Shop power estimate

[John K Jordan]

Jack, I am consulting with my job electrician on this also. He used to teach the NEC code for 10 about years. Seems knowledgable to me.
From this forum I was more concerned about making certain I have identified what the max simultaneous load will be for the shop part of the build, so the chart above is what I call the worst case scenario: jointer running with DC and stock feeder on, all lights on,...
I guess I could add a 2HP compressor recycling in the 'worst case'.

When designing my shop electrical I figured on these possible simultaneous loads:
5 hp ClearVue dust collector (measured 14+ amps after starting, BTW)
5 hp air compressor
all lighting, inside and out, security system, etc.
HVAC with aux resistance heat
20 amps to feed some farm water heaters.

Even though it is usually just me, I do have occasional students and figured several 1 to 3 hp machines (lathes, bandsaw, drill press, grinders) could be used at once. When I'm using the big welders I'm not using the wood.

Even with a 25% overage allowance my worst case load was well under a maximum of 100 amps so I installed a 100 amp panel. One thing that is very important to me - voltage drop. There are recommended voltage drop allowances to avoid excessive light dimming and power glitches when pulling big loads. I wanted zero noticeable light dimming so I oversized the wiring to the shop. My case was complicated by putting the shop 250 ft from my transformer and meter. They laughed at me when I installed #1 copper for the power but hey, it is so much effort to dig the trench and lay conduit that even double the cost for the permissible or even the "normally acceptable" conductors was negligible compared to the total cost of the shop from dirt to roof. BTW, don't forget long internal runs too - my two 5hp motor loads were about 50' from the panel so I fed a sub panel there with oversized cable. I'd rather have too much capacity than too little. Materials are cheaper than the time.

Another thing I'm glad I added to the trench - I ran two extra underground conduits - one with two ethernet cables to feed the shop WiFi, personal cell tower, and security system (one cable is a backup), and one 2" conduit empty except for a rope - for some then un-imagined use.

Also, install a panel with more breaker slots than you can imagine you will ever need. I paneled with ply and screws instead of sheet rock so I can take things apart gracefully to modify things if ever needed. (I already removed one wall panel three times!)

JKJ

[Jim Becker]

I was concerned with this when I built out my shop, too, Mark. I had 200 amp "service" put in to the shop at the same time we were upgrading the house panel considering "more capacity can be better"; both come from the same meter, but are essentially separate, otherwise, and the house side of the service is built and rated for 400 amps. However, the power company refused to upsize the actual service from the street (arial) so that's still a 200 amp supply. Fortunately, there's not been a problem and it's been that way since 2005. Both the licensed electrician and inspector were ok with it, too. Go figure...

[mark mcfarlane]

Thanks everyone. The question wasn't about panels and wire sizes, but about max draw for the shop.

The current plan is to have a separate 200 AMP panel in the shop. The main feed gets splits to two cutoffs, then on to two 200 AMP panels.

[Van Huskey]

The problem is nobody (even an electrician or EE) can even guess in significant part because there is little information about the house current draw. If for example the house is all electric and you have a house full of people and run the 4 top and oven while kids are taking hot showers and running the washer and dryer along with 8 tons of AC starting while you are running heavy cuts on the shaper with both your mini-splits starting you are definitely going to have a problem.

The reality is most all electric homes in hot climates have well over the potential draw to pop the main breaker if you fire up everything at once but it is a very rare occurrence with the current average 200 amp supply.

From a practical POV I have run shops with very similar and slightly higher max current demands on 100A sub panel and never had an issue. The key is machines rarely pull FLA and then usually only for short periods of time (not counting the uber-quick inrush).

The big problem is without enough supply to cover every electrical item you own running at the same time sizing a supply is a guessing game, balanced by experience on the electricians part.

[Van Huskey]

The question wasn't about panels and wire sizes, but about max draw for the shop.

Que? I thought you were asking about how much total supply you need for the house and the shop. The shop based on your machines is more than fine with a 100 amp supply.

[mark mcfarlane]

Thanks Van. Our AC is electric but heat and water are gas. The electrician told me the 'expected max load' (by some named authority, I assumed either power company or county, state,...) for houses in our area of our size was 100 AMPs, but he always put in 200 AMP services.

The current house is 2800 sq ft. The addition is 2000 sq ft.

.. but I fear I am helping the thread get off track.

[John K Jordan]

I was concerned with this when I built out my shop, too, Mark. I had 200 amp "service" put in to the shop at the same time we were upgrading the house panel considering "more capacity can be better"; both come from the same meter, but are essentially separate, otherwise, and the house side of the service is built and rated for 400 amps. However, the power company refused to upsize the actual service from the street (arial) so that's still a 200 amp supply. Fortunately, there's not been a problem and it's been that way since 2005. Both the licensed electrician and inspector were ok with it, too. Go figure...

If the split is hard wired before either panel then the service from the pole/transformer will typically provide far more than you could ever use. A utility guy told me once what a typical aerial line on a pole could handle and I don't remember the numbers but it was surprising.

In my case we ran the feed a few feet from the transformer (on the ground on the property) to a meter mounted in an outside breaker box. In that box I put three breakers: a 220v breaker to feed the house panel, a 220v breaker to feed the shop, and a 110v breaker to feed an outside receptacle below the meter box. A friend from the utility company did the hookup so I assume they are happy with it.

JKJ

[Rick Fisher]

I would consider the compressor as well but you will be fine .

I ran 400 amps to the shop and split the shop and house .. each is only 200 amps. We have an empty conduit 2" from the house to shop which would allow me to poach more power than I have from the house but its not needed.. I have some bigger stuff running, still no issue at all. 200 amps is a lot of power in a one man shop.

[mark mcfarlane]

Here's an update with a compressor added:

Shop - Max simultaneous power usage	Qty	HP	Note	Amps (running)	Circuit
CU300	1	4.8 HP (230V)	30 amp curcuit, probably only uses 20 amps	30	230V	http://www.scmgroupna.com/en/products/classical-machines.c884/universal-combined-machines.887/cu-300-classic.721
DC40 Stock Feeder	1	0.5 HP		3	230V	http://www.cantekamerica.com/machinery/feeders/dc30-3-roll-variable-speed-power-feeder-2883.html
Dust Gorila Pro	1	5.0 HP (maybe 3HP)	30 amo curcuit, probably only uses 20 amps	20	230V	https://www.oneida-air.com/inventoryD.asp?item_no=XGK050105H&CatId={7F6C8978-92E8-4902-9A37-D8A254EDF4FC}
Shop Lights	30	32 watts	960 watts	8
Radio, mini-fridge				3
AC (mini-split) Shop	1	9000 BTU / 30.5 SEER		12	230V	http://www.mitsubishielectric.ca/en/...nit_Spec05.pdf
Compressor	1		1HP	4
Studio Lights				3
AC (mini-split Studio)	1			12	230V
Total Amps				95

[Ole Anderson]

Minor, but 4 amps on a 1 hp compressor can't be correct.

[Roger Feeley]

I ran my shop on 50A for 20 years. I never measured the draw but I only ran one machine at a time.
20 2-tube T12s at 80watts = 1600w. Be generous at 15A
3hp Table saw was the big suck call it 20A cause that was how big the breaker was
1.5hp dust collector. Another 12A

That would be 47A which is kind of close.
In my new shop, I replaced all lights with LED so I cut those amps down to 6.
That brings me to 41A and I put in a 100A sub-panel on a 70A breaker.

I figure I can run those lights and a small TIG welder and be fine.

Studio Lights?

[mark mcfarlane]

Studio Lights?

The build includes a recording studio. I could forget and leave the lights on in there....

[Phillip Gregory]

I was concerned with this when I built out my shop, too, Mark. I had 200 amp "service" put in to the shop at the same time we were upgrading the house panel considering "more capacity can be better"; both come from the same meter, but are essentially separate, otherwise, and the house side of the service is built and rated for 400 amps. However, the power company refused to upsize the actual service from the street (arial) so that's still a 200 amp supply. Fortunately, there's not been a problem and it's been that way since 2005. Both the licensed electrician and inspector were ok with it, too. Go figure...

Utilities are very loath to provide anything more than a 25 KVa (108 amps at 240 volts) transformer for single phase residential service. I have lived in three houses with at least 400 amps of nominal panel capacity running from the meter and all of them had a standard 25 KVa pad transformer. They do that even if you heat with a heat pump with resistive secondaries (and the entire rest of the house is electric as well), and can draw 40+ KW once the temp drops below freezing, or are running 8-10 tons of air conditioners off of that one 25 KVa transformer. The last one is the worst, because the biggest air conditioner is about a 5-6 ton unit that draws about twice the start current as the transformer is rated for and often causes appliances and computers to shut off due to voltage drop when it fires up.

[lee cox]

I have gas in my house. You did not say whether you are all electric or not. I converted my dryer and water heater to gas which reduced my electric load and bills. My only house load now is my refrig, freezer and 5 ton AC as I live in Texas. I run a small detached shop off the same main breaker panel as the house. It seems to work fine. It is just me in the shop so I am not running a lot of tools simultaneously.

[John K Jordan]

Utilities are very loath to provide anything more than a 25 KVa (108 amps at 240 volts) transformer for single phase residential service.

How could I find out what my transformer capacity is? All I know is it has 7200 volts on a single underground cable about 600 ft from the pole, sits on a concrete pad about 50 ft from the house.

Twice in 20 years the end of the cable exploded right at the transformer when some termites crawled in there to keep warm in the winter.

JKJ