Why does microwave trip breaker?

[The Daring Dufas]

I have one of those in the case with my clamp-on meter and test leads. ^_^

TDD

[Irreverent Maximus]

I bet you scratched your head, looking at it, and wondering what it was for. :-)

[Stormin Mormon]

Very good example. What I was thinking.

[The Daring Dufas]

I use it to scratch my head because the prongs aren't too sharp. Another use for it is to crush cockroaches when they crawl across the work bench. ^_^

TDD

[Irreverent Maximus]

Man who goes to bed with itchy butt wakes up with stinky splitter...

[clare]

Easy to make an adapter to put an ammeter inline - just make a short extension cord with one of the wires cut and brought out to connect the ammeter. - makes it a "plug in ammeter"

[clare]

I just make a short extention cord and split the external sheath, allowing the insulated conductors to separate so you can install the clamp-on meter. About $3.

[Metspitzer]

Actually no. The current involved in house wiring is too high to put in series with a meter.

[Irreverent Maximus]

Not if you are using a "rated" shunt meter. :-)

[John G]

Metspitzer formulated the question :

Actually the current in any circuit can be higher than the meter can handle so it is a decision to be made every time you connect.

I never cease to be amazed how little knowledge there is about electricity amongst people risking their lives messing with it.

[clare]

Bollocks. A shunt ammeter can handle hundreds of amps in series with the load. The shunt is a very low resistance high current device, and a voltmeter reads the voltage drop across the resistance, calibrated in amps.

[John G]

[e-mail] explained on 14/12/2013 :

Till you understand electricity please stop spouting rubbish.

An ammeter can only safely handle its rated current. Yes, the shunt is a low resistance but it is only big enough to handle the rated current. ie a 5 amp meter will have a shunt or be intenally capable of carrying

5 amps plus a margin for overload safety. It will explode at "hundreds of amps"

[The Daring Dufas]

Actually Sandy has an itchy butt which I see her dragging on the rug. She just now came up to me and put her tiny paws on my thigh to get my attention. She wanted in my lap or for me to get her comforter off the loveseat to put on the floor next to me so she could burrow under it. ^_^

TDD

[bob haller]

so the microwave was on the same circuit as a coffee maker. breaker tripped frequently when both devices were on

this damaged the breaker, they are designed to get more sensitive as they age or wear.....

so now normal operation is tripping the breaker.....

i bet you will find they need a new breaker.... this is a common failure mode for breakers

[Irreverent Maximus]

[sam E]

The analog meters I've seen use as little as 20uA (.00002A) for a full scale reading. Most of the current doesn't go through the meter, but through the shunt.

IIRC, the current through a digital meter is MUCH less.

BTW, my multimeter has a 10A range (using a low-resistance shunt). That was one reason for choosing that meter (many were limited to 200mA). Later I got a clamp meter that measures AC current up to 400A.

BTW2, have you ever used a clamp meter on DC?

[krw]

That's a pretty impressive meter but irrelevant. The fact is that almost all (every one you're likely to see) analog meters are current meters at the root. The current in the coil creates the magnetic field that moves the needle. From there, everything is scaled using resistors into whatever voltage or current you wish to measure. A shunt is just one such resistor used to scale the meter to measure current. Pick your full-scale, calculate your shunt.

Not a current meter (duh!). The impedance of a digital volt-meter is higher than an analog but you're convoluting two concepts.

There is no law against having a 400A shunt.

Certainly. Even AC ones. ;-)

[clare]

Yes - but it is a different type of "clamp-on" meter - uses hall effect sensor instead of a current transformer.