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Discussion Starter · #1 ·
300ft from disconnect to panel. 200 amps. My calculations show 350 mcm Al for 3.46% vd. The client has a buddy that is a master electrician and is telling him to run 250/250/(4/0). I'm suggesting 350/350/350 as it's a long run and I don't think derating the nuteral is worth the few bucks of cost saving.

What would you do?
 

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300ft from disconnect to panel. 200 amps. My calculations show 350 mcm Al for 3.46% vd. The client has a buddy that is a master electrician and is telling him to run 250/250/(4/0). I'm suggesting 350/350/350 as it's a long run and I don't think derating the nuteral is worth the few bucks of cost saving.

What would you do?
We usually see the wire size double at 300’.
I wouldn’t skimp,
Use Wesleyan.
 

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300ft from disconnect to panel. 200 amps. My calculations show 350 mcm Al for 3.46% vd. The client has a buddy that is a master electrician and is telling him to run 250/250/(4/0). I'm suggesting 350/350/350 as it's a long run and I don't think derating the nuteral is worth the few bucks of cost saving.

What would you do?
What is the voltage and calculated load?

Is the load 200 amps or is it a 200 amp circuit with a maximum legal load @ 80%; 160 amps?
Where in the code book does it say a person can only use 80% of a 200 amp feeder?
 

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Discussion Starter · #5 ·
What is the voltage and calculated load?



Where in the code book does it say a person can only use 80% of a 200 amp feeder?
240 volt/1 phase

I didn't think you could use the 80% rule on the feeder side, only service.

As for load, it's a huge wood working shop. Numerous saws, air compressor, welders, lights. While I doubt there will be 200 amps at all times, I could see it pushing that at points.

Another thing his buddy brought up was installing 2 ground grounds at the new attached building. Wouldn't that cause issues? I've just always sunk them at the service disconnect point.
 

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240 volt/1 phase

As for load, it's a huge wood working shop. Numerous saws, air compressor, welders, lights. While I doubt there will be 200 amps at all times, I could see it pushing that at points.
I think your calculations are the minimum.
Another thing his buddy brought up was installing 2 ground grounds at the new attached building.
Yup (but keep your neutral isolated from the new ground rods).
 

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In my opinion, it would be in your best interest, and the customers best interest, if you would perform a load calc. My gut tells me 250AL would probably run everything and then some, and still fit the 200 amp lugs, versus the 350AL you're proposing that may not be needed, and may require pin adapters/insulated taps to fit the lugs. But you need to verify it with a calc.

You also need to spend some time in article 250 to help yourself better understand grounding requirements for separate detached buildings.
 

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Discussion Starter · #8 ·
We usually see the wire size double at 300’.
I wouldn’t skimp,
Use Wesleyan.

That's what I'm thinking. Not sure if it's worth saving a few bucks to derate the nuteral.
 

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300ft from disconnect to panel. 200 amps. My calculations show 350 mcm Al for 3.46% vd. The client has a buddy that is a master electrician and is telling him to run 250/250/(4/0). I'm suggesting 350/350/350 as it's a long run and I don't think derating the nuteral is worth the few bucks of cost saving.

What would you do?

Magicone are you not a licensed electrician? You're doing this work on the side????? Anyway you need an equipment grounding conductor to the separate structure. 350kcm would give you the full 200 amps at a 3% VD-- totally acceptable.

BTW, you only need 80% if the load is continuous. I am sure that they won't be running everything at once...
 

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300ft from disconnect to panel. 200 amps. My calculations show 350 mcm Al for 3.46% vd. The client has a buddy that is a master electrician and is telling him to run 250/250/(4/0). I'm suggesting 350/350/350 as it's a long run and I don't think derating the nuteral is worth the few bucks of cost saving.

What would you do?
I would go with the Master electrician's suggestion.
He seems to know how to do the calculation better than you.
Ask the client who does he trust with the calculation.
 

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I would go with the Master electrician's suggestion.
He seems to know how to do the calculation better than you.
Ask the client who does he trust with the calculation.

Actually the op's calc is just fine but it depends on the parameters that they used. If you want a full 200 amps and no more than 3% VD then 350 kcm is necessary
 

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Discussion Starter · #12 ·
I am licensed but been a long time since I did something like this. Mostly do 200amp swaps or small stuff now days. I focus on consulting for construction mainly.

But I'm finding there isn't a defentive answer, everyone interpets it differently. I personally like to over build than under hence why I am pushing for the 350mcm. The 250 will probably be perfectly fine.
 

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What is the voltage and calculated load?



Where in the code book does it say a person can only use 80% of a 200 amp feeder?
215.2(A) Feeders for continuous loads shall have an ampacity not less than 125% of the continuous loads. In my career I have only come across three circuit breakers that were listed at 100% continuous duty. The enclosures were about ten times the standard sized enclosures.
 

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215.2(A) Feeders for continuous loads shall have an ampacity not less than 125% of the continuous loads. In my career I have only come across three circuit breakers that were listed at 100% continuous duty. The enclosures were about ten times the standard sized enclosures.
You feel a 200 amp feeder to this woodworking shop based on the information provided qualifies as a continuous load?

Continuous load. A load where the maximum current is expected to continue for 3 hours or more.
 

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I think there is a good chance that this building could grow into a 200-amp service one day.

I still think that one day you will wish you had installed the 350AL.
 

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You feel a 200 amp feeder to this woodworking shop based on the information provided qualifies as a continuous load?

Continuous load. A load where the maximum current is expected to continue for 3 hours or more.
It could turn into that. If you’re not going to size everything for the max load then just make the system smaller. What’s the point of a 200 amp service that cannot reliably handle a full load?


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You feel a 200 amp feeder to this woodworking shop based on the information provided qualifies as a continuous load?

Continuous load. A load where the maximum current is expected to continue for 3 hours or more.
I didn't know it was a woodworking shop on my first post, I was suggesting to to use 80% for voltage drop purposes if the actual loads aren't known. Load would probably never come near 200 amps. I have done machine shops with 70 machines and 40 machinists. Set up a CNC machine and some can run for 5 to 10 hours making components. All of my projects are design/build. My current load calculation sheet is attached. All continuous and non-continuous loads are calculated at 100% and the largest motor is calculated at 125% for total calculated load. We are applying for a 2500 amp service.
 

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I didn't know it was a woodworking shop on my first post,
Fair enough, I saw the guy had "residential" under his name and was asking about feeding a panel from a disconnect, I incorrectly assumed everyone else reading this would have probably made the assumption that he was asking about feeding a house or garage, etc, neither of which fall into continuous load territory. My mistake.
 
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