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# Wire size for large shop lighting

#1
05-18-16, 11:36 PM
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Wire size for large shop lighting

Thank in advance for the help

I am wiring up my shop. It is a pole barn that is 50x90 with the front 50x50 being the shop and the back 50x30 being a storage / animal pen area. The power comes in from a main pole to a sub panel (no breaker) in the 30x50 about 10 feet from the back wall of the shop.

I am wiring the lights but due to the run length having some issues. The total run of the lights will be approximately 140 feet ( 10' from panel up to the ceiling , 10' over to the shop, 50' to front of shop , 10' down to switch, 10' back up to ceiling, 50' back down the shop through the lights.) I was planning on running 12 ga wire but with that run length the voltage drop will be significant and the wire size calculators on line say 8 or 10 ga wire calculated with a 5% drop. 10 ga will work but the circuit with 4x lights will be maxed out. Not sure of the ballast draw but simple math on the lights is approx 2 amps ( 6x bulb fixture = 40w per bulb x 6 = 240W/120V = 2 amps so 4 lights will be 8 amps with two rows I will be at 16 amps.
Already planned on 3x rows of 4 on separate circuits Problem is even worse with plugs as need to provide 20 amps at end plug so Volt drop is even worse and 8 ga wire is what shows up with 5% drop Thought about adding sub panel in middle of barn--- helps with plugs not not really lights as distance is still about the same.

Main power is being provided via Romex from the panel in attic but the inside will be conduit and THHW--- again bigger wire in this stuff is expensive.

Question:
1) Is 5% ok and will more Volt drop is that dangerous
2) 10 ga seems overkill here / expensive / difficult to work with-- 8 ga even worse
3) Am I missing something how could I do this with 12 and be SAFE.
4) All ideas helpful at this point

Note: Live in very Rual Alaska so calling an electrician to even come here if they would come is super expensive.

Thanks

#2
05-18-16, 11:43 PM
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The power comes in from a main pole to a sub panel (no breaker)
I don't understand what you mean. Is this the first panel the power company service is connected to? If so it isn't a subpanel. Do you mean it is a main lug panel? A main lug panel can only have six circuits.

#3
05-18-16, 11:49 PM
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Are these multivoltage ballasts...... like 120-277v electronic type ?
If so..... consider running 240v to the lights for half the current draw.

#4
05-19-16, 01:41 AM
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The power comes from the transformer to a pole outside with the meter and a 200A breaker then runs underground about 75-100 feet to the barn where there is a main lug panel. Currently only a few circuits hooked up for a few lights in the back of the barn.

I am thinking hard that what needs to happen is to put a 100A or 125A breaker in this panel and tie it into a sub panel midway in the shop area (approx) 45 feet. This would give me 125A in the shop and still allow me to run a few circuits for lights and a few plugs in the back of the barn.

Thoughts.

PJmax-- thanks for the reply I was thinking the same thing and looking into that option as well.

I am using the Southwire calculators. Is it ok to applythe 5% volt drop to these circuits? When you go with three sometimes it upsizes the wire.

Oh and by the way I am not under code restrictions way out here in the middle of nowhere BUT i would like to do things right as I believe this helps with resale and also assist with fire prevention.

#5
05-19-16, 07:02 AM
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The "main panel" is the box on the pole under the meter with the 200 amp breaker set. From there you need a 4 conductor feed (includes a ground wire) to the barn. At the barn you need a master switch, either in the first panel there or before a lug panel if that is first (these are technically subpanels although the NEC does not use that term).

You should have less than six percent voltage drop from the pole to the light fixtures. If you really wanted to, you could compute the voltage drop from the pole to the lug panel, then from the lug panel to a sub-subpanel midway in the shop area, then from that panel to the first light, then (minus the amps or watts consumed by the first light) from the first light to the second light, etc.

Almost nobody does all of those calculations, preferring instead to take the upsized wiring result that the Southwire or other brand voltage drop calculator app delivered, and go with that.

Three percent voltage drop from the first barn panel to the light fixtures was suggested because you did not figure out the voltage drop from the utility pole to the first barn panel.

#6
05-19-16, 07:54 AM
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Allan--- are you saying that even if I do not put in another sub panel that I need a master switch (i.e. breaker) at the barn as well. To be clear I thought that the 200 amp breaker at the pole was there to protect the wire leading to the barn. Then WHEN I put in another sub panel I would put in a 100 or 125 amp breaker in the the LUG panel in the back of the barn to protect the #1 wire that is powering the mid shop sub panel.

Thanks for the reply. I am going to explore the 240 volt light option, and since a sub panel is fairly cheap to install at that distance I most likely will do that just to reduce wire size as much as possible and stay in the 3% volt drop part of the calculators.

#7
05-19-16, 08:34 AM
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The breaker inside the building is required as a means of disconnect.

#8
05-19-16, 03:58 PM
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If the lug panel (here, the first panel in the barn) has more than six slots (could hold more than 6 breaker handles) then the barn needs a master disconnect switch. This need not be a breaker but does need to be able to handle the incoming power (here, 200 amps).

If and when you put another subpanel in the barn, then you would of course feed it by putting an appropriate sized breaker set (here, 100 or 125 amps) in side slots of the supra panel (here, the lug panel).

#9
05-19-16, 07:51 PM
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This need not be a breaker but does need to be able to handle the incoming power (here, 200 amps).
Not true. Yes, the feeder must be 200 amp rated because of the 200 amp breaker at the pole, but the actual disconnect at the panel can be any size as long as it doesn't exceed 200 amps. That being said, a 200 amp disconnect or breaker does make the most sense.

#10
05-19-16, 11:58 PM
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Thanks for all the help. I will fix the breaker or disconnect inside the barn when I put the new panel in. Most likely will just buy a panel with a 200 amp breaker and then move the current one in the barn up stream and use it as my sub panel.

What would you suggest for the sub panel in the barn. 100A or 125A or more. Keep in mind this is not a commercial shop and for now I am not even serious hobby out of it. I plan on using it for some wood working... not major 30A tools as of yet. Of course will have a compressor in it most likely at least a 30 amp 60 or 80 gal model unless i find a deal on a bigger one. A welder. I have a radial arm saw, 110V table saw and a ShopSmith. Heat will be done by oil heater unit, no AC (remember Alaska) --Oh and lights... most likely looking at the 240V versions to try and keep wire size down for the runs.

I have never really understood how you can put more than 100A worth of breakers on a 100A service.

#11
05-20-16, 12:53 AM
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I have never really understood how you can put more than 100A worth of breakers on a 100A service.
You aren't using all the circuits to capacity at the same time. If you were so inclined you could have a circuit breaker for every receptacle in your home. You'd have 400A of circuit breakers but the same exact load as you'd have with a 100A panel.

What's important is not to have more than 100A of load on a 100A panel.

#12
05-20-16, 12:55 AM
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I have never really understood how you can put more than 100A worth of breakers on a 100A service.
Actually normally in a residence the total of the breakers could be a 150a or more because none of the circuits run at the full amps of the breakers and some at times have no load on them at all.
What would you suggest for the sub panel in the barn. 100A or 125A
Look for "kits" they are the cheaper way to go because they also include in the price several branch circuit breakers. They probably sell more 100 amp main breaker kits so they will be cheaper. You will in most cases also need to buy and install a ground bar.

#13
06-14-16, 05:44 PM
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thanks for all the help on this one but I have another question.

The early post tell the dimensions of the barn so I will not go into that again.

I have decided that the best thing to do is to put in a sub panel or two. Due to the cost of running a raceway for nearly 150 feet and the cost of THHN single copper conductors I am thinking to feed the panels I could just use SER cable. Either aluminum or copper. Aluminum is cheaper BUT it is aluminum.

I checked with a supply house and they have COPPER SER cable 2/2/2/4 and they are telling me that will work for 100 amps of service. I originally looked at aluminum SER cable 1/0 - 1/0 - 1/0 - 2 and according to the code you must use the 60 degree C table. I would assume that copper SER cable would be the same. Also it will be in the wall and attic under insulation. COPPER SER 2/2/2/4 is rated at 95 amps for 60 degrees and much higher at the 75 and 90 degree. and aluminum 1/0 SER is rated at 100 amps at the 60 degree.

The design would be 100 amp breaker in main panel with SER to subpanel #1 (approx.) 45 feet. Then 100 amp breaker in sub panel #1 to sub panel #2 approximately 100 feet. I realize that I do not really need two 100 amp panels and looking at reducing the second one based on the load but the question still is the same just smaller cable. Reason for doing this is to basically reduce the long runs for lighting and circuits on the other side of the shop and will also give flexibility with conduit runs based on the location with in the shop and will reduce conduit cost.

QUESTION:
1. Thoughts on using the copper SER in this setting much like romex and using the 2/2/2/4 and still pulling 100 amps with it. the code allows for an upsize of breaker since 95 is not standard. I would think I would be OK to do this design just would like some other thoughts.

2. Aluminum is cheaper should I just go with Aluminum SER and cut cost and use the anti oxidizer and ensure the lugs are snug or spend the money and go to copper. Copper is about double the cost.

#14
06-14-16, 07:12 PM
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I would save the money and install aluminum.

#15
06-14-16, 10:29 PM
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Going back to the issue of having more circuit breaker capacity than main CB capacity...I have a 200 ampere service (200 ampere main CB) yet I have over 800 amperes worth of circuit breakers. I seriously doubt I have ever had more than 100 amperes total load and probably never exceeded 75.

#16
06-15-16, 12:21 AM
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Furd I plan to test mine out when i get it all set up and just see. going to run everything at one time just to see what my load would be. Should be a good experiment ....If I ever get this monster finished.

Hoping someone will chime in with some details on the SER cable issue. I am trying to get that accomplished this weekend so I can start to put up ceiling... moving around up in my attic after ceiling is up is going to be considerably more difficult.

On another note is there a good calculator out there for how to size a sub panel. I have found several for residence but this being a shop I did not know if it was about the same. It is a hobbie shop much like a garage just very large...2250 ft2 so the potential is much greater in the long run. I think my second sub panel could be sized a little smaller thus saving money.

Unless someone disagrees or has a better way I was going to run a residential calculator on it with the known other loads put in as appliances to get the overall sub panel #1 service. Then run it again with only the second sub panel known loads to size that one... the only thing with that is the whole square foot thing will get calculated twice unless i cut it in half on both of them ... which is a thought.... I have learned a lot about electrical and sometimes i wished interior alaska just had an electrician cause i am tired of planning and figuring ... I just want to build and put things together.

Thoughts on both the SER and sub panel would be appreciated.

I have a +1 for Aluminum SER

#17
06-15-16, 06:07 AM
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Sub-panel sizing is easy. Simply add up everything powered from the sub that might possibly in use at any particular time. If you have no intention of ever having a second person working in the shop then you take the largest load plus any lighting plus the starting load of anything like an air compressor or dust collector that might start automatically.

If you think that maybe, someday, you might have a second person running machinery in the shop then you have to take the two largest loads, any lighting and then any automatically starting loads. For three people working take the top three loads and the others as already listed. Always use this maximum load when figuring the loads on any panel prior to the sub.

I can't help you with the SER as I have never worked with it.