring then you are a little behind the times.

I'd be nervous about running aluminum in an indoor application since it's an attached garage. Aluminum is typically used for service connections like mobile home feed simply because it's rated for direct bury and is much cheaper than copper. There is some extra fire risk with aluminum.

 

[Rickster55]

Yes, the main panel is 200 amps. Also, this will be run through a finished basement. pattenp - what do you mean "run in insulation"?

 

[pattenp]

The rules for SER cable have to meet the install requirements of NM cable when run within an insulated wall or floor and that means it has to be sized from the 60C degree column of the NEC amp rating table. If the SER cable is run through spaces that do not cover or envelop the wire within insulation the the cable can be sized from the 75C degree column of the table which means a higher amp capacity. It's all about how quickly the wire can release any heat buildup.

Yes, the main panel is 200 amps. Also, this will be run through a finished basement. pattenp - what do you mean "run in insulation"?

 

[Ryf]

The rules for SER cable have to meet the install requirements of NM cable when run within an insulated wall or floor and that means it has to be sized from the 60C degree column of the NEC amp rating table. If the SER cable is run through spaces that do not cover or envelop the wire within insulation the the cable can be sized from the 75C degree column of the table which means a higher amp capacity. It's all about how quickly the wire can release any heat buildup.

ok not to thread jack but on the same vein, does running #2 aluminum in 1.5" plastic conduit count as "insulation" plan to run through my unfinished usable basement as well in conduit to attach to floor joist bottom along center I beam of basement. any problems with conduit and sizing to worry about. was planning on using conduit all the way to the building is this a nono other than wasting money. for "dig" protection

 

[Rickster55]

Ryf - good question. Being that my basement is finished, am I correct in assuming I do not need the #2 SER in conduit?

 

[Ryf]

err I think that depends, I am looking at mobile home feeder cable, no jacket, pretty sure that needs a conduit, if it has a jacket I don't think it does need a conduit, that said if its finished and going to be run on the surface of a wall or ceiling I would for the sake of appearance. and generally impact protection. not sure if jacketed wire can be in a conduit or not, something to think about anyway.

 

[pattenp]

NM is to be sized based on 60C degree and SER is to be sized and installed the same as NM. But the exception is that SER can be sized by 75C if not run in insulation. Individual wires such as the mobile home feeder needs to be in conduit when inside and only needs to meet the fill requirements for conduit. The conduit is not considered insulation. SER has an outer jacket and does not need to be in conduit other than for protection from possible damage.

 

[Ryf]

I know your only allowed 360 degrees for a run of a PVC conduit. Is there a way to reset the 360 degrees. Ie the run in side the house requires 270 and outside requires 270. Are the inside and outside separate runs or can I put in a box or does the right angle feed box count to as a run end. Hope this makes sense

 

[pattenp]

The turn limit starts over at pull points. So as long as you have a pull point between the two runs with 270 each you're okay.

I know your only allowed 360 degrees for a run of a PVC conduit. Is there a way to reset the 360 degrees. Ie the run in side the house requires 270 and outside requires 270. Are the inside and outside separate runs or can I put in a box or does the right angle feed box count to as a run end. Hope this makes sense

 

[Rickster55]

IMHO a 100A sub panel fed with #2 aluminum SER cable will be all you need. SER is installed the same as NM but if very little to none of the SER is run within insulation you can overcurrent protect it to 90A. If a certain amount of the SER is run within insulation then you should over current protect it to no more than 75A. As far as the compressor goes usually a 30A 240V circuit using #10 copper is all you need, but you should look at compressors to make sure of what circuit size you need.

Edit: You can use a Main lug or a Main breaker panel since this will be in an attached garage. I'd get at least a 20 to 24 circuit panel.

Oh.. if you need to max it at 75A because of insulation you can use a 80A breaker because that's the next standard size breaker. You can always use a smaller feeding breaker such as a 60A if you want to.

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So if I get the 100 amp sub panel, the 90A breaker goes in the main, correct?

 

[pattenp]

Yes, the 90A breaker goes in the main service panel if you are using #2 aluminum to feed the 100A sub-panel. The 100A main breaker in the sub-panel (if you got a main breaker panel) is used as a disconnect and the 90A breaker back in the main service panel is providing the over current protection for the #2 Al feeder.

So if I get the 100 amp sub panel, the 90A breaker goes in the main, correct?

 

[Rickster55]

Thank you! Wasn't thinking too clearly without my morning coffee.

 

[Rickster55]

In this picture of my subpanel, does that top bar need to be removed or is it okay as is? I thought I read somewhere here that the nuetral bar and the ground bar has to be separate (or was I having another senior moment again?).

 

[metal4130]

Here is how you wire it up. You need to buy the ground bar separately and yes the ground and neutral DO need to be separated in a sub panel.

 

[Rickster55]

Thought so. At least now I kow I am not TOTALLY crazy. Thanks!

 

[Ryf]

On a compressor circuit I want to run 12/3 but cap one side off in the box OR one side in the breaker box (or both) to give me 120v for my current compressor but leave me a way to upgrade when money allows. Any problems with this setup or ways to do it properly?

I figure since most 220v compressors are direct wire it should not matter much for now?

 

[Highbeam]

On a compressor circuit I want to run 12/3 but cap one side off in the box OR one side in the breaker box (or both) to give me 120v for my current compressor but leave me a way to upgrade when money allows. Any problems with this setup or ways to do it properly?

I figure since most 220v compressors are direct wire it should not matter much for now?

No problem with running 12/3 and capping off the unused conductor at the compressor. That's how my welder is wired, passed inspection.

 

[pattenp]

Ryf, If you do upgrade to a compressor that needs 240V you may find that #12 is not big enough wire. You should look at what compressor you would like and size the wire for it. That way all you need to do is up size the breaker and the outlet if an outlet is used.




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[Ryf]

Just looking at the entry level uprights 60-80 gallons with 4-5 horses claimed if I recall. As found at tractor supply or lowes

 

[pattenp]

If the motor is listed as 5 hp then based on NEC it's 28 FLA. So 28A X 1.25 = 35A. So #12 won't cut it.

Just looking at the entry level uprights 60-80 gallons with 4-5 horses claimed if I recall. As found at tractor supply or lowes

 

[Ryf]

The 60 at lowes is 13amp and the 80 is 18. I did say claimed..

 

[Ryf]

After thinking about this last night I am gonna agree with you guys in this one. 6/3 ( because I have 70 feet of it) with a 30 amp breaker it is!

 

[pattenp]

Verify the the 30A breaker will accept #6. You may need to use a 40A.

After thinking about this last night I am gonna agree with you guys in this one. 6/3 ( because I have 70 feet of it) with a 30 amp breaker it is!