Replacing MCC Feeder Cables
Replacing MCC Feeder Cables
(OP)
Just interested in some opinions on this topic. My building is 40 years old. We are replacing the original motor control centers. The original cables used are older fabric insulated cables run underground in the original bldg slab. I want to replace the feeder cables for reliability, since I am putting a new MCC in. Question is, what are the odds that I can pull out the old cable and put new cable in. Right now, I am thinking it's a bad idea and I should put new overhead conduit and cable in. The run length is probably about 150-200 feet.






RE: Replacing MCC Feeder Cables
On our site, if an underground conduit is more than 10-15 years old, we automatically assume that it's plugged.
I'd go overhead, no question.
RE: Replacing MCC Feeder Cables
The short answer is forget the existing UG raceway!
RE: Replacing MCC Feeder Cables
RE: Replacing MCC Feeder Cables
There is also a chemical product that is said to help release the bond between the raceway and the cable, but I have never tried it.
http://www.polywater.com/cablfree.html
Don
RE: Replacing MCC Feeder Cables
Mike
Mike
RE: Replacing MCC Feeder Cables
We often have to assume the worst, especially if the work is to be publically bid work. Then the only way one is going to be 100% certain is to run overhead. If you have the luxury of being able to have an MCC down while the feeder is removed and/or replaced, I would take advantage of that.
RE: Replacing MCC Feeder Cables
Metal conduits in direct contact with wet or corrosive earth will not last for 40 years. There may be standing water ( I have found that in one case) or the metal might be simply corroded away. On the other hand a dry earth location or conduits encased in concrete would preserve the conduits.
RE: Replacing MCC Feeder Cables
This comment comes from my personal experience, gained at considerable expense.
RE: Replacing MCC Feeder Cables
How about this one:
If the capacity of the existing cables are sufficient for the new MCC, try to test the insulation resistance level of that cables, if its still intact why bother to change it?
RE: Replacing MCC Feeder Cables
I think the consensus is I'm probably better running overhead, especially if being down for an extended period is an issue, which in most cases here, it is.
I could leave the cable in, on the basis that it still works now, megger it to get a base reading, and then megger it yearly to confirm that it has not degraded, but that just adds another maintenance task which adds ongoing yearly cost, especially if you use $100/hr electricians.
Well, thanks for all the opinions.
RE: Replacing MCC Feeder Cables
The particular job I worked on had most of the pipe in the slab, with the ends as surface runs to facillitate a quick cable connection.
The part in the slab when quick, saw cut, dig lay pipe and cover. It may go faster than an all surface run.
Some place don't work so well, you could strike water or pipes that were never "as-built"