Sub Panel service- is this enough?

[Cruisinga]

This is a two part question. Thanks for bearing with me!
1)
105 ft of 1-1/4" conduit is installed from main service panel to 100amp sub panel.

Planned on an 80 amp breaker and #4 copper THHN to feed the sub panel.

This is a small 240 sqft shop, and it is very rare that more than one power tool will be used at a time.
I recently decided to go with electric resistance over natural gas for heat, for this year anyway. I am in the south and the shop is well sealed and insulated so the load is small and infrequent. The payback wasn't there for nat gas.

I need a sanity check. Due to "more is better" I am second guessing my 80 amp service.

Concurrent (not continuous) loads-
Lighting 6 amps 120v
Heater 11-20 amps 240v
Compressor 20 amps 120v

Intermittant loads (select any one to add to above list)
Welder 20 amps
Plasma 22 amps
saw/grinder etc ~12

If I add all the concurrent loads I am at 46 amps when the compressor is starting. This leaves 34 amps for any single tool to be operating when compressor starts.

I think this means I am good with 80 amps. I just don't really want the lights dimming when the compressor cuts on while I am plasma cutting etc.

Part 2)
An electrician friend of mine suggested aluminum to keep costs down. I don't much care for aluminum in a residential setting except for SER, but cutting wire cost by 60% is pretty attractive. What would you do? I'm also a little concerned about the 3 #2 Al conductors and a ground being difficult to pull. I have pull boxes every 360 degrees per code but still concerned.

 

[Cruisinga]

58 views and no comments, I'm surprised !

 

[theoldwizard1]

80A is likely overkill. 60A would probably be adequate. Your biggest load will be while you are using your plasma cutter (its load plus the compressor).

You did not mention A/C ?!! Worst case still, you may have to turn off the A/C for the few minutes you are using the plasma cutter.

Listen to your electrician friend. Use aluminum mobile home feeder (MHF) cable. Very cost effective and commonly used for this type of application. It has one down side. It can be direct burried, but ANY area where it is exposed ABOVE ground, it must be in a conduit. 2-2-2-4 MHF should be adequate. Verify with your electrician buddy.

Personally, I would have direct buried.

 

[Bigbandguy]

While not an expert I cannot imagine 80 amps not being enough for that load. Its it likely that you would get it all on at once? Lights are such low watts that you most likely would not have much of a dimming problem. If all else fails put a master switch on the compressor and turn it off while welding/cutting.

 

[RunninOnEmpty]

80A ought to be fine, but I would NOT drop it to 60 as it is definitely insufficient 100% guaranteed. Turn the AC off when using a tool? Really? Why recommend that?

Actually, I would err on the side of caution and go 100A.

 

[Strouty]

My POCO says when you hit 60% of the capacity, it is time to get a bigger service. So 80 is as small as I would go, as others have said, go with a 100 and it should be fine for a while.

Things change, if you get a bigger compressor, welder, plasma cutter, or what ever, it is nice to be ready.

 

[justsam]

If you are not a fan of aluminum, than don't use it. The copper at 4 ga will be easier to pull, and you already have the conduit run.

Really need to compare an incremental cost increase to go all copper, at the distance you have of 105 feet. Include any transitions that may be required for either one. I suspect the difference is less than $100, certainly not chump change, but if you are more comfortable with copper it may be worth it to you.

 

[theoldwizard1]

Turn the AC off when using a tool? Really? Why recommend that?

'Cause I am a cheap S.O.B !!!!

Come on. How long are you going to be running a plasma cutter for ? 10 minutes ? 20 ?

If you are not a fan of aluminum, than don't use it. The copper at 4 ga will be easier to pull, and you already have the conduit run.

Really need to compare an incremental cost increase to go all copper, at the distance you have of 105 feet. Include any transitions that may be required for either one. I suspect the difference is less than $100, certainly not chump change, but if you are more comfortable with copper it may be worth it to you.

500' of #4 THHN from Home Depot $1,782
500' of 2-2-2-4 MHF from Home Depot $736; Cut to 125' maybe $200 ?

$1,500 is a lot more than your $100 estimate !

 

[RunninOnEmpty]

500 ft., 3 Gauge, Building Wire

500 feet of #3 for under half that, and this is still probably not the best deal around, even if OP did need that much of it.

Home Depot is often not the best deal for stuff.

Edit to clarify: This is the minimum gauge for 100A if you did go that way. Don't go #4!

 

[CNGsaves]

Too little information. What country are you in ??

Now would be good time to Update GJ Profile with City/State/Country.

Why did you pre-iinstall tiny 1 1/4" conduit for 105 ft . . . . BEFORE . . you had decided on wire you were using ?? Is this buried ?? Or what ??

Attached shop ?? Or Detached ??

Any power to building now ??

 

[barnjunkie]

I think this post is from never - never land.

 

[justsam]

'Cause I am a cheap S.O.B !!!!

Come on. How long are you going to be running a plasma cutter for ? 10 minutes ? 20 ?


500' of #4 THHN from Home Depot $1,782
500' of 2-2-2-4 MHF from Home Depot $736; Cut to 125' maybe $200 ?

$1,500 is a lot more than your $100 estimate !

Don't need 500 feet of either one.

105 feet of MHF @ $2.00/foot is $210.
420 feet of 4ga THHN/THWN @ $0.75/foot is $315, and I did not reduce size of EGC.

Not sure where you got home depot price, my local is more like $350 for a 500 foot roll.

 

[Cruisinga]

Whoa whoa guys getting a little out of hand lol

So my original plan was #4 copper, 80 amps, and 1-1/4" conduit is larger than required for that, so I did not install the conduit without some forethought. What HAS changed is my idea to install an electric heater due to the cost of another trench and piping (can't share trench here) for natural gas when I am only occasionally in the shop.

Like I said in the OP the detached shop is small, rare for anyone to be helping me work.

More information- this is a starter house for my wife and I, it is very unlikely we will be in it for more than a few years. While I don't have a crystal ball, I have a hard time imagining a larger compressor or welder than consumes more power than what is listed. The shop currently does not have any power.

I got a nice surprise today and the electrical supply has 330ft #4 Cu for $196, which is ~$130 less than Home Depot. #2 Al THHN would be $86. Savings of $110, but harder to pull and I am not as comfortable with AL.

Much of the run is exposed so SER would have had to been run in conduit anyway, and the conduit would have been much larger and more unsightly.

Long story short, 80 amps has been my plan all along, I just wanted to run it by the varied experience here and make sure I am not forgetting anything.

 

[pattenp]

I'm also a little concerned about the 3 #2 Al conductors and a ground being difficult to pull. I have pull boxes every 360 degrees per code but still concerned.

I got a nice surprise today and the electrical supply has 330ft #4 Cu for $196, which is ~$130 less than Home Depot. #2 Al THHN would be $86. Savings of $110, but harder to pull and I am not as comfortable with AL.

Much of the run is exposed so SER would have had to been run in conduit anyway, and the conduit would have been much larger and more unsightly.

Long story short, 80 amps has been my plan all along, I just wanted to run it by the varied experience here and make sure I am not forgetting anything.

To be clear, are you thinking 3 conductors to the shop? If so you need to add one more conductor because the feeder needs to be 4 wire.

 

[Cruisinga]

Yes, there will be a #8 ground in addition to the 2 hot and 1 neutral.

Whether I choose
80 amps #4Cu or #2 Al
or 100 amps #3 Cu, the ground is still #8.

Soo this brings me back to the question- Which of the three options would you choose? I don't think I will ever need more than 80 amps, but more is always better right?

 

[pattenp]

I would have used 2-2-2-4 MHF but the 1.25" conduit kills that option. If the extra money doesn't matter I'd do the 100A w/#3Cu. The only real cost difference is the wire going fron #4 to #3 which should not be a lot. It's kinda 6 of one or a half dozen of another. I personally don't have a problem with aluminum so you could use #2 AL THHN/THWN-2 and save some money and you can get 90A. Do what ever makes you feel warm and fuzzy.

 

[sberry]

Right, the pipe is too small for number 2 alum that distance but 80A is plenty. I have wired a couple dozen of these garages over they years all fed 2 alum and a 60A breaker, none, not 1 including a couple with 5 hp comp and small AC has ever called with a trip.

 

[Cruisinga]

Only extra $40 for #3 copper so went that route.

I think it's a little ridiculous to have 100 amp service to such as small garage/shop but at least I won't ever say "I wish..."

 

[sberry]

There is nothing wrong with 100A, its a standard. Its good for motor starts, you can weld and not panic if the comp comes on and you wont need to manage loads and mostly this is due to the wire size more than the breaker. Most days you apply a 20a load to a 100A wire other than a little surge for an air comp.

 

[sberry]

Concurrent (not continuous) loads-
Lighting 6 amps 120v
Heater 11-20 amps 240v
Compressor 20 amps 120v

Intermittant loads (select any one to add to above list)
Welder 20 amps
Plasma 22 amps
saw/grinder etc ~12

You couldn't make this 50A if you tried. I seen it done with meter, that same list plus a 5 hp comp on 60. The guys on Self Help and More have a great setup for detached garage with pitchers,, a garage very rarely adds much load demand factor. The loads are so intermitant and chances if you re running this air comp ( 15A draw) you are not in the hot tub, it displaces rather than adds to the load. Its about the same as a microwave or hair dryer.

 

[sberry]

With 100 you can run a full sized welder and a full sized air comp and a few lights concurrent without management along with the heater if you had to. In reality you will never will, your peak will be around 27,,, ha
I remember looking at a mobile home park one time and count the air conds,,, wow but then I realize because they were all on 30A breakers didn't need to account for it all, the runs were 13A. If you have gas available can drop the demand factor a couple more points. I simply added my home to my parents, I have all gas majors, I pull 5A with a fridge and a couple lights and 15 down a pipe with a micro or window ac on occasion. Doesn't even add to the real load.

 

[Redwolf947]

So #4 Copper wire at 100+ feet can be rated at 80a? Is this true for 4/3 romex not in conduit as well?

 

[Cruisinga]

So #4 Copper wire at 100+ feet can be rated at 80a? Is this true for 4/3 romex not in conduit as well?

I don't think so. Romex doesn't dissipate heat like individual conductors in the proper sized conduit.


Next question: pulled #3 copper and noticed the neutral bus in the main panel does not have holes large enough for #3. I'm sure there is a solution but I don't know what it is!

 

[Redwolf947]

I see thank you makes sense.. You should be able to buy a lug kit for your box. Do a search on Home depot or Lowes site for "lug" you'll see what I mean. There are a few different types..