120/240 v or 240 v

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Old 10-10-03, 09:11 AM
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120/240 v or 240 v

Would someone be kind enough to explain the difference between at 120/240 v double pole breaker and a straight 240 v breaker?

I see breakers with one handle and others with two handles with a handle tie.

For all practical purposes, is there a difference? If so, what?
 
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Old 10-10-03, 11:03 AM
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The ones with the handle ties are for multi-wire circuits and the double poles are for traditional 240V uses.
 
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Old 10-10-03, 02:44 PM
DaveB.inVa
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...or are you referring to the ratings stamped on a breaker?

If so a 120/240 "slash" rating means that the breaker can withstand at max a 120v line to ground fault or at max a 240v line to line fault.

A straight 240v rated breaker can withstand a max of either 240v line to ground or 240v line to line.

These are more prevalent on a 3 phase 4 wire delta system because the high leg is 208v to ground so youve got to use the straight 240v rated breaker.
 
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Old 10-10-03, 07:32 PM
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Thanks Dave, I had never paid much attn to the fact that the voltages were listed with the short circuit interuption rating. I wouldnt mind seeing some info and a couple threads about these ratings as I never really paid a lot of attn to them.
 
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Old 10-10-03, 07:47 PM
CSelectric
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As Dave stated, the Voltage rating is the listed voltage of the breaker (or fuse.) There are four common configurations.
1. 120/240 slash rated, used in single phase 240 and 3 phase 208 applications.

2. 240V rated, used in 240 V three phase delta applications.

3. 277/480V. slash rated, used in three phase 480V wye applications.

4. 480V rated, used in 480V three phase, grounded delta applications.


The breaker will also be stamped with an interrupt rating (AIC) which is it's protection threshold for fault currents

You will also commonly see a withstand rating on service equipment, disconnects and the like. This is the limit to which the enclosure can contain an arc flash.
 
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Old 10-10-03, 10:27 PM
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[QUOTE]The breaker will also be stamped with an interrupt rating (AIC) which is it's protection threshold for fault currents [QUOTE] I was actually more interested in the interupt rating. Can you explain this, had it told to me a couple times and I think have a grip, but would like to hear it here.
 
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Old 10-11-03, 08:38 AM
CSelectric
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I could explain it. But a better explanation can be found at


http://www.bussmann.com/services/training


Scroll down the list until you find the "interrupting rating" column (about half way down.) The text document provides good explanation. Better still, if you have powerpoint, the presentation (free download) has some incredible slides of what happens when the interrupt ratring of a OCPD is too low for the available fault current. (If you've ever wondered what a total failure of electrical equipment under load looks like, this is the place.)
 
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Old 10-11-03, 09:27 AM
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Thans Cs, I thought I had saved that page somewhere but couldnt find it last night. I am going to have to get power point to really use it and soon a DSL line is coming here which should make it useful. The motor protection info will helpful too.
 
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Old 10-11-03, 09:59 AM
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here is a link to get a power point viewer, just a viewer can not make presentations with it.


http://www.microsoft.com/office/ork/...ndx/appa13.htm
 
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Old 10-11-03, 09:50 PM
CSelectric
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That is quite the good link to have around SB. Bussman has done some really good work in the area of safety (as well as a wealth of work in the area of overcurrent protection.) Better still, all of the Power Point training presentations are available free of charge (as are several books they'vew published on electrical safety.

I tend to be a tough guy to please as I expect the world out of those I do business with. There are many companies out there that make quality electrical components, but very few that I can honestly say have gone above and beyond the call. Bussman is truly one of those few. Especially in the areas of training and safety.

Get the viewer and take a look at the power point presentation for interrupt rating, and the ones related to arc flash, I think you'll be impressed.
 
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Old 10-11-03, 10:57 PM
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I was going to look at the flash pages too, the downloads seem big and I am on dial up, soon to be dsl I think. I see from SQ D homepage that flash is getting attn. Didnt read much though. I take it that is about switching under loads?
 
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Old 10-11-03, 11:08 PM
CSelectric
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Actually, arc flash has to do with massive equipment failure (which is, generally speaking, most likely to occur when switching under load.) The attention is due to new code regs (2002) that require arc flash warning labels on certain equipment.

I've had the pleasure of viewing both Square D's Arc Flash training videa and Bussmans Power poiunt presentation. If you ever see an electrician flip a disconnect switch or large breaker by standing off to the side, facing his haed 180 degrees away from the switch and using his weak (non dominant) hand, I can guarantee he's seen one of those presentations. Square D's video shows one heck of an arc blast, completely rutpuring the disconnect enclosure and spraying flame and hot slag out violently. Seeing that will make a person think twice before energizing a system.
 
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Old 10-11-03, 11:25 PM
frenchsparky
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as what the cs say about the arc flash i allready have one not too long ago this box is big 600 amps at 480 volts and it did flash like son of gunner and blew the box right off the cement wall and i did not look at drictally and my head was turned away. i am sure you guys and ladys want to know if i am ok ?? of course i am lucky that time but i am not going to push my luck with safety and got the extend stick to stand away some more and yes i have some burn mark on my neck and copule spot on my sholder i will tell ya one thing it happend soooo fast you have no time to react with this one . and my work coat was damaged from the blast and the sound is so loud that my co worker was half deaf for while like M120 stick go off but at diffrent tone . after that happend we regrouped and get the damaged box fixed right and retest everything before turn the juice back on . Sberry , there are some discontion switch say " isloation only " or say " do not switch under load " it mean the concats inside the fuse box or switch box can't handle the current surge and flash when the concats are opened up even it can happend with closeing too


merci , marc
 
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Old 10-12-03, 12:10 AM
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It was a curiosity thing with me, and I do read the labels. Most of my work is all small single phase stuff. I wish I had a hefty 3 phase line running near here for a couple big motors and some shop stuff but am limited to rural single. They like us to limit motors to 7 1/2 hp but I would like a hundred and a 50 or 75 for some irrigation power and one could get some deals on shop equipment in 3 ph. My work is mostly on my own equipment, have about 20 panels on 4 services.
 
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Old 10-12-03, 10:35 AM
brickeyee
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You can use a 3 phase motor as an idler to generate a third phase on a 120/240 system. It is not the prettiest thing, but it will work. The main problems are getting the idler up to speed (no starting torque is available on a 120/240 system without capacitors), the generated leg is a little low in voltage, and you are operating at 0, 180, and 270 degrees instead of 0,120, 240. Post a new question if you want a detailed description of how to do this. You can use a 3 phase motor as an idler to generate a third phase on a 120/240 system. It is not the prettiest thing, but it will work. The main problems are getting the idler up to speed (no starting torque is available on a 120/240 system without capacitors), the generated leg is a little low in voltage, and you are operating at 0, 180, and 270 degrees instead of 0,120, 240. Post a new question if you want a detailed description of how to do this.
 
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Old 10-12-03, 10:43 AM
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I have a roto phase but my prob is to run anything very lare the poco lines are too small. I did run a 15 or 20 hp for testing some equipment on but its not practical here. I was wanting 3 ph for water pumps as I am using engines now. Electric would need to be 100 hp. Nearest set of large 3 ph power lines are 4 miles away.
 
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Old 10-12-03, 02:17 PM
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Contact your state legislator and whatever version of a Public Utility Commision MI has. The POCO is generally required to supply enough power. I had to go after a co-op a few years back for low voltage. A few letters to the VA state utility commmision and a new transformer was in place.
 
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Old 10-13-03, 07:21 AM
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All good information...but I repeat my question.

Does it matter which one is used on a 120/240 v circuit or a 240 v circuit?
 
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Old 10-13-03, 07:36 AM
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For use in a house with 120/240 V service no difference. The only way to get 240 is with a double pole breaker.
 
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Old 10-13-03, 10:06 AM
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I see that SQD double pole breakers are marked with 120/240 as well as the single poles. I guess they would have to for single PH.
 
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Old 10-13-03, 07:47 PM
CSelectric
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The short answer Tom, is that you are most likely dealing with a single phase 120/240 panel. In that case, any breaker made to fit your panel will be just fine. Remember, the voltage rating is a threshhold limit, therefore it doesn't matter as long as the limit is higher than your voltage. 120V single pole and 120/240V 2 pole are the lowest rated breakers made, and will work fine for your app. (So will every other breaker made, but the higher the voltage rating, the higher the price tag.)
 
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