New Shop Project, critique my electrical plan

[jfalcs]

Hi all! My name is Josh and I am currently in the latter stages (hopefully) of planning out the work to my new shop space. I've spent quite a lot of time researching here and am now at the point where I'd appreciate some input on my plan to upgrade the electrical capacity of my shop.

First, the shop itself. Its a stick built, ~20' x 30' building, on a slab. Has a newer roof, and for its age (thinking at least 20 years) its in great shape. A few things to address but otherwise a solid, dry structure. My plans include insulating, heat/AC and of course an electrical upgrade.

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The shop is currently fed power to a 60A box via an underground cable from the house, which is slightly concerning as there is no 60A breaker in the main panel. Currently the only current draw is a refrigerator and overhead lights. I plan to disconnect this at the main once I figure out which breaker is feeding it.



Moving on, I started by calculating my potential power needs and have decided that a 100 amp sub panel would be suitable. My "perfect storm" scenario would have me running a 15A dust collector, 15A pin router (220v), 21A heater, 15A air compressor (pin router has pneumatic head) and the overhead lights, fridge, radio (20A circut). Assuming I'm pulling max amps on everything, at once thats a healthy 86 amps I'm not sure if I would ever pull all that at once, even with all that equipment running at once, but I figure for the sake of planning I should go ahead and plan for the "worst case" scenario.

With that number in mind, my plan as of now is as follows;

- 100 amp Sub Panel
- panel fed by 2-2-2-4 AL MHF, breakerd @ 90A at the main panel

I will dig a trench (straight shot) and am planning to run the entire length (about 50' shop to house) in conduit. I understand that the MHF is rated for direct bury, but I don't really see why a wouldn't enclose the whole thing seeing as I'll already be running conduit out of the ground at both ends. Thoughts on the contrary?

My understanding is that the MHF needs to be in conduit inside both the house and shop. Where I plan to enter the house I will have a 90 degree bend once inside the crawl space, roughly 10' of cable under the floor and then another 90 degrees up through the wall and into the main panel. Can I splice in some sort of SER cable once inside the house to avoid having to mess with conduit in the crawl space? Same for inside the shop? Would I want a junction box in the crawl space or outside the house?

Any advice on my questions, or overall critique of my plan would be greatly appreciated.

Thanks!

 

[pattenp]

Hey there, I'm in Chesterfield.

You can transition to SER by using a large Jbox either on the outside or just inside of the structure.
Use at least 2" conduit.

Edit: I think your spot on with the 100A panel fed with 2-2-2-4 MHF on a 90A breaker.

Also where the conduit is exposed above ground if it is subject to being damaged such as hitting it with a lawn tractor you need to use Sch80 PVC conduit.

 

[jfalcs]

Thanks Pattenp

I was planning sch80 above grade and sch40 in then trench.

Good to hear that I can do an SER under the house, Was definitely not looking forward to working conduit under the house.

 

[pattenp]

I used SER for the run under my house when I ran power to my detached garage. It's definitely easier than doing conduit in a crawl space. And I really like your shop. It has good character.

 

[ez-duzit]

...- 100 amp Sub Panel
- panel fed by 2-2-2-4 AL MHF, breakerd @ 90A at the main panel...

Why a 90A breaker and not a 100A?

 

[jfalcs]

Thanks again pattenp!

Why a 90A breaker and not a 100A?

My understanding is that the MHF is only rated up to 90A, so I couldn't breaker it at the full 100A. I believe that going with the appropriate sized CU wire could get me the extra 10A but for what I'm doing, I don't think I'd need it. The extra cost savings of the AL wire is worth the 10A for me.

 

[pattenp]

As a branch/feeder circuit, #2 Al has a max amp capacity of 90A @ 75deg C. If it was the main service off the meter supplying the structure then it could be 100A. Go figure.

Why a 90A breaker and not a 100A?

 

[jfalcs]

Getting ready to run the service this weekend and had a few other questions I was hoping to get some clarification on.

Initial plan was to splice the MHF into an SER cable as to avoid having to run conduit under the house.

1) What SER cable do I need to use? Was thinking this would fit the bill, but not 100% certain. Not sure if I can buy this by the foot or not?
http://www.homedepot.com/p/Southwire-500-ft-2-2-2-4-3E-AL-SER-Service-Entry-Electrical-Cable-13102915/202316610#.UjhiEtJJOxI

2) What size junction box (will be outside both structures) would you recommend to join the 2-2-2-4 AL MHF to the SER?

3) do I need any kind of clamp where the cables enter/exit the conduit/box? Suggestions?

4) What type of connectors are recommended for joining the MHF and SER?

Thanks again for the help, looking forward to knocking this out!

 

[5mall5nail5]

Thats a cool little building - interested in seeing this happen.

 

[jfalcs]

Thanks 5mall5nail5, looking forward to it too. Been a long time coming. I've got about 90% of the details figured out, figure that's enough to take the plunge.

Hoping to get these last few bits sorted before Saturday. (also hoping the weather holds)

 

[Aceman]

As a branch/feeder circuit, #2 Al has a max amp capacity of 90A @ 75deg C. If it was the main service off the meter supplying the structure then it could be 100A. Go figure.

Only dwellings can use the chart that allows #2 AL on a 100 amp breaker. Residential shops, garages and outbuildings aren't included.

 

[jfalcs]

Would this be what I need to splice the MHF and SER condustors together

http://www.lowes.com/pd_47269-12704-770682L_0__?productId=3370326&Ntt=split+bolt&Ns=p_product_price|0

I'm assuming stick with AL connectors for AL wire?

 

[soj]

Getting ready to run the service this weekend and had a few other questions I was hoping to get some clarification on.


3) do I need any kind of clamp where the cables enter/exit the conduit/box? Suggestions?

Thanks again for the help, looking forward to knocking this out!

Where the conduit enters the box, no clamp needed, the wire is in the conduit. Where the SE cable enters the box you would need a NM/SE clamp type connector, like this or a wet location one, like this.

 

[soj]

Would this be what I need to splice the MHF and SER condustors together

http://www.lowes.com/pd_47269-12704-770682L_0__?productId=3370326&Ntt=split+bolt&Ns=p_product_price|0

I'm assuming stick with AL connectors for AL wire?

Yes, an AL rated split bolt will work. A little more expensive would be an underground splice kit like this.

I have also seen the inline setscrew splicers without the heat shrink, probably closer in price to the split bolts, and are more compact.

You asked about box size. I would guess a 12X12X12 PVC box would give plenty of room to pull wire and make four splices, but experienced electricians can better advise on the size. That may be bigger than what you need. Most boxes, metal or PVC the size you will need don't have knockouts, so be prepared with hole saws or big step drills.

 

[jfalcs]

Thanks SOJ! Yeah, got the hole saws ready.

Probably a basic question but if I use the split bolts, is heat shrink still the best thing to use to isolate everything?

 

[pattenp]

The SER you linked to in post #8 is correct and HD should sell it by the foot. Use a good quality tape to wrap the split bolts. There is a recommend way to wrap using two types of tape. I believe you wrap with cloth tape first then with vinyl tape. Do a search on the web and I'm sure you'll find what's recommended.

Edit: After looking it up it seems cloth then rubber then vinyl is recommended. Seems a bit much to me. I always use splice/reducers with shrink tube.

Thanks SOJ! Yeah, got the hole saws ready.

Probably a basic question but if I use the split bolts, is heat shrink still the best thing to use to isolate everything?

 

[pattenp]

Very true. I misspoke when I said structure.

As a side note in the 2014 NEC the chart is gone. 310.15(7) has been rewritten.

Only dwellings can use the chart that allows #2 AL on a 100 amp breaker. Residential shops, garages and outbuildings aren't included.

 

[jfalcs]

Thanks again PattenP

 

[sberry]

I would pipe it, takes bit more work up front but so does splicing. I havnt looked at 2 inch flex, this wire will go up 1 1/2 but with many turns it is a drag. Another thing,,, do no0t sweat the 86A calc, it will never see that unless you add a stick welder at the same time all the rest of that is on. My Bud has working auto garage, fed with same wire on a 60,,, never tripped.

Over the years must have put a dozen garages maybe more, all on 60,,, never ever had a call about a trip.

 

[jfalcs]

sberry, what do you mean by "pipe it"? The run should be a straight shot, with the two 90 degree elbows at the ends.

Definitely agree that the 86A is probably way over what I'll actually pull but I figure if I'm going to the trouble, might as well overdo it a bit. I suppose I could always run the 2" conduit and run 60A service, upgrade later. Honestly though, the cost of doing the larger service isn't really all that bad, certainly within my budget.

That being said, always open to advise, much appreciated!

 

[jfalcs]

So here's a question, can I just run SER for the whole run through the conduit? Or is it not rated for that? Price is the same per foot.

 

[pattenp]

SER is not rated for below ground even if in conduit. When sberry said "pipe it" that means in conduit. So he was saying to use the MHF and put it in conduit from panel to panel then no splicing is necessary.

So here's a question, can I just run SER for the whole run through the conduit? Or is it not rated for that? Price is the same per foot.

 

[jfalcs]

Thanks again pattenp, figured that was the case. I'll probably stick with splicing in the SER, no desire to mess with conduit under the house.

Picked up my sub panel, conduit and incidentals this morning but got rained out on digging the trench today. Shooting for tomorrow if the ground isn't too soggy.

Thanks again for all the help

 

[jfalcs]

So quick update, got the trench dug, conduit installed and MHF pulled. Yard looks like hell but its done. I'll install the junction boxes (went with 8x8x6) and splice the SER/MHF tomorrow.

I'll shoot some pics tomorrow, didn't finish up until it was dark.

Thanks again for the help!

 

[bjcouche]

You've already finished installing the MHF in the conduit but I thought I'd add a suggestion for others reading this thread. The MHF is conveniently found at your big box stores and that's great. However, if you are planning on doing what jfalcs did and placing the ENTIRE length of MHF inside conduit there's other options. For the same price per foot as the MHF, I was able to purchase, from a local electrical supply, at high non contractor rates, single conductor cable. They commonly sell aluminum single conductor cable with THHN/THWN insulation. When using individual conductors it's easier to pull the cables through the conduit because they aren't twisted together like the MHF is. The type I bought was called SimPull by southwire and it comes pre lubed. Also the single conductors lets you choose your conductor sizing, for example you could go with an undersized neutral and have 2-2-4-4 and be easier to pull and cheaper. Undersizing a neutral should be best done by a qualified person with the appropriate calculations though...

Brian