shielded vs non
- Thread starter easymoney
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Shielding on a power cable is like sheilding on an audio cable. It's a grounded mesh that surrounds the insulated line conductor.
76teach
Member
- Location
- Bismarck North Dakota
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I was on a water plant project in which the engineer had speced a shielded 25KV cable was to be installed to low lift 4160v pump motors, vintage circa 1940 AD. Having a very small peckerhead the union sparky shortened up the manufacture's dimentions. When the first pump was started, one of the joints flashed over to the ground shield. Loudest cherry bomb I've heard in a concrete pipe gallery ever. I was about a 100 feet away and still can't hear well from my left ear. Never cheat the instructions.
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I was on a water plant project in which the engineer had speced a shielded 25KV cable was to be installed to low lift 4160v pump motors, vintage circa 1940 AD. Having a very small peckerhead the union sparky shortened up the manufacture's dimentions. When the first pump was started, one of the joints flashed over to the ground shield. Loudest cherry bomb I've heard in a concrete pipe gallery ever. I was about a 100 feet away and still can't hear well from my left ear. Never cheat the instructions.
76teach
Member
- Location
- Bismarck North Dakota
The shield was a more efective return ground path than the rigid galvanized conduit run back to the 4160v MCC. Allthough the fault was not between conductor and the frame/conduit system. Looking at the event area it showed the fault was within the termination assembly.
I had an electrician/lineman terminate 4160v circuits in a switchboard at a plant using 5KV non shielded cables with no incident. He just simply sharpened back the insulation to the end which was to be terminated in a conical fasion, like a pencle. Thus creating a stress cone for his termination. Heavy duty stuff yet not so terrebly wild if terminated rightly.
I had an electrician/lineman terminate 4160v circuits in a switchboard at a plant using 5KV non shielded cables with no incident. He just simply sharpened back the insulation to the end which was to be terminated in a conical fasion, like a pencle. Thus creating a stress cone for his termination. Heavy duty stuff yet not so terrebly wild if terminated rightly.
zog
Senior Member
- Location
- Charlotte, NC
(OK Iwire, I read this 3 times and am sure he is asking about MV)
Answer: Flux distribution. In an unsheilded cable there is uneven distances to the ground plane when the cable is in a conduit so the flux distribution is concentrated in some places (Picture 1). This leads to premature insulation failure from the high flux density areas.
Sheilding creates equal distances to ground and even flux distribution, prlonging cable life (Picture 2)
There are many different types of sheilding for MV cables (Some in picture 3), each with different applications.
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