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Discussion Starter #1
Greetings,

I'm looking to build a workshop on the back corner of my lot. I have the building quoted, concrete quoted, permit info, etc. What I don't have is the electrical run sorted out. I've researched and listed the amp draws of all of my tools below:

Item Amp Draw
Dust Collector 9
Table Saw 5
Router Table 15
Planer 15
Jointer 12
Belt Sander 5
Bandsaw 10
Air Compressor 15
Drill Press 8
Circular Saw 15
Mitre Saw 15
Hand Jig Saw 6
Scroll Saw 2
Orbital Sander 3
Palm Sander 2
Hand Router 12


Obviously I still need to account for florescent lighting and HVAC. I will have a window A/C unit and a TBD heat source. Looking over that list it looks like my peak amp draw would be (lighting + a/c unit + dust collector + table saw + ac compressor), which totals (10 + 10 + 9 + 15 + 15 = 59). This makes me believe an 80 amp sub-panel will work.

The total length of the run to the shop will be 250 feet, rounding up. First question is, what gauge of wire do I need to run underground to the workshop? After doing some reading online it looks like 8 gauge will work but it is pretty expensive.

Also, I'm unsure of my house's current capabilities. My basement has two breaker panels, a larger and obviously older one, and a smaller one. The bottom of the post has photos of each. If it can be determined from looking at these panels, do I have the capacity to run an 80 amp subpanel off of the house? Obviously I could call an electrician but I'm over budget as is and would like to get an idea of exactly what I need done before calling/paying anyone.

Thanks for any advice provided.

Main panel:


Sub Panel:
 

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You do not have any spaces left to add anything to either panel.

It appears that you have a 100 amp main.

It is time to look into a service upgrade.
Is there a main breaker behind the paper in the bottom photo?
 

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Discussion Starter #3
There is no main breaker behind the paper in the bottom photo. The electric company is going to run a new line from the pole to my house next week. The steel cable in the current line snapped and it's sagging. He said it's old and will be replaced with a better line. If that's the case, would simply getting a bigger breaker box (200 amp), moving the circuits/breakers from the existing panels to the new box, and moving the small breaker box to the shop work out?
 

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It would work only if the wire from the weatherhead to the meter, and from the meter to the panel is rated for 200 amps.
The meter also has to be rated for 200 amps.
 

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Discussion Starter #5
Ah, ok. That makes sense. Is that information the electric company can tell me for sure when they get here? I think I remember it being listed on my inspection report when I bought the house. If so it seems that would work out great, I could upgrade my breaker box and reuse the old one for the shop. Any idea on what gauge of wire I should bury?
 

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Lic Electrical Inspector
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1,843 Posts
Greetings,

I'm looking to build a workshop on the back corner of my lot. I have the building quoted, concrete quoted, permit info, etc. What I don't have is the electrical run sorted out. I've researched and listed the amp draws of all of my tools below:

Item Amp Draw
Dust Collector 9
Table Saw 5
Router Table 15
Planer 15
Jointer 12
Belt Sander 5
Bandsaw 10
Air Compressor 15
Drill Press 8
Circular Saw 15
Mitre Saw 15
Hand Jig Saw 6
Scroll Saw 2
Orbital Sander 3
Palm Sander 2
Hand Router 12


Obviously I still need to account for florescent lighting and HVAC. I will have a window A/C unit and a TBD heat source. Looking over that list it looks like my peak amp draw would be (lighting + a/c unit + dust collector + table saw + ac compressor), which totals (10 + 10 + 9 + 15 + 15 = 59). This makes me believe an 80 amp sub-panel will work.

The total length of the run to the shop will be 250 feet, rounding up. First question is, what gauge of wire do I need to run underground to the workshop? After doing some reading online it looks like 8 gauge will work but it is pretty expensive.

Also, I'm unsure of my house's current capabilities. My basement has two breaker panels, a larger and obviously older one, and a smaller one. The bottom of the post has photos of each. If it can be determined from looking at these panels, do I have the capacity to run an 80 amp subpanel off of the house? Obviously I could call an electrician but I'm over budget as is and would like to get an idea of exactly what I need done before calling/paying anyone.

Thanks for any advice provided.

Main panel:


Sub Panel:
Voltages would help.
 

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Lic Electrical Inspector
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I don't have a single 220V tool. Everything is 110V.

Are you planning on operating a business with more that one employee. The reason asked is because if you are the only person using the tools then the feeder to the shop does not have to sized to run all the tools at the same time. What tools and appliances will ran at the same time?
 

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Discussion Starter #10
So, for a peak of 59 amps 250 feet from the house am I looking at UF 3 conductor plus ground 8 gauge? Or could I get away with something cheaper?
 

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I would go with THWN wires in conduit rather than UF. I think you will find it cheaper for materials - and can be buried 18" instead of 24". The deeper you go the harder to dig, and you have 250' of it to dig.

59 amps at once? Which tools (and lighting) will be running at the same time to draw that much? Seems like a lot. I would think worst case would be compressor plus a tool or two and then lighting.

In my workshop I have a 100 amp subpanel fed via a 60a breaker in the main - compressor, 240v welder, drill press, grinder, large table saw, etc. Works great.
 

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60 amp service will be fine. That "projected" 59 amp load is over two poles; 30 amps per side. That's only half of breaker capacity. Now if you plan on having multiple tools used at once you may want to upgrade to a larger service.
 
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