5 kv motor lead short

[0700pat]

We spliced a # 2 shielded cable to a motor lead on a 400 hp motor. The motor lead was damaged therfore the reason to cut it and splice the shielded cable. It lasted for 2 weeks. What happened.

 

[drbond24]

Welcome to the forum!!

What happened.

Why don't you answer that first as it pertains to the event(s) that occurred two weeks after the splice was installed.

Did the cable burn up? Did the motor quit? I can't tell you why something happened until I know what it was that happened. A couple of people on this forum might be that good, but I ain't one of them.

 

[zog]

We spliced a # 2 shielded cable to a motor lead on a 400 hp motor. The motor lead was damaged therfore the reason to cut it and splice the shielded cable. It lasted for 2 weeks. What happened.

Splicing and terminating MV sheilded cables is an art form, knowing how to do it and neing good at it are 2 different things. Was this done by a certified MV cable splicer?

 

[nakulak]

I'm guessing one of the splices melted away and boom .

 

[zog]

I'm guessing one of the splices melted away and boom .

It wont melt till after the boom, the smallest little imperfection in any part of the splice will allow tracking to break down the organics in the insulation, which leaves a conductive residue, which causes more tracking, etc..., finally you get the "boom". 2 Weeks is a very common failure time for poor craftsmanship on a MV splice.

 

[masterinbama]

It's possible the cable was already damaged by the previous failure. That is why whenever possible new or reworked terminations should be Hi-Potted or at the very least megged before returning to service.

 

[jdsmith]

Splicing and terminating MV sheilded cables is an art form, knowing how to do it and neing good at it are 2 different things. Was this done by a certified MV cable splicer?

What type of cable splicing certification do you typically look for? National Cable Splicing Certification Board (NCSCB)? We have a lot of 35kV splicing and terminating coming up in October and I'm wondering how to qualify the individuals doing the work.

 

[masterinbama]

What type of cable splicing certification do you typically look for? National Cable Splicing Certification Board (NCSCB)? We have a lot of 35kV splicing and terminating coming up in October and I'm wondering how to qualify the individuals doing the work.

Our local Raychem rep set up a class for us. I believe it was through the NCSCB. I'll pull the paperwork Monday.

 

[zog]

What type of cable splicing certification do you typically look for? National Cable Splicing Certification Board (NCSCB)?

Yep, thats the one.

We have a lot of 35kV splicing and terminating coming up in October and I'm wondering how to qualify the individuals doing the work.

I highly recommend you send your people to this certification course. It is also usually available through your local IBEW, if you are union. If not others (Like raychem) may offer it.

 

[zog]

It's possible the cable was already damaged by the previous failure. That is why whenever possible new or reworked terminations should be Hi-Potted or at the very least megged before returning to service.

No DC hipots, destructive test, AC dielectric testing methods are the only ones to use (TD, VLF, PFT, or PD)

 

[weressl]

It wont melt till after the boom, the smallest little imperfection in any part of the splice will allow tracking to break down the organics in the insulation, which leaves a conductive residue, which causes more tracking, etc..., finally you get the "boom". 2 Weeks is a very common failure time for poor craftsmanship on a MV splice.

Sure it could melt first if the compression connector was just slipped on the conductor but was never pressed. Don't tell me this never happens:grin:

 

[weressl]

Splicing and terminating MV sheilded cables is an art form, knowing how to do it and neing good at it are 2 different things. Was this done by a certified MV cable splicer?

While this used to be true, with today's splicing kits any competent electrician could successfully install a MV splice or termination kit by following the manufacturers instruction.

Certified by whom? Is there a national authority I am unaware of that performs such certifications? Is there a national standard to meet?

 

[masterinbama]

No DC hipots, destructive test, AC dielectric testing methods are the only ones to use (TD, VLF, PFT, or PD)

Thanks Zog. That's why I hire outside testing agencies for this type of work.

 

[zog]

Certified by whom? Is there a national authority I am unaware of that performs such certifications? Is there a national standard to meet?

Go read the earlier posts, we already discussed this. And yes, some jobs require certified splicers inthe specs.

 

[weressl]

Go read the earlier posts, we already discussed this. And yes, some jobs require certified splicers inthe specs.

We're talking about 5 kV splices for small motors in the OP.

 

[texassparky]

We're talking about 5 kV splices for small motors in the OP.

See Post # 7....

While this used to be true, with today's splicing kits any competent electrician could successfully install a MV splice or termination kit by following the manufacturers instruction.

Certified by whom? Is there a national authority I am unaware of that performs such certifications? Is there a national standard to meet?

This is becoming a very common misconception, people seem to think if you can read the instructions you can do the work. The instructions in MV term kits only give you the dimensions of each layer of insulation, and the order of the parts of the term to install. Which does relieve a lot of the "hand taping" that we used to have to do, but there are no instructions for actually stripping the layers of insulation, which is a craft in itself that comes with lots of time and practice. The term is only as good as the insulation and cable you leave under it. One nick too deep and have a source of failure.

 

[weressl]

See Post # 7....



This is becoming a very common misconception, people seem to think if you can read the instructions you can do the work. The instructions in MV term kits only give you the dimensions of each layer of insulation, and the order of the parts of the term to install. Which does relieve a lot of the "hand taping" that we used to have to do, but there are no instructions for actually stripping the layers of insulation, which is a craft in itself that comes with lots of time and practice. The term is only as good as the insulation and cable you leave under it. One nick too deep and have a source of failure.

There are complete instruction sets specifying the details down to the solvent types to remove the semi-con screening material, etc. The 'wholeness' of all remaining layers is indeed different from what a LV insulation material may be able to tolerate and attempting it to restore it - taping over - would be futile. Again the OP was talking about 5kV low power - relatively small conductor - application.