Check an electrical plan before the first cable goes in
Three checks that catch most mistakes on an electrical plan while they are still cheap. Does every device reach the board, does each switch control the right light, is any circuit carrying too much. Try each one here.
Most mistakes on an electrical plan are ordinary. A socket placed and never wired. A switch that controls the wrong light, or none. A kitchen circuit that quietly collected the dishwasher, the washing machine and the dryer. Each is cheap to fix on the plan and expensive to fix in the wall, and three checks find them: reach, switching and load.
1. Does everything reach the board?
Every device on the plan is on a circuit, and every circuit starts at the board. So start at the board and follow the wires. Anything you cannot reach is not connected, whatever the plan looks like. On paper this is a finger on the drawing; on a screen it is a connectivity check that walks every wire from each board and lists what it does not reach.
Two things to know about the check:
- It starts from boards only. A solar inverter or a generator is a source in the real installation, but on the plan it is a device fed from the board like any other. If it counted as a source, every device wired to it would pass.
- It checks the drawing, not the house. It tells you the plan is incomplete. It cannot tell you the plan is right.
2. Does each switch control what it should?
Clients care about this more than anything else on the plan: can I turn the hall light off from the landing, does the kitchen have its own switch by the door. And it is the easiest thing to get wrong on a drawing with thirty switches.
The check is a simulation. Treat every switch as open or closed, light a lamp when a closed path exists from the board to it, and try the switches one at a time. If turning off S4 darkens the bedroom and nothing else, S4 is right. If it darkens the hall as well, two circuits were drawn as one. If it darkens nothing, the switch is in series with nothing. A two-way pair shows up correctly only when both switches are drawn to each other and to the light.
The model is simple on purpose: it knows nothing about the lamp's own switch, timers, sensors or smart controls, and it treats a dimmer as a switch. It is still the quickest way to find a wrongly drawn switch. The two-way switching article explains the pair in full.
3. Is any circuit carrying far too much?
The third check is a rough load per circuit. Add up what is on each circuit, each device with a typical load, divide by the voltage, and compare the current with the breaker's rating. A lighting circuit with a dozen lights comes to a few amps and is comfortable. A 16 A socket circuit with the kitchen's appliances on it comes to well over its rating and stands out at once.
Two warnings belong beside every such figure:
- It is indicative. The loads are typical, not measured, and the sum ignores diversity, the fact that not everything is on at once. Your regulations say how a circuit is designed. This check shows which circuit needs that attention first.
- It depends on the voltage. The same devices draw almost twice the current at 120 V as at 230 V. A load figure without the voltage it assumes is not a figure. The load calculation article goes further.
When to run the checks
Before the client sees the plan, and again after every change. A plan that passed on Tuesday can fail on Thursday after one socket moved to another circuit. If the checks take a minute, they get run; if they take an afternoon, they get skipped, and the plasterer finds the mistake.
ePlan's Test mode is these three checks in three tabs. Check walks the wires from every board and lists what it cannot reach. Simulate lets you flick each switch and watch the lights. Loads shows the indicative load per circuit against its breaker, with the voltage it assumed written underneath. They take seconds and run on the plan as it is.
Questions
Can a plan pass all three checks and still be wrong?
Yes. The checks find devices that are not wired, switches that control the wrong thing and circuits that are plainly overloaded. They do not know the regulations, the cable sizes, the lengths of the runs or the protection each circuit needs. They make the plan complete, not compliant.
What does a dangling wire mean?
A wire with one end attached to no device. On paper it is a line that stops in the middle of a room. It usually means a device was deleted or moved and its wire was left behind, and the check lists it beside the unreached devices.
Why does the simulation ignore dimmers and sensors?
Because a conducting-path model has no notion of a level or a trigger. A dimmer is treated as a switch that is either on or off, and a sensor as a switch you set by hand. That is enough to find a wrongly drawn circuit, which is what the simulation is for.