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jdiamond · Nov 14, 2007, 01:30 PM

Every time we use our microwave it blows the fuse after about 30 to 45 seconds max.
We have a Sharp Carousel R426. It's plugged into a GFCI receptacle that is the only receptacle on a 15 Amp breaker. Do I need a 20 Amp breaker for the microwave?
Is there something that could be wrong with this particular microwave?
Thanks!

tkrussell · Nov 14, 2007, 05:05 PM

You say it blows a fuse, but you mention the GFI and the circuit breaker.

Exactly which is tripping?

The breaker or the GFI could be defective. I have to assume this is not new, that the microwave has operated on the circuit for sometime.

Without actually measuring the amp load, hard to tell. I suppose it could be the appliance, but I have no knowledge of this symptom of happening to microwaves.

KISS · Nov 14, 2007, 05:08 PM

The magnatron may be dying especially if the food hasn't been as hot as it used to. This is a classic symptom. What's the age of the unit?

jdiamond · Nov 15, 2007, 07:27 AM

It's a new unit, and it's always been like this. From the day I got it. I assumed that I needed to switch the 15 amp breaker to a 20 amp one and the wires from 14 to 12.

I guess I could bring it to a different place in the house where the outlet is on a 20 amp breaker and try it first?

Stratmando · Nov 15, 2007, 07:33 AM

I would sure try On a 20 Amp circuit. You are not talking about Micro's internal fuse as mentioned? Also make sure wire is tight at the fuse, if in Panel.

labman · Nov 15, 2007, 07:46 AM

Check the name plate. Unless it is over 1440 watts it should be fine on a 15 amp fuse.

KISS · Nov 15, 2007, 09:38 AM

The, "It's always done that" is indicative of the circuit that you have it on is overloaded. Since it's more than likely in the kitchen, the resaon why it may not do it every time is that it could be sharing the circuit with the nearly silent refrigerator. It may pop just when the fridge and microwave are running at the same time with a short delay.

jdiamond · Nov 15, 2007, 09:43 AM

I'm sorry I should have given all this information in the first place.

The Microwave is plugged into a receptacle that is the only receptacle on the circuit.
That is why I thought it would be OK, even though it is onlt a 15 amp circuit, there is only one receptacle on this circuit, and nothing else is ever on this circuit other than the microwave.
The microwave has always had this problem, whether I plug it into that receptacle or any other receptacle in the kitchen.
I assume(stupid me) that the gas range would be on a higher amp circuit, so I tried to plug it into the oven receptacle (I unplugged the oven). It still didn't work. But then I check and the oven is also on a 15 Amp circuit. I will have to bring it to another room in the house with a 20 Amp circuit to see if that solves the problem. I'll write back tomorrow when I check that out.

Thanks!

KISS · Nov 15, 2007, 10:21 AM

The manual, here: http://www.sharpusa.com/files/mic_man_R426H.pdf

Says it's 14.3 AMPS. That will pop a 15A fuse in a heartbeat. It's going to need a separate 20 AMP circuit.

Replacing the standard 15A fuse with a 15 Amp Time delay fuse, sometimes called a dual element fuse may or may not fix the tripping issue. But it's worth a shot.

jdiamond · Nov 15, 2007, 10:25 AM

Thanks! I'll try it on a 20 Amp circuit, see if it works and then switch the circuit to 20 Amp.
The kitchen is right over the basement where the service panel is and it won't take too much time to run new wire. I guess it's good to have at least one 20 Amp receptacle in the kitchen!

I know I have to make sure the house can handle it, but I've done a quick look over (need to do a more thorough one) all the appliances in the house and the Amps being used.
I think the extra 5 amps will be fine.

Thanks!

KISS · Nov 15, 2007, 10:46 AM

A reminder. The sum of the fuse/breaker ratings can exceed the main breaker rating and there are methods for determining the required service entrance size.

A 120V 20A location requires 12 AWG wire and a 20 A outlet.

tkrussell · Nov 15, 2007, 01:02 PM

The manual clearly states that a 15 amp circuit is required. This unit should work just fine on a 15 amp circuit.

A 14.3 amp load should not trip a 15 amp breaker that is in good working condition.

A full 15 amp load, that does not run more than 3 hours, is allowed on a standard, everyday 15 amp circuit breaker.

Either the breakers you have tried it on are weak, or the unit is drawing more the nameplate rated amps, for some reason.

Without knowing the actual amp draw by measuring, you are only guessing. If the unit does work on a 20 amp breaker, it maybe drawing more current that it should, and you will not know it.

I also asked exactly what is tripping, the GFI outlet, or the breaker, and Stratman asked if it is the internal fuse. At this point, we have no answer to these questions, and everyone is still guessing.

jdiamond · Nov 15, 2007, 01:04 PM

The outlet if I plug into the outlet, or the surge protector if I plug in through a surge protector. Never the Actual Breaker

tkrussell · Nov 15, 2007, 01:18 PM

Now we are getting some where.

This info up front would have been helpful to eliminate all the guessing.

So the 15 amp breaker holds fine?

Try using a standard receptacle, and not with a surge protector.

jdiamond · Nov 15, 2007, 01:42 PM

Originally Posted by tkrussell

Now we are getting some where.

This info up front would have been helpful to eliminate all the guessing.

So the 15 amp breaker holds fine?

Try using a standard receptacle, and not with a surge protector.

I guess the question I have (not being an electrician and just reading stuff in books)...
If the receptacle is in the kitchen, and not too far from the sink wouldn't I need a GFCI?
What does the surge protector do between the microwave and a standard receptacle that would cause a problem?

If I want to use a GFCI receptacle, should it be 20 Amp?
Thanks!!

KISS · Nov 15, 2007, 02:37 PM

Yep, GFCI's when not to far from the sink. 20 amp GFCI circuits are recommended in the kitchen. GFCI's are not recommended for refrigerators. Trouble is, the GFCI 20 amp recepticles, I've seen will not allow 20 AMPS at the GFCI, but will allow 20 Amps for any outlet downstream.

If you have ever taken apart some surge protectors, you'd understand.

This is one brand I'd recommend. Tripp Lite Isobar Surge Suppressors

Note their equipment warranty. If you ever had to exercise a surge supressors equipment warranty, you'd understand. Surge supressors without an equipment warranty won't help you much.

We can ask what is the rating of the circuit breaker/fuse in the surge supressor. What AWG wire is the cord? How long is the cord? How many Outlets? What Brand? Do you have a web link?

jdiamond · Nov 15, 2007, 02:42 PM

Originally Posted by KeepItSimpleStupid

Yep, GFCI's when not to far from the sink. 20 amp GFCI circuits are reccomended in the kitchen. GFCI's are not recommended for refrigerators. Trouble is, the GFCI 20 amp recepticles, I've seen will not allow 20 AMPS at the GFCI, but will allow 20 Amps for any outlet downstream.

If you have ever taken apart some surge protectors, you'd understand.

This is one brand I'd recommend. Tripp Lite Isobar Surge Suppressors

Note their equipment warranty. If you ever had to exercise a surge supressors equipment warranty, you'd understand. Surge supressors without an equipment warranty won't help you much.

We can ask what is the rating of the circuit breaker/fuse in the surge supressor. What AWG wire is the cord? How long is the cord? How many Outlets? What Brand? Do you have a web link?

I guess the answer to the surge protector question after looking at the link you posted, is a cheap junky one. I guess that would answer my question.

With respect to the GFCI receptacle, there's a chance that the 15 Amp GFCI receptacle is not allowing 15 Amps at the GFCI and that's why I'm probably having a problem with that unit?

Thanks

labman · Nov 15, 2007, 03:13 PM

Is it possible the GFCI is doing its job and detecting a small ground fault? I would be tempted to take it back where I bought it and let them prove to me it is OK or give me a different one. .

KISS · Nov 15, 2007, 05:55 PM

This is getting tough.

Given: The 15 A GFCI receptacle trips with a 14.3 A microwave load.
You need a GFCI if the receptacle serves counter space.

GFCI's don't trip with current overloads.

So it's microwave oven or GFCI receptacle.

I've read that some microwaves can cause nuscence trips of GFCI's. I can conceivably think of why (lack of an RFI filter). The ISOBAR Surge supressor could correct that. It has an RFI filter.

2nd. I might consider installing a premium GFCI receptacle such as the 15 A GF52 series.
http://www.hubbellcatalog.com/bryant.../section-f.pdf

If that doesn't work, I'd suspect the microwave. A half-way decent repair shop should be able to actually measure leakage currents.

In any event, items 1 and 2 can be put to good use.

EDIT: There are two types of leakages with a microwave. One is microwave radiation, the other is electrical.

jdiamond · Nov 19, 2007, 07:38 AM

Hi,
After going home and checking out the whole situation, here was the solution.

Since my microwave has a short cord it was plugged in using either an extension cord or a surge protector. Neither of these were rated at 15 Amps.

I'm sorry, I am just learning about electricity now, and for someone more experienced that would have been a simple problem.

I bought a 15 Amp extension cord and it works well in the 15 Amp Receptacle.

Thank you for all of your help!