sub panel install for a noob

[matemike]

Hello folks,
I plan on making a sub panel in my shop coming off one of my two main 150 amp each (300 total) panels. I am a total noob when it comes to making a sub panel, so I got a quote from an electrician to do it for $3500. Being a major DIY'er I'll just make my own cable run and call him for the final hook up to alleviate that absurd cost. I do have some electrical experience with wiring up fixtures and receptacles, but none with making a sub panel in a detached building. So that's where the electrician comes in, to make the hook-ups, I'll make the run and mount the new panel in the shop. Should be simple enough just running cold cable from point A to point B.

That being said I know I'll need to run a ground from the new sub panel to a ground rod.

Now the questions I have are so elementary that I can't even find answers on google.

First thing is that I'll only need 70 amp service out there; I would like 100 but not sure if it can be done off my 150 amp house panel. Suggestions?

Anyways, 70 amp panels are a rare find and the ones I found only have 2 spaces, 4 circuits. I'll need more than that. So could I just install a 100 amp panel having more spaces with 70 amp service going to it?
Weird thing is that 125 amp panels are cheaper than 100 amp panels; could I just use a 125 amp panel to get my power distribution in the shop whether it's 70 or 100 amp service?

What size wire do I need to get 70 amps? I figure I'll need #1 wire to get 100 amps as it is about a 250 ft run total going through the attic in the house and down the side then under a side walk and ultimately out to the shop. Everything will be in conduit.
Could I stick with the #1 wire size should I need to go with 70 amp power? I figure if it's rated for 100 amp it will carry 70 no problem.

Is it reasonable to try and pull 70 or even 100 amps off of the 150 amp main panel in my house?

I can certainly get pictures of everything later today as I'm sure those will help.

Thank you folks for all the assistance and dealing with a noob like me.

 

[sublime68charger]

have you done searches in this forum for Subpanel install's?

lots of great information.

break this down into different parts. Wire type and size you need.

size of conduit you'll need

size for your subpanel

for my off the hip advice and I'm very far from being a expert at all.

I just did a subpanel into my garage my self,

2" conduit, then get MHF feeder wire
http://www.homedepot.com/p/Southwir...ice-Entry-Electrical-Cable-28712801/202316409

then get your 125amp panel.

I could be way off as I don't have any direct knowledge? so take my advice with a a lot of salt, there be others on here to shortly to tell you how to due it correct!

good luck!

 

[pattenp]

If there was one size fits all for sub feeds to a small one man shop it would probably be to use 2-2-2-4 MHF in conduit to a 100A or 125A sub-panel fed from the main panel with up to a 90A DP breaker.

Edit: I didn't catch the distance. At 250ft you need to upsize the wire to reduce voltage drop. You'd need to use 2/0-2/0-2/0-1 MHF. That will cover you easily to a full 70A load with reasonable voltage drop. You could push it to 100A full load and still be within a tolerable voltage drop.

 

[matemike]

If there was one size fits all for sub feeds to a small one man shop it would probably be to use 2-2-2-4 MHF in conduit to a 100A or 125A sub-panel fed from the main panel with up to a 90A DP breaker.

Edit: I didn't catch the distance. At 250ft you need to upsize the wire to reduce voltage drop. You'd need to use 2/0-2/0-2/0-1 MHF. That will cover you easily to a full 70A load with reasonable voltage drop. You could push it to 100A full load and still be within a tolerable voltage drop.

Thanks,

That's exactly what I was looking for. And I actually understand it.
So could I install that 90A double pole breaker onto this 150A panel? like this
http://www.homedepot.com/p/Square-D-Homeline-90-Amp-Two-Pole-Circuit-Breaker-HOM290CP/100206837

And I guess a 100A DP breaker is out of the question? like this:
http://www.homedepot.com/p/Square-D-Homeline-100-Amp-2-Pole-Circuit-Breaker-HOM2100CP/100156187
I ask because they have 100A brkrs in stock at my HD and a 90A would have to be ordered.

So This is what I'm working with. As you can see the right panel is tapped out, but there's plenty of room on the left panel.







And thanks for the help on the wire size. The distance adds up so quick! I swear all it does is cross from the front of my house to the back of my house in the attic, down the wall then straight shot across a small area of grass to the closest corner of the shop.
I stepped it off and got 90' across the house for the attic section. I accounted for 8' up and 10' back down into the ground and I rounded that total up to 120'. Then it's 75' stepped off from that back corner of the house to the corner of the shop slab where the 2.5" conduit is already in place. And it's about 15' of conduit under concrete to the inside edge where the sub panel will be installed. So that's another 100' rounded up. That comes out to 220' rounding up, doesn't hurt to round up one more time when buying the cable so I say 250'. Although the true run might be closer to 190'-210'. Should I still go with the 2/0-2/0-2/0-1 MHF? I'll only have two 90's in the 2.5" conduit. One inside the shop where it turns up and one on the side of the house where it will be burried and turns up toward the roof eve. The attic run is straight besides the turn from the eve the the turn back to the main 150A panel.

 

[FordTruckWench]

That's quite some distance. The electricians $3500 quote likely includes a hefty amount for the cable and conduit to run that far.

Weird thing is that 125 amp panels are cheaper than 100 amp panels

The 100 amp panels are likely just 125 amp panels with a preinstalled 100A main breaker. The price is higher because of this breaker. BTW, you probably need this main breaker (detached shop, many circuits in the future). Its main purpose will be as an on/off switch, so the "higher" rating doesn't matter - your feed to this panel will be protected by the breaker at the other end in the house.

So could I install that 90A double pole breaker onto this 150A panel? like this
http://www.homedepot.com/p/Square-D-Homeline-90-Amp-Two-Pole-Circuit-Breaker-HOM290CP/100206837

Your existing panels are not Square D. While that breaker may kind of fit your panels, it isn't rated for use in them. You should install breakers of the same brand as the panel.

Also, may I suggest using the same brand panel in the shop as in the house. This will let you interchange breakers between them. Say in the future you decide to power the "Sprinkler" from the shop panel. Then you cold just move that breaker over.

 

[matemike]

Roger that. It's a Cutler Hammer panel.

So this 90A DP breaker?
http://www.amazon.com/dp/B000BLEN0Q/?tag=atomicindus08-20

Or when I googled cutler hammer breakers, this was the first one that popped up and available at my HD.
http://m.homedepot.com/p/Eaton-90-A...gclid=CPKwyPSlvskCFQ6OaQodA6UNCg&gclsrc=aw.ds

This breaker is an Eaton, but says its for use in CH type panels. Would it work?

Good catch. Thanks.

And I suppose this would be a good panel for out in the shop?

http://m.homedepot.com/p/Eaton-Cutl...eaker-Panel-Value-Pack-BR2020B100V4/100203297

 

[pattenp]

If your Cutler-Hammer is a BR type panel then use BR breakers. If you use 2/0 MHF then use a 100A and don't mess with finding a 90A. The 90A limit is for #2 aluminum.

Like this... http://www.homedepot.com/p/Eaton-100-Amp-Double-Pole-Type-BR-Circuit-Breaker-BR2100CS/202959642

 

[matemike]

Okay I'm pretty set on the 2/0 wire to have less voltage drop.
So 100A DP breaker it should be.

What's BR and how do I know if mine is BR type?

 

[pattenp]

Okay I'm pretty set on the 2/0 wire to have less voltage drop.
So 100A DP breaker it should be.

What's BR and how do I know if mine is BR type?

It should say it on the label. Look at the model#. It should start with BR. Such as..BR3030B150V2

Edit: Also read the fine print on the front of a breaker.



*

 

[matemike]

I've got a Cat. No. BR3040N200/CLB203040 on a sticker inside the box

On the BW 10k 150A breaker itself it says Cat. BW2150 , Style: 7803C08G71

Edit: all the breakers say style: BR250, BR240, BR120, BR115 etc

 

[pattenp]

No question, it's a BR.

 

[matemike]

Awesome!

Now the last technical question I promise is how do I get a wire from the sub panel to a ground rod?
I want to go through the same conduit that the 100A service comes in through, so I'm thinking I'll need to T or "Y" off of that conduit to run a wire to a ground rod. This is probably answered a million times on google and YouTube but I'm liking all this info from the GJ pros.

 

[wyliesdiesels]

The subpanel u buy may need a ground bar kit which is purchased separately.

Also, the neutral bar needs to be isolated. Make sure that its not bonded to the panel.

The MHF needs to be in conduit inside and can be direct buried but its best to run comduit the whole way.

Also, its a good idea while youre at it, to put in a smaller conduit in the trench for future communications wire such as ethernet.

Did the ECs price include trenching?

Awesome!

Now the last technical question I promise is how do I get a wire from the sub panel to a ground rod?
I want to go through the same conduit that the 100A service comes in through, so I'm thinking I'll need to T or "Y" off of that conduit to run a wire to a ground rod. This is probably answered a million times on google and YouTube but I'm liking all this info from the GJ pros.

U can either put a T in or just drill a hole in the side of the conduit.

U can use bare solid #6 and will need 2 ground rods.

 

[matemike]

The MHF needs to be in conduit inside

Did the ECs price include

U can use bare solid #6 and will need 2 ground rods.

Every elec I spoke with said the attic run did not need a conduit? None of the other wires up there have co suit (there are a lot).

The specs price included trench digging which was 1800 itself. 1700 for the rest. This has me thinking it'll be a grand just for wires and parts, so I may just dig the trench myself; but only if I rent a witch ditch because these holiday times are precious.

Why 2 rods? Never heard that. Do I run the same wire to both, connecting one then the other?

 

[Pwrgeek]

Did your construction contractor expose some slab rebar at the location of the electrical panel? If so then you would want to use that as your ground for the sub panel. Search Ufer if you are not sure.

On panel sizing the load on the wire is determined by the lower of two things. Either the main in the new panel (say 100/125 A) or the size of the breaker in the main panel that supplies it (say 90A)

One other thing. Before you buy wire and a breaker make sure you look at the spec sheet on the breaker. I've never seen a BR branch breaker that would take 2/0 wire (most of them top out at #1). Also if you do go with 2/0 prepare for a bear of a time installing it. Anything bigger than 1/0 is not a one man job to pull through conduit with ANY 90s in it.

Yours is a case where it would actually make sense to go with copper. In copper you could get away with #1 THWN. Much easier to install and not that much more expensive.


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[Crazyjake8493]

Every elec I spoke with said the attic run did not need a conduit? None of the other wires up there have co suit (there are a lot).

The specs price included trench digging which was 1800 itself. 1700 for the rest. This has me thinking it'll be a grand just for wires and parts, so I may just dig the trench myself; but only if I rent a witch ditch because these holiday times are precious.

Why 2 rods? Never heard that. Do I run the same wire to both, connecting one then the other?

Code requires 2 ground rods unless you can prove the resistance to ground of a single rod is less than 25 ohms. It's almost always easier and cheaper just to put the second ground rod in. No breaks in the wire, one continuous run from the panel to both rods.

If you have a second type of grounding electrode such as an Ufer, only one ground rod is required.

 

[pattenp]

The Cutler-Hammer 100A BR breaker should take up to 2/0 wire. If you use MHF it is a non jacketed cable and must be in conduit where inside the structure. You can use SER cable inside without conduit and transition to MHF where exiting the structure.

 

[CNGsaves]

OP . . . follow advice of GJ Sparkies WyliesDiesel and PattenP with the larger MHF aluminum END-TO-END in conduit if possible, as that will be lifetime low cost solution. For that distance, copper is lot of extra money spent that you can avoid.

If you can't run conduit across attic, then PattenP has that option covered with SER wire (aluminum) for inside house structure, then MHF aluminum buried in conduit all the way to detached garage subpanel.

Below is drawing of Subpanel wiring that shows the 2 ground rods and unbonded/isolated Neutral and Ground bar kit.

 

[pattenp]

Code requires 2 ground rods unless you can prove the resistance to ground of a single rod is less than 25 ohms. It's almost always easier and cheaper just to put the second ground rod in. No breaks in the wire, one continuous run from the panel to both rods.

If you have a second type of grounding electrode such as an Ufer, only one ground rod is required.

The continuous only applies to the electrode conductor from the panel connection point to the first rod and then from rod to rod. The electrode conductor to the second/supp rod can be connected to the first rod using a listed lug/clamp. NEC 250.53(C) and 250.70. It does not need to be continuous from beginning to end.

 

[theoldwizard1]

Every elec I spoke with said the attic run did not need a conduit? None of the other wires up there have co suit (there are a lot).

The rule say MHF requires conduit when above ground, PERIOD.

You may save some time and money by running a different type of cable from your load center (breaker panel) to where the cable leaves the house.

 

[wyliesdiesels]

Every elec I spoke with said the attic run did not need a conduit? None of the other wires up there have co suit (there are a lot).

The specs price included trench digging which was 1800 itself. 1700 for the rest. This has me thinking it'll be a grand just for wires and parts, so I may just dig the trench myself; but only if I rent a witch ditch because these holiday times are precious.

Why 2 rods? Never heard that. Do I run the same wire to both, connecting one then the other?

The other wires should be a jacketed type cable. Individual conductors and cable bundles such as MHF are not jacketed.

If u have individual conductors in your attic, then its not to code.

Code requires 2 ground rods unless you can prove the resistance to ground of a single rod is less than 25 ohms. It's almost always easier and cheaper just to put the second ground rod in. No breaks in the wire, one continuous run from the panel to both rods.

If you have a second type of grounding electrode such as an Ufer, only one ground rod is required.

Actually u got that backwards. If a UFER is installed and useable, then that is the ONLY electrode required. A UFER doesnt need to be supplemented by a grounding electrode.

 

[Pwrgeek]

The Cutler-Hammer 100A BR breaker should take up to 2/0 wire. If you use MHF it is a non jacketed cable and must be in conduit where inside the structure. You can use SER cable inside without conduit and transition to MHF where exiting the structure.

Eaton lists their 100A breakers as taking #10 - 1/0. Having shoved 1/0 in one before I think they are being optimistic. I wouldn't put anything bigger than #1 in a residential (not bolt on) branch breaker but to each his own.



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[Norcal]

If concrete encased electrode "UFER" is available then it must be used and no supplemental electrode is required.

 

[pattenp]

Eaton lists their 100A breakers as taking #10 - 1/0. Having shoved 1/0 in one before I think they are being optimistic. I wouldn't put anything bigger than #1 in a residential (not bolt on) branch breaker but to each his own.



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Yeah I see that in the Eaton catalog 1/0 is the listed max for the BR2100. I saw somewhere else it was listed as 2/0, but that was on a supplier site, so 2/0 is most likely wrong.

 

[My Old Tools]

You started out wanting 70 amp service. You are driving up your costs and work load. Go back to 2-2-2-4 MHF with a 90 amp breaker to what ever panel you want. Put it in conduit for future proofing.

 

[Pwrgeek]

You started out wanting 70 amp service. You are driving up your costs and work load. Go back to 2-2-2-4 MHF with a 90 amp breaker to what ever panel you want. Put it in conduit for future proofing.

Ops distance kills the idea of #2 AL. Even at 70A he is looking at almost 6% voltage drop. In AL at 70A he could do 1/0 AL. He could do 100A in #1 Cu.


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[wyliesdiesels]

You started out wanting 70 amp service. You are driving up your costs and work load. Go back to 2-2-2-4 MHF with a 90 amp breaker to what ever panel you want. Put it in conduit for future proofing.

@ 50a, the VD will be about 8v /just over 3%.

@ 70a, the VD will be about 11v / just over 4.6%.

#2 aint gonna cut it for good sized loads.