Cable Limiters

[charlie]

The following is from our Goldbook Section 310H in the downtown network:

In the event more than two cables per phase are required, cable limiters shall be installed at both ends of the service cables. The customer shall provide and install cable limiters on all ungrounded conductors at the line side of the service switch.​

We do not require cable limiters in other than the networked area. ​

 

[iwire]

We do not require cable limiters in other than the networked area. ​

I guess that is the same here, the only job I have seen cable limiters installed was the service for a building in a networked area of Boston.

 

[ron]

The down side with cable limiters is that it is difficult to know when one has opened, thus leaving the other cables to carry the rest of the load and possibly resulting in a more catastrophic fire because of an undetected overload on unfused primaries.

 

[Cold Fusion]

The down side with cable limiters is that it is difficult to know when one has opened, thus leaving the other cables to carry the rest of the load and possibly resulting in a more catastrophic fire because of an undetected overload on unfused primaries.

Side note - not intending to hyjack

ron -
I've only seen one install with cable limiters. It was a high-reliability feeder to a military installation. The cables had current monitors to alarm a failure. I was never sure that mattered, since anything that would open the cable limiter would be readily apparent and may even take out others on the paralleled cables.

In addition, this particular design was such that losing a cable didn't hurt anything. The rest would carry the load.

As I recall a cable limiter characteristic is short circuit only - designed not to trip on overload. It's kind of like a mag-only fuse

Applied within their design scope, I don't see any increased risk - perhaps even decreased risk of equiptment damage.

cf

 

[charlie]

. . . anything that would open the cable limiter would be readily apparent . . .

Actually, if a fault happened on one of the paralleled conductors to a service, the others (on a large service) may not see enough to open up but would feed back into the fault and take out the cable limiters for just the faulted conductor. :smile:

 

[ron]

cf,
Thanks, I was not paying attention.

Now to the op.

 

[charlie]

. . . Thanks, I was not paying attention. . .

I think you will find that it was my error. :roll:

 

[Cold Fusion]

Actually, if a fault happened on one of the paralleled conductors to a service, the others (on a large service) may not see enough to open up but would feed back into the fault and take out the cable limiters for just the faulted conductor. :smile:

I've never heard of using cable limiters on "services". I'm surprised the utility would take on the responsibility. But then again that would be only one of many things I've not heard of that are in common use.

cf

 

[charlie]

OK, since this thread was hi-jacked, I have split it so the conversation may continue in the other one and this one will be about cable limiters.

 

[Cold Fusion]

The following is from our Goldbook Section 310H in the downtown network:

In the event more than two cables per phase are required, cable limiters shall be installed at both ends of the service cables. The customer shall provide and install cable limiters on all ungrounded conductors at the line side of the service switch.​

We do not require cable limiters in other than the networked area. ​

I'm not faniliar with some (most?) distribution stuff.

What is a 'networked area"?
What voltage levels are normal for this "networked area"?

cf

 

[charlie]

. . . I'm surprised the utility would take on the responsibility. . .

Actually, that is protecting ourselves. There was a fault in the service to a downtown Indianapolis building several years ago, circa 1965 that resulted in the loss of the building. The fault was in a cable that was fed back from the bus in the customer's service equipment and the building burned down. If we had required cable limiters then, we would have lost a conductor on one phase and the remaining conductors on that phase would have continued to provide power. I don't know the size of the service but I am guessing it was north of 2000 amperes. :smile:

 

[charlie]

. . . What is a 'networked area"? What voltage levels are normal for this "networked area"?

Normally, networked areas are in major downtown areas where all utilities are underground, including transformers. When walking in those areas, you will notice gratings in the sidewalks with a 60 Hz. hum and perhaps warm air rising. That is where women tend to walk around because of their heals and guys laugh at them for doing so.

The secondaries are almost always 208Y/120 volts and are all connected together in a network. If done properly, a new building will get a new vault with a transformer and service conductors. If the transformer needs to be replaced in the future, it can be totally disconnected while the service to the building is still getting power from the surrounding vaults albeit a lower voltage.

With the advent of taller and larger buildings, we have 'spot networks' that are several adjacent vaults that are tied together into a small network just for that building and are usually 480Y/277 volts.

In much larger buildings, the primary conductors are taken into the building and feed transformers on utility floors. The customer's service is taken on those floors and not at the basement or street level. :smile: