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Thread: House sub-panel replacement questions.

  1. #1
    DIY Junior Member romumok's Avatar
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    Default House sub-panel replacement questions.

    Hello all.
    I got some questions regarding sub-panel replacement but first a background. Sorry if is a bit long. House build in 1947, mixed of old wiring (no ground, cloth type insulation) with some romex and THNN wires. Original service panel is from Federal Pacific. Sometime in 1980ís house got remodeled and addition was added and a new service with meter panel was added outside of the house (Eaton style main breaker 100A..GE brand??) The original FP panel became a subpanel inside the house. The FP panel is being fed by 30A breaker from the outside panel. Looking at the wires at the outside panel it seems that these are 8 AWG wires which seem ok for the 30A breaker. EMT conduit attached outside wall with approx 25ft length before entering in the house by some type of 6 x 6 Jbox in the attic.
    Since the issues of FP panels and the mess with illegal wirings, I would like to replace it first then change all the wiring through the whole house to be per the current code. Planning to pull homeowner permit and do the wiring myself.

    My plan is to get a 100A Eaton CH or Murray panel to replace the FP subpanel. The sub-panel breaker at the service would be 70 or 60A. The original feeding conduit will be abandoned or removed. Instead of going up and sideways along the wall, it is planned to start from the bottom of the service panel for about 4 feet then go inside the house and reach the subpanel through the craw space.
    Here my questions:

    1- Is 6 AWG wires enough for 70 or 60A or should use 4 AWG? Not sure at this point. Estimated run lengh of 20-25 feet.
    2- If I understood, romex NM wire not allowed in conduit. THNN or similar only. Romex wire ok on craw space by itself and properly attached. How can I go from wires in a conduit (outside 4 feet ) then go inside the house in the craw space without a conduit? If this is not allowed, do you recommend running the wires with grey PVC conduit from panel to panel?
    3- Is 1Ē conduit ok for 6 or 4 AWG ie. 3 wires plus bare ground?
    Thanks in advance.

  2. #2
    Electrician ActionDave's Avatar
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    6AWG romex is only good for 50 amps.

    You can put romex in conduit but it is a royal pain. Better to set a junction box and splice the wires in conduit to the romex in said box.

    1" conduit would be ok for 6 or 4AWG if you use a properly sized equipment grounding conductor.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    1- The ampacity of the conductors would depend on what type of cable or raceway you install. Are the conductors or cable passing through insulation? This would also make a huge difference. Neither size conductor you mentioned here is large enough for the breaker you mentioned
    2- Non-metallic cable or romex if you please can be installed in a raceway but it can’t be installed in a raceway on the outside. Non-metallic cable can’t be installed outside for any reason.
    3- It depends on which type conduit you choose and the type of conductors you choose.

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    DIY Junior Member romumok's Avatar
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    Thank you all for your insight. I have still a lot to learn. The conductor will not be passed through insulation. The craw space is not insulated. We have mild weather here, but it doesn’t hurt to add insulation later.
    It seems that I am over reaching about the size of the breaker. Right now is sub is being fed with a 30A in the service panel. As far as the loads, should be pretty low since all the major appliances (excluding the refrigerator, and microwave oven) are being fed by the service panel and not the sub. So, I should do a load audit to see if I really need 60 or more amps in the sub panel. Perhaps 50A is more than enough.
    Let’s say that I am running romex in the craw space, I could run it below the joist and secure them every other joist. If this is a non code compliance, I can drill the joist and feed the romex. Which way the appropriate? what is a raceway? Is a open metal or plasic chanel?
    Just thinking for the 4’ outside section. Can I use romex, strip out the outside sheathing of the required length for that section then the un-striped will be at the craw space. Am I crazy in thinking this? Please advice.
    Last edited by romumok; 10-13-2011 at 09:00 AM. Reason: added microwave oven

  5. #5
    Electrical Contractor/Instructor jwelectric's Avatar
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    A raceway is something in which conductors are installed for protection such as Rigid conduit, EMT (which is not a conduit) PVC, Metal Wire Way, so on.

    No the sheathing cannot be stripped from NM cable and then installed in a raceway (conduit).

    One rule I stand pat on is if you donít know what you are doing it is better left to someone who does.

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    DIY Junior Member romumok's Avatar
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    Thanks, for the clarification. For sure I appreciate your recommendation to call a pro if its gets too much to handle (at least I know when to raise the white flag). If I decided to to have someone else handle it, at least is a good intellectual workout for me. At this point I am willing to run EMT or PVC from panel to panel with THNN wires to be safe. Will post the total Wattage usage later.
    One more question for now. As you know, I am also planning to replace and clean all the messy wiring through the whole house. I know that it may take several days to do it. After installing the new subpanel and running the new feed wires, can I put a temporary j-box to tie between the new romex and the old wiring to provide power to some of the outlets?

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    DIY Junior Member romumok's Avatar
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    Update: The total load of the subpanel is 35A based on the excel worksheet that is found at Mike Holts website. I also did the whole house and my current service panel of 100A has plenty capacity (total of 73A). In any case based on your inputs a 6AWG conductors plus a 40A breaker should satisfy the load demands.

    As for my last question, please disregard it. It is really stupid from my part. I realized that is better to leave the circuit OFF until it gets the old wires replaced than rig something that is not approved and unsafe.

    I am still trying to see if there any other option of running THNN/THWN conductors between the panels. What about SER type(copper) cable for this application? As far as I understand, the specs from Southwire is sunlight resistant. So, it seems that it can be exposed outdoor.
    Thanks.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Yes SE-R will be alright to run for the entire circuit. As for you last question about a “J” box that would be up to the inspector and one that I will not address.

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    DIY Junior Member romumok's Avatar
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    JWelectric,
    Thank you for your advice. I appreciate your patience. I think I still need a small section of rigid conduit from the main service; run it down with a LB box to protect the conductors before reaching the crawl space.
    Last edited by romumok; 10-14-2011 at 04:22 PM. Reason: correction from EMT to rigid conduit

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by romumok View Post
    JWelectric,
    Thank you for your advice. I appreciate your patience. I think I still need a small section of rigid conduit from the main service; run it down with a LB box to protect the conductors before reaching the crawl space.
    Nothing wrong with doing it like this just don't strip off the sheathing
    Last edited by jwelectric; 10-15-2011 at 05:16 AM.

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    DIY Junior Member romumok's Avatar
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    I understand.
    thanks

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