Help needed with DIY 200 amp upgrade

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  #1  
Old 01-25-07, 03:21 PM
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Help needed with DIY 200 amp upgrade

I am planning on upgrading my existing service from 125 AMP's to 200 AMP's. This is in a new house (3.5 years old). I am doing this because I am adding a pool and extention that will require a fair amount of power (60-80 AMP's). I also plan on adding some circuits for woodworking, etc. The existing service has the following specs.

1. Wire - aluminum with unknown size (I assume 1/0 and #2 but I am not sure)
2. Conduit - 1.5"
3. Panel - 42 slot GE with about 8-10 slots left. This is the same as the 200 AMP panel with the only execption is the 125 AMP main.
4. Meter base - I am 99% sure the existing meter base is a 200 AMP base. It is a Milbank 3R that is 4-1/8 x 11 x 15-1/2. Looking in their site only 200 AMP bases or larger have those dimenisions.
5. Ground - It looks like a #6 but I am not sure.

My plan is to do the following:

1. Wire - 4/0-4/0-4/0 aluminum. I think I can downsize the netural but I think they sell a feeder cable here that is all 4/0.
2. Conduit - I am not sure if 2" or 2 1/2" is the right way to go here.
3. Panel - Leave panel and swap main breaker.
4. Meter base - Like I said above I am 99% the meter base is OK.
5. Ground - #4 looks like the right size for this service.

My plan was to trench along the existing conduit (18" down) to the transformer. My power company says it needs to brought within 24" of the transformer. The transformer is a straight shot from the side of my house and about 75-80' away. Once that is done I was going to have the power company pull the meter and disconnect the existing service. Once that is done I will pull the new wires into the meter base, run new jumper wires from the meter base to the panel (I assume I need to do this as they will be undersized), change the main breaker and swap the ground, call back the power company to engerize the new wires.

I am am an avid DIY'er but have never changed service. I do a lot of electrical around the house. I am outside the city limits so there are no permits or inspections. My questions are:

1. Is my plan sound.
2. Is this something that I can do? It seems pretty easy but I have never done it so I can't really comment.

I appreciate any help with this.

Thanks!
Steve
 
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  #2  
Old 01-25-07, 06:57 PM
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I am not an electrician but I have done a bit of DIY trenching. Comments:

1. Trenching close to energized wires, even in conduit, sounds pretty challenging. Locators have always told me to allow 18" on either side of the markings.
2. Maybe you are trenching by hand, but with a walk-behind ditch witch, it took me about 30 feet just to get the hang of it, let alone do a good job.
3. I am guessing the existing conduit is undersized for your upgrade. Otherwise it would be convenient to re-use it.
4. Is your power company metering manual online? Or can you get a copy? That might have some good info for you, for example make sure that 18" is still deep enough.
5. Make sure you use no-ox and properly torque all your connections.
6. For my 200A UG service of about the same length, I think the local utility used 3/0-3/0-2/0 so you're in the ballpark. The metering manual probably tells you what meets spec.
7. Find somebody who owes you to do the backfilling!

Seek professional help with anything you're not sure about. Good luck.
 
  #3  
Old 01-25-07, 07:20 PM
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7. Find somebody who owes you to do the backfilling!***

Digging!

Seek professional help with anything you're not sure about. Good luck.

Great advice!!
 
  #4  
Old 01-26-07, 03:47 AM
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I didn't know there was anywhere in the US that did not have an electrical code. But what lectric said, if in doubt consult an expert. Your families lives may depend on it.
 
  #5  
Old 01-26-07, 05:20 AM
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Originally Posted by ArgMeMatey View Post
I am not an electrician but I have done a bit of DIY trenching. Comments:

1. Trenching close to energized wires, even in conduit, sounds pretty challenging. Locators have always told me to allow 18" on either side of the markings.
2. Maybe you are trenching by hand, but with a walk-behind ditch witch, it took me about 30 feet just to get the hang of it, let alone do a good job.
3. I am guessing the existing conduit is undersized for your upgrade. Otherwise it would be convenient to re-use it.
4. Is your power company metering manual online? Or can you get a copy? That might have some good info for you, for example make sure that 18" is still deep enough.
5. Make sure you use no-ox and properly torque all your connections.
6. For my 200A UG service of about the same length, I think the local utility used 3/0-3/0-2/0 so you're in the ballpark. The metering manual probably tells you what meets spec.
7. Find somebody who owes you to do the backfilling!

Seek professional help with anything you're not sure about. Good luck.
1. I was planning on having the utilites marked. I have had this done in the past when I installed my sprinkler system. I am going to have teh trench hand dug next to existing conduit. There is a gas line fairly close and I don't want to use a trencher. I live in Houston and labor is very inexpensive.
3. I wish the conduit was large enough. I read I may be able to fit 2-2/0 and #1 if I use copper but that is super expensive. Also I think it would be very tight. It is cheaper to trench next to the existing conduit.
4. They do have the specifications online and that is what I used. 18" in conduit is what they call for. They can be found on page 48 here http://www.centerpointenergy.com/files/106816_ServiceStandards.pdf.
5. I forgot to mention the no-ox and tourque but I was planning on that.
6. I has going to have some hired help do the backfill.

Thanks for your comments!

Steve
 
  #6  
Old 01-26-07, 05:27 AM
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Originally Posted by Just Bill View Post
I didn't know there was anywhere in the US that did not have an electrical code. But what lectric said, if in doubt consult an expert. Your families lives may depend on it.
I did mean to say that just becuase I live outside the city limits that the NEC does not apply. I was just saying I can do the work without a permit. I am the most paraniod person on the planet when it comes to doing a job correct. I did a lot of research before making my post and came here for suggestions to make sure I do the job safely and correctly. I appreciate the concern. Nothing is more important to me then the saftey of my family. When I looked at this project it not seem like a huge deal. I am really only swapping the existing service wires for larger ones. I have a lot of experience trenching and a fair amount of experience with home electric. I am not rewiring the panel or house. I think I have all my bases covered to do this safely. I wanted to get some feedback from the experts to make sure I did not miss anything critical like undersizing the cables or something like that. Thanks!

Steve
 
  #7  
Old 01-26-07, 08:01 AM
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1) The conductors between the transformer and the meter are part of the service lateral. These conductors are not sized by NEC standards, similarly the burial depth is not set by NEC standards, but instead is set by power company standards. Find out from the power company what size conductors are required.

2) In general it is poor practise to install a cable assembly in conduit. The cable assembly will be less flexible than separate conductors, and much more difficult to work with. Generally, cable assemblies _may_ be installed in conduit, but you are generally better off with suitable separate conductors.

How far are you extending this conduit? Does it go into the ground with direct bury conductors to the transformer, or does the conduit run the full length to the transformer? If the conduit is just for the last stretch from the ground into the meter, then a cable assembly is probably the way to go; if the conduit runs the full length to the transformer, then who actually finishes the run into the transformer, and who is responsible for pulling the conductors?

3) Grounding Electrode Conductor: The size of the GEC depends upon the material used and the grounding electrode, which you don't specify. If this is a water pipe electrode and a Copper conductor, then #4 is the correct size. Some grounding electrodes would permit the use of a smaller GEC.

4) You can downsize the neutral as long as it is sufficient to carry the largest imbalanced 120V load.

-Jon
 
  #8  
Old 01-26-07, 08:16 AM
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Originally Posted by winnie View Post
1) The conductors between the transformer and the meter are part of the service lateral. These conductors are not sized by NEC standards, similarly the burial depth is not set by NEC standards, but instead is set by power company standards. Find out from the power company what size conductors are required.

2) In general it is poor practise to install a cable assembly in conduit. The cable assembly will be less flexible than separate conductors, and much more difficult to work with. Generally, cable assemblies _may_ be installed in conduit, but you are generally better off with suitable separate conductors.

How far are you extending this conduit? Does it go into the ground with direct bury conductors to the transformer, or does the conduit run the full length to the transformer? If the conduit is just for the last stretch from the ground into the meter, then a cable assembly is probably the way to go; if the conduit runs the full length to the transformer, then who actually finishes the run into the transformer, and who is responsible for pulling the conductors?

3) Grounding Electrode Conductor: The size of the GEC depends upon the material used and the grounding electrode, which you don't specify. If this is a water pipe electrode and a Copper conductor, then #4 is the correct size. Some grounding electrodes would permit the use of a smaller GEC.

4) You can downsize the neutral as long as it is sufficient to carry the largest imbalanced 120V load.

-Jon
Jon,
I appreciate the help. Here are my responses.

1. I agree the power company specifies the conductor size but it was not clear in their document. I am contacting the local office to find out what they require for 200 AMP service. For grouding their document refers to the NEC.

2. That is fine with me. The existing install is 3 individual wires. I have no problem doing that. The way it is done here is the conduit runs from the meter base underground 18" min all the way to within 12" of the transformer. At that point the power company (Centerpoint) takes over. Their specification calls to leave 10' of cable bundles and stakes within 12" of the transformer. Page 28 and 29 of this doc covers it. http://www.centerpointenergy.com/files/106816_ServiceStandards.pdf. So the bottom line is I was planning on pulling the cables through the conduit and leaving it 12" from the transformer. They will bury the rest and connect it. I plan on having them come out and pull the meter and disconnect the existing wires from the transformer. I will then run my wires into the meter base and disconnect the existing wires. My meter base has 3 punchouts on the bottom so I will leave the existing conduit installed and just cut the old wires.

3. I am not sure what is meant by a waterpipe electrode but the way the existing ground is all the water pipes and gas lines are grounded to the center ground and there is ground from the panel running to a 8' rod in the ground. I was going to switch the ground going from the panel to the rod to the correct size which seems to be #4.

4. Ok.

Thanks for all the help on this!

Steve
 
  #9  
Old 01-26-07, 08:45 AM
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On the conduit depth: You appear to be required to have 18" of cover over the conduit. This means more than an 18" trench, because you have the thickness of the conduit to consider. Note also paragraph 415.3 of the POCO document: the end of the conduit must be low enough to provide 24" of cover; presumably because the conductors will be direct buried in this location.

You will need to check with the power company about abandoning the old service conductors.

By 'waterpipe electrode' I mean a metal underground water pipe that is used as a grounding electrode, differentiated from interior metal water piping that is 'bonded' back to the service. Different grounding electrodes have different requirements. Per 250.66, the GEC to a simple ground rod need not be larger than a #6 copper... I should note that a _single_ ground rod is uncommon; this is because a _single_ ground rod must be tested to determine if it meets the ground resistance requirements, but dual ground rods are permitted without testing. I suggest that you investigate your grounding electrode system more closely.

-Jon
 
  #10  
Old 01-26-07, 08:58 AM
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Originally Posted by winnie View Post
On the conduit depth: You appear to be required to have 18" of cover over the conduit. This means more than an 18" trench, because you have the thickness of the conduit to consider. Note also paragraph 415.3 of the POCO document: the end of the conduit must be low enough to provide 24" of cover; presumably because the conductors will be direct buried in this location.

You will need to check with the power company about abandoning the old service conductors.

By 'waterpipe electrode' I mean a metal underground water pipe that is used as a grounding electrode, differentiated from interior metal water piping that is 'bonded' back to the service. Different grounding electrodes have different requirements. Per 250.66, the GEC to a simple ground rod need not be larger than a #6 copper... I should note that a _single_ ground rod is uncommon; this is because a _single_ ground rod must be tested to determine if it meets the ground resistance requirements, but dual ground rods are permitted without testing. I suggest that you investigate your grounding electrode system more closely.

-Jon
Yea, my plan was to gradually get to 24" deep towards the transformer. The last 1' or so is directly burial so it does need to be at 24". I know the top of the conduit needs to be at 18" so I will trench to make sure I have the correct depth.

I am not sure the power company cares about the old wires as they won't locate and state the cables on my lot are my responsibility. I will ask them to make sure.

As far as the grounding, I need to check but I only see one ground rod. The ground from the panel connect directly to it. I do not see any other rods or connections coming off the existing ground rod. All the houses around here have the same arrangement. I find it a bit weird given we have hard clay. I will double check later to make sure I am not missing something.

Thanks!
Steve
 
  #11  
Old 01-26-07, 05:58 PM
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RE: ground... 3.5 yrs ago was different. With your changes you must come to current code. Check into it to be on the safe side, save some last minute agrivation.

Your on the right track, get all the current changes.
 
  #12  
Old 01-26-07, 07:17 PM
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Originally Posted by lectriclee View Post
RE: ground... 3.5 yrs ago was different. With your changes you must come to current code. Check into it to be on the safe side, save some last minute agrivation.

Your on the right track, get all the current changes.
Ah, I see. I will check into that for sure. We have a ton of lightning here so I would rather have the best ground possible. Thanks!

Steve
 
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