My parents recently bought a new over-range Maytag microwave, and it's
throwing the breaker occasionally. They told me they had somebody out
to look at it (still under warranty), and he measured the current
going over 16A occasionally. It's a 15A breaker, so no surprise that
it's tripping. But I looked at the sticker on the microwave and it
specifies 120V, 14.8A. Given that, I think that the microwave should
not be drawing >16A long enough to even measure on his meter. I guess
some very brief spikes would be OK, but apparently he was repeatedly
measuring currents over 15A during normal operation. (Unfortunately,
I didn't actually see it; I'm relying on my mother's telling of the
story, and I didn't bring my own meter with me.)

The repair guy said this was normal and told them to upgrade the
breaker to 20A. I say an appliance rated at 14.8A should draw no
more, and if it does, it is defective and should be replaced. Anybody
who knows more about this than I care to comment? Should they demand
a new unit? It was installed just a few weeks ago.

TIA,

--
Randall

"Randall Nortman" > wrote in message
...
> My parents recently bought a new over-range Maytag microwave, and it's
> throwing the breaker occasionally. They told me they had somebody out
> to look at it (still under warranty), and he measured the current
> going over 16A occasionally. It's a 15A breaker, so no surprise that
> it's tripping. But I looked at the sticker on the microwave and it
> specifies 120V, 14.8A. Given that, I think that the microwave should
> not be drawing >16A long enough to even measure on his meter. I guess
> some very brief spikes would be OK, but apparently he was repeatedly
> measuring currents over 15A during normal operation. (Unfortunately,
> I didn't actually see it; I'm relying on my mother's telling of the
> story, and I didn't bring my own meter with me.)
>
> The repair guy said this was normal and told them to upgrade the
> breaker to 20A. I say an appliance rated at 14.8A should draw no
> more, and if it does, it is defective and should be replaced. Anybody
> who knows more about this than I care to comment? Should they demand
> a new unit? It was installed just a few weeks ago.

This is normal and acceptable. When a motor starts, (and the microwave has
one for the turntable) the draw can easily be 2x or 3x the running draw as
specified. I don't know if the magnetron has a draw like that, but it may
spike at startup. Circuit breakers are built to take that.

If an appliance is rated at 14.8A, it MUST be on a 20A breaker according to
electrical codes. If should be upgraded to 20A and with 12 gauge wire. A
15A breaker can take 80% or 12A for a constant load. Sorry, but that's the
way it is and a new unit will do the same thing.

How about this from the manual
ELECTRICAL REQUIREMENTS

Product rating is 120 volts AC, 60 Hertz,

-MMV4205, AMV5206, MMV5207, JMV8208 (USA):

14.8 amps and 1.7 kilowatts.

-MMV5207,JMV8208 (CANADA) / AMV6167:

13 amps and 1.5 kilowatts.

-JMV8166/JMV9169:

14.5 amps and 1.6 kilowatts.

This product must be connected to a supply circuit of

the proper voltage and frequency. Wire size must

conform to the requirements of the National Electrical

Code or the prevailing local code for this kilowatt

rating. The power supply cord and plug should be

brought to a separate 20 ampere branch circuit single

grounded outlet. The outlet box should be located in

the cabinet above the microwave oven. The outlet

box and supply circuit should be installed by a

qualified electrician and conform to the National

Electrical Code or the prevailing local code.

On 2008-01-01, Edwin Pawlowski > wrote:
>
> This is normal and acceptable. When a motor starts, (and the microwave has
> one for the turntable) the draw can easily be 2x or 3x the running draw as
> specified. I don't know if the magnetron has a draw like that, but it may
> spike at startup. Circuit breakers are built to take that.

This I know, but the way I heard the story, it is not on startup that
it spikes, but rather gets up to >16A during ongoing operation. I'm
not sure how brief these spikes are. If they're 1/10 second, it
should be fine, but if it's above 15A for more than a second or so, I
think there's something wrong with the microwave. They're long enough
to show up on the meter the repair guy brought, and seem to happen
quite frequently. The breaker usually trips after the microwave has
been running for several minutes, not due to a spike when it first
turns on.


> If an appliance is rated at 14.8A, it MUST be on a 20A breaker according to
> electrical codes. If should be upgraded to 20A and with 12 gauge wire. A
> 15A breaker can take 80% or 12A for a constant load. Sorry, but that's the
> way it is and a new unit will do the same thing.

That makes sense, and whomever installed the microwave probably should
have checked on that. For that matter, the person who sold it to them
should have pointed it out. I certainly hope they have 12ga cable
installed, or else it's going to be an expensive fix. But none of
that changes the fact that the microwave should not be drawing >16A
for more than a fraction of a second, right? 80% of 20A is 16A. If
the microwave draws >16A for extended periods, then even a 20A breaker
might trip (seems unlikely, though). I wish I knew how long the
spikes last and how frequent they are.

Thanks for the info.

--
Randall

"Randall Nortman" > wrote in message
>
> But none of
> that changes the fact that the microwave should not be drawing >16A
> for more than a fraction of a second, right?

The formula is: Watts ÷ Volts = Amps
Assuming 1780 Watts, a perfect 120 volts = 14.83A That may be true in
perfect conditions as tested in the laboratory. The electric company is
allowed to vary the voltage and it may be a bit higher or lower at times,
especially during heavy use in the summer.
So, given the same 1780 Watts, we can have:
1780 ÷ 110 = 16.18 Amps. This is within the normal and acceptable range. I
doubt you'd have trouble with a 20A breaker and that is why the code
requires a safety factor.

On 2008-01-02, Peter A > wrote:
> In article >,
> says...
>>
>> "Randall Nortman" > wrote in message
>> >
>> > But none of
>> > that changes the fact that the microwave should not be drawing >16A
>> > for more than a fraction of a second, right?
>>
>> The formula is: Watts ÷ Volts = Amps
>> Assuming 1780 Watts, a perfect 120 volts = 14.83A That may be true in
>> perfect conditions as tested in the laboratory. The electric company is
>> allowed to vary the voltage and it may be a bit higher or lower at times,
>> especially during heavy use in the summer.
>> So, given the same 1780 Watts, we can have:
>> 1780 ÷ 110 = 16.18 Amps. This is within the normal and acceptable range. I
>> doubt you'd have trouble with a 20A breaker and that is why the code
>> requires a safety factor.
>>
>>
>>
>
> If the voltage goes down from 120 to 110, the current drawn will be
> less, not more. The wattage will be less too.
>
> current = voltage / resistance
>
> Resistance is a constant property of the microwave.

This assumes that the microwave is a passive, linear load, which is
probably not true. Many loads are not linear, and are designed to
draw constant power. This means their effective resistance
(impedance, actually) will decrease as voltage drops to keep power
constant (which requires drawing more current). Switching power
supplies for computers are a great example of this.

Now, I'm not saying I know whether microwaves are linear loads or not,
but I suspect they are not, and might draw more current as voltage
drops in order to maintain constant power.

--
Randall