Detecting available load on a circuit

Matt Irwin · February 9, 2006

Is there a way to use a meter (or something) to safely determine how much juice is available on a circuit? It would be good to know in case a situation comes up where not all plugs on a circuit can be checked or there is limited or no access to the breaker panel.

Andrew Alward · February 9, 2006

Is there a way to use a meter (or something) to safely determine how much juice is available on a circuit? It would be good to know in case a situation comes up where not all plugs on a circuit can be checked or there is limited or no access to the breaker panel.

You should beable to use a multimeter to determine the amps comming from the circuit. Then, you must figure how many amps your going to be pulling, as to not overload the circuit.

Phil Rhodes · February 9, 2006

Hi,

Yes, you apply load until the breaker drops out or something catches fire. That's your maximum load!

Seriously, no, there isn't. You may be able to go and look at the breakers and find out what the safety is, but that's an upper limit not a lower guarantee, and other things (principally diversity) can complicated matters.

Phil

Tim J Durham · February 9, 2006

Is there a way to use a meter (or something) to safely determine how much juice is available on a circuit? It would be good to know in case a situation comes up where not all plugs on a circuit can be checked or there is limited or no access to the breaker panel.

One thing you can do is go to the clothes dryer outlet (if it's electric) and use a 220 breakout. Those circuits usually are rated for 60 amps and only have the dryer on them.

Mitch Gross · February 9, 2006

Look into a device known as an amp probe. While it does not tell you the capacity of a given line, it can tell you what is currently being drawn on that line.

Luke Prendergast · February 9, 2006

Or a clamp meter - measures current via the induced magnetic flux in a wire, without physical intrusion of the circuit.

timHealy · February 9, 2006

It may help to know the ampacity of the wire. Usually the gauge of wire is printed on the jacket, but not amperage. Wire size should be matched to the breaker ampacity.

http://www.susitnaenergy.com/batteries/Wiring.htm

This "maximum ampacity for copper" as a general guide. wires do vary in ampacity based on wire size, type of wire, insulation, etc., etc. and other electrical codes in whatever town or country you may live in.

Best

Tim

Matt Irwin · February 10, 2006

Thanks guys,

I'll definitely look into the "amp probe" and "clamp meter".

Rolfe Klement · February 10, 2006

I assume you are asking about residential and commercial properties as opposed to generator loading. The best method that works for me is to isolate the load on the circut board, by seeing switching things on and off from the main board and each wall power point - then from a reading of the unit on the mains box (in UK 16A or 32A) and knowing the voltage I can figure out the load - assuming my test also made sure there are no other loads on the circut or I am running of a spur (very difficult to tell in UK) - but things tend to trip pretty quick if you over load in residential situations.

I had a gaffer and they were saying it is very difficult to use any tool to figure out loading on circuts where you cannot physically see all variables (Spurs, other loads, physically restrained trip switches etc) -

hope that helps

thanks

Rolfe