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Clamp ammeter: is this any good?

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[OP]
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Jul 7, 2017
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Clamp ammeter: is this any good?

Not a professional but just need a tool to determine current draw of various electrical loads around the home.

Will the following tool suffice? It is <25% of the cheapest sold at HD

https://www.kmstools.com/magnum-1000a-d ... ter-105405
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Deal Addict
Nov 24, 2004
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Toronto
I have no comment about that particular model, just a note that the clamp-on ammeters are for measuring current in AC "wiring" (individual current-carrying conductors, such as those inside your furnace fan unit, fridge compressor chassis, etc.). Clamping it over e.g. the power cord of a lamp or TV will give a zero reading. So they're not very useful for measuring current draw of ordinary household devices, unless you want to start cutting power cords open.
[OP]
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It'll be for the HP compressor and air handler. I want to see what the draw is for the air handler to see if I can change the supply to the back-up generator
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Nov 24, 2004
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As long as you can get it around the "hot" wire alone, it should do the job. Those kinds of device are pretty simple (also not terribly accurate in many cases, but probably OK for your uses) I don't think the cheap models will be that big of a loss in your case.
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Feb 11, 2007
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thriftshopper wrote: It'll be for the HP compressor and air handler. I want to see what the draw is for the air handler to see if I can change the supply to the back-up generator
You could also use a kilowatt type of device to measure power usage if it has a standard plug.
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JHW wrote: As long as you can get it around the "hot" wire alone, it should do the job. Those kinds of device are pretty simple (also not terribly accurate in many cases, but probably OK for your uses) I don't think the cheap models will be that big of a loss in your case.
So if I am measuring the current draw of a 240V line (either paired into a single 240V hot, or two individual 120V lines in 2 phases?), I have to run the clamp around each strand, and not both and the neutral/ground?
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[OP]
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engineered wrote: You could also use a kilowatt type of device to measure power usage if it has a standard plug.
The small stuff isn't that important. Not that obsessive, for now.
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Deal Expert
Jan 27, 2006
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If you are going to spend the money and not in a hurry, I would look for a clamp on meter that is auto-ranging over one of these. They will generally be a few bucks more but it's well worth it. Also, I wouldn't necessarily use meters at this price range directly with AC power (ie with the test leads and not the clamp) as you don't know if they are properly isolated and fused.

BTW> A quick search on the product turns up this link on Amazon for the same product - https://www.amazon.ca/Digital-Multipurp ... B001CWJ5Y2. The two reviews aren't exactly glowing.
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Nov 24, 2004
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thriftshopper wrote: So if I am measuring the current draw of a 240V line (either paired into a single 240V hot, or two individual 120V lines in 2 phases?), I have to run the clamp around each strand, and not both and the neutral/ground?
I don't know about measuring 240V appliances, but generally speaking if you have both a "hot" wire and the neutral / ground in the clamp, the magnetic fields cancel out and you'll read zero current. Same as if you e.g. ran the power cord of a lamp or refrigerator through it.
Sr. Member
Jan 19, 2013
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Ottawa
Unless you variable speed compressor in your heat pump or a fairly large kw generator, you wouldn’t be able to do it I think.
Startup amp draw on a compressor is quite high
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1chinaman wrote: Unless you variable speed compressor in your heat pump or a fairly large kw generator, you wouldn’t be able to do it I think.
Startup amp draw on a compressor is quite high
The HP compressor is unfortunately single stage and has a tandem pair of 40A breakers on the circuit (air handler is on the main panel). Generator appears to be 13 KW.
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Aug 12, 2007
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thriftshopper wrote: It'll be for the HP compressor and air handler. I want to see what the draw is for the air handler to see if I can change the supply to the back-up generator
you cannot go by the measured current. you have to go by what the manual says. also note the manual may or may not state the startup current which is much higher than the running current.
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Mar 4, 2007
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Hi,

Your heat pump motor is 240 volts, does your generator output 240 volts? What are the heat pump circuit breakers rated for? For instance, if the heat pump is on a 40 amp circuit, the back up generator is probably going to have to be capable of 30 amps or more. Otherwise the backup generator circuit breaker will trip when the heat pump motor starts up.
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Jan 19, 2013
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thriftshopper wrote: The HP compressor is unfortunately single stage and has a tandem pair of 40A breakers on the circuit (air handler is on the main panel). Generator appears to be 13 KW.
That’s a pretty big hp. No way your generator can start it.
That compressor will probably pull 100 amps on startup.
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The generator does have a pair of 55A breakers for 240V output, or not enough? Compressor is wired to the generator transfer panel with a pair of 40A breakers. The air handler is not - this has a pair of 50A breakers but I think that's due to it using electrical auxiliary heating. There is a switch by the transfer panel that appears to turn the auxiliary heating on and off (manually). Air handler should draw less power (startup and running) as I have replaced the PSC motor with an ECM one.

Otherwise, the only other things connected to the generator panel are 1) hot water tank (will move this to the regular panel), 2) fridge, (and will connect the freezer), and a 3 outlets hardly used.

Specs
Annotation 2019-12-21 093823.jpg
FWIW, one of the neighbours who used to be a (ship) mechanic rigged up some timer delay switch for the air handler (I disconnected it when I put in the ECM motor). It was supposed to delay air handler startup if power was cut and came back on, so the generator panel would not be overloaded, not that the air handler was connected via the generator panel.

FWIW, the lights don't dim in the house when the heat pump kicks on. That may be due to the fact that I replaced most of the lights with LED and CFL bulbs before the first heating season we were in the house. The entry hallway and dining room lamps each had 9 x 60W bulbs and there were well over 60 halogen track lights (we converted the direct-powered GU10s to LEDs and very sparingly use the rest.
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