Current Limiting Fuses

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curious101

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Atlanta, GA, USA
Hi,

Is the following statement true? "The current-limiting characteristics of fuses may be used to determine protection from high prospective faults of almost everything, including contactors; but not circuit breakers."

Thanks!
 
I used them for semiconductor devices, usually on SCRs. Ferraz and GEC types mostly.
 
Used BY is an important consideration though. They can be used BY manufacturers and assemblers making “listed” assemblies that have tested series listings with the components involved. They can’t be used by contractors in the field to allow the use of equipment not rated for the available short circuit current.
 
It's not really an accurate statement since as jraef says, the rules are different for manufacturers and the rest of us. Current-limiting fuses can actually be used to increase the ratings of low voltage circuit breakers when they are a *tested combination*. Circuit breaker manufacturers can provide a list of breakers and fuses that they have tested. What you can't do is just look at the "up-over-down" fuse let-through curve and use that result to increase the short circuit rating of a circuit breaker. See NEC 240.86 (B). In theory, 240.86 (A) allows a PE to select a series rating even if not a tested combination, if they are willing to sign their name to it. I've never seen it done.
 
Jraef said:
Used BY is an important consideration though. They can be used BY manufacturers and assemblers making “listed” assemblies that have tested series listings with the components involved. They can’t be used by contractors in the field to allow the use of equipment not rated for the available short circuit current.
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Thank you!
 
David Castor said:
It's not really an accurate statement since as jraef says, the rules are different for manufacturers and the rest of us. Current-limiting fuses can actually be used to increase the ratings of low voltage circuit breakers when they are a *tested combination*. Circuit breaker manufacturers can provide a list of breakers and fuses that they have tested. What you can't do is just look at the "up-over-down" fuse let-through curve and use that result to increase the short circuit rating of a circuit breaker. See NEC 240.86 (B). In theory, 240.86 (A) allows a PE to select a series rating even if not a tested combination, if they are willing to sign their name to it. I've never seen it done.
Click to expand...
Thank you!
 
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