Window AC Fuse Blown

The current drawn and the fuse rating and type would help in identifying the cause.

Since the fuse is blowing randomly, i suspect it is due to the starting inrush which may be causing it to blow. Perhaps it is underrated. There are some motor-starting fuses which allow starting inrush without nuisance-blowing. In US, they are called 'slow-blow' perhaps.

Thanks

It is 11A and 32A fuse is used .But I am suspecting contactor or motor winding some how .

Sorry, you did say 11A in your question, i missed it. The 32A rating seems low to me as per the practice in India. Was this the recommendation by the manufacturer?

On the other hand, there is usually a thermal trip embedded in the compressor motor casing if it is a sealed unit. Any overload including locked rotor would cause this to trip. Obviously this is either not there in your AC or if it is there, it is not tripping.

If the motor has a short somewhere, yes, the fuse can blow often, but i would expect the AC also not to run properly?

i would still suspect an underrated fuse as the cause. However, i look forward to your findings .. good luck.

i believe that it is already 300 % more i am thinking to make it 45 ampere

lets hope it works

One recommendation i have seen for 11A motor is a 32M40 fuse...in effect, a 40A fuse in a 32A body, for withstanding motor starting inrush better.

60Hz would indicate to me you are in North America somewhere. One of the biggest problems for homeowners here is that hardware stores continue to sell NON style fuses, which are NOT time delay (slow-blow). They are cheaper, but really should come with a warning label for the average homeowner that these CANNOT be use on anything with a motor, which is about 99% of applications here that still use fuses! The reason for my vehemence against them is exactly what you are considering doing; increasing the fuse size to avoid nuisance clearing.

THIS IS INHERENTLY DANGEROUS!!!!!

THIS POSES A SEVERE RISK OF FIRE!!!

DO NOT DO IT!!!

There are specific rules as to what the maximum fuse size is that you can use, based upon the motor size. Violating that can cause too much current to flow in the conductors and/or motor windings during an overload and the insulation can catch fire before the fuse clears. Once started, insulation fires are difficult to stop and spread along the conductor path.

Most likely what is happening is that when your compressor starts, it is pulling high current, something that is perfectly normal. But NON fuses cannot handle that high starting current and clear prematurely. What you need to do is read the manual for your A/C unit and find the recommended maximum fuse size, then buy a Time Delay fuse fr it of that size. DO NOT increase the fuse size beyond what the manual says. It is illegal and dangerous.

By the way, if your hose catches fire and an insurance inspector sees the wrong size or type of fuse installed, it may void your fire insurance! So how much cheaper was that fuse now?

Could you please tell us more about the loads you have in details?

Awaiting for ...

in an AC unit there is a fan motor and a compressor. The compressor will be on and off depending on the room temperature and the thermostat setting.Therefore there will be no of starts of compressor. If the compressor is defective the fuse will blow.if the thermostat is not set correctly then also and the timer between the starts may be defective please check

Several people have mentioned special fuses, some call them "Slo-Blo", which is what I would call them with my electronics hat on.

With my Electrical Engineers hat on I would call them HRC fuses (High Rupture Capacity)....that is what you MUST have installed.....

They allow the high starting current of a motor, far longer than a standard fuse of the same value, but would eventually break in the case of a fault current.

I was unable to find a good link with explanation on the web......

But can you confirm 100% that you have either Slo-Blo or HRC? If not, that is most likely your problem!!! As several others have already stated before me.

Have you tried Cooper-Bussmann's handbook ? http://www.cooperbussmann.com/2/SPDTableofContents.html

The 'dual-element' fuses are what you call 'slo blo' i believe, please check and let me know, thanks.

HRC fuses have many "fuse" wires in them all embedded in a fine sand. The wires take far longer to heat up and eventually melt than a normal single wire fuse does.

That gives them a High Rupture Capacity.

In general, a 3 phase motor will only take high currents for the first second or even less....

Well, BS88 specifies gM as the category for fuselinks capable of withstanding the 6In inrush current for 6 sec or so that a DOL started motor takes. All reputed manufacturers make these motor-starting fuselinks with type designations like 32M40, which are similar in performance to the slo-blo i expect. Here is a link to the Ferraz-Shawmut catalogue.

Ferraz Shawmut BS88.pdf

However, as the OP is mentioning 60Hz, maybe 'slo blo' is more useful.

HRC has to do with the fuse's ability to safely clear a fault in a circuit with higher available fault current. It has nothing to to with being time-delay or not, you can get HRC fuses both ways. For example a standard fuse may have an interrupt capacity of 30kA, where an HRC fuse would be 200kA. If you used a standard 30kA fuse in a system capable of 200kA and a fault occurred down stream, when the fuse clears the fault, the energy in that process may cause the fuse to explode, like a small stick of dynamite! An HRC fuse would not. HRC fuses are also "Current Limiting" which is why they are used in motor controllers a lot. They will limit the let-through current to a level that the contactor and overload can withstand. All moot points however for a homeowner, whose system rarely exceeds 10kA in capacity.

But to help the OP avoid confusion, HRC is an IEC (International) term, we don't use the term HRC here in North America, specially when discussing household appliances. You want "slo-blo". If you go to the hardware store and ask for an HRC fuse, they will just give you a blank stare.

But then again, they probably will no matter what you ask for...

Sorry, you do not have a clue about the subject of HRC fuses......nothing you wrote was correct with regard to such fuses for 1000 volts or less.... BS88.

Really? Nothing? Nothing at all?

Damn...

Seriously though, I'll have to accept that criticism. HRC is not a term we use here, at least not in my circles, so I was going by what I read. Although this isn't where I read it, somebody who wrote in the Wikipedia article about fuses seems to have the same opinion as me.

"Breaking capacity

Main article: Breaking capacity

The breaking capacity is the maximum current that can safely be interrupted by the fuse. Generally, this should be higher than the prospective short circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Some fuses are designated High Rupture Capacity (HRC) and are usually filled with sand or a similar material. Fuses for small, low-voltage, usually residential, wiring systems are commonly rated ^[3] to interrupt 10,000 amperes. Fuses for larger power systems must have higher interrupting ratings, with some low-voltage current-limiting high interrupting fuses rated for 300,000 amperes. ..."

This upsets me quite a lot. I have followed your posts and you come across as a person that knows what they are on about. Now it just looks like you can use google. Had you simply made reference to the wikipidea article in your original post then OK, but you posted it in such a way as to give the false impression that you actually knew what you were talking about. How many of your other posts are just copies of what others have written. Sad day for CR4 I feel.

Wow...I make an error in judgment posting on something I didn't know enough about, admit it, but explain myself. Now a coward hiding behind anonymity decides I'm worthy of character assassination. Tough crowd...

Seriously though, as I said, it's not a term used here in the US with regards to low voltage fuses, my exposure to this issue was in having to find suitable replacements when I worked for Klockner Moeller and Siemens and people would send equipment to us with IEC fuses that were virtually impossible to procure in a reasonable amount of time. So back in the day, we (not me alone) investigated what "HRC" meant with regards to the use in the equipment we were retrofitting. Apparently we were wrong. So excuse me for not being omniscient.

The main point I was making in doing that was that someone said "use HRC fuses" to the OP who, from all evidence, was in a part of the world where that advice was almost completely useless. No indignation on that issue, only chastisement for the fact that I posted erroneously on what the term meant.

And Yes, I can use Google to find corroborating information to what I post, unlike about 99% of the "Guests" who post here...

Does it do blow the fuse when it hot, not during the night?

11 amps is a crazy amp rating, but make sure the condenser (the part outside) is clean. Take the machine out of the window and take a hose to it, let it dry, and good luck.

If that doesn't work, maybe you need a new compressor (read air conditioner).

Check line voltage with unit running. Also as suggested before clean condenser and confirm good air flow. Some manufactures can supply a "hard start kit" if the problem is at compressor start-up. Those fuse ratings are strange to me-not standard here in US. Also check fuse holder.

If a motor was defective the replacement fuse would blow immediately. When a compressor stops, it should stay off for 5-30 seconds to allow system pressures to equalize before the next start. A momentary power interruption (Either from the thermostat or the power supply) causes the compressor to attempt a re-start before pressures have equalized. The compressor draws locked rotor amps for several seconds, and blows a fuse. Consider a time-delay between starts, or a Hard-Start-Kit sized specifically for your compressor. And YES, use a properly sized time-delay fuse. And NO, do not oversize the fuse.

A high compressor discharge pressure will cause over-amping. A common cause of this is debris on the entering air side resulting in low air flow through the condenser coil such as the fuzz from cottonwood trees. The coil surface can be cleaned with a stiff brush. Also check the voltage with a good voltmeter...low voltage will cause over-ramping. Less obvious problems will require the services of a qualified technician. Lou Bindner

So finally the fuse is replaced by a circuit breaker of 15 A rating the unit is running fine day and night .

Thanks