2/0 wire connected to 60A circuit breaker?

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Old 05-22-06, 10:34 PM
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2/0 wire connected to 60A circuit breaker?

A 60A double pole circuit breaker takes up to #2 wire, according to the markings on the breaker. Is there a way to connect a larger diameter wire to the circuit breaker? Would it be considered unsafe?

Thanks.
 
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Old 05-23-06, 05:12 AM
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There is nothing inherently unsafe about using conductors in a circuit at less than their ampacity. In fact, this is good design for long runs where 'voltage drop' may be an issue.

When you use larger conductors, you must meet all of the various code rules associated with those conductors, eg. sufficient size for conduit or fittings, large enough splicing devices, etc. Additionally, when the circuit conductors are increased in size you must increase the size of any associated equipment grounding conductor; normally with a 60A circuit you would use a #10 EGC, but a 60A circuit on 2/0 wire would need a #3 EGC.

For making the connection to the breaker, the common technique is to use a suitable splice and connect a short 'pigtail' of the largest wire the breaker is listed to take. The splice could be a split bolt connector, or an insulated set screw connector, or something similar. There are also lugs that fit on the end of the big cable and have a smaller 'pin' that fits in the breaker. I'd recommend the splice and pigtail technique.

-Jon
 
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Old 05-23-06, 11:43 AM
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Originally Posted by winnie
There are also lugs that fit on the end of the big cable and have a smaller 'pin' that fits in the breaker. I'd recommend the splice and pigtail technique.
The pin lugs being mentioned here are applied using a high pressure crimp tool. They make a very neat job if the panel wiring trough provides enough wire bending space. The original poster's number two ought (2/0) AWG wire needs three and a half inches between the cabinet wall and the terminal. Some supply houses will rent you the tool if you buy the lugs from them.
 
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Old 05-23-06, 11:49 AM
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These pin lugs...are they commonly referred to as a "ferrule"?(sp)
 
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Old 05-23-06, 09:06 PM
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After reading your replies, I googled for "splice pigtail." But I was still without a clue. So I gave up on using 2/0 and settled with #2 that 60A circuit breaker can take.

Now I have a new problem. I went to Lowes to buy a 70A main disconnect (the 60A circuit is the only circuit). The lug hole seemed too small for #2. The instruction inside the box specifies torque up to #4.

Is there an easy way to connect #2 aluminum wire to #4 sized hole without borrowing the high stress crimping device? I am not an electrician by training or education. Thanks.

PS: I know a full sized panel would have no problem with #2 conductors, but I have only one circuit. Pls advise.
 
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Old 05-24-06, 04:12 AM
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A 'pigtail' is simply a short length of wire that is used to actually make a connection to a device. For example, if you are wiring a circuit with multiple outlets, you might have the cable that supplies power to the box, and the cable that feeds the next outlet in the chain. You can connect the 'feed hot', the 'fed hot' and a 6" length of wire using a wire-nut, and run the 6" 'pig tail' to the receptacle.

A splice is simply an electrical connection between two or more wires. There are many different splicing devices, such as wire-nuts, split bolt connectors, insulated set screw connectors, etc.

In your application, what I was suggesting was that you connect your 2/0 wire to a suitable splicing device, connect a short length of #2 wire to the same splicing device, and then run this short length of #2 wire to the breaker.

At the disconnect box you could use the same splicing technique, or you could probably buy new larger lugs. Usually lugs just bolt on to bus bars or terminal strips.

-Jon
 
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Old 05-24-06, 05:43 AM
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Thank you for the explanation. If I can replace the lugs with larger ones, that will be my first choice. If not, I will do the splice pigtail. I didn't know they make wire nuts big enough to join #4 and #2. By the way, is it okay to join #2 aluminum to #4 copper? I will use antioxidant paste. Thanks.
 
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Old 05-24-06, 05:53 AM
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They don't make wire nuts large enough for #2 conductors. For conductors this large you need to use split bolt connectors or insulated set screw connectors. I much prefer the latter type.
http://www.nsipolaris.com/pdf/polaris.pdf

Forgive me if I sound insulting, but from your various basic questions I wonder just how much background you have, and are quite concerned that you make not know some important details and not even know to ask if they are problems. Could you possibly describe your entire project, describing the components that you are using, where and how cables will be routed, etc?

-Jon
 
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Old 05-24-06, 07:33 AM
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[They don't make wire nuts large enough for #2 conductors. For conductors this large you need to use split bolt connectors or insulated set screw connectors.]

Thanks for the pictures. That's exactly what I was gooling for. Now I know what to look for.

[Forgive me if I sound insulting, but from your various basic questions I wonder just how much background you have, and are quite concerned that you make not know some important details and not even know to ask if they are problems.]

No, you are not insulting at all. I have no background in electrical wiring. My only experience was house wiring as a volunteer at Habitat for Humanities and a branch circuit I added to my attic. I am a metallurgist by training.

[Could you possibly describe your entire project, describing the components that you are using, where and how cables will be routed, etc?]

Most gladly. It's a new service, pump only, 60A. I will set up meter base, main disconnect, pump panel, and a pump.

The meter base and main disconnect will be at the entrance of my property. The pump and the pump panel will be 100' away from the meter base.

For meter base and main disconnect, I will set up two 4"x4" pressure treated posts and put 2"x8" PT boards across. The utility company gave me the meter base. For the main disconnect, I will buy a 70A Square D Homeline 3R 2/4 panel. I will put a 60A double pole circuit breaker as the disconnect.

For the pump panel I will buy Square D Homeline 100A 3R 3/6 panel. I will put one 20 or 30A double pole circuit breaker for the pump (have not decided on HP yet) and one 15A single pole for timer. I will eventually use all the 60A as my need of irrigation grows. The panel will also be mounted on 4"x4" PT posts.

Between the main disconnect and the pump panel will be 2-2-2-4 aluminum direct burial cable. 2' depth.

#4 bare copper and 5/8" x 10' grounding rod will be used for grounding the meter base.

#4 copper THWN will run between the meter base and the main disconnect through a short grey PVC conduit. The same PVC conduit will cover 2-2-2-4 aluminum cable on the posts. By the way, how deep should PVC conduit extend below grade? I read 18" somewhere in 2002 NEC. And what size do I need for 2-2-2-4?

Once I get the county approval, utility company will come out and put an underground cable to the meter base.

That's all my plan is about. If I did not go through the details of the project, it's because I do not know the details. I will post questions here as the project goes.

I am doing this project by myself because I could not find a contractor who is willing to travel far out to my property that's in the middle of cow pastures. Or wait for months.

Thank you for your advice in advance.

PS: Someone suggested 4"x6" posts if the installation is permanent. And it is. I am considering this upgrade.

I plan to complete the project during the Memorial day weekend.
 

Last edited by puter; 05-24-06 at 08:10 AM.
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Old 05-24-06, 08:18 PM
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It sounds like you've been doing your homework. This is my rough evaluation. Other may have comments.

At your 'service entrance' you are actually required to have 1 grounding electrode that tests to less than 25 ohms, _or_ 2 grounding electrodes. Most electricians simply use two grounding electrodes rather than test. The electrodes need to be at least 6 feet apart. 250.56

At your 'detached structure', you are again required to have grounding electrodes. If there is a metal well casing, this might serve. Even if you use ground rods, you should still bond the metal well casing.

The required minimum depth for direct burial cable in your location is 24". 300.5(A) Protection needs to extend 18" down. 300.5(D)(1)

I cannot tell you the size conduit to use, however the method for calculating this is as follows: find the largest diameter of the cable that you are using. Multiply this number by 1.38, to give the minimum inner diameter that you can legally use. Look up a table of conduit dimensions and pick one that is larger. (The actual requirement is that the cable, treated as a single circular wire of its largest diameter, can take up no more than 53% of the conduit cross section.)

You may need to screen the backfill going into the trench to protect the cable if there are any rocks or materials that might cut into the cable.

Direct burial aluminium runs the risk that a slight nick in the insulation will cause the conductor to fail over time. For most users, we recommend using conduit so that you can pull the conductors out. However given that this is an agricultural situation, digging a 100 foot trench is probably pretty easy for you, so the is probably less of an issue.

You may or may not want to provide a convenience receptacle at your panel.

-Jon
 
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Old 05-24-06, 10:29 PM
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Thanks for the long reply.

I checked 2002 NEC, chapter 9 table 1. For more than 2 wires, 40% is allowed. 1 1/4" will do. By the way, table 1 does not apply to a piece of conduit used for protection of wires from physical damage. It applies only to continuous conduit. So, technically, any sch 80 pvc conduit large enough to hold the cable will do. The diameter of 2-2-2-4 is 0.944" and 1 1/4" PVC is 1.25" ID. I will settle with 1 1/4". (NEC is fun!)

Thanks for checking 18" extension below grade for me.

I bought two 100A panels, one for main disconnect and the other for pump panel. The lugs are larger than 70A panel and accept #2 wires. No pigtails! No specialized crimping tool!

I think I need a separate panel for the pump for I will add second pump down the road.

The drawing I got from the utility company shows one grounding rod, 5/8" x 10'. Considering we have a high water table and soil is water saturated several feet under, I will follow their drawing and use 1. But I will drive an additional grounding rod at the pump.

I will keep an eye on the backfill dirt, and be careful not to nick the insulation. Thanks for the warning.

I think I now know all I need to know (Scary thought!)
 
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Old 05-25-06, 03:50 AM
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Originally Posted by puter
I checked 2002 NEC, chapter 9 table 1. For more than 2 wires, 40% is allowed. 1 1/4" will do. By the way, table 1 does not apply to a piece of conduit used for protection of wires from physical damage. It applies only to continuous conduit. So, technically, any sch 80 pvc conduit large enough to hold the cable will do. The diameter of 2-2-2-4 is 0.944" and 1 1/4" PVC is 1.25" ID. I will settle with 1 1/4". (NEC is fun!)
This is an 'angels on the head of a pin' comment, since you are correct about chapter 9 table 1 not applying for raceway sections used for protection of a cable. But for future reference: when you run a cable in a conduit, you must treat that cable as a _single_ wire with the same diameter as the largest diameter of your cable...in your case of a single cable in a conduit, that gets you to the '1 wire' 53% column. Additionally, the actual ID of conduit is different from the nominal ID, since it is the _outer diameter_ that is standardized, and different types of conduit have different wall thicknesses. 1-1/4"SCH 80 has an ID of 1.255"; 1-1/4"SCH 40 has an ID of 1.360"

I would be careful to double check that the cable easily fits through any fittings used to mount the conduit to the boxes.

Good Luck!

-Jon
 
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Old 05-25-06, 06:09 AM
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Thank you for bringing up "fittings." I have been thinking about conduit only. You already showed me that I don't know all I need to know.

I may have to go up to 1 1/2" conduit because of fittings. I will have to make one more visit to Lowes. Thanks.
 
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