Will 40 amp be sufficient..

[timst]

Hello all, new to the forum here, (been lurking awhile) so here is what I have for a first post.
I have a 1728 sq foot house with 100 amp service and a detached 24x24 garage with 10 ft ceilings and an attic. The garage is 35 ft from the main panel, and I already have the proper schedule 40 pvc run under ground and ready to run a 4 wire setup. Is 40 amp service to the garage sufficient? I want at least one 240v circuit to run a compressor for basic mechanical work and possibly another for a heater (I also have natural gas run). I imagine a garage door opener and three runs of outlets including lighting, with one of them being a 20a 120v limited to 3 or 4 outlets for occasional use of power tools. In my house I have a gas furnace, hot water heater, central air, electric range (switching to gas within a year),and brand new high efficiency washer and dryer (electric 240v on a 30 amp circuit) and two adults, and two college students home for the usual breaks. What do you think? Should I consider 50 or 60? There will be no more expansion or addition to this property and I will not consider upgrading my main service. Thank you for any input.

 

[rockwithjason]

with conservative use you will be fine.

 

[volleyball]

You could do 100A service to the garage and not upgrade your service. I would think 60a as a minimum. You may not get a hi power tool but who to say your kids won't. And when it comes time to sell, it won't hurt. The wire cost is marginal, breakers the same price.
I'd route the wire so that you have a little extra going into the main panel as I suspect it will get upgraded some time.

 

[Mustang51js]

What size pipe did you run, if you can spend the little extra make it 60 amps, your prob looking at a $50 difference in cost of wire from #8 to #6. Breakers are basically the same price. You just need to make sure your pipe is big enough to handle 4 #6thhn. You never know if your going to get new ideas or equipment in the future and 40 amps will hold you back some

 

[alfredeneuman]

The same #8 THWN is suitable for a 50 Amp circuit, if you just change the breaker's size.

If you'd have been using NM or UF you wouldn't have had the option.

Breakers are basically the same price. You just need to make sure your pipe is big enough to handle 4 #6thhn.

Why (4) #6 THWN? The ground wire only needs to be a #10. Any circuit rated 30 thru 60 amps uses a #10 ground.

 

[ez-duzit]

You could do 100A service to the garage...

This is the right way.

 

[sberry]

The run is short, the wire cost modest and not a huge factor. Youj got it piped I would run a number 6 if I was going to run copper or 2 alum with a 60. The breaker is cheap, there is no savings to run smaller, leaves a modest comp a1/3 to 1/2 the capacity and would allow for the use of a 50A service welder should the need ever arise. I cant recall anyone ever tripping a 60 in a residential garage. My bud ran auto shop out on one for 25 yrs.

 

[Stuart in MN]

Tell us what size conduit you already have in place. 40 amps will likely be enough; more is better, but the conduit size will limit how big you can go.

 

[bobcatdan]

Go 200 or go home.

 

[timst]

Thanks for the replies so far. I ran 1 1\4" schedule 40 with max wire temp rating of 90 deg Celsius. I definitely am considering going with #6 wire and upping to 50A or 60A, I just figured to play it safe, I should consider only going with a 40A service.

 

[Mustang51js]

The same #8 THWN is suitable for a 50 Amp circuit, if you just change the breaker's size.

If you'd have been using NM or UF you wouldn't have had the option.





Why (4) #6 THWN? The ground wire only needs to be a #10. Any circuit rated 30 thru 60 amps uses a #10 ground.

I was figuring it's easy enough since it's a small run and don't have to buy different size wires.

 

[Mustang51js]

Thanks for the replies so far. I ran 1 1\4" schedule 40 with max wire temp rating of 90 deg Celsius. I definitely am considering going with #6 wire and upping to 50A or 60A, I just figured to play it safe, I should consider only going with a 40A service.

Off the top of my head with that size pipe you could run #4 thhn and do a 75 amp panel. Might be able to get#2 copper in there and run 100 amps

 

[sberry]

Thanks for the replies so far. I ran 1 1\4" schedule 40 with max wire temp rating of 90 deg Celsius. I definitely am considering going with #6 wire and upping to 50A or 60A, I just figured to play it safe, I should consider only going with a 40A service.

You can slide by on 40 but 60 leaves a little headroom without great expense and number 6 is easy to work with. After 60 breakers cost a bit more, the only increase in cost from 40 to 60 in this case is the difference in wire price. All the other fixed cost are the same.

 

[timst]

So 60A would be O.K. off of my 100A main provided I used the proper wire\breaker\panel combination?

 

[augustus]

go as big as you can with your conduit size (budget permitting), but otherwise your 40 is fine for you what you said you'll be doing.

 

[Jester1]

Off the top of my head with that size pipe you could run #4 thhn and do a 75 amp panel. Might be able to get#2 copper in there and run 100 amps

this^^^

3-#2 and #6 bonding wire

 

[adcrawfo]

So 60A would be O.K. off of my 100A main provided I used the proper wire\breaker\panel combination?

Yes. I had 2 garages on a 100 amp panel like what you're doing (both 60 amp) for over 20 years in my house without any problems. Just upgraded to 200 amp this spring but only because I ran out of breakers.


Sent from my iPhone using Tapatalk

 

[Jester1]

Breaker listing is not cumulative, other wise you would only be able to have 10-20 amp breakers on a 200a panel (per phase). Yes you will be fine

I have a 50 amp welder 50 amp range and 50 amp hot tub plus all my house stuff plus all the heat.

You don't pull 60 amps all the time

 

[timst]

Breaker listing is not cumulative, other wise you would only be able to have 10-20 amp breakers on a 200a panel (per phase). Yes you will be fine

I have a 50 amp welder 50 amp range and 50 amp hot tub plus all my house stuff plus all the heat.

You don't pull 60 amps all the time

Yes, that does make sense. I guess the most important factor would be my total load at any one given time. I keep trying to come up with scenarios where I would ever put an 80A load on my service, and I suppose if I had a larger shop (or one to myself without sharing storage with my wife) and more equipment I could possibly do that. I really need to learn to better understand how to calculate max load.

 

[Mustang51js]

If you know the watts for each peice of equipment then take the watts divided by voltage and that will give you your amps. Some things have it right on the there,full load amps. The main thing you need to remember is to balance out the phases such as putting a sander and vacuume on breaker 1 and 2 which is side to side and then under that have breakers 3-4 with nothing on them. Over time it will ruin your main breaker.
When you do figure the amps out then you need to add them up and divide by two and that's a rough idea of amps per phase you would be pulling if everything was on at once. And some equipment starts up and pulls high amps then settles down so that's something to think about also

 

[sberry]

Yes, that does make sense. I guess the most important factor would be my total load at any one given time. I keep trying to come up with scenarios where I would ever put an 80A load on my service, and I suppose if I had a larger shop (or one to myself without sharing storage with my wife) and more equipment I could possibly do that. I really need to learn to better understand how to calculate max load.

This is confusing and there are a lot of options, some great, some for the future etc and most home brew load calcs are way off.

1st,,, you could get by with 40A but ther service panel is the same, breaker cost the same and its really a little too light for an air comp. 100A or now 90 is considered standard as the cost is similar, I would have said the same thing except for the ease in this case, pipe size, distance.

But.. Mustang makes the real point to consider. The max load is not much but the potential for out of balance is here, a bigger service wire handles this so much better without management. The vac and the sander or other tool running down the same line wont matter,,, if it was a 30A wire it would, not so much with a 40 and V drop would be less as the wire was increased. A number 6 would give enough overhead that the V drop caused by the comp wouldn't be an issue for the lights or prevent the use of another tool.

I got a panel across the shop, 100 ft away, instead of a branch circuit there is a panel, instead of 110 ft of 12 wire there is 10. I got one 240 circuit which I rarely use and 18 others at 120 randomly loaded including a small water heater but peak load is very minor, chances are they not all down one leg but even if it was it would be 30A, not a problem with a 100A wire. Even at that distance no issue.

 

[sberry]

I am not sure that made sense to anyone besides myself,,, but,,, while the total amperage in general and even in peak may be sufficient it leaves some opportunity for heavily loading one side of it.
I have seen this in extreme. I got a call to a village park during a festival. 200 ft of 6 from a service fed by 60A. Its all dim and trips well they had the band and a beer tent with cooler all on same leg, minus 1 100 watt lamp. 49A down one and 1 down the other, I move a space and put 25 down each line and all was well,,, its still not 60A service at that distance but served a managed load.

We had arguments here about adequate amperage and as I said the focus becomes about peak and that can be rare. The number 2 alum at 300 would have been sufficient to run a small cottage office especially with some designed management but it morphs into a the speculation of future need for a commercial coating oven.

In a common garage lights and air comp is the 2 items most used, almost everything else is a deliberate one off effort. I am all for a couple circuits. Use 3 generals in a u shape. One along 2 walls on same leg and one in the middle on the bench on another. If I was welding away on this service might stop when I heard the comp come on, resume when off.

 

[sberry]

I live on 250 ft of number 2 alum. I have all gas appliances and water fed from another source. Only a few lights and in super hot weather a 12K air cond on 120 opposite the fridge and lights and from one of the kitchen ctops which was a thing I fed with multi wire before I moved in. I use a little electric heat opposite the micro/toaster circuit. None of this going on while running vaccum. Its fairly rare for someone to use hair dryer and its modest, I would never trip a 30. I did remove an electric dryer and laundry though.

So the short version is that 40A will likely be sufficient but it doesn't mean you want to use 40 wire, a 60A wire would enhance the performance some especially with the addition of an air comp.

 

[ez-duzit]

OP--If you install a 100-amp panel, you won't likely have to concern yourself with balancing loads (except to not run high draw house appliances while you're welding/cutting/heating... in the garage/shop).

 

[TractorJeff]

I worked out of a 50/60 for years.
Moved to my new place and found the same thing!
Lights, Ceiling Fans, Radio, Air Compressor and a big Miller Welder!
Is it a short coming? No
Just unplug the Compressor when running the Welder!

 

[volleyball]

That is fine that it was enough if you were smart. Since the OP isn't stuck with 40, why cripple yourself? This is the chance to give yourself some room to grow. I bet the 50/60 seems way more than you would ever need when it was put in.
Heck I am wondering if 30 is enough for my shed.

 

[RossABQ]

...
Just unplug the Compressor when running the Welder!

If you weld like me, you're frequently grinding as much as welding , so the prudent thing is to size the panel for running loads on both the compressor and welder.

 

[raddksn]

In my experience if you go with just sufficient, you will soon wish you went with all you could have!

 

[bjcouche]

40A will probably be "sufficient" but I would do it a bit different, and get more current for less money.
Because you have 1.25" conduit, and I'm assuming it's continuous from the house load center to the shop, I would use 3 conductors of 4awg THWN ALUMINUM and 1 ground conductor of 10awg copper. You won't find the THWN aluminum at your big box store but most electrical distributors sell it. 4awg aluminum will get you a rated capacity of 65A at 75C rating, so I would use a 60A breaker in your house. If you price out the cable cost of your 40A, 8awg copper option and compare it to my 60A aluminum option, you'll find the 60A aluminum option less expensive.

Brian

 

[sberry]

Yes, that is probably the cheapest way.