Panel design

[Rick Densing]

Re: Thanks for the info

. I use rubber bands to hold the wires securely in the wire duct. I just stretch them across the duct. Helps keep everything nice and organized.

We often use left-over push button gaskets.

 

[elevmike]

Tip of the day..

Another benifit to the round hole duct.. to hold the wires in place we weave a back and forth through the top row of holes, around the entire duct. The cover can still be place on and when the field tech remove the cover the wires dont all fall out..

 

[pstephens]

Re the fuses vs. breakers issue...

The other day, on a different topic, someone posted a link to the Littlefuse website. I wound up spending some time there reading various articles, and I happened to notice this one.

Now, maybe Littlefuse is just trying to sell more fuses, but they raise some good points about the differences between fuses and breakers that I wasn't aware of. Electrical dummy that I am, I always just assumed that, apart from cost and resetability considerations, they were essentially equivalent. It appears that they are not. Even taking the authors' possible bias into consideration, it was an interesting read.

Paula

 

[Rick Densing]

My understanding is that with the new arc-flash standards, a circuit must open within a cycle. Breakers will not be allowed in a lot of circumstances.

 

[testsubject]

You may be referring to the interrupt current rating of the device. It sounds like UL might be changing how they look at interrupt current ratings, although I haven't heard anything about that either.

I believe as it is now a breaker or fuse just needs an interrupt rating equal to or greater than the lowest current limiting rating of any device upstream of it. I believe this is the basis of coordinated protection. If what you say is true the coordinated protection concept is going by the wayside.

Keith

That's what it was!!

He said that this is the new standard and it will be effective sometime in '06. It will not be optional. So they are switching back to fuses now because they are so much cheaper than comparable CBs.

 

[ShawnK]

I have always thought Europeans were more inclined to use fuses over circuit breakers, is this true? Maybe these changes are the way the UL is going to globalize their standards.

 

[ArikBY]

In one word the difference between fuses to CB are SPEED.
When you need to protect delicate equipment I use fuses "rapid" or "Ultra Rapid"
In all other cases I use CB.
BTW overe here and in Europe they much cheaper then in the States.

ShawnK

In Europe and here we tend to use CB more then fuses.

In all the panel I have made in the States I had to argue with the UL inspectors about that,when I show the proper documentation I convinced them.
Even in Chicago.

 

[CaseyK]

Tom mentioned "NO FUSES"

I agree with Tom. I may go back to using some in the future. Many times I would get an out of state call from some Cateerpillar field tech, whose generator wouldn't start or run, becuase of a blown 5 or 10 amp fuse, and no spares. On panels I designed, there was a multiple fuse holder with TWO spares.

Do fuses protect?

Many years ago, I was bored, and spent a Sunday afternoon (off duty) at work (Peoria Police Radio Shop) with a huge box of 20 amp fuses, and a really heavy duty adjustable power supply.

Setting current limit to 20 amps, the 20's blew instantly every time.

Bringing the current up slowly from zero amps, ALL fuses tested blew at 35 amps, OR HIGHER.

House fuses act similarly

Just think of all those old houses out there with knob and post wiring, with slow blow 30 amp fuses, and they turn on the tv, then the stereo, then a couple of lights, maybe the vacuum, and a couple of more lights, then a computer or two. Then I get a call that the fuse box is buzzing, or arcing, or some wires or warm or HOT!

Corcuit Breakers

I like the circuit breakers Eric used in his 8 x 12 slope panel.

BREAKERS

PANEL

(Yes, I get a commision every time I link thhis thread)

RANT

Over the years I am surprised at all the plants that DO NOT HAVE SPARE FUSES.

regards.....casey

 

[leitmotif]

I may be old school, and some of my experience was as a submarine electrician. I was the smallest of the group for a long time. It was amazing where the designers could stuff boxes where you had to wriggle in and then use a droplight to see what you were trying to do.

This design it right and make allowances for the future has got to go!!
How do I as an electrician make money when you guys make the conduit larger than needed??
Panduit that is not jam packed full - what is this?

LEAVE EXTRA ROOM ?? I just love the drill of trying to stuff the next size larger item in a control panel -- sort of like jamming 5 pounds into a 3 lb bag.

2" inches to allow space for termination?? What happens to the challenge of it all??

COOLING FANS and FILTERS How do you expect electricians to make a living if you design to prevent failure ??

AND LAST BUT NOT LEAST -- an installed light fixture in a cabinet?? I always loved getting burned from the trouble light or the flashlight rolling away.

Hoo boy -- and my brothers call me the king of overkill -- keep it up you have your minds right.

Dan

 

[Gerry M]

I believe as it is now a breaker or fuse just needs an interrupt rating equal to or greater than the lowest current limiting rating of any device upstream of it.

This doesn't make sense to me. A fuse or breaker should be rated to handle the available short circuit current. As you move out from the supply transformer the available short circuit current drops. So, the interrupting rating of your CB or fuse usually can decrease also, not be the same or higher. I can see possibly using that as a rule of thumb if you don't know what the available short ciruit current is though.

My understanding is that with the new arc-flash standards, a circuit must open within a cycle. Breakers will not be allowed in a lot of circumstances.

As far as NFPA 70E I don't think you need to have fault clearing in one cycle. But, if you use fast clearing CB or fuses, in less than a cycle, then your arc-flash hazard decreases dramatically. I think its just a method of reducing the flash hazard.



As far as fuses or CBs, I like CBs in my panels because they are more convenient.
However, on the plant power level we use alot of current limiting fuses in our power distribution. Its a good thing because we are now doing a formal short circuit/flash hazard analysis. And so far it shows where we use CBs, some of them are under rated for short circuit current. In places where we use fuses we are covered because the fuses have a much higher interupting rating.

Do fuses protect?

Often, they protect better than CBs, if you use the correct fuse for the correct application.



External programming ports can also be found at Saginaw Control & Engineering. We also now use these due to NFPA 70E. I still put an in cabinet outlet here and there, usually for a computer or bar-code.

 

[CT782]

We are purchasing some new machinery from a German manufacturer. They refused to even discuss the fuses vs. breakers issue. Their position was quote:

"NO BREAKERS, Breakers can fail and not trip, if fuse fails, it will always fail open!"

So it's all fuses for us, the problem there is the lazy electrician that just puts a 10A fuse in place of the 4A that keeps blowing rather than troubleshoot the problem.

 

[Mylo]

One would suppose that the age old arguement comes into question,
However the simple fact remains, Fuses can fail too !!!!! the only way to test is to trip them, hence you cannot use them after, at least an MCB you can test then reset

 

[cbohn]

Fuses vs CBs, Ferrules, Europe

I have always thought Europeans were more inclined to use fuses over circuit breakers, is this true? Maybe these changes are the way the UL is going to globalize their standards.

The "Great Debate" over fuses vs circuit breakers isn't going to be resolved here, even with so many great minds attacking the issue. Best advice is to know what you're trying to protect and make sure your choice will do the job. All fuses are not created equal, and neither are all circuit breakers. For certain loads, there is usually suitable breaker available to protect it. It seems that there are more flavors of fuses available for specific requirements. Data is generally available for all over-current protection devices that shows Current vs. Time.

My first experience with European machines goes back to 1982, and the Europeans were then and still are using a lot of breakers. They also used marginally sized contactors for motor loads. (Back then they didn't bother with mechanical links between wye-delta or reversing contactors, so there was always a potential for short circuits when a contactor partially welded as a result of repeatedly "drawing the silver" over time when the contactor opened the load). Combined with the slower response time of the breakers, these marginal contactors resulted in much higher maintenance costs.

Since then, the Europeans have adopted mechanical interlocks in addition to the electrical ones, and do a better job of advertising the need to de-rate contactors for number of starts, etc. (Properly de-rated, the IEC contactors end up costing almost as much as a NEMA starter with equivalent rating). The breakers have gotten better, too. If you're protecting motors, be sure to use breakers with thermal AND magnetic trip.

A word of caution about using ferules. Be sure to use the right crimp tool!! An improperly crimped ferule can actually lose its grip on the copper strands when it is tightened into a cage clamp terminal.

Overall, the IEC standards seem to have won out. Still, there are good reasons to consider fuses. Circuit overloads occur for various reasons. Start there and work your way back to determine the best way to protect your load and your system.

 

[MikeW]

Fuses are needed for flash protection, don't ever rely on a CB. Period.

I have only witnessed plasma once in my life and nearly had severe injuries because a 100HP 460V motor was "protected" by an appropriately sized CB. The operator had only finger tightened the nuts to the motor leads on a run off test stand before heading to break and saying the unit was "ready to run". In the post accident investigation with my ears still ringing and purple spots still visible at least in my vision, it was determined fuses were needed. I have been specifying a lot of Bussmann RK1 and RK5 fuses depending on the application since then. I have had to replace fuses because of someone with a below average IQ doing something they shouldn't have done but have not had any other significant emotional events related to bright lights and loud bangs.

For all applications, I order twice the fuse quantity required and put a complete set of extra fuses in a bag inside the panel. We also have an unwritten rule that if "You take something out of the bag, replace it immediately as you may be the next one to need another one. BTW, you did figure out was wrong BEFORE installing the new fuse?".

For small (<30 A) fuse applications, I like the fuse holder that have a built in LED to show it's working and have a lever so it can be used as a switch during troubleshooting.

 

[cbohn]

AMEN!