Pull-out fuse disconnect verses Main CB

[maghazadeh]

Good Morning everyone,
We have this new commercial project consist of (27,000sq ft total) 2-story office building with a garage basement. Electrical room is in the basement w/ a post tension type floor between basement and 1st floor The full height of basement floor is even with grade level where incoming secondary utility ducts comes in to utility pull sect.. Plans call for a 1200A, 208/120V 3ph, 4w, 65K AIC, MSB. consist of U.P.S., Meter/main 1200A, (3) sects. totaling (15) 200A Meter/Main w/ 200A CB for future tenants, (1) 400A Meter/main as house-panel.
Since future tenant unknown, we are thinking to go with 200A pull-out fuse disco. instead of main CB. Reason if future tenant needs only 100A then they just put 100A fuse into 200A pull-out instead od replacing CB.

Q1.) Do you see any problem with fuse pull-out disco verses CB in regards to ground fault coordination.

For indoor MSB installation with underground service ducts, we come in from bottom of U.P.S. all open no sheet metal to punch for. I have not done this type of install where incoming utility ducts inters U.P.S. from the back wall- top sect. of uderground pull sect.

Q2.) Coming into U.P.S. from the back wall with (5) 5" PVC ducts,, do we need to punch the back wall sheet metal enclosure? or cut a big enough rectangle? or remove the back half-top sheet metal completely?

Thanks for any reply.

 

[kwired]

Are you talking actual pull out fuse carrier type units or just a fusible safety switch. I can't even recall seeing any pull out carrier type devices in recent years unless it is 30 or 60 amp size.

I would also guess that they don't have a very high AIC rating as compared to a fusible safety switch.

 

[maghazadeh]

Are you talking actual pull out fuse carrier type units or just a fusible safety switch. I can't even recall seeing any pull out carrier type devices in recent years unless it is 30 or 60 amp size.

I would also guess that they don't have a very high AIC rating as compared to a fusible safety switch.

I don't know the right name for it, as you call carrier type device. Just lets say a section with 6-200A meter base on top with either 6-200A CB's, or 6-200A pull out fused disconnect switches, Switch is a 2-peice where fuses are mounted in the piece that is pull out to disconnect. May be I should not call this a switch since there is no mechanism, simply by pulling out the fuse carrier it does the disconnect. I have seen then for upto 200A rating.

 

[maghazadeh]

BTW, Electrical room walls, ceiling, floor are all concrete.

 

[maghazadeh]

Are you talking actual pull out fuse carrier type units or just a fusible safety switch. I can't even recall seeing any pull out carrier type devices in recent years unless it is 30 or 60 amp size.

I would also guess that they don't have a very high AIC rating as compared to a fusible safety switch.

My thinking is with using Fuses instead of CB, higher AIC rating can be obtained for lesser expense. is that right?

 

[Jraef]

I don't think anyone makes a 200A pull out switch. Absolute insanity. There may be a fuse carrier, but it will be part of a fised disconnect switch and interlocked so that you cannot pull the fuses out unless the switch has already been opened. But I haven't even seen those in years.

 

[jim dungar]

My thinking is with using Fuses instead of CB, higher AIC rating can be obtained for lesser expense. is that right?

Someone has been 'drinking the koolaid'.

There is no single answer as to which is the best/cheapest/most reliable/??? when it comes to circuit breakers vs fuses.

Likewise, for any specific set of circumstances each device has definite advantages over the other one. Is your available fault current 22kA or 220kA?

You may be solving a problem that does not exist.

 

[maghazadeh]

Someone has been 'drinking the koolaid'.

There is no single answer as to which is the best/cheapest/most reliable/??? when it comes to circuit breakers vs fuses.

Likewise, for any specific set of circumstances each device has definite advantages over the other one. Is your available fault current 22kA or 220kA?

You may be solving a problem that does not exist.

Available fault current is unknown at this time, no poco package yet. maximum length of secondary service conductors from poco tranny to MSB is 40 ft, I am assuming the A.F.C. will be under 42KA.

 

[jim dungar]

Available fault current is unknown at this time, no poco package yet. maximum length of secondary service conductors from poco tranny to MSB is 40 ft, I am assuming the A.F.C. will be under 42KA.

42kA is not an extremely high fault current for 208V equipment, there is usually relatively little cost adder. I just looked at one manufacturer's catalog, they use the same tenant breaker all the way up to 65kA. Of course, for most multi-metercenter applications, you will eventually be confronted with series-combination ratings.

 

[kwired]

I don't know the right name for it, as you call carrier type device. Just lets say a section with 6-200A meter base on top with either 6-200A CB's, or 6-200A pull out fused disconnect switches, Switch is a 2-peice where fuses are mounted in the piece that is pull out to disconnect. May be I should not call this a switch since there is no mechanism, simply by pulling out the fuse carrier it does the disconnect. I have seen then for upto 200A rating.

I think we are talking the same thing. I'm assuming you mean a pull out assembly that holds the fuses and opens circuit at same time when removed. Like the old fuse boxes had for the main and range fuses for homes. I have only seen this feature on newer equipment in the 30 or 60 amp sizes. I have seen panelboards from about 1950 or earlier that used this type of feature in up to 200 amps. I kind of assumed that 100 and 200 amp sizes were not made anymore. I don't know what kind of fault current rating they may have but would not want to be attempting to plug one in if the available current was very high. Same fuse in a safety switch is at least enclosed when you turn the switch on.

 

[texie]

Wow, it gives me the willies just thinking about plugging one of those babies in with an unknown downstream bolted fault. Speaking of 70E....