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I'm closing a new construction residential build. The builder did not include any documentation on how the wiring was done. My question to the community is two-fold.

  • First, should I ask for some documentation on how the electrical wiring is done?
  • Second part, if so then what exactly should I ask for?

I've found references online to things called Wiring Plans/diagrams and schematics but I want to make sure that I use proper vernacular when I bring it up. Ideally, this would be something I could show to any future electrician to give them a good idea of how things are done in case I ask to have something added.

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  • If you bought a tract home built by a large builder, expect the layout to be somewhat nonsensical, so they could save a few bucks in wire so the CEO can afford another yacht, even though it makes any modification down the road obnoxious.... Apr 16, 2023 at 6:18
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    It would be nice if homes came with maintenance manuals, wouldn't it?
    – keshlam
    Apr 16, 2023 at 6:59
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    Are the walls closed in yet with drywall? If not, go take clear and well-lit photos of every open wall that you can. This helps finding studs and wiring and pipes later on.
    – Criggie
    Apr 16, 2023 at 12:44
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    To follow what @Criggie has said, walk through the house before the drywall is up and figure out where the switches are (and whether they make sense). In my house, the electrician put a single switch for the master bedroom sconces in the center of the bed (behind where the headboard would be) and a bathroom light switch behind the bathroom door. Changes are easy when there is no drywall. Do the same with sockets (imagine where shelves, etc. will be). Our electrician really had no sense of the practical
    – Flydog57
    Apr 16, 2023 at 20:29
  • I've been in several houses that are exactly like mine (same everything, just copy-pasted onto another lot). The electrical, plumbing, ductwork, etc. was different in every one of them. Even something as simple as the kitchen light switch placement was different. The architect likely drew up an electrical plan, but I doubt the people building the houses have ever seen it.
    – bta
    Apr 17, 2023 at 23:54

4 Answers 4

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I would not expect any detailed schematic or wiring diagram, for a bunch of reasons. But what I would expect is that the breaker panel be clearly labeled, which is normally done prior to the electrical inspection by the city/county/state. If it is reasonably labeled then you will know which circuits control all large (240V) devices (oven, cooktop, dryer, water heater, HVAC, etc.), all major hardwired appliances (e.g., dishwasher, disposal) and the following 120V circuits:

  • Laundry Room
  • Kitchen Receptacles
  • Bathroom Receptacles

The remaining challenge will be to figure out which "general purpose" breakers control receptacles and/or lighting fixtures. Ideally they should provide a complete diagram, but as far as I know there is no obligation to do so.

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  • 2
    One of the first things I did after moving in was run around the house with a breaker-identifier, plugging the transmitter into outlets and using the receiver wand to try to determine which breaker fed them. When I had the box replaced they labelled every breaker with at least one of the things it controls; I really should reconcile the two lists.
    – keshlam
    Apr 16, 2023 at 3:22
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    Residential you are lucky if the breakers are labeled correctly. Best thing is to take pictures right before insulation of every wall / ceiling so you have a very good idea of what is behind the drywall. This helps with pipes / sprinkler / drain line and electrical. Apr 16, 2023 at 4:49
  • I think I'm missing something here: 240 and 120V circuits in the same house?!?
    – Karl
    Apr 16, 2023 at 20:59
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    @Karl The US and Canada are actually a 240V system. Power comes in from the utility as two hots + neutral. Hot to hot is 240V (in some industrial and apartment buildings 208V) and either hot to neutral is 120V. Standard "plug in stuff" is 120V. Large electric appliances - clothes dryer, water heater, oven, cooktop, HVAC are all generally 240V (unless they use gas for heating). There are some exceptions, but most houses are wired that way. Apr 16, 2023 at 21:02
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    @Steve Only in buildings where hot to hot is 208V, thats why it sums to 208V not 240V. If hot to hot is 240V, then that's 180 degree apart, generated by center tapped secondary transformer from a single phase. Apr 17, 2023 at 1:51
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I tried keeping such documentation. But it isn't that helpful, and it goes out of date too quickly.

Code requires that all electrical connections be made inside junction boxes, and all junction boxes remain accessible forever.

That means that your entire house's electrical system contains only 2 things: a) junction boxes which are accessible, and b) cables or conduits connecting junction boxes which have no joins or splices in them.

This creates a world where wiring is largely "self-documenting" - one needs to simply look at where the wiring is likely to go, and open up junction boxes in that vicinity. This reveals everything that there is to see. Assuming rules were not violated. Circuits can be ascertained by shutting off a breaker and seeing what goes dead, and there are more sophisticated pro tools to trace any given cable leaving a box, but they're usually not necessary. An experienced person can usually just tell by recognizing the connection patterns given the usage.

Also, the most important documentation method is how the wiring is hooked up presently. About twice a year, a novice opens up a complicated box, unhooks every single wire from whichever terminal or wire nut it is on, splays out all the individual wires and takes a photo and posts it here. "How do I hook this up?" they ask. Well, we can't tell them because they just destroyed all the clues! So yeah - take great heed for how it is connected.

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  • +1 "About twice a year, a novice opens up a complicated box, unhooks every single wire from whichever terminal or wire nut it is on, splays out all the individual wires and takes a photo and posts it here. "How do I hook this up?" LOL
    – J D
    Apr 17, 2023 at 9:13
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    "Assuming rules were not violated." - what a touching faith in human nature. Apr 17, 2023 at 9:50
  • @Martin Just a matter of seeing a lot of electrical questions here, and not seeing much evidence that would shake such faith. If it was popular, we'd notice! Apr 17, 2023 at 20:16
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Wiring diagrams would be extremely unusual in a single domestic build

As would plumbing diagrams. Or HVAC diagrams.

I’ve been a building services engineer for over 30 years and I’ve only ever encountered electrical diagrams for a house once - the cost of the electrical build was AUD1.3 million (USD 870k). In a regular home, the electrical systems are just not that complicated.

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The electrical layout on a set of blueprints simply indicate where the location of devices are. They tell the electricians and their helpers where to place the breaker panel and things like switch and outlet boxes and such.

You can easily see these things in your home. How the cables are run to the devices for termination are not indicated. this is done by the electrical crew according to the code in place at the time.

Therefore the electrical layout page is useless to you and a complete schematic does not exist.

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