How to protect ac transformer with 5amp fuse full

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View our Privacy Policy here. Toggle navigation subscribe. Log in. Remember Me? Login with Facebook Log in. Forgot Password? New Posts. Today's Posts. Community Member List. Forum Actions Mark Forums Read. Quick Links View Forum Leaders. Thread Tools. Clint Holland. I know this question has been asked 7 ways to Sunday but I don't see the exact issue I am having and I am not even sure they are related.

I have a single stage heat pump and when I turned it on the other day, it ran for maybe 10 minutes and then quit altogether. I am pretty good with electronics and such so I figured I would give it a shot. After checking the wiring at the tstat I realized it didnt have the 24v it needs. Looked in the air handler unit and traced the wires back. Noticed the transformer which supplies the 24v had on the primary but 0 on the secondary.

Took it out and it was obviously burnt. Looked burnt, smelled burnt and tested open on the primary. So I replaced it.What fuse to use? Posted: Feb Fri 18, am. How do you right-size the in-line primary power fuse when there are no manufacturer specifications for that equipment?

What are the factors that need to be considered? What decides Fast or Slo-blow is more appropriate? I'd appreciate discussion on this subject by the forum.

I consider un-fused equipment a home fire-hazard and that fuses allow opportunity to fix a problems before they cascade into more severe equipment issues like burned out transformers.

This time it's a lab-grade voltmeter but have seen many examples of heathkit and other brands that are not fused. In this particular instance of the voltmeter I've taken current readings of the VAC supply line and get:. I've already installed an in-line fuseholder and right now it's loaded with a ma Fast Blow but I suspect that's probably a over-rated high for this unit. To prevent a fire, a one amp fuse is probably fine and cheap for your application. If you want to protect a diode in the power supply of your equipment, then I2t rating is important.

If you are trying to save a power transformer, then you will want to reduce the fuse current to less than a half amp, for your example.

how to protect ac transformer with 5amp fuse full

I generally look at the nameplate power rating. Divide the power rating by the line voltage and that's a good starting point. It depends what you want to do. Since your current draws and most likely dead shorts occur on the secondary side of the transformer, perhaps fusing the secondaries with a pico fuse would be a better idea?

I saw it written that some transformers do not increase primary current enough to blow fuse in case of a short in the high voltage section etc. Since a short in the secondaries would cause excessive current draw, causing an overheating of the windings and ultimately failure of the transformer, I would choose to fuse secondaries.

Posted: Feb Fri 18, pm.April 1, 11 Comments. B as per NEC Amp. Filed under Uncategorized. About Jignesh. Parmar B. Tech Power System ControlB. E Electrical. Membership No:M He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. Use of ester based transformer oil in new transformers. Replacement of mineral oil based trf oil in old trf with ester based oil, their reliability and improvement in useful life of old transformers.

I would like to thank you for this such a wonderful Notes and articles that you have posted on your blog.

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Your explaination Methods of Calculations are quiet simlpe amd better understandable. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. This site uses Akismet to reduce spam.

Learn how your comment data is processed. Jignesh Parmar has completed M. Membership No:F ,M Follow This Blog by Email. The use of this content on any other websites breaches copyright Act. If You find this content in any other site,it makes the page you are viewing an infringement of the copyright. Posts Comments. Rate this:. Like this: Like Loading April 1, at am. Pankaj says:. April 4, at am. Naitik says:. April 4, at pm.

Gaurav Kumar says:. July 27, at am. Thank you very much. August 1, at pm. September 25, at am.Premium Membership. Study specialized technical articles, electrical guides, and papers. The overcurrent protection required for transformers is consider for Protection of Transformer only. Such overcurrent protection will not necessarily protect the primary or secondary conductors or equipment connected on the secondary side of the transformer.

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This results in a large inrush current which is greatest during the first half cycle approximately 0. To accommodate this inrush current, fuses are often selected which have time-current withstand values of at least 12 times transformer primary rated current for 0.

Some small dry-type transformers may have substantially greater inrush currents. To avoid using over sized conductors, overcurrent devices should be selected at about to percent of the transformer full-load current rating.

And when using such smaller overcurrent protection, devices should be of the time-delay type on the primary side to compensate for inrush currents which reach 8 to 10 times the full-load primary current of the transformer for about 0.

Protection of secondary conductors has to be provided completely separately from any primary-side protection. A supervised location is a location where conditions of maintenance and supervision ensure that only qualified persons will monitor and service the transformer installation.

Overcurrent protection for a transformer on the primary side is typically a circuit breaker. In some instances where there is not a high voltage panel, there is a fused disconnect instead. It is important to note that the overcurrent device on the primary side must be sized based on the transformer KVA rating and not sized based on the secondary load to the transformer. First notable condition is Primary Overcurrent Protection.

Great explanation. Do you have a BibTex that I can use for my publications? Because I am willing to use your work as a reference to my work. Anything is saved or stored in a transformer from cycle to cycle? You make the good point that the protection is for the transformer and may or may not protect the conductors.

how to protect ac transformer with 5amp fuse full

Thank you for this. I found the article to be very helpful though you may want to double check your math in the last example. Specifically the item below should be Please please show if a line of medium voltage If you can publish an article on this subject is appreciated.

Per NEC This caveat should be listed at 3 Supervised Location in Primary side only of Transformer. Dear Parmar,what about the over protection of transformer with respect of IEC following countries?. Whether there is any connection and formula for design of the transformer protection circuits?While most modern homes these days have breaker panels to bypass the need for fuses, you might still experience problems with your breaker panel tripping because of similar issues.

However, homes that still have fuse boxes will be familiar with the headache of a blown fuse. What you may not know is that it is a very common issue that can indicate an AC unit in need of repairs.

Small Transformer Fuse Requirements

In summer, when you least want to deal with air conditioner problems, your machine is more prone to blown fuses that will require repairs. Remember, anything electricity-related can be dangerous. One effective way to combat repairs this summer is to have your machine regularly checked by an experienced technician.

A fuse is a metal filament or wire, usually in some type of casing. It is there to protect your machine, to avoid more serious problems. It does this by stopping the flow of electricity — whenever an overload of electricity occurs, the filament melts and stops the flow of electricity, in other words, it blows.

You can be sure that something has gone wrong when this happens. Fuses react very quickly to a dangerous overload, causing over-heating and, consequently, a blown fuse. They are important because they protect your sensitive electronic devices, like your air conditioner. There are many possible reasons for AC fuses to blow, and sometimes they are connected.

Here is a list of some of the most common reasons:. An old or blocked motor causes the capacitor to work over-time. The capacitor is important because it helps run the cooling system, known as the condenser. This small part helps to regulate the electrical current as it flows through the condenser. Extremely hot weather can also cause other problems in your air conditioner.

how to protect ac transformer with 5amp fuse full

If the compressor is not working properly, the air is not being cooled enough. This could be because of too-high levels of refrigerant in the AC, or as a result of frequently turning the machine off and then back on very quickly within a minute of turning it off. The lifespan of a fuse can be up to 20 years. This means that they are at work every time you turn the machine on and off and eventually, will simply wear out due to the strain of the operation.

For help with replacing a blown fuse or repairing a unit that blows them often, contact the professionals at Art Plumbing, AC and Electric today. All Rights Reserved. Privacy Policy Terms of Use. Please provide the following information and one of our Commercial Services Representatives will contact you shortly. We take your privacy seriously and will not share or sell your information to outside companies.

How did you hear about us? How Does a Fuse Work? What Causes them to Blow? Here is a list of some of the most common reasons: Old or Blocked Motor An old or blocked motor causes the capacitor to work over-time. A Malfunctioning Compressor Extremely hot weather can also cause other problems in your air conditioner. Wear and Tear on the Fuse The lifespan of a fuse can be up to 20 years. Share on Facebook Share. Share on Twitter Tweet. Share on Digg Share.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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Background: I have a step-down transformer Pwhich is a single mains primary coil to 36V Center Tapped secondary. I'd like for both me and the power supply to not be destroyed if I happen to accidentally produce a short circuit on the secondary side.

The data sheet says for my particular transformer, "36V C. Question: Do I place a fuse on the primary or secondary coil, or both and should I use a 0. I think the fuse needs to be on the primary coil though I'm not sure the valuebut when the transformer spec identifies 0.

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Research: I researched linear regulated power supply circuits and found the following schematics:. While these schematics all to very different things, they all share a commonality in that they show a fuse on the primary side of the transformer.

I read through this post asking general safety questions about a PSU schematic.

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That individual's schematic showed fuses on both the primary coil AND secondary sides. Proposed Schematic: Here is the schematic I plan to use for my power supply up to the linear voltage regulators.

It is dependent upon the correct location and value of a fuse - I took a guess here:. Please note: I included a switch to float ground because I may want to probe with my oscilloscope and connect the probe's ground clip to something other than ground on my circuits.

Your transformer has 0. You can fuse those with a [say] 0. The center tap doesn't nee a fuse. The fuse in the primary [if you want it] needs to be much smaller. For V primary, you have a turns ratio of about 3. A mA fuse should work there. Beware that if put the secondary side fuses after the rectifier they need to be DC fuses. AC and DC fuses are not the same because the latter need to cut the arc while in the former it gets cut by the AC sinewave itself.

Use a fuse for the primaries rated for 1.

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Reason is, that the inrush current is much higher than the average current. Fuses on the secondary are optional but if you have the space for them I suggest to add them. It's much easier to drop in a new fuse than to change burned out voltage regulators. You just have to add a few resistors and a transistor. There is an example for this in the datasheet. The fuse on the primary is there to prevent a short on the transformer melting wires in your wall and starting a fire in your house.Latest Projects Education.

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how to protect ac transformer with 5amp fuse full

Small Transformer Fuse Requirements. Thread starter KG Start date Aug 2, Search Forums New Posts. Thread Starter KG. Is there a rule where under a certain VA rating, protection is not required on a transformer? The fuse for the rest of the control panel is protected by a 5AMP fuse. Do I need a separate fuse for the xfmr? Scroll to continue with content. You do not need primary fuses unless you are using a VA transformer or above. If it is 24VAC secondary then you are correct in using a transformer.

I am not sure about UL requirements but you should have a fuse on either the primary or the secondary side.

Why Does My AC Keep Blowing Fuses?

If there is a short even 40VA can cause something to burn. Not sure if you meant the secondary is protected by a 5 amp fuse. If so, this is too large. So you should put 2 amp fuse. Yes you should fuse the primary.

I would fuse it and ground the neg too.


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