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Combination Starters 3

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tulum

Industrial
Jan 13, 2004
335
Hey folks,

Why is it that when I look in AB catalog unfer combination starters (513, 1233x) the Max. Available Amperes for the starters is based on type of enclosure?

I need starters for a system with approximately 20kA available @ 600V. From the literature this means if I buy a NEMA 4x box a size 4 would could handle 10kA but then if I buy a NEMA 1, 4 or 12 it is good for 25kA...

Regards,
TULUM
 
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Only AB could answer that question definitively, but if I had to guess, I'd say that when short circuit withstand testing their starters in "Rossite" fiberglass N4X boxes at greater than 10kA, something in the box system became shrapnel. If you look again, you will see that it's only their non-metallic box that could not stand up to the physical forces of a 25kA fault, as I would expect from any non-metallic box. Look above that in their chart and you will see that in the Stainless Steel N4X enclosure, the withstand is 25kA.

AB combo starter spec page

Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
Thanks, jraef.

I have another question. I am designing a layout for a distribution system for an underground mine.

The 600vac feeders will be a combination of the following;

Rockbolter 215hp 206A
Shotcrete 135hp 133A
rock breaker 100hp 99 /100A
Vent Fan1 50hp 52A
Vent Fan2 0R Sump 30hp 32A
Long Hole Drill 200hp 192A
Diamond Drill 125hp 125A
Lighting transformer 15kVA 15A

A 1000kVA xfmr with a main NDL MCCB will be feeding a disconnect that feeds a bus that feeds the above. I was thinking of combination starters for all the above. Maybe using MCCB's in each with vacuum contactors (AB 1102C) for the larger size starters and magnetic type starters (509) for the smaller units.

So from the above link this should be OK because they are rated for 25kA.

Now even though they are rated 25kA will the contactors/staters be properly protected during short circuit? Should I switch to fused disconnects?.... or should I fuse the main switch?...

Any comments appreciated.

Regards
TULUM


 
I'm not sure of your reasoning on vacuum contactors for low voltage motors that small. I have used them in the past because people in mining perceive their lasting longer in the presence of the extreme dust. My experience however has been that they are more trouble than they are worth for low voltage, they tend to be a little frail (not to mention expensive) compared to regular contactors. Better yet, consider using solid state starters for the 200HP and up units.

Have you done a proper fault study to determine the available fault current on the 600V buss? If it's 25kA or under, I wouldn't go with fuses, too much of a risk of lost production if the replacement isn't on hand, and Murphy's Law prevails in mines, so it's almost guaranteed that the one fuse size they are out of is necessary for the unit that blew.

If your fault current is higher that 25kA, you could look into CB combo starters with a higher withstand rating, i.e. ones using current limiting breakers. Usually you will find those higher ratings in MCC formats because that makes more sense in this type of application. I usually recommend MCCs to mines anyway because of the ease of swapping out starters. You'll find that AB's MCCs carry a minimum rating of 42kAIC and bracing, even though they may use the same components as in the combo starters. This is because it is more economical for AB to test an entire group of equipment at higher levels than each individual combo.

Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
Jraef,

I was thinking Vacuum contactor because I have seen it used before and because I was told there was a space savings... not the greatest reasons...

I took your advice and looked at the E1 solid state relay (592). The manual shows this relay being mounted either on a contactor or with ct's. Do you know if any size starter has this option or is it something like when you get to size 5 you have to use CT's etc.?

Thanks again
TULUM
 
I'm not sure of theirs, but most SSOLs can be used directly on a small range of motor currents, but at some point it becomes imractical to connect cables to the relay any longer. That tends to happen at around 85A, but that is strictly dependant on the SSOL design. After that threshold level it becomes more economical to use CTs, either built-in or external. There is nothing wrong with that however, in fact it allows a lot of flexibility as to where you locate the SSOL to make it convenient to get access to it.

By the way, a vacuum contactor for a 600V 200HP motor is going to be bigger than most air-gap contactors. Where that size issue comes into play is at maybe 600 or 700HP 600V.

Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
Tulum: A/B's and other's kA ratings for their device boxes: combo breaker/motor starting relay are in many ways based on HEAT REMOVAL ability. The heat created by normal current flow thru the components of the rated boxes, etc. must be safely removed. Heat created by the identical devices and loads is the same in any box. The rated enclosure must have the ability to keep this unwanted heat to a safe operating amount. Conductive materials of construction and volumeteric size are main points of consideration. The same concerns hold true with, for example, the motor o/l heater ratings. MOIRA

 
Moira,
When he referred to 10kA, he was not speaking of a 10,000A continuous rated starter, he was referring to the withstand rating. While heat plays a role in the continuous current rating of an enclosed breaker or starter, withstand ratings are based on instantaneous fault currents, typically 30 cycles. Heat is not really a factor in that other that the fact that at extreme level, heat makes some components explosive. Withstand is almost entirely based on mechanical strength, the ability of the components to stay together without becoming projectiles with enough force to exit their enclosed space and cause collateral damage.

http:/Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
Hi, Jaref: Must appolige for my incorrect interpetation of the question. Thanks for the correction and education. MOIRA

 
Excuse me for saying so. I have complained about threads a few times. But not here! This is what a good question and a set of good answers should look like. No nonsense. No superstition. No fantastic ideas. Let's keep it like this. Please.

Gunnar Englund
 
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