GeoffM

With a UK ring main you had a very rough idea of the number of sockets etc, assuming the rings were reasonably logical. But how do I determine the load on a US spur (IIRC wiring in modern houses is fanned out from the fuse box)? All I want to do is string 2-3 more outside lamps on an existing outside switched lamp so load probably wouldn't be a problem but it would be useful to know in the future.

BTW I don't trust the "labels" in the fuse box at all. Obviously I could turn every light on in the house and plug portable lamps into as many sockets as I could, flick the switch, and see which switch off, but that doesn't seem very reliable, especially as I found yet another hitherto unknown socket just the other day after 6 months of living here!

Michael

There is no way to be absolutely sure if there are wall sockets on the circuit. The kitchen is the most complex since the microwave and/or over head lights may be on the same circuit as the kitchen wall sockets and then if you have the microwave, a toaster oven, a mixer, and a coffee maker on all the same time, the breaker may kick but that is what breakers are for.

Even if you find every possible wall socket that is on the circuit, you'll never know what you might eventually be using on those sockets.

Hotscot

Is there any way you can locate the original plans or electrician?

Otherwise, it's probably not worth bothering about other than a curiosity.

RICH

I did exactly that, and marked the outlets on a plan of the house and on the breaker board.

GeoffM

So you agree, it's an unreliable method!

In my new house in the UK I asked if I could have plans. They refused on the basis that wiring (and plumbing) is fairly "at whim" of the electrician/plumber so giving plans could mislead you into thinking an area was free of wiring and pipes. I could kind of see their point.

Added to that, the previous owner was not terribly bothered about code it seems. We have outside lights on the driveway that are wired in but have absolutely no protection as in tubing/trunking (was found on inspection).

Yeah probably in this case. Just wanted to at least try and do things right! I even downloaded the California electrical code but at 940 something pages it's not exactly light reading.

GeoffM

It's certainly feasible, though would have been a lot easier before we moved in! Our fuse box is at one end of the house (outside) while the nearest entry door is 3/4 of the way down the other end of a long ranch-style house so it's a lot of walking!

AZ_Alba

you could use a fox and hound to trace individual sockets back to the breaker box. The fox and hound works by plugging a tone generating device into the socket and then using a listener to slide up and down the breaker box to locate the breaker with the loudest tone. Sometimes you need to switch the breaker off just to confirm that it is the correct breaker as the tone will stop. As to finding hidden sockets good luck with that.

RICH

True. 2 people and a walkie talkie would help.

Michael

Believe it or not, even though the contractor has to file building plans including electrical wiring and the city inspector inspects each stage of construction, contactors don't always follow the plans.

My neighbor's townhouse would trip the breaker for the microwave and overhead lights in the kitchen about every two months and I had exactly the same plan except 180 degrees opposite but I didn't have the problem. In his townhouse, the overhead lights and the microwave were on the same circuit as well as a couple of wall sockets in the living room but in my townhouse the over head lights and microwave were on separate circuits with each having a couple of sockets in the living room.

Michael

If you are going to add LED lights, I wouldn't even worry about it since so little power is used.

GeoffM

Interesting, thanks.

Good idea.

Yes, one contractor's idea of up and left is another's left and up.

This particular circuit actually tripped last week when we had rain. I suspect our former occupant wasn't too bothered about shielding that particular lamp post either. This is, in fact, the same circuit I wanted to extend and, as far as I could tell, that tripped that outside light, the wall light outside, two pairs of kitchen spotlights, 1 family room spots, and 2 sockets. Being an open plan kitchen/family/dining/whatever it didn't surprise me really - except perhaps the sockets. I thought ideally you're supposed to have lights on separate circuits to sockets but I see lots of comments elsewhere that imply either it doesn't matter or people don't care!

(In the UK the lighting rings and socket rings have different fuse sizes - 15A and 30A? - so it's really frowned upon to mix them)

Probably. Just thinking through the logistics of it first. The wall light I want to go from is on stucco which - as I discovered a few months ago - is a good 1½" thick. So if I can come out of the bottom of that light, U-turn up to the patio roof, across, then down the two support pillars to the new lights, I think that would do the job. One existing outward facing light, then adding two inward facing lights on the pillars. Probably even the energy saving equivalent of 40W in each would be enough.

Anyway, the original question was obviously triggered by this relatively minor issue so the answers were more for the future if I wanted to add sockets somewhere and run an electric oven off it! (No, I wouldn't. Just an example)

Pulaski

Wiring in the US is a dark art. I have two sockets on the kitchen island that trip the AFCI breaker if you do anything more than plug a phone charger into them. I have replaced both sockets, and the AFCI breaker, but it made no difference. There appears to be something wrong with the actual wire.

I have a "dead" socket in the garage, and my electrician can find no reason why, it just appears to be a break in the cable buried in a wall somewhere in the garage.

A neighbour's house has three "mystery switches", none of which seem to do anything, but all appear to be connected. They have 37v power connected to them! One was on a twin switch plate, so as it wasn't doing anything it was removed, capped off and the twin switch plate was replaced with a "switch & blank" plate. Another switch is the center of three switches, so can't really be removed. The third switch is on its own, so it was just a matter of removing the switch, capping the wires and installing a blank plate over it. ....... Except then the well pump stopped working! WTF? The well pump runs on 230v, so what a switch with 37v connected to it has to do with a 220v appliance, heaven only knows. ..... Anyhow, the switch was in the way of a remodeling project, so the wire was pulled back from whence it came, up into the attic, and was reconnected to the switch, with a label saying "Do not remove, reqd to make the well pump work". Oh, it it doesn't make any difference if the switch is up or down, the well works either way- the switch just has to be connected, otherwise the well pump stops working.

Steerpike

Are you saying a UK Ring Main is easier to 'reverse engineer'? With no documentation, it would appear equally difficult (but all my practical experience has been gained here, so I can't really judge)

I've lived in my current house for almost 20 years and soon after moving in, I was determined to document every circuit breaker (25 in all, with 8 being two-phase pairs, for 4 appliances). There's still two circuit breakers I can't tie to a function.

GeoffM

Slightly easier yes, but same caveats apply. Assuming no funky wiring like an upstairs pair of sockets spurred off the downstairs ring main, or chained spurs (which I think are not allowed), then theoretically you could trace the ring around the house with a bit of guesstimation and a live wire detector. I'll concede that lighting rings are more difficult because of the switches in the walls though!

I did have a thought that maybe my wiring goes up from the fuse box into the attic and down the walls. But there is a ton of insulation up there, literally 6' deep in places.

Pulaski

That is usually the way in my experience. Plumbing in the crawlspace, wiring (generally) in the attic. I'd sooner be an electrician than a plumber!