Twin 50AMP outlets in outbuilding 130' away.

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  #1  
Old 11-07-15, 09:53 AM
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Twin 50AMP outlets in outbuilding 130' away.

What is the best way to add two NEMA 6-50 outlets to an outbuilding 130' away? I have had a very mixed bag of advice so far!

The outlets are needed to run two electric kilns in an outbuilding and need to be usable at the same time without a serious voltage drop, the recommended wire size for up to 100' is #4 each. The main supply breaker panel is outside but the through lugs have already been used to go inside to the main breaker panel a further 30' away.

So should I put a sub panel next to the main supply breaker and then use two supplies with #3 cables, or should I try 2-2-2-4 off the main supply breaker (though I don't know how to do that if the through lugs are already used) and put a sub panel in the outbuilding? Also what conduit size should I be looking at for any of the options?

Obviously the 2-2-2-4 would give me a Neutral at the building, but is that big enough to run 100amps at 130', and how do I wire it into the main supply breaker with the through lugs used?

The twined #3 option doesn't give me a Neutral but it isn't needed in any expansion plans so isn't that important, the outbuilding already has a regular sized supply for lights and 110 receptacles that isn't readily upgrade able. But if I do that what size conduit is allowed for two 50amp outlets and what size Earth needs to be run?

Any help would be greatly appreciated.
 
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  #2  
Old 11-07-15, 09:56 AM
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Since you can only have one supply to a building on one system you need to look at adding a feeder and subpanel.

You also need to see if there is enough capacity in the service for the added loads. Do a demand load calculation.
 
  #3  
Old 11-07-15, 10:07 AM
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IIRC, per the NEC, you can't have more than 1 circuit in a separate structure without a sub-panel. An electrician should be along before too long and they can give you definite answers to all your questions (and correct me if I'm wrong).
 
  #4  
Old 11-07-15, 10:09 AM
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OK so that would be the 2-2-2-4 route, but is that the right size and what size conduit do I need for that?

Does that mean I should also move the current outbuilding supply to the new subpanel and how do I connect a new feed to the main supply breaker box if the through lugs are already used?

I did amp meter checks with all the current house AC's, pool pumps etc on and there is a lot of supply capacity.
 
  #5  
Old 11-07-15, 10:13 AM
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But where does the subpanel location need to be? Is it on the main building with individual breakers or is it on the outbuilding with the breakers, the crux of the question is that it can be done both ways, but which is the 'correct' way? Further, if there are two dedicated subpanels on the main building are they both allowed to service the outbuilding?

Thanks both of you for your help so far.
 
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Old 11-07-15, 10:25 AM
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if there are two dedicated subpanels on the main building are they both allowed to service the outbuilding?
No, as stated you can only have one feed. The subpanel will be installed in the outbuilding. If there is currently a feed to the out building it will need to be abandoned.

All loads in the outbuilding will need to be supplied by that subpanel. That means the new subpanel must have enough capacity for not just the kilns but everything in the building. You may need a 150 amp or greater feed to the outbuilding. Even if you have an all gas home that would be difficult if you main panel is 200 amps. What are the actual amps the kilns draw? What other loads do you have in the barn? That will tell us if a 100 amp subpanel will be enough.

You'd be looking at a minimum of 2/0 aluminum for a 150 amp feed. (Copper would be 1/0 but a lot more expensive.) If the local electric company allows it a separate meter may be the better solution especially if your house has a 200 amp or less feed.
 
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Old 11-07-15, 10:54 AM
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The outbuilding has very little other power usage, just a couple of LED strip lights and a double 110 receptacle, so very low amps.

The kilns draw 48 amp and 45 amps but the need to run them both together is not crucial, also, for what its worth, they are constantly switching loads and only draw full currently continuously towards the end of a firing. Until this latest move they were both run off one outlet (at different times :-) ) but the new location physically separates them by enough to make that not ideal so the twin outlet option was mooted, and it is turning into the predictable ever expanding nightmare.

So that implies a 125amp sub panel would be sufficient for the outbuilding? At 130' does that allow for 2-2-2-4 copper feeder ($700 of wire) or do I need to pull 2X #1 for the hot legs and 2X #2's for neutral and ground ($1,300 of wire)? And how do I attach feeder wire of that size to a main panel with the through lugs already used?

The main building is a 200amp supply and I did amperage checks of the house in a standard draw situation at 40amps.
 
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Old 11-07-15, 11:26 AM
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Using aluminum direct burial mobile home cable would be a cheaper.
 
  #9  
Old 11-07-15, 11:56 AM
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That is a good point, but most of the run has to be above ground, so inside a conduit, is direct burial alu allowed to be run in plastic conduit for overheating reasons?

Whilst I am happy to go as far as I need to do this right one thing kilns are very susceptible to is low voltage, they don't get up to full temperature if the voltage drop is too low. Worst case scenario I spend a lot on cable and it doesn't do the job!

So far I have learnt that I need to amalgamate the two supplies to the outbuilding, for that a 125 amp sub panel on the outbuilding is good. I need a four cable supply to accommodate the 110VAC. That sub panel needs a dedicated ground rod as it is a separate building. Does that mean the Neutral and Earth are bonded in the sub panel also, specifically because it is a separate building?

So, what feeder cable size do I need for a 125amp sub panel 130' away, what conduit size does that need, and how do I attach that feeder wire to the main supply box when the through lugs are already used?

Many thanks for all the help so far..........
 
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Old 11-07-15, 12:44 PM
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If I use 4/0,4/0,4/0,2/0 direct burial feeder (thanks for that pointer! $574) the question becomes about the ground rod and Earth arrangement of the outbuilding.

Do I need a dedicated ground rod and are the Neutral and Earth bars in the sub panel bonded because it is a separate building? Or are they unbonded and rely on the main building earth for grounding?
 

Last edited by privatebydesign; 11-07-15 at 01:01 PM.
  #11  
Old 11-07-15, 01:47 PM
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That is a good point, but most of the run has to be above ground, so inside a conduit
How are you going to run conduit above ground?

You need at least one "x8' ground rod at the subpanel. You need a separate bonded ground bar in the panel. All grounds go to it. Most panels do not come with a ground bar so you will have to buy and add one. The neutral bar is isolated from the panel any bonding screw or strap is not used.

If you have more than six breakers in the subpanel you need a disconnect at the subpanel so a main breaker panel is a good choice. The main breaker acts as a disconnect. Even if you don't plan to use six or more breakers a main breaker service panel kit is usually cheaper than other panels especially taking into account it includes an assortment of branch circuit breakers and others usually don't.
 
  #12  
Old 11-07-15, 02:17 PM
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Along the eaves of the main building and then the out building. There is only a 40' gap between the actual structures but the orientation of them and the position of the main connect panel on the main building necessitates the length of the run.

All the rest sounds great, a lot of common sense! Thanks!

Effectively it is a 'new structure' supplied by the main house instead of the utility company.

So I end up with two nagging questions:-

1/ As this is effectively a 'new building/structure' don't I just need a three wire feeder cable? Two hots and a neutral as the earth is taken care of with the new outbuilding grounding rod, so 4/0,4/0,2/0, not a 4/0,4/0,4/0,2/0 feeder?

2/ How do I connect that feeder wire to the main breaker panel when the through lugs have been used to go to the interior main breaker?

Many thanks.
 

Last edited by privatebydesign; 11-07-15 at 02:50 PM.
  #13  
Old 11-07-15, 03:16 PM
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1/ As this is effectively a 'new building/structure' don't I just need a three wire feeder cable?
No, You need four. Ground and neutral are only connected together at the panel that has the first breaker. At all other points ground and neutral must be separate.
How do I connect that feeder wire to the main breaker panel
It must be connected to a breaker. An unfused feed is not allowed. Have you looked at http://www.doityourself.com/forum/el...-diagrams.html
 
  #14  
Old 11-08-15, 07:40 PM
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OK, thanks for that, the Sub Panels diagrams made it clear.

Two questions.

1/ What could you ever use a pass through lug for if not a sub panel?
2/ What size feeder do I need to run a 125amp sub panel 130' away?

Many thanks for all your help!
 
  #15  
Old 11-08-15, 08:27 PM
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If the subpanel was close enough you might be able to use the lugs per the tap rule. Understanding the Rules for Feeder Taps

2/0 aluminum minimum so the 4/0 cable would be fine. One thing to note if the mobile home cable isn't dual rated it can not enter a building.
 
  #16  
Old 11-08-15, 08:49 PM
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Yet again, many thanks!

Would 4/0-4/0-2/0-4 Alu be suitable for the feeder?

I believe the 'Outside feeder tap of unlimited length rule [240.21(B)(5)]' covers my installation. Understanding the Rules for Feeder Taps

And the fact that the feeder does not enter either structure covers that aspect.

I can't thank you enough for the help you have given me for this project. I am a marine engineer/captain by trade and whilst I have done many generator installs and panel rewires on boats for AC and DC systems, the scale and scope of this project is a completely different area from my expertise.
 
  #17  
Old 11-09-15, 09:38 AM
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Would 4/0-4/0-2/0-4 Alu be suitable for the feeder?
If you use this feeder you could connect it to the feed-through lugs in the main 200 amp main breaker panel. It would be protected by the 200 amp main breaker. This isn't part of the tap rule.
 
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Old 11-09-15, 01:34 PM
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Thanks casual joe,

That had been a hope and I had thought I could do that, but the main breaker panel feed through lugs are already used going off to the main interior house breaker panel.

It also seems, looking at the forums, there is a lot of confusion on taps, as in the actual cable tap kind, taps/through lugs that form part of the actual bus bars in the boxes, and taps/twinned lugs that are used before the main breaker.

So just for interest I have this lined up:-

A/ 125 amp main breaker panel with 12 outlets on the outbuilding.
B/ An 8' x 5/8" grounding rod for that new sub panel.
C/ Two 60 amp 2-pole breakers one each for the 6-50 receptacles for the kilns.
D/ Enough room to incorporate the other low amp circuits for the out building.
E/ Separate the N and E bars in that new sub, the E goes to the new grounding rod and back to the supply panel on the house. The N only goes back to the house supply.
F/ 4/0-4/0-2/0-4 Alu for the feeder direct buried 24" with conduit down to 18".
G/ A 200 amp main breaker panel with a replacement 150 amp main fuse on the house supplied via a 150 amp breaker from the main feed panel that is currently full and the through lugs are used. I use the through lugs on this second 200 amp panel (converted to 150 amp) because there is no way to connect 4/0 cable to a regular breaker, the only breaker in this panel is a 15 amp supply for an outside pump.

I am pretty happy up to G, wherein I realise I might attract some criticism, nobody enjoys that but I am open to alternative solutions!

As always, many thanks for any input.
 
  #19  
Old 11-09-15, 02:31 PM
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If the lugs are unused on the 150a panel, yes, that would be okay.
 
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