Cable Limiters to Reduce Arc Flash

[xguard]

I've just heard of cable limiters recently. I'm wondering if they can be used to reduce incident energy on the line side of our service disconnect. In ETAP I'm able to use them to drastically reduce the incident energy. In this application, with 4 conductors per phase, if I lose a conductor due to the cable limiter blowing the remainder of the conductors will now carry the full load for that phase. Is there a way to detect or monitor for this condition? Anyone familiar with using them to reduce incident energy?

 

[ron]

Do an internet search for Blown Fuse Monitoring Relays

You just have to figure out a legit way to connect the sensing conductor to each side of the limiter.

 

[jim dungar]

Anyone familiar with using them to reduce incident energy?

I have never seen them used for this type of result.
Arcing fault currents are often well below the operating point of current limiting devices resulting in very long clearing times and high incident energy levels. Remember each limiter will only see about 1/4 of your fault current.
Probably, the most common equipment mitigation technique I see is the use of a main switch mounted remote from the rest of the the typical 'service equipment'.

 

[kwired]

Incident energy not only has amount of current factored into it but also time duration of that current, be careful and don't assume lower current directly equates to less incident energy, you need to factor in how long the incident will last and lowering available current can mean longer duration before the circuit is opened. Some cases may lower incident energy, some may increase it, depends on the trip curve and actual mechanical response.

 

[mayanees]

Cable limiters used for IE reduction

Cable limiters used for IE reduction

I've just heard of cable limiters recently. I'm wondering if they can be used to reduce incident energy on the line side of our service disconnect. In ETAP I'm able to use them to drastically reduce the incident energy. In this application, with 4 conductors per phase, if I lose a conductor due to the cable limiter blowing the remainder of the conductors will now carry the full load for that phase. Is there a way to detect or monitor for this condition? Anyone familiar with using them to reduce incident energy?

I'm running into the same application with parallel 350kCM conductors with a Bussman 500-amp cable limiter catalog number KCM. And just as in your situation the IE level is drastically reduced from 130 calories to 1.5. That was modeled just as it's wired with two 350s connecting from the utility with a limiter in each phase.

A fault on the line side of the service-entrance switch would result in half current flow through each cable, and the limiters provide the fast-acting trip that greatly reduces the IE level.The SKM model runs such that the fault current splits between the two parallel conductors, so each limiter is seeing half of the fault current.

I'm inclined to model it that way, but I need to scrutinize it because I don't want to mislabel.

Any thoughts are appreciated.

 

[mayanees]

additional data

additional data

I was able to get a more realistic IE level when using the Utility's reported minimum fault level of 21 calories.

I think that if properly modeled with a limiter in each phase, one can see from the arc flash report that each cable contributes to the fault and consequently to the IE level.

John M

 

[augie47]

I had been told at one time they would not contribute to a reduction but Bussmann's literature speaks otherwise:
http://www.cooperindustries.com/con...l_library/BUS_Ele_Tech_Lib_Cable_Limiters.pdf

 

[mayanees]

I had been told at one time they would not contribute to a reduction but Bussmann's literature speaks otherwise:
http://www.cooperindustries.com/con...l_library/BUS_Ele_Tech_Lib_Cable_Limiters.pdf

Thanks Augie.

That's exactly what I'm looking for.

 

[Tony S]

How long have these been available? I can think of several projects I’ve been involved with where they would have been useful.

 

[ron]

How long have these been available? I can think of several projects I’ve been involved with where they would have been useful.

Cable limiters have been around for a very long time.

They have the down side of potentially one failing and causing the problem to focus on the remaining feeders that have an un-opened cable limiter.

 

[jim dungar]

How long have these been available?

At least forty years or so. Their main purpose, is to isolate individual cable making up parallel runs (typically 3 or more). When a cable is isolated, the remaining conductors must be able to carry the entire load or the loading need to be reduced until the limiter is replaced.

Problems with using them for arc flash incident energy reduction include:
the extended down time required to replace them (they are crimped on, so cutting them off may result in conductors needing to be 'lengthened')
the lack of availability for replacements (they are not usually off the shelf items)
the amount of current required to operate them may not be available during an arcing event.

 

[Tony S]

You live and learn, although a bit late now I’m retired.

One project in particular springs to mind was two transformers each with four 240mm² 4 core cables. The cables were about 600 Ft running though a chemical plant, the only protection before the LV ACB’s was the MV OCPD and REF.

 

[iceworm]

I'm running into the same application with parallel 350kCM conductors with a Bussman 500-amp cable limiter catalog number KCM. And just as in your situation the IE level is drastically reduced from 130 calories to 1.5. ....

130 cal/cm^2 down to 1.5 cal/cm^2. That is really impressive. It went from a top rated 40 cal suit would not leave any recognizable DNA to working on it in your skivvies.

(edit to add) I'm thinking I mis-understood your post.

Look at the TCC for a Cable Limiter and compare to a time delay, current limiting fuse. A 350kcmil cable limiter is little different from a 500A fuse.

I'm not saying you are wrong, but I would suggest you really take hard look at the model.

Curiosity question:
Where did you find a reference to cable limiter sizes is amps?. Years back, as I recall, (that's code for I don't clearly remember) cable limiters were rated in amps. All the current literature I have seen, they are rated in wire size.

 

[iceworm]

I had been told at one time they would not contribute to a reduction but Bussmann's literature speaks otherwise:
http://www.cooperindustries.com/con...l_library/BUS_Ele_Tech_Lib_Cable_Limiters.pdf

The link really only says:

Residential Service Entrance
With Single Cables Per Phase

Cable limiters may be located on the supply side of the service disconnecting means. The advantages
of using cable limiters on the supply side of the
service disconnect are multi-fold:

...

4. Their current-limiting feature can be used to minimize arc-flash hazards by reducing the
magnitude of the arc-flash current and the time of the arc-flash exposure. ...​

The application is narrow.

 

[iceworm]

...
Problems with using them for arc flash incident energy reduction include:
the extended down time required to replace them (they are crimped on, so cutting them off may result in conductors needing to be 'lengthened')
the lack of availability for replacements (they are not usually off the shelf items)
the amount of current required to operate them may not be available during an arcing event.

Jim -
I pretty much agree: I have not seen any evidence they are a fix-all for arcflash.

However:
The extended down time for repair and lack of availability would not be an issue. Once there is a arcflash incident, there is a lot of stuff to fix besides replacing the cable limiter. They are high current, time delay fuses. They are not going to open unless something went catastrophic.

"the amount of current required to operate them may not be available during an arcing event"
Absolutely agree

 

[Jack Sprat]

Proper application of cable limiter is to install on the source side when (1) or (2) cables are in parallel. When more the (2) cables are in parallel per phase they are placed on each end of the cable. When a single cable faults, current goes through all cables in parallel to get to the fault location. So with (2) cables in parallel, the fault will not be cleared until both limiters trip. When I use these solely for arc flash reduction I install only on the source side of the cable. The cables must be verified to have a withstand capability to be protected by the primary device. The limiters on each phase will continue to trip until the fault is cleared. It will not be as fast as a current limiting fuse but it will be orders of magnitude safer than relying on a transformer primary overcurrent device. To ensure the limiters trip however you much take the minimum available fault current and divide it by the number of cables you have in parallel (25kA across 5 limiters is 5kA each). When one goes, they will all go.

 

[bwat]

(2 year old thread)

 

[Jack Sprat]

I thought I would contribute since it is still first on google!