What underground feeder cable should I use?

[Jhenry1745]

I need to run 250' of underground cable carrying 100 amp service to a new garage/shop building. Looks like I will have to use #1 gauge wire to minimize voltage drop due to the distance. I prefer to use direct burial cable that I can run directly into the building and hookup to the service panels which are both within a few feet of the service entry locations. I prefer not to have to use pvc conduit except where the cable passes under a gravel driveway. My question is what type of cable do I need to use?

 

[pattenp]

I also answered your question in your other post. To not have conduit inside you'd need to use SER inside and transition via a large junction box to the URD for outside, but the URD still needs to be in conduit where above ground. The SER cannot be placed underground.

 

[Jhenry1745]

I also answered your question in your other post. To not have conduit inside you'd need to use SER inside and transition via a large junction box to the URD for outside, but the URD still needs to be in conduit where above ground. The SER cannot be placed underground.

How about USE cable? I'm hoping to avoid the transition box and conduit over the entire run. Will 2/0-2/0-2/0-1 MHF carry the load over that distance without excessive power drop?

 

[pattenp]

How about USE cable? I'm hoping to avoid the transition box.

USE is not a cable, it's an insulation type. URD is USE rated and can only be used outside. There is only one option I know of for a cable that can be direct buried and run inside without the use of conduit that is Southwires PVC jacketed armorlite cable but is expensive. I think the 2/0 MHF is your best option but will need to be in conduit where exposed above ground and where installed inside. You'll be good on voltage drop with 2/0.

 

[Jhenry1745]

USE is not a cable, it's an insulation type. URD is USE rated and can only be used outside. There is only one option I know of for a cable that can be direct buried and run inside without the use of conduit that is Southwires PVC jacketed armorlite cable but is expensive. I think the 2/0 MHF is your best option but will need to be in conduit where exposed above ground and where installed inside. You'll be good on voltage drop with 2/0.

The cable will be run in conduit where it enters the building. Thanks for the advice!

 

[theoldwizard1]

How about USE cable? I'm hoping to avoid the transition box and conduit over the entire run. Will 2/0-2/0-2/0-1 MHF carry the load over that distance without excessive power drop?

I am not a professional electrician.

Even with USE-2, I think you will still have to run it in conduit, above ground. MHF must also be in conduit above ground.

USE-2 #1 copper $1.88/ft PER CONDUCTOR

MHF 2/0-2/0-1-4 is $1.92/ft. I think it is limited to 90A, but yes, it will have a similar voltage drop.

(I don't know why this place only stocks MHF with #1 neutral and #4 ground.)

 

[pattenp]

The cable will be run in conduit where it enters the building. That is no problem.

Not only does it need to be in conduit where it enters the building, any length of it inside the building going to the service panel needs to be in conduit. If the panel is located inside on an outside wall where the conduit will connect directly to the panel where the conduit enters the building will be okay. In other words the MHF needs to be in conduit from where it leaves the ground to where it enters the panel.

 

[pattenp]

I am not a professional electrician.

MHF 2/0-2/0-1-4 is $1.92/ft. I think it is limited to 90A, but yes, it will have a similar voltage drop.

(I don't know why this place only stocks MHF with #1 neutral and #4 ground.)

#2/0 Al is 135A, not 90A. #2 Al is 90A. I don't suggest using the reduced neutral. Use 2/0-2/0-2/0-1 MHF.

If you can't find 2/0-2/0-2/0-1 MHF you can buy single USE-2/RHH/RHW-2 wire and make up your own cable. USE-2/RHH/RHW-2 is what MHF is made up from.
https://www.wireandcableyourway.com/XLP-USE-2-RHH-RHW-2-Aluminum/


*

 

[rburke65]

There is a difference between #2 and #2/0. The first one is number two. The second one is two 0's.....or 00.

 

[Jhenry1745]

Would this work?
https://www.ebay.com/itm/160664070119

According to the calculator, 1/0 wire is recommended for this length of run. I would be running it in conduit inside the building.

 

[ard]

Why no conduit?

Cost? Or philosophical issue?

 

[pattenp]

That cable is URD and is not to enter the structure. I don't know what calculator you are using but pulling close to 100A with 1/0 aluminum the voltage drop is beyond the recommended 3% max. 2/0 will be 3.3%.

What are your calculated max loads? To use 1/0 the load needs to be no more than 75A to be at 3%.

 

[mm08822]

Would this work?
https://www.ebay.com/itm/160664070119

According to the calculator, 1/0 wire is recommended for this length of run. I would be running it in conduit inside the building.

As pattenp stated above, your numbers are way off. No, 1/0 Al is no good for your situation.

3/0 AL will get you 2.8% vd
2/0 AL will get you ~3.3% assuming you ever really draw 100a on both legs.
1/0 Al is only good for 172'. You would need 1/0 Cu for <3%vd. $$$$.

"I'm hoping to avoid the transition box and conduit over the entire run. Will 2/0-2/0-2/0-1 MHF carry the load over that distance without excessive power drop?"

Yes, 2/0-2/0-2/0-1 MHF will work. You can even use 2/0-2/0-1-4 MHF - a few $ cheaper.. No need to to have any splices. Go direct from point to point. Run pvc fully inside buildings starting before you leave the earth. An LB on each end of the run will work nicely to enter the building.

Seriously consider pvc all the way. Why don't you want to protect your investment in the ground? $200 and you're done. unless you have a ready supply of select fill to place above and below the wires - and that is no guarantee.

What are your soil conditions?

And how did you get to 100A load?

 

[Jhenry1745]

The run is nearly 250' in the ground with multiple bends and a 20' steep elevation change. Running hard conduit would be a pain. Looking to minimize time and expense. Soil conditions are sandy loom with two passes under a gravel driveway where conduit would be used.

I don't see MHF widely offered in 2/0-2/0-2/0-1.

 

[Bighead38]

Imo spend the money and time now and put it in conduit all the way. You will have to worry about it way less than direct burial. Plus if you run a big enough pipe it's there in the future if you ever need to run anything else or redo the original wire. Material wouldn't cost too much and it doesn't involve much more work since your going to have to dig for the direct burial anyway.

 

[pattenp]

Get 750' of #2/0 USE/RHH/RHW and 250' of #1 USE/RHH/RHW.

 

[mm08822]

The run is nearly 250' in the ground with multiple bends and a 20' steep elevation change. Running hard conduit would be a pain. Looking to minimize time and expense. Soil conditions are sandy loom with two passes under a gravel driveway where conduit would be used.

I don't see MHF widely offered in 2/0-2/0-2/0-1.

What does multiple bends mean? Are they hard turns or can you bow the conduit or put several lazy kicks in 20' of conduit to steer it?

Sandy loam is a good start.

Don't worry about getting 2/0-2/0-2/0-1. The Oldwiz already provided you with a link and pricing for 2/0-2/0-1-4 <<<<This is all you need.

 

[pattenp]

Not so fast on suggesting a #1 reduced neutral. The OP needs to know the calculated 120V loads to determine if a reduced neutral is okay.

 

[mm08822]

Not so fast on suggesting a #1 reduced neutral. The OP needs to know the calculated 120V loads to determine if a reduced neutral is okay.

He needs more than 70A actual load on one leg and only one leg before it is a problem. You would have to plan that very carefully to make that a problem. It's really a non-issue with alternate buss stabs.

 

[Jhenry1745]

Do I need to use 4 conductors? I have read that the separate ground wire was not needed if there was no other connection (water pipe) between the house and garage.

 

[pattenp]

You need 4 conductors. The equipment ground is now required.

 

[mm08822]

Do I need to use 4 conductors? I have read that the separate ground wire was not needed if there was no other connection (water pipe) between the house and garage.

Yes you need 4 wires. An equipment grounding conductor must be run separately from the grounded conductor. nec article 250.32

 

[Jhenry1745]

He needs more than 70A actual load on one leg and only one leg before it is a problem. You would have to plan that very carefully to make that a problem. It's really a non-issue with alternate buss stabs.

Then perhaps I don't need 100 amp service? I have a 4 post lift (15 amps), 120V welder (20 amps), compressor (15 amps), all of which could theoretically all be running at the same time, plus 12 4' LED ceiling lights and other electric power tools. I figured it might be a good idea to over design the system for possible future additions, but maybe I am being over zealous.

 

[Jhenry1745]

Yes you need 4 wires. An equipment grounding conductor must be run separately from the grounded conductor. nec article 250.32

Thanks for clarifying!

 

[mm08822]

Then perhaps I don't need 100 amp service? I have a 4 post lift (15 amps), 120V welder (20 amps), compressor (15 amps), all of which could theoretically all be running at the same time, plus 12 4' LED ceiling lights and other electric power tools. I figured it might be a good idea to over design the system for possible future additions, but maybe I am being over zealous.

That's why I asked before - how did you determine 100A?

For all of the work involved to provide a feeder to the garage, a larger feeder is pennies in incremental cost.

You need to do a load calc of current and possible future loads specifically running simultaneously and balance that against the value of a few extra $$ for a larger feeder. Maybe you can drop down a size or two on the feeder.
What's the plan for heat?

What ever you do, you only want to do it once!

 

[wyliesdiesels]

SMH

25 comments about wire sizes and were just now talking about load calcs.

I bet 100a is overkill for the OP which means all these wire size comments were a waste of time.

Best to ask about loads in the beginning.

 

[Jhenry1745]

That's why I asked before - how did you determine 100A?

For all of the work involved to provide a feeder to the garage, a larger feeder is pennies in incremental cost.

You need to do a load calc of current and possible future loads specifically running simultaneously and balance that against the value of a few extra $$ for a larger feeder. Maybe you can drop down a size or two on the feeder.
What's the plan for heat?

What ever you do, you only want to do it once!

Heat will be via a 75K BTU Modine gas unit.

 

[Jhenry1745]

SMH

25 comments about wire sizes and were just now talking about load calcs.

I bet 100a is overkill for the OP which means all these wire size comments were a waste of time.

Best to ask about loads in the beginning.

The 100 amp requirement was predetermined and I believe within reason considering the equipment that will be used as well as projected future use. That is why it was not included in the original question. I'll be sticking with 100 amp service and I do not see the previous comments as a "waste of time". I appreciate everyone's input.

 

[wyliesdiesels]

The 100 amp requirement was predetermined and I believe within reason considering the equipment that will be used as well as projected future use. That is why it was not included in the original question. I'll be sticking with 100 amp service and I do not see the previous comments as a "waste of time". I appreciate everyone's input.

Predetermined by whom?

Did they use load calcs?

How many people working in the shop?

HVAC/AC?

Electric heat?

Large welder? Large plasma cutter (which requires air at the same time)

Large compressor motor?

Most people tend to way over exaggerate their service requirements... we see it every week on here...

The loads you listed do not come close to 100a... a 120v welder and lift that is momentarily used are not big loads.

A ~3HP compressor is not much either...

If this is a one man shop, then 100a IS overkill...

 

[Jhenry1745]

Predetermined by whom?

Did they use load calcs?

How many people working in the shop?

HVAC/AC?

Electric heat?

Large welder? Large plasma cutter (which requires air at the same time)

Large compressor motor?

Most people tend to way over exaggerate their service requirements... we see it every week on here...

The loads you listed do not come close to 100a... a 120v welder and lift that is momentarily used are not big loads.

A ~3HP compressor is not much either...

If this is a one man shop, then 100a IS overkill...

I have listed the actual amp ratings on some of the equipment above. Like I said, my question was regarding the type of direct burial cable to use for 100 amp service. I'm a one man show, but it is still possible that I may have to cycle the lift while the welder is powered up and have the compressor kick on unexpectedly which could result in a total 50 amp draw, not counting lights and heater. And what if I decide to add a refrigerator or microwave to the equation. From what has be mentioned here, it may be wise to spend a few extra dollars for the added peace of mind.

 

[ard]

The run is nearly 250' in the ground with multiple bends and a 20' steep elevation change. Running hard conduit would be a pain. Looking to minimize time and expense. Soil conditions are sandy loom with two passes under a gravel driveway where conduit would be used.

I don't see MHF widely offered in 2/0-2/0-2/0-1.

Schedule 40 PVC isnt 'hard' conduit- generally you can snake it around if you have a bit of radius. Elevation changes are immaterial. The protection it gives, and the ability to use cheaper wire that you can run into the structure to either splice or continue makes it a good option.

You should price out whatever you finally decide on versus 2" PVC and 3+1 individual conductors (ground is smaller). I had a 325 ft run a while back- a 1000ft roll worked nicely, cheaper way to buy as well

 

[Jhenry1745]

Schedule 40 PVC isnt 'hard' conduit- generally you can snake it around if you have a bit of radius. Elevation changes are immaterial. The protection it gives, and the ability to use cheaper wire that you can run into the structure to either splice or continue makes it a good option.

You should price out whatever you finally decide on versus 2" PVC and 3+1 individual conductors (ground is smaller). I had a 325 ft run a while back- a 1000ft roll worked nicely, cheaper way to buy as well

Thanks ard. I'll do that.

 

[wyliesdiesels]

I have listed the actual amp ratings on some of the equipment above. Like I said, my question was regarding the type of direct burial cable to use for 100 amp service. I'm a one man show, but it is still possible that I may have to cycle the lift while the welder is powered up and have the compressor kick on unexpectedly which could result in a total 50 amp draw, not counting lights and heater. And what if I decide to add a refrigerator or microwave to the equation. From what has be mentioned here, it may be wise to spend a few extra dollars for the added peace of mind.

Adding up amp ratings is not how a load calc is done.

Welders are limited draw and yours is 120v so half the wattage that a 240v unit could be. And the welder will not draw full current or even 1/8 of its current rating when its powered on and only idling.

Your heater is gas so that is inconsequential and a refrigerator(~6a) and microwave(~15a?) are not high draw. LED lights will be somewhere between what the heater motor draws and the refrigerator. All 4 are 120v so not a lot of power.

Remember, since you have mostly 120v equipment, and if you run 100a service, you will have 200a worth of 120v power minus whatever the lift is pulling. Thats a LOT of power- 24,000 watts.

You dont have any high draw 240v equipment which would change the equation. Lifts are limited duty cycle and current.

 

[pattenp]

SMH

25 comments about wire sizes and were just now talking about load calcs.

Sometimes I find it best to just answer the question at hand and not go down another road. But I did ask about load cals back in post 12. But didn't get a response.

 

[pattenp]

Jumping back to mm08882 #13 post. Go with the 2/0-2/0-1-4 MHF or if you decide to do conduit the whole way then check out XHHW-2 wire and get pieces of the above sizes. XHHW-2 is not direct bury and may save you a little money to help cover cost of conduit.

 

[mm08822]

Sometimes I find it best to just answer the question at hand and not go down another road. But I did ask about load cals back in post 12. But didn't get a response.

Likewise in #13.

 

[Jhenry1745]

Sometimes I find it best to just answer the question at hand and not go down another road. But I did ask about load cals back in post 12. But didn't get a response.

I agree and didn't feel it was necessary to go down that road. However , Based on the results of the NEC electrical load calculator here www.zenfixit.com/load_calculations.shtml, my current requirements are relatively low, less than 20 amps. However, I want to leave the door open for future expansion of my operation and the possible acquisition of additional manpower and equipment such as an additional lift, 240v welder, larger compressor, etc. It appears some here want to deter me from over-estimating the requirements. Is there a down side to doing so?

 

[Jhenry1745]

Jumping back to mm08882 #13 post. Go with the 2/0-2/0-1-4 MHF or if you decide to do conduit the whole way then check out XHHW-2 wire and get pieces of the above sizes. XHHW-2 is not direct bury and may save you a little money to help cover cost of conduit.

Thank you for you help pattenp. I appreciate your input!

 

[mm08822]

I agree and didn't feel it was necessary to go down that road. However , Based on the results of the NEC electrical load calculator here www.zenfixit.com/load_calculations.shtml, my current requirements are relatively low, less than 20 amps. However, I want to leave the door open for future expansion of my operation and the possible acquisition of additional manpower and equipment such as an additional lift, 240v welder, larger compressor, etc. It appears some here want to deter me from over-estimating the requirements. Is there a down side to doing so?

There are a few ways of looking at that comment, each with valid concerns.....
It is undersized and wont meet initial or more likely future needs.
It is so grossly oversized that you are wasting hard earned $.
You have lots of $ and you WANT it, regardless of whether you NEED it.
It is a hard spec. Deliver it. No questions asked.

I've seen all of these scenarios installing whole house gen systems. Understanding the end user's needs/expectations usually takes some work. Sometimes like pulling teeth.

Trying to understand where your situation fits into the above determines what really needs to be worried about and what can be dismissed. When you are frequently called upon to deliver a functioning end-product, you typically ask lots of q's upfront. You initially ignored those additional information requests. Its all about understanding your true needs and a solution that fits.

 

[ard]

I agree and didn't feel it was necessary to go down that road. However , Based on the results of the NEC electrical load calculator here www.zenfixit.com/load_calculations.shtml, my current requirements are relatively low, less than 20 amps. However, I want to leave the door open for future expansion of my operation and the possible acquisition of additional manpower and equipment such as an additional lift, 240v welder, larger compressor, etc. It appears some here want to deter me from over-estimating the requirements. Is there a down side to doing so?

Good question

This comes up in virtually EVERY 'what size wire' thread.

My personal belief is that once you know the ACUTAL load calcs/needs, and you still want to upsize it for some tangible, rational reason- go for it.

If it is jsut some emotional, 'I've got a 200Amp he-man garage" motivation, you are just being a bit ignorant. (I am NOT saying this is you, to be clear.)

As long as the owner understands and can rationalize the current, planned and future loads, then it is reasonable.

Your post which I quoted, IMO, tends to fall into this category.

Oh, while we are at it. You might consider a 3/4" conduit or two in that trench. Once for low voltage (telephone, cable, Internet) and one for switching. (Lighting, pump, whatevers...). Even if empty for a year or two, I guarantee that if you every do need it, you will think you are the smartest guy in the world.