Class CC Fuses

[Saturn_Europa]

Looking for a fuse to protect a small 115 v, 0.5 hp, capacitor start motor.

Would an LP-CC-20 time delay be a good choice? Or is a FNQ a better option

Class CC Fuses are listed as current limiting, but aren't all fuses current limiting?

The fuse will be protecting a cooling pump on a 350 hp blower, so I really want to avoid nuisance trips.

 

[GoldDigger]

Looking for a fuse to protect a small 115 v, 0.5 hp, capacitor start motor.

Would an LP-CC-20 time delay be a good choice? Or is a FNQ a better option

Class CC Fuses are listed as current limiting, but aren't all fuses current limiting?

The fuse will be protecting a cooling pump on a 350 hp blower, so I really want to avoid nuisance trips.

A standard fuse may conduct a very high current during the first few half cycles of fault current while the fuse element is heating up and may also take until the next current zero crossing to extinguish the arc. As a result you may not be able to count on the peak fault current being below the current that actually corresponds to the blowing time on the current/time curves.

A current limiting fuse is designed to interrupt the current early enough in the first half cycle that you can be guaranteed that the instantaneous current will under no circumstances exceed the rated let-through current.
You generally do not need current limiting fuses to protect a .5HP motor, no matter how critical it is. Instead you would want to be sure that you can sense the fuse opening and do an orderly shutdown of the 350HP motor before it is damaged.

There are several different types of time delay fuses available. Is the fuse supposed to be acting as the overload protection for the motor too?
The way to avoid nuisance trips is to use a higher value OCPD and a real thermal or electronic overload device of the required size to protect the motor.

 

[Saturn_Europa]

A standard fuse may conduct a very high current during the first few half cycles of fault current while the fuse element is heating up and may also take until the next current zero crossing to extinguish the arc. As a result you may not be able to count on the peak fault current being below the current that actually corresponds to the blowing time on the current/time curves.

A current limiting fuse is designed to interrupt the current early enough in the first half cycle that you can be guaranteed that the instantaneous current will under no circumstances exceed the rated let-through current.
You generally do not need current limiting fuses to protect a .5HP motor, no matter how critical it is. Instead you would want to be sure that you can sense the fuse opening and do an orderly shutdown of the 350HP motor before it is damaged.

There are several different types of time delay fuses available. Is the fuse supposed to be acting as the overload protection for the motor too?
The way to avoid nuisance trips is to use a higher value OCPD and a real thermal or electronic overload device of the required size to protect the motor.

Golddigger, thank you for the reply.

This is what I have right now:

Its an overload, short circuit combo with a lockable switch. Its been tripping at start up and shutting down the blower. I pulled amps on the pump and it was a solid 7.6 all day long. Starting amps were 12 for a few seconds. I am pretty sure the motor protection circuit breaker is going bad. Its a three phase motor protection circuit with the hot lead wired in series through all three poles.

I want to replace the current contactor and the motor protection circuit breaker with a NEMA 1 starter and electronic motor overloads that I have in supply. So yes I only need short circuit protection. But I was thinking that the NEC only allowed 175% for time delay fuses of full load current which table 430.248 lists as 9.8. Which left me at 20.

Whats your view on wiring a single phase circuit in series with all three poles on a 3 phase motor starter.

The pump runs off of small transformer that does not have secondary OCP. It is the only circuit of the transformer.

How do you decide if you should use Class 10 or Class 20 on the motor overloads?

 

[GoldDigger]

Whats your view on wiring a single phase circuit in series with all three poles on a 3 phase motor starter.

The pump runs off of small transformer that does not have secondary OCP. It is the only circuit of the transformer.

It is common practice to run a single phase motor winding through all three poles of a three phase overload, especially where the three overload poles share a common thermal environment. (or where the electronics is trying to accurately model the thermal state of the motor.)

A three phase motor with one winding at 120% and the other two windings as 0% is probably not thermally stressed (although it would also clearly not be working right) and it would be OK for the overload not to open.
A single phase motor with its one winding at 120%, on the other hand, is going to get hotter than it should.
Wiring all three poles of the overload in series makes it look like a three phase motor with all three phases at 120%, making the OL much more likely to effectively protect the motor.
Some OLs also include phase loss protection, so you would have to wire through all three poles to prevent a phase loss trip.

 

[jim dungar]

You started off asking about fuses. Now you ar showing a picture of a motor protector/overload.

Which one is 'tripping on startup'?

You need to be more specific about how long the motor pulls +12A during starting.

A Class 10 overload relay will carry 6X FLA for 10sec. A Class 20 overload relay will carry 6X FLA for 20sec.
The device in your picture is a Class 10 device which appears to be set to 10 FLA. It has a single phase sensitivity function, so a current must flow through each pole. One common method for the poles to be series connected, to feed a 120V motor, would be: Incoming line into L1, a jumper from T1 to T2, a jumper from L2 to L3, and the load connected to T3.

 

[templdl]

Looking for a fuse to protect a small 115 v, 0.5 hp, capacitor start motor.

Would an LP-CC-20 time delay be a good choice? Or is a FNQ a better option

Class CC Fuses are listed as current limiting, but aren't all fuses current limiting?

The fuse will be protecting a cooling pump on a 350 hp blower, so I really want to avoid nuisance trips.

And no integral thermal overload in the 1ph. Motor?

 

[ptonsparky]

Does the opening of that MP/CP stop the 350 HP now?

I would be very careful about putting a fuse in front of that motor unless, when it blows, it opens the control circuit to the 350 HP by what ever means you choose.
At least a very loud and obnoxious alarm that can be heard throughout the county.

 

[Jraef]

Looking for a fuse to protect a small 115 v, 0.5 hp, capacitor start motor.

Would an LP-CC-20 time delay be a good choice? Or is a FNQ a better option

Class CC Fuses are listed as current limiting, but aren't all fuses current limiting?

The fuse will be protecting a cooling pump on a 350 hp blower, so I really want to avoid nuisance trips.

So back to your original question, they are BOTH current limiting fuses and the same class. The difference is very subtle. The FNQ was designed first as protection for control power transformers, so the clearing time functions were based on transformer inrush, but they CAN be used for motor protection as well. The LP-CC was a response to the marketplace not liking the performance of FNQs in some motor applications, so they tailor made the LP-CC curves as a motor protection fuse. Most of us would never notice the difference, but if you are concerned at all, then go with the LP-CC.

Does the opening of that MP/CP stop the 350 HP now?

I would be very careful about putting a fuse in front of that motor unless, when it blows, it opens the control circuit to the 350 HP by what ever means you choose.
At least a very loud and obnoxious alarm that can be heard throughout the county.

I think that's a good idea. If you are using that little contactor to control the cooling pump, put the contactor coil circuit behind that fuse too, so if the fuse blows, the contactor drops out. Then put an aux of that contactor in the 350HP motor starter circuit to drop it out too.
{Edit, it appears you are already doing that...}

 

[Saturn_Europa]

Thank you everyone for their comments.

There is an AB compact Logix that handles the automation. So yes, there is an orderly shutdown of the blower if the cooling pump trips out.

 

[kwired]

You started off asking about fuses. Now you ar showing a picture of a motor protector/overload.

Which one is 'tripping on startup'?

You need to be more specific about how long the motor pulls +12A during starting.

A Class 10 overload relay will carry 6X FLA for 10sec. A Class 20 overload relay will carry 6X FLA for 20sec.
The device in your picture is a Class 10 device which appears to be set to 10 FLA. It has a single phase sensitivity function, so a current must flow through each pole. One common method for the poles to be series connected, to feed a 120V motor, would be: Incoming line into L1, a jumper from T1 to T2, a jumper from L2 to L3, and the load connected to T3.

My understanding is the motor protector/overload is what is there now and trips while starting sometimes, but is not overloaded once it is up and running. OP is considering using the mentioned fuses instead of the motor protector.

But your mentioning of class 20 overload could be some of the problem depending on the current drawn when starting this motor. Many devices like pictured are only class 10 overloads and won't hold on a load that takes time to accelerate compared to using a class 20 device on the same load.

 

[kwired]

Does the opening of that MP/CP stop the 350 HP now?

I would be very careful about putting a fuse in front of that motor unless, when it blows, it opens the control circuit to the 350 HP by what ever means you choose.
At least a very loud and obnoxious alarm that can be heard throughout the county.

The blank space on the lower end of the MP/CP in his picture is where an aux contact can be installed that would open an external control circuit should the device trip. I believe there are two types of aux contacts, one that only operates on a trip, one that operates on both trip and manual off.