CB or Fused Switch as Main Svc. Disconnect?

[Jraef]

Probably. That situation is "opposite" of the way it would usually go, but still valid. Here is one list of series ratings

http://www.cooperindustries.com/con...ducation/solution-center/series_ratings0.html

I agree kind of the opposite of the way one usually looks at series ratings. If you had RK-5 fuses upstream, you probably wouldn't shell out extra $$$ for 65 kA breakers to be located downstream. I think most "standard interrupt rating" breakers will be series rated for use with RK-5 fuses. Most all that I have encountered in Square D certainly are.

What they said.

The important thing to remember about series listings is that what you THINK is irrelevant. The only thing that counts is what the manufacturer has documented.

But if you had 65kA available and 65kAIC rated breakers, you would not need RK5 fuses ahead of them. But you MIGHT be able to use 25kAIC breakers by having RK5 fuses ahead of them, and that could save significant coin. Likewise if you have 90kA available, you can possibly use 65 kAIC rated breakers + upstream fuses. But ALWAYS remember to RTFM.

As to someone constantly replacing fuses and closing into the same fault, I’ve seen people do that with breakers too, until they weld the contacts or blow. Nothing is idiot proof, the universe just keeps making better idiots.

 

[kwired]

What they said.

The important thing to remember about series listings is that what you THINK is irrelevant. The only thing that counts is what the manufacturer has documented.

But if you had 65kA available and 65kAIC rated breakers, you would not need RK5 fuses ahead of them. But you MIGHT be able to use 25kAIC breakers by having RK5 fuses ahead of them, and that could save significant coin. Likewise if you have 90kA available, you can possibly use 65 kAIC rated breakers + upstream fuses. But ALWAYS remember to RTFM.

I agree.

As to someone constantly replacing fuses and closing into the same fault, I’ve seen people do that with breakers too, until they weld the contacts or blow. Nothing is idiot proof, the universe just keeps making better idiots.

Not exactly on topic, but one time had a call for small industrial client of mine. Motor overload kept tripping, they needed to get that order done as it is shipping soon. I get there, it is for an auger that moves product - they had a guy sitting in the electrical room that would reset the motor overload immediately every time it tripped. Motor was hot enough to cook dinner on it. Don't know how much longer it may have gone without needing to replace motor. (probably didn't do the motor much good either). Of course cause of the problem was non electrical - but tripping overloads are an electrician's problem, so I become a mechanic to some extent on such calls.

 

[petersonra]

I agree.

Not exactly on topic, but one time had a call for small industrial client of mine. Motor overload kept tripping, they needed to get that order done as it is shipping soon. I get there, it is for an auger that moves product - they had a guy sitting in the electrical room that would reset the motor overload immediately every time it tripped. Motor was hot enough to cook dinner on it. Don't know how much longer it may have gone without needing to replace motor. (probably didn't do the motor much good either). Of course cause of the problem was non electrical - but tripping overloads are an electrician's problem, so I become a mechanic to some extent on such calls.

Years ago I designed a machine for one of the big 3 automakers. They wanted to have some way for the operator to be able to reset motor overloads without having to call the electrician so we had to use motor starters that had some kind of electrically driven overload reset. The program was written to allow the overload to be reset a certain number of times per hour. If it tripped too many times in an hour an electrician had to be called to reset it. I never quite understood what the thinking was. If the motors are overloaded make them bigger.

 

[Jraef]

Years ago I designed a machine for one of the big 3 automakers. They wanted to have some way for the operator to be able to reset motor overloads without having to call the electrician so we had to use motor starters that had some kind of electrically driven overload reset. The program was written to allow the overload to be reset a certain number of times per hour. If it tripped too many times in an hour an electrician had to be called to reset it. I never quite understood what the thinking was. If the motors are overloaded make them bigger.

One of the things I like about some of the more advanced Solid State Overload Relays is that they often have "starts-per-hour" and "minimum time between starts" limitation features built in.