New disconnect vs sub-panel


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Old 01-02-08, 07:52 AM
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New disconnect vs sub-panel

Happy New Year Guys/Gals,

I have read many posts here over the last 2 months and I have formulated a project. Thanks to all the moderators for their thoughtful guideance.

I am planning on installing power to an outbuilding. The exisiting house sub-panel will be difficult to run a circuit for a "sub-sub-panel" so I want to run 2 separate disconnects. 1for house, and 1 for outbuilding. Here is my plan, please comment.

1) Run a second SEU cable from Meter to disconnect. This is additional to house SEU. So, 2 separate connections from meter. My meter will accept 2 feeds per the electric company.

2) Disconnect: 100A grounded with #6SWG copper to both ground rods that serve the house.

3) I have two options on wire from the disconnect to the outbuilding sub-panel. I would like to get several opinions on this one. I prefer to use option b and save my single wire THHN for another project.

a) Run three 2AWG copper THHN (hot, hot, neutral) and one 6AWG copper THHN (ground) in 1.5" electrical conduit buried. Ground and Neutral will be separated at the disconnect and panel. I calculated this at 33% fill so no problems with pull (damage) for fill (heat) or should I go with 2"? Can I only have black wire so can I paint or tape or etch the neutral and the ground wire to identify each wire's use?

OR

b) I have some 4 wire cable that I could use. It is stranded copper, metal sleeved. Can I run this in conduit? I prefer conduit because I can more easily identify its location.

4) If I use conduit, I will plan to have enough pull boxes along the run. I plan on having no more than 180deg between boxes. I will glue conduit before pulling wire.

5) If I use conduit, can I run RG75 and phone lines in this conduit? or run a separate .5" or .75" conduit in the same trench?

6) At outbuilding, I will have 100A panel. Should I have dual ground rods at the outbuilding as well? There seems to be a difference of opinion in previous threads as to separate ground rods at the outbuilding.

7) Does 2008 code require that ALL circuits have to be GFI in the outbuilding? If so, it probably make sence to have the disconnect breaker a GFI. Any concerns with this?


I welcome all comments and opinions as there is many ways to "skin this cat". thanks so much in advance.

Thonati
 
  #2  
Old 01-02-08, 10:06 AM
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Originally Posted by Thonati View Post
Run a second SEU cable from Meter to disconnect. This is additional to house SEU. So, 2 separate connections from meter. My meter will accept 2 feeds per the electric company.
The meter may be able to accept accept two cables ("double-lugged"), but your service may not be able to accommodate the added load. For example, if your house is currently a 100A and you add a 100A for your outbuilding, you now need a 200A service drop and meter. If you already have a service drop and meter which can support the sum of the house service and proposed outbuilding service then you are okay.

100A grounded with #6SWG copper to both ground rods that serve the house.
Assuming the new cable run entirely outside and underground the new disconnect needs to be at the outbuilding not at the meter. The main breaker in the outbuilding panel is a sufficient disconnect.

Run three 2AWG copper THHN (hot, hot, neutral) and one 6AWG copper THHN (ground) in 1.5" electrical conduit buried. Ground and Neutral will be separated at the disconnect and panel. I calculated this at 33% fill so no problems with pull (damage) for fill (heat) or should I go with 2"?
The 1.5" conduit is fine; 2" will be easier to pull. It's up to you. If you come directly off the meter, you only install hot-hot-neutral, no ground. If you want a four wire feeder, then you'll need to install a main panel at the meter location and feed both your house panel and outbuilding panel as subpanels which may require a reconfiguration of your house panel. Depending on your actual service and meter, this may be the preferred option anyway.

Can I only have black wire so can I paint or tape or etch the neutral and the ground wire to identify each wire's use?
The neutral wire may be marked on each end with white paint or tape to identify it. The ground must be green, bare or have a green stripe along its entire length. Many inspectors will allow green tape or paint on the ground conductor, but you should check with him first since it does not meet the letter of the code.

I have some 4 wire cable that I could use. It is stranded copper, metal sleeved. Can I run this in conduit? I prefer conduit because I can more easily identify its location.
You would need to identify the exact type of cable. I generally recommend against installing large cables in conduit as it can be extremely difficult to pull in and out if necessary.

5) If I use conduit, can I run RG75 and phone lines in this conduit? or run a separate .5" or .75" conduit in the same trench?
Low voltage conductors may not run in the same conduit as power. What I usually recommend is to bury the power conduit at 24-30" deep, backfill 12", then install a low voltage conduit, then backfill to grade. This way you dig one trench and get two conduits with enough separation to avoid interference.

At outbuilding, I will have 100A panel. Should I have dual ground rods at the outbuilding as well?
Ground rods are required at the outbuilding because you have a panel. If it was only a single circuit, ground rods would not be required.

Does 2008 code require that ALL circuits have to be GFI in the outbuilding?
If the outbuilding is a garage/shop/etc then GFCI protect all 120V receptacles. Lighting and 240V receptacles or hardwired appliances do not require (nor is it advisable to use) GFCI protection. Previous versions of the code would not require GFCI protection for inaccessible receptacles like those behind a large appliance or on the ceiling for a door opener.
 
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Old 01-02-08, 12:02 PM
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How do I use 1 disconnect for both house and outbuilding? I think this would be the best option now that you mention it. I need to re-wire the house for the disconnect anyway so why not add the outbuilding to it. I like the way you think.

Is there a 100A double pole breaker that can accept (2) #2AWG copper wires on each (1) leg?
 
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Old 01-02-08, 01:24 PM
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The most common way would be to replace the existing meter base with a 200A meter/main combo box. You would then install two 100A double-pole breakers and feed the house panel from one and the garage panel from the other.

This makes the new outdoor meter/main panel your "main" and the other panels all subpanels. You would then need to ensure that grounds and neutrals are separated in both subpanels and that you have a four wire feeder to each subpanel.

As described, this is a pretty big job. It is basically a service upgrade considering the amount of stuff that gets replaced or re-done in the process. You would also need to do a load calculation and make sure that 100A is still adequate for your house; many homes would need to bump up if they've installed A/C, spa, etc. Generally this type of job should be done an electrician.

***

The other option is to use a double-lugged meter base, which is a 200A meter that can accept two 100A service cables. One runs to the house MAIN breaker, one runs to the garage MAIN breaker. You have two main panels on one service. In this case, you have three-wire feeders to each panel and the grounds and neutrals are bonded at the panels.

There are some technical complications with this method because you want to install low-voltage wiring between the buildings. When a three-wire feed is used, there can be no other metallic pathways (phone, tv, water pipes) between the buildings. Someone else may be able to comment some more on the code ramifications of this method.
 
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Old 01-02-08, 01:53 PM
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Thanks ibpooks,

This is not my house but my cabin just north of you in Glennie Mi. I will perform a load test next time I am up there. I do not have A/C, or Spa. I have a 12 amp fridge, 10amp dishwasher, 10 amp furnace, basic lights, vacuum, TV, computer and a few fans. The pole barn will be for lights and a few power tools and maybe an air compressor.

I do not want to make this too complicated by re-doing the meter base. So how does this sound.

1) SEU to 100A disconnect panel grounded onto 2 interconnected rods.
2) Run 2 100A circuits (3 #2AWG H-H-N and 1 #6 AWG Ground). 1 circuit will provide 100A to cabin and the other will provide 100A to the pole barn. The 100A main will protect the SEU and incoming mains.
3) Subpanel in pole barn grounded with additional 2 rods near the pole barn.


If I have any issues with the pole barn useage tripping the main disconnect then I will downsize it to 60amps. I cannot forsee anything more than a garage door opener, lights and maybe a small air compressor. I will not have electric heater or welder in the pole barn.

Thanks for all your help.
 
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Old 01-02-08, 02:44 PM
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Originally Posted by Thonati View Post
This is not my house but my cabin just north of you in Glennie Mi.
Ought to be some good snowmobiling this week.

I will perform a load test next time I am up there. I do not have A/C, or Spa. I have a 12 amp fridge, 10amp dishwasher, 10 amp furnace, basic lights, vacuum, TV, computer and a few fans. The pole barn will be for lights and a few power tools and maybe an air compressor.
Sounds like 100A for the cabin and the barn is plenty enough for your needs. I think a 60A subpanel to the barn is certainly sufficient. I would run 1.5" or 1.25" PVC conduit and install #6-6-6-10 THWN with a 60A breaker; or use #6/3 UF-B cable directly buried. If you choose to install the conduit you could always upgrade to 100A at the barn if ever needed. You will save a small fortune buying the #6 copper instead of the #2 that will will most likely never use to its full capacity.

I do not want to make this too complicated by re-doing the meter base. So how does this sound.
How exactly is it set up now from the power company drop to the main panel? What are the approximate distances involved?
 
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Old 01-02-08, 04:57 PM
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Thanks ipbooks for all your help. Your advice is certainly appreciated by me for all your posts, not only today but previous posts that I have read.

I hope to get up there next weekend (MLK Day) and ride over to Mio and then over to Grayling. It depends on my back but more importantly Momma's back.

I called Consumers and they do not have the incoming wire size in my account file so I have to call back to talk to a "specialist" tomorrow.

Basically, I have a transformer at the pole to step it down to 120V AC per leg (overhead line). (Although I rarely get over 110V AC. I wonder if I can get a discount hehehe).

It looks like (but I cannot confirm) that it is 1/0 AU from the pole. It is tied into the leads that are 1/0 AU SEU. I wired the meter myself and they just tied into it at the head of my mast and installed the meter globe.

I have the standard DTE/Consumers meter box with H-H-N. From there I have 1/0 AU SEU going into my house panel. The pole to meter is about 100', the meter to house panel is 2'.

I have some #2 AWG THHN copper anyway. The pole barn will be no more than 100' from the disconnect. I will have to buy a bare #6 AWG for the ground. Can I put a bare #6 AWG in conduit?

I have been working on bringing everything up to code (neutral & ground separated, 2nd ground rod, water pipes grounded, bubble covers on all outside recepticles, inter-connected AV smoke alarms). All I need to do is put Arc Fault breakers and an outside disconnect. I have been doing this on weekends as I go.

I plan on installing 2 more ground rods at the pole barn as well along with a complete panel.

I calculated the voltage drop (#2 AWG, 100' one way, 100 amps) = 3.8 volts or 3.2%

So I guess then having 1 disconnect with 2 100A circuits is the way to go. Or maybe I will buy a 60A breaker on sale and save the $25 and go to the bar )
 
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Old 01-03-08, 05:18 AM
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The pole to meter is about 100', the meter to house panel is 2'.

sounds like your meter socket is installed on the house, is this right?
 
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Old 01-03-08, 06:47 AM
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Yes. Meter socket is mounted on the house directly outside of the panel. So the lead from the meter into the panel is only 2'. I have plenty of room to install a disconnect direcly off the meter. Then run to the house sub panel and the pole barn sub panel.
 
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Old 01-03-08, 07:24 AM
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how many amps is you house main breaker panel

If it is a 30 pole space it is probably 150 amp service 1/0 wire

or is it a 100 amp 12/24 or 20 pole space mb panel

That would tell you the meter socket size.

If it was 150 amps you may be okay with a 60amp sub fed panel out of the main breaker house panel. You need to calculate the loads though
 
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Old 01-03-08, 09:04 AM
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The main house panel is 100A. Being a cabin, there is no A/C, spa, electric heaters or electric water heater. I do have a 50A electric range but I can change over to Propane if the load becomes too much.

Let me run this by you. (I have the #2 copper already)

1) I will install a 100A disconnect outside near the meter.
2) Separate neutral and ground at house panel, add 2nd ground rod 6' away from existing rod. I will measure the Ohms for these 2 rods to ensure compliance.
3) I will run #2 copper H-H-N and #6 bare through 1.5" conduit into the house panel.
4) Run 60A breaker with 3 #2AWG copper (H-H-N) and 1 #6AWG bare in 1.5" or 2" conduit back outside to the pole barn.
5) Run the 1.5 or 2" conduit 24" below grade, then 12" run 0.75" conduit for Phone, etc.
6) Run the conduit up the wall and into the pole barn, into another panel. Keep ground and neutral separate
7) Add 2 ground rods at the pole barn in addition to the ground back to the house panel. I will measure the ohms at the pole barn ground rods to ensure compliance.
6) Run circuits as needed from the pole barn sub-panel.
 
 

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