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Thread: Wiring Questions For Small Bath Remodel

  1. #1
    DIY Junior Member bosscogg's Avatar
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    Default Wiring Questions For Small Bath Remodel

    Hi all, first time poster here. Gotten lots of good advice through the search function, but I've finally hit a wall. And man, what a wall.

    I'm remodeling a small bath and have upgraded the existing fixtures and added a couple more. Previously there was a ceiling light and a medicine cabinet with integrated lights and single outlet, all fed by a single circuit that appears to be 40 amps. I say "appears" because the only way I can kill the power to that bathroom is by flipping a 40a breaker in the main panel. This also kills power to several outlets in other rooms that I know of, and likely others that I don't. There is a sub panel in the house, but none of those breakers affect this particular bathroom. So as far as I can tell, this room is on a 40a circuit. Can this possibly be correct, or is there something I must've missed? My house is almost 80 years old, and it definitely shows in the crazy variety of wires in the attic.

    Clearly I'll need to get this bathroom on its own circuit(s), but how many and what amperage? It now has an LED can in the shower stall, a fan/ light combo in the ceiling, and a vanity light controlled by a single 15a gfci outlet/ switch combo at the sink. As I understand it, bathroom outlets now require dedicated 20a circuits, though there seem to be exceptions (such as when the circuit feeds nothing but the particular room). Does this negate my plan to use the single 15a outlet/ switch? Because also as I understand it, you can attach a 15a outlet to a 20a circuit, but only if there's more than one. That isn't the case here, as my plan only includes a single outlet. Short of adding a duplex outlet or sourcing a 20a outlet/ switch (which doesn't appear to exist in the style my wife wants), is there any safe workaround to this requirement? And further, am I able to wire any/ all of the other fixtures into this circuit as per the exception I noted above? Running an additional circuit is not a big problem, only added work and expense I hope to avoid if at all possible.

    Whew. I'm asking a lot, I know. If anybody's still reading this, thanks for your time and any guidance you might provide.
    -Dell

  2. #2
    DIY Senior Member Reach4's Avatar
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    I think you want to find the other sub panel.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Today's code requires a bathroom to have a GFCI circuit for the outlet(s) and be 20A. It can also feed the lights in the room.

    If those things are on a 40A circuit, ALL wiring should be sufficient for 40A, and I doubt that's true! This is a safety (and code) issue. For example, it would be hard to get the wire size required for a 40A circuit to fit onto a 15 or 20A receptacle or switch!

    FWIW, I find the need for more than one duplex receptacle in the bathroom. Charger for my toothbrush, shaver, and a couple of other things keep all of my outlets full pretty much all of the time. I've thought about expanding it to add another!
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member bosscogg's Avatar
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    Quote Originally Posted by Reach4 View Post
    I think you want to find the other sub panel.
    I get what you're saying. I mean, this simply doesn't make sense. Thing is, after 9 years here I'm confident there is no other exposed panel...perhaps some ancient who-knows-what buried in a wall somewhere? Circuit mapping by a qualified electrician is definitely in order.

    Quote Originally Posted by jadnashua View Post
    Today's code requires a bathroom to have a GFCI circuit for the outlet(s) and be 20A. It can also feed the lights in the room.

    If those things are on a 40A circuit, ALL wiring should be sufficient for 40A, and I doubt that's true! This is a safety (and code) issue. For example, it would be hard to get the wire size required for a 40A circuit to fit onto a 15 or 20A receptacle or switch!

    FWIW, I find the need for more than one duplex receptacle in the bathroom. Charger for my toothbrush, shaver, and a couple of other things keep all of my outlets full pretty much all of the time. I've thought about expanding it to add another!
    The wire is ungrounded 12g in a woven sheath, so clearly not rated anywhere near 40a. There's something else in the system I'm just not catching. However, good to hear I can run other fixtures in the room on a new circuit. We have a main bathroom where all the charging, hair drying, etc. takes place, and all I've ever plugged into this back bath in all these years is a shaver. Still, we probably won't be here forever, so surely some expandability will be appreciated by the next guy.

    Thanks for the responses, guys.
    -Dell

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Is it 12 at both ends? Are there one or two 12s in the 40?

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    DIY Junior Member bosscogg's Avatar
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    Quote Originally Posted by jwelectric View Post
    Is it 12 at both ends? Are there one or two 12s in the 40?
    As obvious as it seems now that you've asked, it didn't even cross my mind to check. I'll do so this afternoon after work and report back.
    -Dell

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    Moderator & Master Plumber hj's Avatar
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    NO matter HOW MANY #12 wires are in th e40 amp breaker it is unsafe and "illegal".
    Licensed residential and commercial plumber

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    DIY Senior Member Reach4's Avatar
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    Is the breaker feeding the known sub-panel a tandem (240 volt) breaker? How about the bathroom 40 amp breaker?

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    DIY Senior Member dj2's Avatar
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    The 40 amp breaker was probably installed by someone who didn't have a 20 amp at that moment.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The CB is there to protect the wiring. When the CB is larger than the wire's ability to transfer power without heating up too much, it cannot do that. This means, that before the CB would sense a fault from overload, the wire in the wall could have overheated and burned the house down. Except maybe to feed a subpanel, no typical branch circuit with receptacles or lights would use a 40A breaker in a home.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    DIY Junior Member bosscogg's Avatar
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    Thanks for your interest, guys.

    I took a few pics and learned a couple things.


    First, the wires coming from the 40a breaker (lower left in pic) are in fact not #12, they're #6:

    Name:  Main Panel.jpg
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    They feed through the lower left conduit to a pair of small boxes about 6' away. Was aware of these, but didn't think they were the sub panel(s) Reach4 suggested I find:

    Name:  Sub Boxes.jpg
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    Had to chip through several layers of paint and mortar to open the right hand box, and found several splices inside. Not pretty, but all wires exiting the box appear to also be #6:

    Name:  Box Open.jpg
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    It will take some heavier demo to pop the left hand box open, and will do so when I have a bit more time. Wires from the right box enter it, so need to see if that's where they reduce to #12. These boxes are on what was originally the back wall of the house, but a bedroom and bathroom were added years ago. Above these small boxes is a section of wall that has apparently been patched in a different texture pattern. Not too clear in the pic, but quite obvious in person. Perhaps the site of the original, or at least an earlier, main panel?

    Name:  Wall Repair.jpg
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    Where the wires step down in size is still eluding me.
    -Dell

  12. #12
    Electrical Contractor/Instructor jwelectric's Avatar
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    At this point we know that the 40 amp breaker that is controlling the circuit has proper sized conductors. Now awaiting what you find in the other box

  13. #13
    Retired Defense Industry Engineer jadnashua's Avatar
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    EVERYTHING that that 40A breaker feeds should have wire capable of safely carrying 40A. Since you have 12g on some of the things controlled by that breaker, unless there's a subpanel somewhere and some more breakers, it is very wrong.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member Reach4's Avatar
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    That is a tandem breaker. That is almost certainly feeding a sub-panel.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    quote; installed by someone who didn't have a 20 amp at that moment.

    He probably wished they were plug fuses so he could use a penny instead.
    Licensed residential and commercial plumber

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