new detached load calc - multiple users....

[jpcjguy]

Hi all,

The topic of 100/200/etc. power to detached garages has been well documented but I wanted to get y'alls take on multiple users in the garage.
My current situation is 400A to the house (twin 200 panels) - 100% electric (heat, AC, dryer, stove).
About to start on a 48x30x12 stick built garage that about 250 feet from the panel.
Current stuff:
Air Compressor - Husky 60 gallon (15 amps on the motor sticker)
Miller 252 welder
Tig welder
full size refrigerator
Outlets
Lights
Stereo/TV

Planned:
Plasma cutter
10k lift
HVAC - mini-split(s) more than likely

Based on that I would think that 125A (largest breaker to fit my existing panel) would be plenty - if I was working solo.
However.....
I have identical 9 year old boys (and a 5 year old daughter) who are showing interest in tools/building stuff.
How do I plan for them being out there with me working on stuff when they get older and learn to weld, grinder, use sandblast cabinet, etc.
There could be a time that 2-3 of use could be using higher amp draw tools at the same time with the AC or heat going. I have no problems with "don't use the lift while your brother is blasting and I am welding" statements, but don't want to be in a situation where everybody has to wait for each other to be done with their tool for "their turn". I am exaggerating this a bit - not like we will be a production shop or anything. But I am looking for advice on how to best plan for this. Who else has been in this situation? Maybe not family but multiple friends over and working on projects? How did you manage tool usage? - or is everyone totally overbuilt in wiring?
Or maybe with 125A, I will be fine even with multiple users?

Thanks!

 

[jpcjguy]

anyone?

 

[Stuff]

What you need to do is to add up all of the loads that could possibly be used at the same time. Do your homework. Get the ratings for each 240v device and see what you come up with.

Seat of the pants: You'll be fine as long as you don't use electric heat strips for the HVAC.

 

[mike93lx]

125a is a lot as it is, but that is a big shop.

Any budget? With a 250' run, you're going to spend a lot on wire to even just get started.

How many people are really going to be using high amp draw gear at the same time? Someone using a grinder or table saw while another is welding, sure, but that's peanuts in the grand scheme of things.

 

[dcg9381]

You're fine at 125 amps. Honestly, I bet you'd get away with 60A (realistically) - as long as the air compressor, 2 mini-splits, lift, fridge, and welder were not all running at once...


My recommendation would be to install 2" conduit to a 200A panel, run your feed wire. If you ever "had" to go bigger, the shop is setup for it.

Wire calculations for 250' say 1/0 AWG Copper or 3/0 AWG Aluminum for 125 Amps. However, if you're willing to do 90 Amps, you drop down to 1 AWG Copper or 2/0 AWG Aluminum. So play with that a bit...


Note, currently, on 90A I run:
Hot tub
2 x 24k Mini-spits
50A RV connection (active in-use)
Full time refrigerator
1/2 hp water pump
Stereo, sub, 2 TVs, internet, IP cameras, blah blah.
I don't have a lift, but I do regularly run a MIG welder, grinders, table saw, typical metal working tools.

I don't have an amp meter on the main, but my all-time high KWH usage is 53KWH in 24 hours. That's just 2208 watts per hour, averaging less than 10 amps. You need "PEAK" usage, but I think you're fine with 125 Amps.

 

[jpcjguy]

Ok thanks for the feedback! I feel like 125A would be fine - I also forgot I will have a 1/2 bath and small shop sink for cleaning up. So I will probably get a small point of use electric water heater - that could be up to 30A - but again, that is a limited point in time.
I guess a good plan is to size my conduit for more power and then go with 125A. Worst case is years down the road I have to **** it up and run new wire. At least no digging!

 

[dcg9381]

So I will probably get a small point of use electric water heater - that could be up to 30A !

Funny. I'm going through this right now. Might double check that 30A estimate. If you're going to do a point-of-use water heater capable of more than just a hand-wash sink, it eats a lot of power.

30A @ 240V will probably heat 1 GPM and a 40 degree rise. A typical shower is around 1.5 GPM. So, if your inlet water is warm, it's probably fine... If not, there isn't going to be much you can do except take a less-water shower.

Here's a good spec sheet so you can eyeball amps vs heating capacity for electric instant water heaters:
RHEEM

The low draw alternatives are:

• Traditional Water heater, apartment sized
• RV Water heater (5-10Gal, limited volume)
• Propane (LP Gas) anything - tanked or tankless

Like you, I'll have a "future" apartment and I'm working on a full kitchen (with laundry). For me, I want 3 GPM capable water heater and I'm going propane tankless. Heating 3GPM with electric would definitely bust my 90A feed in combination with other things, never mind the expense of running the copper wire.

 

[jpcjguy]

Funny. I'm going through this right now. Might double check that 30A estimate. If you're going to do a point-of-use water heater capable of more than just a hand-wash sink, it eats a lot of power.

30A @ 240V will probably heat 1 GPM and a 40 degree rise. A typical shower is around 1.5 GPM.

Here's a good spec sheet so you can eyeball amps vs heating capacity for electric instant water heaters:
RHEEM

The low draw alternatives are:

• Traditional Water heater, apartment sized
• RV Water heater (5-10Gal, limited volume)
• Propane (LP Gas) anything - tanked or tankless

Like you, I'll have a "future" apartment and I'm working on a full kitchen (with laundry). For me, I want 3 GPM capable water heater and I'm going propane tankless. Heating 3GPM with electric would definitely bust my 90A feed in combination with other things, never mind the expense of running the copper wire.

thanks for the good info - but no shower for me - just a simple half bath - with an additional sink on "the other side of the wall" for the shop. no future apartment in my plan. I am not opposed to having a small propane tank behind my shop to not consume amps....

 

[mike93lx]

This would be a good application for MHF. Direct burial to save on conduit costs over a long run. Either 2/0 or 4/0 depending on where you settle on a load calc. I'd probably go for 4/0 and not worry about future capacity.

https://www.wireandcableyourway.com/2-0-2-0-1-4-aluminum-mobile-home-feeder-cable.html

 

[mm08822]

at 250', I would do the 4/0 and consider I'm good for the worst case. use sand bed/covering for cable.

 

[jpcjguy]

I would think running a line for 200A - 4/0-4/0-2/0-4 Aluminum Mobile Home Feeder Cable - https://www.wireandcableyourway.com/4-0-4-0-2-0-4-aluminum-mobile-home-feeder-cable.html would cover me and the difference in price for 250 from the 2/0 is $260.

My issue is off the panel - largest breaker is 125A - can I reduce down to a wire that fits that breaker at/near the panel and if, down the road, I need the 200A, I can figure it out from there? For me $260 in the scheme of 60K for this garage is a worthwhile cost.

 

[mike93lx]

What size range can the breaker accept? Should say on it

 

[jpcjguy]

What size range can the breaker accept? Should say on it

Not sure. I researched the panel - 1993 build - and found out that it can accept a 125A max. Have to do more research!

 

[mm08822]

Not sure. I researched the panel - 1993 build - and found out that it can accept a 125A max. Have to do more research!

probably 2/0. check the breaker/catalog.

Yes you could transition to 2/0 from 4/0 to make connections on the 125a cb. Transition may be easiest in jbox away from panel. E.g. - use jbox instead of LB coming out of ground.

If you were to put in a 200a panel w/main cb in garage, it can handle ~250-350mcm so no problem on that end.

 

[sberry]

That will be plenty of power and 2/0 to fit a 100 breaker wouldn't bother me. These kids are not going to be multiple users like a professional body or fab shop might. I have wired a couple dozen garages with number 2 alum and 60A breakers including a couple busy ones,,,, NEVER had one come back with a trip.
NEVER saw 100 overloaded or trip in a common garage/shop.

 

[jpcjguy]

That will be plenty of power and 2/0 to fit a 100 breaker wouldn't bother me. These kids are not going to be multiple users like a professional body or fab shop might. I have wired a couple dozen garages with number 2 alum and 60A breakers including a couple busy ones,,,, NEVER had one come back with a trip.
NEVER saw 100 overloaded or trip in a common garage/shop.

Thanks - that makes me feel better! For the tools and usage and full size fridge - that I was fine with. What made me question is the addition of a on-demand water heater and 2 decent sized all-electric mini splits....

 

[TRWham]

I would think running a line for 200A - 4/0-4/0-2/0-4 Aluminum Mobile Home Feeder Cable - https://www.wireandcableyourway.com/4-0-4-0-2-0-4-aluminum-mobile-home-feeder-cable.html would cover me and the difference in price for 250 from the 2/0 is $260.

My issue is off the panel - largest breaker is 125A - can I reduce down to a wire that fits that breaker at/near the panel and if, down the road, I need the 200A, I can figure it out from there? For me $260 in the scheme of 60K for this garage is a worthwhile cost.

Just keep in mind the trap in oversizing ungrounded conductors is that the ground (EGC) and grounded conductor (neutral) must now be upsized proportionally.

 

[dcg9381]

What made me question is the addition of a on-demand water heater and 2 decent sized all-electric mini splits....

OF those, the on-demand electric water heater by far the big item. Tell us how many GPM you want to heat (shower and sink at same time?) and tell us how cold your inlet water is.

I have 2 2-ton mini-splits. They both run on 15A 240V circuits, so I know they pull under 12 amps each peak continuous.

 

[dcg9381]

Just keep in mind the trap in oversizing ungrounded conductors is that the ground (EGC) and grounded conductor (neutral) must now be upsized proportionally.

Do these ever get out of spec in MHF type cable?

 

[ddawg16]

Ya know, your house and shop really screams for the like of a Tesla power wall or other load sharing system.

Basically, you charge up a bunch of Li battery modules at a slower rate at night when it's cheaper or off solar cells.

Then when you need lots of power for short periods of time, you have it. Size it right, and you could downsize your service to 200A

 

[TRWham]

Do these ever get out of spec in MHF type cable?

I've never run the numbers to see, but it is a Catch 22 that is often overlooked and worth double checking.

 

[jpcjguy]

OF those, the on-demand electric water heater by far the big item. Tell us how many GPM you want to heat (shower and sink at same time?) and tell us how cold your inlet water is.

I have 2 2-ton mini-splits. They both run on 15A 240V circuits, so I know they pull under 12 amps each peak continuous.

not sure of the needed gpm - but there is no shower. It's a half bath and a shop sink. As for temp of inlet water, I don't know but I am on a well

 

[bjcouche]

DCG9381, Yes absolutely, the neutral and ground conductors can get "out of spec" when using MHF cable, if you are over sizing the wire due to voltage drop. For instance, some cable is 2-2-4-6, which is a 4awg undersized neutral, and 6awg ground, all OK for a 90A breaker, but 6awg aluminum is the minimum required. If you used that wire on a 70A breaker, you'd have to upsize the ground larger than 6awg... I'm not sure if you'd have to up size the neutral, because if you had a load calc, my might be able to justify a "reduced" neutral.
To the OP, 100 or 125A should be plenty. For your shop 1/2 bath, I would recommend a Point Of Use hot water tank instead of an On Demand unit. The point of use units are less expensive to purchase and take less current. My shop 1/2 bath has a 5-6 gallon point of use tank under the sink. I think it's 120V and only 1500W. It must be fairly efficient and well insulated because the tiny bathroom doesn't get warm due to the hot water heater...

 

[Falcon67]

FWIW - in my old shop I did an experiment (20x24). Turned on the 12K AC, the 5kW heater, small lathe, 1 HP mill, all the lights, fans, TV, 60 gallon air compressor - everything except the Hobart 140. But a clamp on the 60A feed legs, got 49A on one and 47A on the other.

Current shop has two AC units, 5kW heater, 3/4 HP drill press, 3/4 HP lathe, 2 HP lathe, 1 HP mill, band saw, welder, compressor, lights, 2 post lift, RV plug on exterior, 3/4 well pump and misc small stuff. 100A panel fed by 70A breaker, no trips. So if you went 125A IMHO you should have zero issues. Even at 90A I'd say no issues.

 

[mike93lx]

FWIW - in my old shop I did an experiment (20x24). Turned on the 12K AC, the 5kW heater, small lathe, 1 HP mill, all the lights, fans, TV, 60 gallon air compressor - everything except the Hobart 140. But a clamp on the 60A feed legs, got 49A on one and 47A on the other.

Current shop has two AC units, 5kW heater, 3/4 HP drill press, 3/4 HP lathe, 2 HP lathe, 1 HP mill, band saw, welder, compressor, lights, 2 post lift, RV plug on exterior, 3/4 well pump and misc small stuff. 100A panel fed by 70A breaker, no trips. So if you went 125A IMHO you should have zero issues. Even at 90A I'd say no issues.

This is a great, real-life example.

 

[sberry]

Get rid of the demand heater and put in a baby tank type.

 

[jpcjguy]

Thanks all for the great advice! So something like a 5-10 gallon "under sink" water heater appears to be the best option. I looked at a Rheem spec sheet and for their 6-30 gallon models is a 2000W element - so at 120V that is 16.67A.

 

[sberry]

FWIW - in my old shop I did an experiment (20x24). Turned on the 12K AC, the 5kW heater, small lathe, 1 HP mill, all the lights, fans, TV, 60 gallon air compressor - everything except the Hobart 140. But a clamp on the 60A feed legs, got 49A on one and 47A on the other.

Current shop has two AC units, 5kW heater, 3/4 HP drill press, 3/4 HP lathe, 2 HP lathe, 1 HP mill, band saw, welder, compressor, lights, 2 post lift, RV plug on exterior, 3/4 well pump and misc small stuff. 100A panel fed by 70A breaker, no trips. So if you went 125A IMHO you should have zero issues. Even at 90A I'd say no issues.

Yes, have done that, had a neighbor do it in his house and struggled to hit 50.

 

[TRWham]

FWIW - in my old shop I did an experiment (20x24). Turned on the 12K AC, the 5kW heater, small lathe, 1 HP mill, all the lights, fans, TV, 60 gallon air compressor - everything except the Hobart 140. But a clamp on the 60A feed legs, got 49A on one and 47A on the other.
...

Similar result when I did this on my house and attached garage last year. Loads included 60 mBh of AC (2x2.5 ton units), dryer, oven, 7.5 hp compressor, all lights, fridge, etc. Only major load not running was my welder and the lot was pulling about 60A on a 150A service.

 

[jpcjguy]

This is all great information everyone! Looks like going with the 125A breaker in my existing panel and running it with the appropriate rated cable to the garage will be more than enough power for my needs!

 

[bjcouche]

I designed and wired my shop very similar to your situation, and had similar thoughts on 100A, versus 125A and voltage drop to the new shop / garage.
Here's my suggestion:
You stated your cable run is about 250' from your existing house panel to your new shop panel. You should take voltage drop into account for that distance. I suggest going with a 100A breaker in your main panel instead of a 125A breaker. Both will likely accept the same size wire, but the 100A breaker is often cheaper. Bumping up from 100 to 125A also requires a larger ground wire.
For wire sizing, I always go with aluminum for subpanel feeds so the following is based on THWN aluminum, some calculations based on 75C and 250 feet (500' round trip). Based on other's input on expected real life current draw, I used 75A for voltage drop calculations.
1awg 100A 0.1265 ohms at 500' 9.5V drop 3.96%
1/0 120A 0.1005 ohms at 500' 7.5V drop 3.1%
2/0 135A 0.0795 ohms at 500' 6.0V drop 2.5%
3/0 155A 0.0630 ohms at 500' 4.7V drop 2%
4/0 188A 0.0500 ohms at 500' 3.75V drop 1.6%

The NEC does not specifically require a voltage drop but suggests keeping it below 3%. You can certainly draw MORE than 75A on this proposed 100A feed, you'll just have more voltage drop.

In your situation I would recommend a cable of 2/0, 2/0, 1awg,2awg. The 1awg neutral is not needed to be oversized for voltage drop because it only carries the unbalanced load. So essentially, the neutral is not undersized, it's simply not oversized. The ground IS oversized at 2awg because for a 100A service the minimum size is 6awg.
I'm a fan of using conductors in conduit compared to direct burial, and this makes extra sense in your situation. MHF (direct burial Mobile Home Feeder) usually only comes in 2awg or 4/0, and in your case 2awg is too small based on voltage drop, and 4/0 is too big because it will not fit in your 100 or 125A breaker terminals. You could still use 4/0 but you'd have to transition in a junction box near your house panel to a smaller size to fit your breaker. A junction box adds additional space, and expense.
I'd bury 2" PVC conduit. The 2/0, 2/0, 1awg, 2awg will fit easily in that. Many electrical supply houses stock these sizes in aluminum THWN single conductors. IF they don't have the 1awg, then you could go up 2/0. I'd feel find going down to 2awg or the neutral, but you might have to provide an inspector a load calc to justify under sizing the neutral.
With 2/0 the cable will fit in you house 100A breaker terminals AND your shop main breaker if you use a 100/125A subpanel. I used a 32 space 125A subpanel in my shop and I can tell you that 4/0 doesn't fit! Using a 200A subpanel is perfectly OK too, and probablly recommended to get lots of breaker spaces. The main 200A breaker would then be just a disconnect function, and a label added on it like, "100A sevfice fed from house breaker #**"
Brian

 

[jpcjguy]

bjcouche -

Thanks for the great information! I think I will just go ahead and wire for 125A breaker, the incremental cost is acceptable to me. So if I went with MHF - would this be correct?:
https://www.wireandcableyourway.com/2-0-2-0-1-4-aluminum-mobile-home-feeder-cable/

Or would doing individiual strands:
https://www.wireandcableyourway.com/2-0-xhhw-2-aluminum-building-wire/

 

[mike93lx]

If conduit end to end, use xhhw-2. Is some will be direct burial, use MHF

 

[dcg9381]

Thanks all for the great advice! So something like a 5-10 gallon "under sink" water heater appears to be the best option. I looked at a Rheem spec sheet and for their 6-30 gallon models is a 2000W element - so at 120V that is 16.67A.

I've got an RV, with a 6 gallon dual-fuel water heater, it's certainly enough for a sink, but showers get pretty quick. A 20 gallon water heater would definitely get it done (for me anyway) - that's the best combination (IMHO) of reasonable eletrical load and water capacity.

 

[jpcjguy]

I've got an RV, with a 6 gallon dual-fuel water heater, it's certainly enough for a sink, but showers get pretty quick. A 20 gallon water heater would definitely get it done (for me anyway) - that's the best combination (IMHO) of reasonable eletrical load and water capacity.

This will support a 1/2 bath and a shop sink only, no shower - but looking at the $45 difference in cost between the 6 and 20 gallon, I might just go with the 20.
What I did not plan for is the location of this thing!

 

[mike93lx]

This will support a 1/2 bath and a shop sink only, no shower - but looking at the $45 difference in cost between the 6 and 20 gallon, I might just go with the 20.
What I did not plan for is the location of this thing!

Bigger will just mean more water to keep hot and more money. Go small and add insulation to the outside of the enclosure.

Hand washing doesn't need 20 gallons of hot water

 

[jpcjguy]

Bigger will just mean more water to keep hot and more money. Go small and add insulation to the outside of the enclosure.

Hand washing doesn't need 20 gallons of hot water

very true - sucked into standard Garage Journal thinking - "must get bigger!"

 

[dcg9381]

I was assuming bath would have a shower. 20 gallons is way overkill for a sink.

 

[theoldwizard1]

Or maybe with 125A, I will be fine even with multiple users?

Properly MANAGED your still good !

The heavy hitter will be the plasma cutter because the air compressor will have to run at the same time. No welding while cutting.

Worst case, also turn off the mini-splits while cutting.


You are OVER THINKING THIS !

 

[bjcouche]

Jpcjguy,
Either wire that you linked to will work fine. The MHF cable has the advantage that it can be direct buried. The XHHW-2 MUST be inside conduit underground.
BOTH types of cables MUST be in conduit when above ground, even behind drywall.
The MHF cable will be harder to pull through conduit compared to the XHHW because the MHF cable has all 4 conductors twisted together. If you have a good portion of the distance above ground with lots of 90 degree bends, the XHHW might be a good option.
On the site you linked to, the MHF cable is the cheapest option.
2/0, 2/0, 1awg, 4awg will be fine for your proposed 125A breaker, but note that you can't go any smaller than 4awg on the ground because you went with the 125A breaker instead of the 100A.
Before you place an online order for that large of a quantity of wire, double check with them on shipping.... Your order might be too big or too heavy to ship UPS and have to go freight....
I'd call your local electrical distributors too and check pricing. By me I have both a CED distributor and a Rexel distributor. Ask them on a price for the MHF cable. If going conduit, even underground, ask for price on the aluminum XHHW, but also if they have aluminum THWN. The CED by me carries this and I like it better because it comes pre lubed.