What could cause a 15kV MC cable to be very hot to the touch?
What could cause a 15kV MC cable to be very hot to the touch?
(OP)
This situation has 3 parallel 3/0 15kV MC cables feeding a productin facility. One of the three cables is very hot to the touch (I couldn't keep my hand on it for more than 10 sec.) while the other two are not even warm. I'm not sure of the age but probably 30+ years.
My first thoughts are bad terminations, but 2 0f 3 conductors of one phase would have to be bad to cause only one cable to get hot. that seems unlikely.
Does anyone know of any other cause for a cable to be hot the entire length. If ther were insulation issues would that cause the cable to get hot?
Any help would be much appreciated.
My first thoughts are bad terminations, but 2 0f 3 conductors of one phase would have to be bad to cause only one cable to get hot. that seems unlikely.
Does anyone know of any other cause for a cable to be hot the entire length. If ther were insulation issues would that cause the cable to get hot?
Any help would be much appreciated.






RE: What could cause a 15kV MC cable to be very hot to the touch?
Second, have you checked the currents in the cables with a clamp-on ammeter?
How far from the termination were you touching the cable? A hot termination will conduct heat down the conductor very nicely.
Do you have the capability of doing infrared scan of the conductors and terminations?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Is it type MC cable?
RE: What could cause a 15kV MC cable to be very hot to the touch?
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: What could cause a 15kV MC cable to be very hot to the touch?
They are planning on doing an infrared scan this week.
The load seems to be balanced over all but current readings have not been taken on each individual condustor.
There are 3 conductors per phase and the phases seem to be ballanced.
If a ground or shield connection would be bad would that cause only one cable to be hot? Unless there is a ground fault there shouldn't be any current in the grounding conductor.
Thanks for the feedback, keep it coming.
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
You could have one phase of one conductor in the hot cable disconnected on one end or the other ( or it could have a high resistance connection.) That would mean 2 phases in the armor enclosure of a cable. If the system is not fully load the other two cables would carry the load.
Normally the current in the three conductors will even out in the A-B-C conductors for a Zero sum. If there not zero they will cause inductive heating.
Something isn't right, so something is wrong. Start looking systematically, as I said a detailed diagram is a good way.
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Thanks again to all of you for your help, it's much appreciated.
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Regards
Marmite
RE: What could cause a 15kV MC cable to be very hot to the touch?
When the utility runs it's overhead feed they don't have a grounding conductor do they? In this situation the utility protection (On the pole) is about 1000 ft away from where the transition from the overhead to the parallel MC cable takes place. I don't think there is any GF protection on the utility end but I don't know that for sure. I'll have to check that out.
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Where are you located?
RE: What could cause a 15kV MC cable to be very hot to the touch?
For many years overhead circuits sometimes used earth as the return path for single-phase loads. But in many areas that is no longer permitted. New overhead installations in the U.S. with line-neutral loads must have a neutral/ground conductor.
RE: What could cause a 15kV MC cable to be very hot to the touch?
I'm guessing earth ground is being used as the return ground path for the utility but I am working on finding out for sure.
Hopefully the IR scanning will tell all and I will be able to get this issue resolved.
RE: What could cause a 15kV MC cable to be very hot to the touch?
I'll try to describe this properly so it makes sense.
I call the utility conductors A, B and C phase layed out from left to right.
I call the three parallel conductors 1, 2, and 3 layed out from closest to me to farthest away from me. so this forms a 3 X 3 matrics.
The IR scan found three hot spots, one on each phase.
At connection A2 the differential compared to the other A phase connections is about 65 deg F, with a temperature of 135 deg F.
At connection B1 there is a 430 deg F differential with a temp. of 515 deg F. (this is bad)
At connection C2 the differential is about 70 degF with a temp. of 146 deg F.
So there are deffinitely some issues here and they will be addressing these as soon a possible.
One thing they told me is that all of the connections to the utility from the cable conductors are pigtailed using split bolts. Is this a common practis?
One other thing I just found out is that there is evidence of arcing from the armor on the MC cable and the cable tray. I'm thnking Maremite's comment about a high impedence ground fault might account for this. Any thoughts?
Again thanks for all the feedback. Long term we will be replacing all this cable I just hope that nobody or nothing gets hurt before we get that done.
RE: What could cause a 15kV MC cable to be very hot to the touch?
I'd be making immediate plans to de-energize this feeder. This is not something you can wait to deal with. You really have a responsibility to get this taken care of ASAP - like today. Or stand a 24x7 fire watch.
RE: What could cause a 15kV MC cable to be very hot to the touch?
One question I have has to do with the cable that is running hot. I don't think fixing these terminatins will fix the problem with the entire cable being hot, I think there are some issue with the cable still, I also found out that these cables are at least 40 years old.
When they reenergize this cable, is there a big risk that the insulation will fail (I'm assuming at this point that the insulation isn't in the best of shape on that cable that has been running hot)?
RE: What could cause a 15kV MC cable to be very hot to the touch?
If the insulation is as hot as it sounds, it may have already basically failed.
I'd budget to replace the whole thing.
RE: What could cause a 15kV MC cable to be very hot to the touch?
Another possibility is that for some reason you have high shield current, causing a cable shield to overheat. This could be caused by improper grounding.
And what dpc said about shutting it down... Now, before something bad happens.
RE: What could cause a 15kV MC cable to be very hot to the touch?
Thanks, Hopefully it won't be long and this will be resolved with out incident.
RE: What could cause a 15kV MC cable to be very hot to the touch?
I suspect that you have bad terminations diverting current away from one phase in the hot cable. The unbalanced current could explain both the heating and the marking on the cable tray. The diverted current will be causing an unbalance in the other two cables also but the unbalance will be divided between two cables and the effects will not be as severe.
The first step is to have the crew clean and redo the terminations at both ends.
If you suggest to the tradesmen to take the time to do a good job cleaning the terminations, and when in doubt, take the time to do it right you will probably be succsessfull.
A couple of tips;
Avoid bending the old cables. For overhead connections use a rope to suppoprt the cable close to its normal position rather than letting it hang down.
If you are connecting copper to aluminum outside, the aluminum must be above the copper. If the copper is above or beside the aluminum, rainwater will react with the copper and cause corrosion of the aluminum.
Use anti-corrosion compond such as Penetrox or No-alox.
respectfully
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Not sure what you comment, "you haven't said one important thing" means.
Any way we reterminated the connections from the MC cabel to the overhead wire and things seem to be fine for now. We will replace all of this cable in the near future but for now I think the imediate concerns have been addressed.
Thanks to all of you for your input.
RE: What could cause a 15kV MC cable to be very hot to the touch?
RE: What could cause a 15kV MC cable to be very hot to the touch?
Keeping my fingers crossed that we don't see the same temperture difference in the cable as we did before. They are suppose to take readings again this morning and then on Thursday. We will keep an eye on it until we actually replace all of it in the fall.