Is there a way to determine the order of items on a circuit?

Question

Just purchased a new house and have been doing some electrical work, and I've been surprised at how many things have been crammed into single circuits.

For example, one circuit seems to serve four light fixtures and five outlets across three rooms. That feels super overcrowded! I'm considering my options with re-wiring some of them as well as strategic use of GFCI/AFCI/DFCI breakers/outlets. But I'd like to really understand what is happening before I do all that.

Is there a way to determine the order of items on a circuit? And if a circuit branches into multiple branches, is there a way to determine that?

Answer 1

To figure out the order of items on a circuit:

(warning, tedious and laborious, but accurate)

First, sort out which items are on the circuit - i.e. what turns off/on with the breaker.

Turn the breaker off.

Pick any device on the circuit, open it up. If there's only one cable coming into the box, close it up again, noting that it's an end.

If there are two or more cables coming into the box, note exactly what is connected to exactly where, and disconnect one cable. Turn the breaker on and see what no longer works. Note that those things are "downstream" of the item in question. Turn breaker off and repeat if there are more than two cables. Reassemble everything as it was, move to the next device location, repeat.

If you find any "backwired" connections, remove them and move that wire to the associated "side screw" when reconnecting.

Answer 2

I think there's a way along a single branch to map out what's closest to the breaker and what's closest to the end of the line. It's somewhat dependent on wiring quality, having it consistent along the branch under test.

You need a voltmeter and a 1500W space heater.

1. Unplug everything you know about from the branch.
2. measure +note the voltage at each outlet on the branch.
3. plug in the space heater and turn it on full blast.
4. re-measure the voltages at each outlet.

If the outlet is between the heater and panel, it will have higher voltage than the heater's outlet. the heater should have basically the same voltage as all other outlets on the branch that are further away from the panel than the heater.

Highly simplified and exaggerated for clarity, here's what that looks like in a perfect sim:

The 10 ohm resistor connecting "live and neutral" is the space heater, and the 1 ohms resistors represent the old wiring. All the slots after the heater are the same voltage, while in front of the heater the voltage drops off a little on it's way to the heater.

I think this could help you not only index the nodes, but also map out where your weakest wiring; the segments that drop the most voltage would be primae candidates for replacement.

Answer 3

I have worked on older homes that all the lights in the entire home were on the same circuit (plus a few receptacles).

The requirement for residential pre 2021 is 1ea 15a circuit per 600 sf or 1ea 20 amp circuit for 800 sf (I haven’t looked it up to see if that has changed I doubt it because residential is still 3va per sf on the lighting calculations where everything else is smaller.

These are minimum requirements and if you wish you can have each room on its own circuit.

The only way to know for most home owners is to turn a circuit off and track what is not powered. Or this is the easier way to figure it out things branch as they get further away from the breaker panel.

You could also spend a nice chunk of change and purchase a tracer like I have CS8000 , quick check on line they are running 750$ currently. This can trace the wires through the walls but that is really not needed to figure out a home where everything is working.

There is a limit to the number of wires allowed in boxes by code this is called box fill. Things do get snug when close to the max but that snug level is not unsafe and regulated by the NEC in the US.

So turn a circuit off and track it from the panel would be your best bet.

Answer 4

Dandavis has the right general idea for when you can use a high current to get a significant voltage drop on your cables. This voltage drop will be significant enough when compared with the nominal mains voltage to be distinguishable from socket to socket.

For lighting circuits, you have much less voltage drop. When measuring each socket, your meter resolution may not be enough, and small fluctuations in the incoming voltage will make a mess of trying to compare socket voltage measurements made at different times.

The answer for lighting circuits (and it makes the measurements of a power circuit more reliable) is to measure the voltage drop along a conductor. This means either measuring along the neutral (ideally) between a pair of sockets, or measuring from the neutral at your board to one socket at a time. Now the small voltage can be read on a meter scale of volts, rather than hundreds of volts.

An alternative is to remove the breaker at the board, and inject a current source into your circuit, and short-circuit the far end. This allows you to measure at each socket as before, but on a volts range rather than hundreds of volts. The last time I did this, I used a bench power supply with a constant current output as my current source.