Measuring load on a circuit breaker.

Hi, Does anyone know of a way to measure the current being used on a single circuit breaker from just one of the wall outlets on that circuit?

ie; I want to be able to plug something in anywhere in the house and be able to tell from there how many amps the circuit breaker is using. thanks

Nope. You need a clamp-on ammeter around the wire going to the breaker.

Chris

Circuit breakers don't "use" amps, they let amps flow through them and open the circuit when the current exceeds their ampere rating.

Just take the front panel off the breaker box and snap a clamp-on ammeter over the white wire exiting the breaker. That'll tell you how much current is flowing.

This cheapy clamp-on from HF will do it for you:

Jeff

,,,

That would be the black wire from the breaker for a single-pole (120V) circuit, the white for the same circuit should be terminated on the neutral bar.

What are you plugging into the outlet? The easiest method is just estimate it from the power rating of the device you are plugging in. There should be a Wattage (Power) marking somewhere on a nameplate on the device. The current will be approximately = P/120 (assuming your voltage is 120V). Example - If you are running a 1200 W space heater, that would take 10A.

If it is a motorized appliance, such as a vacuum cleaner, it will have a power factor of less than one, which means it will draw slightly more current than it actually consumes in measurable output power.

If it is a heavy duty appliance like an air-conditioner, the startup currrent may be high (almost double) during the fraction of a second that it is coming up to spead.

Ummm, the circuit breaker is fed by a bus ... that you cannot clamp around.

There is usually a black wire connected to the circuit breaker. If you can clamp around that wire with the appropriate ammeter (Google clamp-on ammeter) you can measure the current in that circuit.

What are you trying to accomplish?

Looks like someone can't tell the difference between "to" and "from". That reminds me of the numerous people who kept confusing "inputs" and "outputs" on audio/video equipment.

Hummm, but the buss is fed by a main and that main is fed by wire that you can clamp around.

Not in any power panel that I have seen recently.

I think he meant that the bus was fed through the main breaker, which IS fed by a wire, usually coming from the meter base.

But, to make a meaningful measurement using that wire he'd have to switch off ALL the other breakers on that feed's side of the panel. Not a very practical solution, is it?

Jeff

No Jeff, it surely is not!

OTOH, since he's wondering about the power used on one circut, many people might suggest clamping the ammeter on the wire that feeds that circut. You know, where it comes off the breaker. I know that sounds crazy, but it might work anyway.

I have an adaptor for my ammeter that I can plug into an ordinary wall receptacle. It has a loop on it to clamp around and I can plug an appliance into it to see what the load is for that appliance. I think Amprobe makes it.

John Grabowski

The circuit has one wire attached to the breaker, and the other goes to the neutral bus (assuming a 120V circuit). You can put a meter around the wire that is connected to the breaker.

Are you seriously arguing about wether a wire goes "to" or "from" a breaker? In an AC circuit where current flows both ways?

Chris

Consider that while current does flow both ways (or more correctly, is ALTERNATING direction), POWER goes one way. "Direction" is useful there.

I'm using a Kill-A-Watt meter for that now, but previously I had a VOM attachment for that. I made it from a remote control cord (just a switch at one end) with the switch removed and replaced with banana plugs.

Do your breakers really have white wires hooked to them?

Why not?