The reason for the voltage rating is the arc over voltage. That is if the voltage is high enough when the fuse element melts there will be an arc created in the fuse and the current flow will still not be cut off.
At work we had some fuses that were about 8 inches long and over an inch in diameter. They were rated for only one amp, but for 6000 or so volts.
Fuses that have a higher voltage rating are fine to use in the low voltage applications. They only work on the curent. In those inexpensive meters with fuses only rated for 250 volts, they could be dangerous at higher voltages. We were shown a trainging film by the Fluke salesmen. They showed what could hapen if you had a low voltage fuse and had the meter set for ohms or amps and put it across a 480 volt line with plenty of curent. The fuse would arc over and the leads would melt down. You would too if you were holding the leads. They make some special fuses for them to get the higher CAT ratings.
Ok, that makes sense. Apparently the element inside the fuse must melt for a wider gap on higher voltage rated fuses. Which would occur because of the type of metal used and/or shape of the wire. I have seen fuses with that element looking wavy, so I suppose that has something to do with it. This is all mostly just a guess, but something has to make that gap wider to prevent arc-over.
I can see arcing at voltages above 250 V. I have worked on lots of old tube tv sets, and have seen the B+ high voltage jump across tube socket pins and other places. Most of the time the voltages were from 300 volts up to nearing 600 volts. Apparently these meters are not really suited for that higher voltage tube gear, even though both the AC and the DC ranges go to 1000 V.
I do find the 32 V limit on some of those fuses sort of an oddball figure though. Any voltage from 32 to 100 V is not going to arc much. Even 120 V AC line voltage really does not arc very much. Most of the arcing I have seen has been over 250 V. The CRT anodes on old CRT tv sets were notorious for arcing, but that was several thousand volts. I have seen (and felt) the arcing from electric livestock fences (that bites, and always makes me use my worst vocabulary). Those fences are generally 2000 to 6000 volts.
Anyhow, this has been an interesting thread. I learned more about fuses, which I have used for decades but never given much thought to them, other than selecting one that is the right amperage and fits the holder. It is likely I have used automotive fuses on tube gear that were not rated for the voltage. Now I will be more aware of that.
Speaking of arcing. There is a youtube video where a main high tension line on a tower is disconnected, and that forms am arc that keeps growing taller. (Called a Jacobs Ladder). If I recall, the voltage is something like 500,000 volts. The guys open 3 switches on the tower (3 phase), and that arc occurs. Those switches are probably one of more feet of gap, but at that voltage it dont seem to matter. That's an awesome video.....
Just to mention it, I ordered some fuses on Ebay. 5 X 20 mm. I found they wanted around $6.50 for five 500ma fuses. Then I found a whole kit of 100 of that size fuse, for around $7.25. The kit has ten of the 500ma size and ten more each of other amperages, up to 15A. Needless to say, I bought the whole kit for pennies more.
Amazon was pulling their usual shit. They list something for a certain price but require a minimum dollar amount order, and add even more if I am not a "prime" member and then add high shipping in the end. I began with a $7 box of fuses and would have had to pay double that amount in the end. Precisely why I never buy from Amazon..... They can keep their bullshit games, and shove their "prime" service up their a$$.
The initial item was cheaper on Ebay, and with free shipping, Thats all I paid, and checking out was much quicker too. I dont know why anyone even bothers with Amazon. They're crooks....
Until Radio Shack closed their doors, they DID have a decent selection of fuses, switches, and certain other parts. They were lacking with capacitors and semiconductors though. Yea, their prices were a little high, but they were convenient....
Places like Digi-Key, Mouser and others like that all have minimum orders, and high shipping. I dont even bother looking on those places anymore, unless I intend to buy a whole bunch of stuff that I dont really need, just to obtain one part.
Den onsdag den 31. januar 2018 kl. 21.07.57 UTC+1 skrev snipped-for-privacy@tubes.com:
arc welding is done with around 20V, once you get the arc started the the ionized air is like a short and just keep going until the distance gets to large
Mouser: "No minimum order dollar amount on products normally stocked in our warehouse."
Digi-Key: "There is no minimum order or handling fee."
"Except as otherwise provided on the Site, (1) shipping or freight charges and insurance will be paid by the customer*,
When a check or money order accompanies your order, Digi-Key pays all shipping and insurance (our choice for method of shipping) to all addresses in the U.S. and Canada."
So, if you want to order a single pack of fuses from Digi-Key, you can do so very inexpensively - simply MAIL them your order (rather than submitting it on-line) and include a check or money order.
A while back I ordered some coffee off Amazon. It shipped from Target. I looked at the Target site and it was less from them, so from then on I go to the Target web site. Would go to Target, but it is about 30 miles one way from here.
I live in a small town so not too much around here. Even with some shiping charges, it is less expensive for me to order things.
Really came out a while back with Best Buy. Ordered a 60 inch TV tht had free shipping. Two people came out and set it up. They turned it on,but said they could not mess with the cable TV as per company policy. They carried off the packing material and offered to carry off the old TV. All that service was free. The nearest BB is about 30 miles away.
While I do order from Amazon, I also check other places for the best price.
There is a lot more to the fuses than meets the eye..
I don't know about the low voltage fuses, but wild guess for the 32 volts is most of them were used in cars and trucks where 24 volt batteries were the highest and the 32 was some safety factor.
The 250 volt is good for common house voltages in the US.
My Fluke meter has 2 fuses in it and they are both rated for 1000 volts. One is for 11 amps and I don't recall the lower curent one. That is so it will meet the CAT 3 requirements. If you have not heard of the CAT requirements, you should look it up on the internet. I don't know wht the voltage ratings are for my old Simpson 260, but should look one day. I do have abox of fuses that will fit in my Fluke but they are only rated for 600 volts AC. As I don't work around anything but around the house I would use them if one of the origional ones blow. If I was still working and around the 480 vot 3 phase stuff that had 500 amp or more fuses in it, I would only replace with the origional type.
I do have a hand full of the Harbor Freight 'free' voms scattered around the house and cars. Good enough for quick checks. They are really very accurate for the price (usually less than 1 % off the Fluke) as I compaired them with some of the Fluke meters.
I do remember drawing arcs of several inches off the old black and white TVs. I think they ran about 10 to 12 thousand volts.
You mentioned the Jachobs ladder. I have made them out of old neon sign transformers and some furnace igniter transformers and some rods about 2 feet tall.
The fuses are not just voltage rated. The fuses Fluke uses are rated for interrupting on circuits with high available fault current.
The available fault current rating is very familiar to electricians working on power circuitry, like where you used to work.
"Category rated" meters need to be used on high capacity power equipment
- you must have used them where you used to work.
Why use the right fuse, and in particular Cat rated meters:
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"Arc flash" has been recognized as a danger, and provisions are creeping into the US National Electrical Code, and it is a particular issue with OSHA. "Personal Protective Equipment" may have to be worn when access covers are removed, and some equipment is not safe to work on live.
The smartest electrician I have met was on a trouble call to a food plant. He wanted to measure the motor current on a moderately large motor. The only place to do that (and a good location) was the motor starter. It was in a 480V motor control center - a frame with module spaces that motor starter "buckets" were installed into. He opened the door and put a clamp on ammeter on the motor lead, absolutely common practice. It is not known what happened next, but there was an arc flash. He was in the hospital for quite a while. Some of his injuries were from copper vapor condensing on his skin. He looked younger after the plastic surgery. Among the damage to the plant - one of the high voltage primary fuses to the supply transformer for the building blew and its fuseholder was damaged and had to be replaced.
It can be a problem at lower voltages too. A downtown building had a mere 208/120V service, but high available fault current with 4 or 6 supply conduits. The service 'burned down' (no one around). Some of the service wires burned back into the conduits, with a few welding themselves to the conduit. (The were attached to the utility transformer vault bus bars with "cable limiters", a combination lug and fuse - fuse was blown.) Some of the wires burned back and remained live.
Some of you probably have exposure to high capacity power equipment, like where you used to work.
Where I worked was in a very large plant. The primary feed came in from
2 directions so we would not loose power if just one of them failed.
From there it was cut to 13,200 volts and feed to other parts of the plant where much of it ws converted to 480 volts 3 phase. We were always working on 480 volt circuits that could have up to 500 amp fuses feeding them. We used either Fluke meters or the good old Simpson 260 and the old analog Ampprobe . No 'hobby' or consumer grade meters in the plant.
One fellow at work was just turning on a 480 3 phase breaker for the motor starter in one of the motor control centers. It was only about 10 or 20 amps as I recall. Good thing the door was closed on it at the time. There was a major melt down. It took out the buss bars behind it. Those were rods about an inch or more in diameter. Hollow, not solid. We had to replace the whole MCC. That was about 50 circuits ranging from a few amps to about 50 amps in that particular MCC.
Then there were the low 24 volt circuits ar about 20 milliamps. Nothing to get excited about. Just had to really keep in mind what we were working on .
Years ago, I ordered a few books and DVD movies from Amazon. That was before they started playing all their stupid games. Back then, I was able to look at the item, see it's ACTUAL price and shipping, and checkout easily without any minimum order or requirement to join their damn "club". Back then Amazon was mostly just there to sell books and recordings.
I am the kind of person who hates money games both online and in brick stores. I once shopped at a Walgreens store that required membership to their "rewards club". I only went in there to buy a cold drink (soda) on a very hot day. The soda was on sale for something like 79cents. When I got to the checkout I was asked for my rewards card. I told them I did not have or want one. I was then told that this soda would cost me about $2, without the rewards card. She handed me the sign up form. I quickly looked it over and said "sorry, I dont give out personal information, due to the risk of identity theft". She said, ok, but then you dont get the sale price. I replied "and then you dont make a sale", and I walked out of the store and have never gone back to any Walgreens store since.
I guess Amazon is now the online version of Walgreens, and from what I understand, I would have to pay them to join their bullshit "club". NO THANKS!
Even though I'm retired, I have a lot of things to do and even if I am not real busy, I have projects to do, friends to visit, and personal things that need to be accomplished. I do not have the time or the interest in playing these money games, which waste my time. When I shop, I make a list, grab what I need and want to exit the store as quick as I can. While I like saving money, as do most people, I am not selling my identity for a bag of free potato chips or to save a few pennies. If people knew how much money those stores make off selling their mailing lists, they would have a panic attack, when they realize all they get in return is a couple bucks worth of savings from time to time.
I too live in a rural area, and our local town has little for shopping. We have a dollar store (I like that place). We have 2 grocery stores which have fair prices. We have a Shopko, that place has outrageously high prices. And we have a local ripoff hardware store that charges 2 or
3 times what the item would sell for at most other stores. Our local lumber yard is the same, very over priced. That's about all we have for stores.
The nearest larger city is 55 miles away for me (each way). That's the only place I can go to shop at electronic stores, home improvement stores, or buy anything beyold the very limited things in our small town. There is however a Walmart about 25 miles from here. Either way, its costly for fuel and time consuming to go to those stores. So, if I need some special thing, I add it to a list and try to limit my trips to the big city to once a month. Or I go to that Walmart. Otherwise I am stuck paying the very high local prices, or shopping online. I do a lot of business on Ebay. At least Ebay puts the price upfront including the shipping and I dont have to play stupid games. Ebay also does a decent job of dealing with defective items and other problems for the most part.
No, I'm not angry. I just dont shop at places that annoy me with bullshit games, and I dont give out personal information to businesses. My choice!
You made my point. I regularly buy $3 items online. Just today I ordered some XLR adapters that cost around $5. When I need a $5 item, I buy it and dont expect to meet a $25 minimum. Same as when I buy a can of soup in the grocery, for $2.79. Thats what I need and that is all I intend to buy.
When I go to Ebay, I can order small items one at a time and checkout with no hassle. If they want me to pay $5 shipping for a $3 item, I can find another seller, or not buy the item.
And what is a "handling fee"? Shipping is a REAL thing, but handling fees are bullshit. If they dont want to handle the item, they should not be in business. If the local grocery store tried to charge me $1 for a $2 can of soup, I'd tell them where to shove that can. Why should I have to pay someone to handle an item, when that is THEIR BUSINESS. If they dont want to handle items, dont run a mail order business.
I tried to buy something from Amazon this week. For an $8 item, they said the shipping would be free if I bought $25 worth. Then insisted I be a "prime" member. I didn't need $25 worth of stuff nor do I want to join their club. So, they made me go thru thru the entire checkout process before telling me that I'd have to pay around $17 to buy it.
I found the identical item on Ebay for $7.25 with FREE shipping and no other costs. Guess where I bought it?
An order at an Amazon warehouse does not assemble and ship tag and handoff to the shipper all by itself.
And you go to the store. There is no ship cost. Not even a valid comparison.
It has always been shipping and handling.
It has simply been only referred to as "shipping". You can bet, however, that those merchants have agreements with those shippers and get far lower rates than what you see. So the number reflects the ship fee *and* the handling fee, even though the moniker used does not and there is always the single price. That is why is some cases they can eat the "shipping".
basically it's the non-refundable part of the item price. it would be more reasonable to include it in the price, but mention it as restocking fee, but customers aren't smart enough to demand that.
At least they told you. My last order through amazon they didn't tell me the true price until I had paid.
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Amazon has both, items that are what they say upfront and ones where you only get free shipping if you spend 20 notes or pay to join 'prime.' Most things are just what they say, so although the time wasting stuff is there there isn't much of it.
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