Wiring a load center for detached shop

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Old 12-07-16, 06:04 PM
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Wiring a load center for detached shop

Hi all. My name is Steve and I'm a newbie here.

I've decided to tackle my detached shop wiring myself. I'm putting in an Eaton 125a main lug fed from a 60a breaker in my main panel, using 2-2-2 URD. I will use a separate grounding rod at the shop. I have one 20a 240v circuit, 3 20a circuits for outlets, and 1 15a circuit for lighting.

I've attached a picture of my load center with the wires drawn in. I'd like to get some feedback to see if this is correct.

The top 2 pole breaker is 20a (30a shown), the next 3 are 20a, the bottom one 15a.
Name:  Panel_markup.jpg
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Thanks,
Steve
 
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  #2  
Old 12-07-16, 06:28 PM
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Welcome to the forums!

Nice sketch.

You must run a ground from the main panel even though you will have a ground rod (which is also required by code for a detached building).

Also, you should use a main breaker panel even though it is a sub. Code says if it takes more than six actions to disconnect all power you need a (local) main disconnect. A main breaker would serve as the disconnect. While you only show 5 breakers, the panel has room for more so you may as well deal with it up front.

Finally, you will need to remove the bonding strap between neutral and ground as this is a sub and neutral and ground are only bonded at the first disconnect (usually the main panel).

I see you show the white on the two pole breaker marked to indicate it is hot. Good!

Otherwise, looks good.
 
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Old 12-07-16, 06:35 PM
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In addition to disconnecting the neutral from the ground, you will need to connect the ground bar to the metal case of the sub panel bonding it.

While #2 aluminum is fine for 60 amps it is overkill unless the run is very long. You could use #4 aluminum.

URD also is required to be in conduit when it is not in the ground.
 
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Old 12-07-16, 07:13 PM
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I will use 2-2-2-4 URD buried. It is a fairly long run.
I will detach the bonding strap, and add a connection from the ground bus to the case.
Since I already have the main lug, could I use a 60a AC disconnect prior to it?
Modified sketch:
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Old 12-07-16, 07:32 PM
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Since I already have the main lug, could I use a 60a AC disconnect prior to it?
You could. You could install a 2 pole 60 amp Air conditioning disconnect like this: GE 60 Amp 240-Volt Non-Fuse Metallic AC Disconnect-TFN60RCP - The Home Depot but it might be hard to get #2 under the lugs or bend the wire in the enclosure. A better option would be to install a 2 pole 60 amp breaker in the panel and back feed the breaker. You will loose 2 spaces but likely not a big deal. Save the main lugs to feed another panel if needed.
 
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Old 12-07-16, 07:35 PM
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Yes, or you could use a 2 pole breaker with a hold down kit to serve as a main. A hold down kit is required when using a breaker as a main so there is no chance of the breaker coming unplugged and flopping around with live wires on it. The breaker could be 60 amps or larger since it's acting as a disconnect and the current limit protection is provided by the breaker in the main feeding the sub. That would use up two more slots, but you would still have extra.
 
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Old 12-07-16, 08:50 PM
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So you're suggesting that I put a 60a 2 pole breaker (with hold down) in say the top 2 slots on the left, then connect the black and red coming in to that breaker, which will then feed the 2 poles of the main buses to the other breakers? So effectively the current flows thru the breaker in reverse?

Great idea, but is that allowed in the NEC?
 
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Old 12-08-16, 12:25 AM
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Lightbulb

It is not just an idea. It is a let's say maybe a
'common' practice.

NEC does not prohibit it. As long as you comply with this:

This is what 408.36(D) states:
(D) Back-Fed Devices
- Plug-in-type overcurrent protection or plug-in type main lug assemblies that are back-fed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means of the panel.


However, never end with a Back Feed mismatched not tied together double pole breaker like this:

Mismatched Main Disconnect Breaker(s)


///


Finally, I have to congratulate you on how perfectly, clean look and skilled your job is. Also about how accurate and fast you was to correctly interpret the suggestions of a few details to be corrected at your subpanel regarding removing the bonding strap from the neutral bus bar, and bonding the grounding bus bar to the metal enclosure. It is gratifying to me to encounter people like you in these Forums.

You would be a great electrician!
 
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Old 12-08-16, 06:50 AM
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If this feed is running to the inside of either structure you are not to use URD. Straight URD is only USE-2 rated and has to be terminated on the outside of the structure because it does not have fire resistant insulation. You can use 2-2-2-4 MHF (Mobile Home Feeder) which is RHH/RHW-2/USE-2 rated. MHF can be direct buried but needs to be in conduit where above ground and inside the structure. THHN/THWN-2 or XHHW-2 are other choices for approved wire for inside installations.

It is a fairly long run.
Just how far is fairly?
 
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Old 12-08-16, 07:05 AM
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And yes, a backfed breaker is legal by code as long as you use the hold-down kit so the breaker can't pop off the bar.
 
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Old 12-08-16, 08:50 AM
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After reading some nightmare stories about direct burial cable, I'm thinking I'll go with 2-2-4-6 MHF in conduit. My run is about 250 ft ... paige's wire size calculator says I need 3awg aluminum. This cable is just under an inch in diameter ... is 2" conduit OK?
New sketch ... 60a main on upper right, 3 20a single pole bottom right, 20a 2 pole, 15a single pole bottom left. I've removed the bonding bar.
Name:  Panel1_wired.jpg
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I sure do appreciate all the feedback ... very important to get this right.

Thanks,
Steve
 
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Old 12-08-16, 08:54 AM
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One more thing ... I want to be sure I do the main service panel 60a breaker right. This is what I think it should be:
black to 1 pole of breaker
red to other pole of breaker
white to neutral bus
bare to ground bus

I think the ground bus is bonded to the neutral bus ... is this a problem? The box is a nqob type - bolt on breakers

Steve
 
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Old 12-08-16, 10:04 AM
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Neutral bar is not to be grounded/bonded in a subpanel. And do use 2" conduit. Also you will need 2 ground rods at least 6' apart from each other. Also at 250' using #2 Al at a full 60A will have about a 4% VD. So 60A is the max you should be pulling using #2Al at 250'.
 
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Old 12-08-16, 10:30 AM
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Yes, in the main service panel you would expect the neutral and ground buss to be bonded, just not in subpanels or anywhere else. Your description of the wiring in the main panel is correct.
 
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Old 12-08-16, 10:42 AM
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OK ... 2-2-4-6 MHF in 2" conduit, 2 ground rods 6'+ apart it is.

Thanks so much for all your input ... this has been a very good experience to be sure that I'm doing it right.

Steve
 
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Old 12-08-16, 11:51 AM
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Personally for that distance I would not use a reduced neutral cable. Do you not have access to 2-2-2-4 MHF?

Here's an online source. https://www.wireandcableyourway.com/...der-cable.html

Edit: To have a reduced neutral you need to calculate the unbalanced loads to know if the reduced neutral is sized correctly. I think it's just simpler to not reduce the neutral. The cable will be a little more expensive but not enough to take the chance using the reduced neutral.
 

Last edited by pattenp; 12-08-16 at 12:12 PM. Reason: Added more info.
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Old 12-08-16, 11:52 AM
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Thumbs up

You are doing it right, and what is always a plus you are doing an excellent up to code electrical installation!


If you can upload some pictures once the actual wiring is complete, of both the subpanel and of the 60amp breaker that is at the main panel. It will be nice to see the actual job done.


Thanks.
 
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Old 12-08-16, 12:43 PM
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pattenp, That is where I priced the cable from. The cost difference on 300 ft is only $31 ... I'll go with 2-2-2-4 MHF.

Jos Electrician, I'll upload pics when done, but it will probably be January before I finish the job ... maybe Feb.

Thanks again guys
 
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Old 12-08-16, 12:55 PM
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Be sure to use Noalox on the terminations of the aluminum. Also take care when pulling the cable to not slice the insulation at all. The slightest exposure of the aluminum conductor will corrode and fail over time. Even in conduit there will be water/moisture which aluminum does not like. Even though you'll be using 2" conduit it will be beneficial to use pulling lube. Also the conduit should be fully assembled before pulling the conductors. You hear of people putting the conduit together as they pull the cable but they run the risk of uncured glue compromising the wire's insulation.
 
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Old 12-08-16, 03:15 PM
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You can though add a pull string as you assemble. Tug on it occasionally to make sure cement hasn't dripped on it and locked it up.
 
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Old 12-08-16, 08:16 PM
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You can turn that panel 180 degrees if it make it easier to arrange the larger conductors.

That does not look like a bolt-on panel.
 
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Old 12-09-16, 03:00 PM
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This is the panel I have. The cover is removed and the base is screwed to the studs. All in/out connections will be thru the bottom of the box.
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Slightly different plan: the backfed 60a 2 pole breaker will be located top left, the 20a 2 pole (240v) top right, 15a single pole below, followed by 3 20a single pole. New sketch:
Name:  Panel_new.jpg
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For this shop, built inside my old tobacco barn. there is an 8h x 6-8w opening between rooms, and the larger room has a 10 ft ceiling. I alternated outlets on the 2 outlet circuits in the large room because I'll probably have a table saw on one and a planer and jointer on the other. the 240 is for an air compressor.
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Old 01-03-17, 08:50 AM
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I've decided to go a different route. Rather than running the power feed from the house, I will have a new service added by the power company. The supply pole is closer than the house, so the trench will be shorter (but deeper ... they require 3' depth rather than the 2' that local code requires). The main reason is that the power company will cover the first $1K of the cost when adding a new service. I still have to dig the trench, but they supply and install the wire and conduit in the trench.

So I need to add a meter base and run the supply from there to the breaker box. I'm changing the supply breaker from 60a to 100a and plan to run stranded copper THHN from the meter base to the breaker box. The distance is about 6 feet ... 1 AWG?

So for some new questions:
  1. Do I need a ground from the meter base to the breaker box, or do I just connect the breaker box to the ground rod?
  2. Does the wire from the meter base to the breaker box have to be in conduit? all 3 wires will be insulated.
  3. Do I need to add the bonding strap back to the breaker box to bond the neutral bus to the ground bus? If yes, do I need to disconnect the ground bus from the breaker box case?
  4. Since the THHN is all black, what is the proper way to indicate hot1, hot2, and neutral at each end?

Thanks,
Steve
 
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Old 01-03-17, 09:35 AM
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I suggest you check with utility to find out what the monthly minimum charge will be for the new service...you may change your mind back.

I suggest you consider adding a disconnect right under/next to meter base and then go from there to your main panel. That gives you a way to totally kill the panel without having to have the utility pull the meter, should you need to do panel work down the road. Easy and cheap to do now.

THHN must always be in conduit.

Grounding depends on whether you install the suggested disconnect or not. If you do, then ground and neutral are bonded at the disconnect and your main becomes a subpanel with separate ground and neutral buss. Neutral buss is isolated from the box, ground is not. You would run 4 wires from the disconnect, two hots, neutral, and ground.

Mark the neutral conductor with white paint, white tape, or a ring of white heat shrink. No need to differentiate the two hots. Ground will be green or bare.
 
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Old 01-03-17, 10:59 AM
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The distance is about 6 feet ... 1 AWG?
For 100 amps I'd use #3 copper THHN/THWN-2 and a 100 amp main breaker panel.
 
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Old 01-16-17, 06:53 AM
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A new service would cost $17 per month PLUS the electricity cost, so back to plan A (60a).

The 2" conduit will come thru the basement wall about 2' below the bottom of the floor joists. I want to go up the wall and then along the wall at the underside of the joists to the supply panel (~50 ft).

I'd like to keep it flush against the wall, but it doesn't seem like the MHF will bend at that tight of an angle. So maybe I need a junction box where it comes thru the wall and splice the wire in the box. Would it be OK to run 4 awg copper from the service panel to the junction box and splice to the MHF?

Or maybe I could remove several inches of the sheathing on the MHF and bend each wire separately at 90 degrees? what is the standard practice on this?
 
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Old 01-16-17, 07:41 AM
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MHF doesn't have an overall sheathing cover to remove. Use a large PVC junction box (8X8X4) and transition to aluminum 2-2-2-4 SER for the run to the main panel. The SER can be run along the bottom of the joist. Use splice/reducers to splice the SER and MHF together and tape the splices well. Install methods for SER is the same as NM (Romex). You will need a hole saw to cut the openings in the PVC box and add the needed fittings.
 
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