4/0 cable undergrnd run to subpanel?


Old 09-28-01, 06:54 PM
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Not sure which size main meter panel to use. have 4/0 copper cable to run to a shop and a Mobile 325' away. Want to have PG&E read main meter on property line. Have 2" sch40 for run not sure if I need one or 3runs of 4/0 to buildings and then divide the load between the two structures. Any Sugestions?
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Old 09-29-01, 04:19 AM
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Service entrance conductors.

The language below is from the 1996 NEC because that is easier to quote as I have an electronic copy. This rule was not changed in the 1999 code.

Number of Service-Entrance Conductor Sets.
Each service drop or lateral shall supply only one set of service-entrance conductors.
Exception No. 1: Buildings with more than one occupancy shall be permitted to have one set of service-entrance conductors run to each occupancy or to a group of occupancies.
Exception No. 2: Where two to six service disconnecting means in separate enclosures are grouped at one location and supply separate loads from one service drop or lateral, one set of service-entrance conductors shall be permitted to supply each or several such service equipment enclosures.
Exception No. 3: A single-family dwelling unit and a separate structure shall be permitted to have one set of service-entrance conductors run to each from a single service drop or lateral.

You can run one set of conductors and tap them off to the two seperate buildings. You may have a problem with PEPCO over the two inch conduit size. You can make that none of their business by installing a service disconnect at the meter location but then you will need a four wire feed to the buildings and 325' of Equipment Grounding Conductor is not a lightweight expense. Since the ampacity of the 4/0 copper THHN is 260 amperes you should run #4AWG copper Equipment Grounding Conductor. I base this on the assumption that you upsized the service conductors to compenste for voltage drop and you would therefore upsize the EGC proportionately.
Old 09-29-01, 01:37 PM
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Marica56 wrote:
Thanks Tom! The main disconect will be off the transformer to my main (meter). I am then responsible for the 325'run of 4/0. When I looked at my present panel it has 3- 2/0 cables from the transformer but only about 50'. I was told many things by the Wholesale counter clerks. I did not know how to calculate the power loss for the distance so I quessed 4/0 would work. I am having trouble seeing the run from the main breaker panel to my 200amp subpanel. I think I have to place 4- #4/0 cables in conduit to the subpanel (200amp shop) then place cable undergrnd to the mobile which has a 125amp panel. Can I use 2/0 for the grounding instead of 4/0 copper and what is 4AWG? I am not sure what a grounding conductor is. I wired my present house for solar so the wire is larger. I did not do the panels. I will have a contractor wire up the panel. I am just trying to same some on labor. This is all new for this gal. I am very visual and I know I am having trouble seeing the needed setup.
Old 09-29-01, 03:21 PM
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Hold the phone guys we may have a special condition involved in this system.

Hornetd, either you missed a vital part of his post or I am miss reading this post. From what I am picturing that marcia56 has is an estate with both a shop building that is stick built and a mobile home service. If this is true, the way you answered would only apply if the meter is placed on the property line, then a service disconnect is installed at that property line and making the shop as the second building as you discribed. I suspect the power company will require that service disconnect at that meter location, therefore you would be right in powering that stick built shop. Then I am reading into what is said in this post that a 200 amp panel is in a mobile home that also must be powered. If this is so then we must refer to article 550 to serve power to that mobile home with a mobile home disconnect within 35' of that mobile home and with a four conductor feeder including an insulated equipment grounding conductor between that mobile home service disconnect located within 35' of that mobile home and within sight of that mobile home. We might want to confirm my suspicions to be right and if so then refer to 550-23 of the NEC that has been changed between the 96 and 99 NEC.

Maria56, is this true that your plan involves serving power to a mobile home and also a separate stick built shop?

Old 09-29-01, 10:02 PM
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Yep, shop is stick built and tiny (330 sq ft) - mobile about 1260.
Old 09-30-01, 01:31 AM
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A couple of questions come to mind.

Are you planning on having a disconnect on the utility pole?

If so, are you planning on having one disconnect at the utility pole, or two?

Are you planning on running a four wire feeder, or three wire feeder to each building?

Are you using a direct burial wiring method, or will you run PVC conduit the entire way?

Answering these questions will help us help you.

Enjoy your day!
Old 09-30-01, 04:38 AM
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We have a lot of if ands and buts on this subject. While S1nuber's questions need answered to get where you need to go we really need to give you a jump start on what you really want before we get committed any further from here. We need to stay in the planning stage for a while and answer questions like S1nuber asked before you buy or install any material. Problem is I read in your post that you may have already installed the 4/0 cable on the property. How was this 4/0 cable installed? Is it is conduit and what type of cable is it? What initials are on the side of the cable?

While you are coming back on what you already have done check with your Utility supplier and ask them if they have the new technology to read electronically by phone, cable, infrarred reader, etc. allowing the meter to be mounted on one of the structures and the Utility to read the meter remote from the road. This shoud affect how you design your project. Keep in mind that if you mount the meter on the structure the Utility may obsorb a lot of the cost involved in getting the wire to the meter. Most Utility Companies limit their secondary runs to 250'. If the distance is over that they install a ground transformer running primary to the area where the structures are thus limiting the secondary lengths.

Do some research with the Utility company capabilities, and what they will do. Then also tell us how far the shop is from the Utility power and how far the mobile home is from the Utlity power and between the shop and the mobile home.

This should get us to the same point where we can grow in plans and options from there.


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