Cable limiter availability?

[petersonra]

How does thus compare to a typical OCPD? Your example is for a limiter to protect 500kcmil which is typically applied at roughly 380A. The TCC shows this limiter would carry roughly 2500A for10 sec before opening. This doesn't seem like it would be easy to coordinate with.

I don't think they are supposed to be coordinated with. I think they are there solely in case one cable of a parallel set has a fault that needs clearing.

I can't imagine this would be a legal NEC install. Utility side only. I could see a utility not wanting to trip a whole service if just one cable faulted.

The code does not seem to allow for an ocpd that only opens one of the parallel conductors, plus there is the problem of the code not allowing for ocpd in parallel.

 

[jim dungar]

These are not intended to be branch or feeder OCPD. At best they might be called supplemental devices.
However they should still be coordinated with downstream devices.

Because each limiter only protects the conductor it is attached to, they are not truly parallel protective devices.

 

[ggunn]

In earlier code cycles they could be used in PV systems to extend the allowable distance between a supply side tap and its OCPD. That language has been removed.

 

[ramsy]

The code does not seem to allow for an ocpd that only opens one of the parallel conductors, plus there is the problem of the code not allowing for ocpd in parallel.

Julius Right linked to Bussman's use on 1 cable per phase.

Great idea after for all residential at risk for 100A service conductors on un-permitted 200A breaker.

Blown cable limiters would clarify Code Enforcement retroactive permits, for remodel hack jobs overloading the service.

this limiter would carry roughly 2500A for10 sec

David Castor's link to #500 cable-limiter curve of 2500-3300A for 10 seconds, would need to show damage to 380A rated insulation, before utility replaces that cable.

 

[David Castor]

These are intended only for short circuit protection for individual conductors. Coordination is not really a consideration.

 

[jim dungar]

These are intended only for short circuit protection for individual conductors. Coordination is not really a consideration.

Unless they open before the device they are feeding.

They were designed to remove damaged conductors from service, before other conductors are damaged. As such, it is often recommended to have a limiter on both ends of a conductor.

 

[ramsy]

it is often recommended to have a limiter on both ends of a conductor.

Probably because termination temperature rise is first to damage insulation, or destroy conductors.

 

[jim dungar]

Probably because termination temperature rise is first to damage insulation, or destroy conductors.

Most likely due to heat and fire from arcing faults inside of raceways. These limiters are installed 'before' or as part of the terminations.

 

[ggunn]

... it is often recommended to have a limiter on both ends of a conductor.

That makes sense; if a fault occurs in the middle of one of a set of parallel conductors, the current feeding the fault gets to it from both directions.

 

[ramsy]

Most likely due to heat and fire from arcing faults inside of raceways. These limiters are installed 'before' or as part of the terminations.

Most thermal imaging uses a cool cabinet reference to calibrate overheated wire, since not differentiated from conduit exteriors.

Cables fail Megger and fault inside pipe, but other equipment damage is unique to terminations, such as loose lugs, exposed conductor corrosion, carbon deposits accumulating I^2R loss, and multiple heat sources accumulating inside enclosures.

 

[jim dungar]

Most thermal imaging uses a cool cabinet reference to calibrate overheated wire, since not differentiated from conduit exteriors.

Cables fail Megger and fault inside pipe, but other equipment damage is unique to terminations, such as loose lugs, exposed conductor corrosion, carbon deposits accumulating I^2R loss, and multiple heat sources accumulating inside enclosures.

Don't forget insulation nicks/damage, rodent damage, shifted race way sections. Limiters are about probabilities of occurrence and length of time to repair during an unscheduled outage.