Everything To Know About Medium-Voltage MV 105 Power Cables

A MV-105 Power Cable is one of the most popular power cables on the wire and cable market both in the United States and worldwide. This blog is a tell-all about MV-105 Power Cable, from its applications to variations and unique characteristics.

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What Is A MV-105 Power Cable And Where Is It Used?

A medium-voltage power MV-105 cable is a cable with a voltage between 2,4kV and 35kV that is used within the power grid to supply and transport electrical energy.

Despite the fact that medium-voltage cables are a part of the power grid, they do not actually transport the electric level from state to state across the country. This is the job of high-voltage cables on high-voltage power lines.

Medium-voltage cables like MV-105 are used on the preliminary stage between the national high-voltage network and the residential, commercial, and industrial buildings which are the end receivers of electricity.

Medium-voltage cables can be a part of state medium-voltage lines, but they are also very often owned by private companies. Large office premises, production, hospital and campuses, public premises, and radio towers possess their own medium-voltage lines.

What is the difference between MV-95 and MV-105 Cables?

MV-95 and MV-105 are essentially the same type of medium-voltage cable. The difference between them stems from the fact that MV-105 has a maximum conductor temperature of 105 ºC, while MV-95 has a maximum conductor temperature. This impacts the applications of these cables, as they are suitable for environments where the temperatures differ from each other.

The Voltage Of MV-105 Power Cables

MV-105 cables are available in different voltages that fall under the definition of medium voltage, from 2,4kv to 35kv. Some standard variations of medium-voltage cables are 2,4kv, 5kv, 8kv, 15kv, and 25kv/35kv. The 15Kv MV 105 power cable is the most popular one.

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Insulation Levels of MV-105 Power Cables: 100%, 133%, and 173%.

One concept that is quite unique to medium-voltage power cables is its insulation level. MV-105 cables are available with 100%, 133%, and 173% insulation levels. The insulation level essentially determines how good the insulation is at dealing with mechanical stress.

An insulation level of 100% means a standard level of coping with the mechanical stress on cables.

An insulation level of 133% is primarily for 15Kv cables, the voltage of which varies within the 15kV/1.732 range. This insulation level is great for environments where voltage variation occurs up to 1 hour at a time.

If the instability lasts more than an hour, then an insulation level of 173%, the strongest one available, is required.

What is an MV-105 Cable With A Concentric Neutral, And When Should It Be Used?

When a cable like MV-105 has a concentric neutral, it means that the said neutral will carry the faulty currents during the faulty conditions, ensuring safe operation of the cable within the electric circuit. 

Because of this additional safety measure, MV-105 cables are used during power distribution, bringing electricity from the transmission lines to devices and equipment. While using an MV-105 cable with a concentric neutral in unstable currents is a necessity, one has to mind that this cable is not flexible and a bit more challenging to install.

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Where to Buy MV-105 Cable?

Nassau National Cable offers a large collection of high-quality MV-90 and MV-105 at excellent prices. Cables are available with and without concentric neutral, at any voltage from 2,4 kV to 35 kV. The cables are available with and without shielding. The insulation/ jacket combinations to choose from are XLP/PVC, EPR/PVC, and EPR/CPE, among others.

I work at a large University in Texas. When the electrical deregulation happened here the utility built us our own 138kv/12,470kv substation. Ever since we have had issues with our concentric neutrals burning up on our pole tops and splices burn up in our manholes every few years.

Although my SEL relays only show about 25amps of neutral current, I have measured 200 amps on the pole top jumpers between the concentric neutrals on the cable to the main neutral cable. See attached pictures for examples of the very strange readings.

I recently walked the line and noticed there are still some interconnections between our circuit's neutrals and the utility company (Center Point) city circuits that all originally came from the utility substation that these circuits used to originate in. Could this cause circulating neutral current at these levels?

The SEL relay also does not show excessive harmonics.

These are our main feeders from our substation Delta/Wye 138/12 KV transformer to our main gear on campus which connects to a ring bus. Entire run is about 1.1 miles from Sub to Central Plant. Some underground, some overhead.

We have 3 circuits, 2 of which feed a Main tie Main gear. 1 of which normally only feeds our Central Plant. The 2 that go to the main tie main gear each break out into 8 sub feeders which power our campus buildings. The Sub feeder cables do not have concentric neutrals tape shield only.

I should also mention that our incoming Main Feeders have a Nexus + power quality meter and although they do not have neutral CT's installed the meters do not show any calculated neutral current. But if I put an amp probe on the concentric neutrals at the back of the gear i can read up to 200 amps.

Anyone ever see this before? Any ideas?

Thanks for all the replies. I will attempt to address all the questions below:

wcaseyharman said: One technique we tried to use was to determine the phase angle of the neutral current relative to say phase A to see if we could rule anything out by the phase of the current.
I would also look at the transformer configurations and make sure your neutrals aren’t providing a path for other ground sources. You also might ask the utility if they have unbalanced feeders.

No sure what you mean by " Path for other ground sources." Our substation transformers (2-33 MVA) are 138kv Delta to 12.470KV Wye.
They leave our substation underground to the Utility substation that the circuits used to originate from before our sub was built.
Then it transitions to overhead for about 1/2 mile.
Then it goes underground again for about 7,000 ft.
Transitions to overhead again for about 300-400 ft.
Transitions to underground for the remaining ft to the back of our gear.

Cable is parallel 1,000 MCM with 1/3 concentric neutrals. All concentric neutrals are bonded in each manhole and on overhead.

Kiribanda said: Would you please tell us whether your 12.47kV distribution is 3Ph/ 3Wire or 3Ph/ 4Wire. I guess that depends if you consider the Concentric neutral as a wire. Since it is a Delta Wye transformer and the cables have a concentric, I would consider it a 4 wire.
If it is 4Wire then could you please mention
1) How & where the 4th wire is terminated? The Concentric is terminated at every terminal pole and every manhole to ground.
2) Does the 4th Wire consist of the concentric neutral of 12.47 cables or otherwise? It consists of both, where it transitions to overhead, there is a separate MCM cable. But as mentioned in the original post there are strange interconnection with CenterPoint city circuits so there is NOT 1 Neutral for all these circuits.

waross said: Are you seeing a corresponding ground current anywhere? Not much, a few amps at most as measured by the SEL relay.
Are the concentric neutrals grounded at both ends? Yes, and at each manhole and terminal pole.
You may have induced EMF in the concentric neutrals which is shorted out by grounding at both ends. I know we do have some issues with induction due to the way the Utility originally ran part of the underground. Instead of ABC in one conduit for each parallel run they ran 2 A's and a B or 2 C's and a A. Really strange stuff. We have corrected one of the 3 runs. Are you saying that the concentric should NOT be bonded at all points?

Even a relatively low induced voltage in a sheath or concentric neutral will drive a relatively heavy current through a closed loop. So, are you suggestion disconnecting the ground connection at one end?

davidbeach said: Unless you have an unusual connection of the relay, the "neutral" current on the relay is the residual current of the three phase currents. I believe that is the case, It was wired according to the SEL diagram. If that's that case, anything that's on the neutral than isn't unbalanced return from single phase loads isn't going to be seen by the relay. I am not sure what you mean here. We only have 1 small /240 transformer on campus.

jghrist said: I think you are on to something with possible circulating currents from the utility neutrals. I'd inspect the utility neutrals to see if there is an open point somewhere that is forcing utility neutral current to flow through two points on your neutral. This could be severe during a utility ground fault, causing thousands of amps of fault current to flow through your concentric neutrals. Yeah, I wish it was easier to explain the strange connections I have seen.

See below pictures for how the Neutrals are connected on CGR 1,CGR2 and CGR 3. Each different color is a different neutral conductor. CGR 2 is the reddish line. Aqua line is CGR 3. Dark Blue is a CenterPoint circuit.
The terminal pole in the CP yard is tied to a neutral on a CP circuit.
The CGR 1 neutral at terminal pole by the railroad is tied to the CGR 3 Neutral and also jumps to a different CP circuit and continues down the line.

Waross, Thanks for the input.

waross (Electrical)4 Apr 23 01:54 A concentric neutral on a single conductor cable will mimic a shield. It is common practice to ground shields at only one end. [COLOR=#F said: I understand that it may mimic a shield, but it is not just a shield. It is a neutral. From what I have been reading, it is common and accepted practice to do it this way.
and : [url=https://peguru.com//12/power-cable-neutral-and-system-grounding/]Link[/color]

You may be able to greatly reduce or eliminate the unwanted current by transposing the concentric neutrals.
At each transposition, the load end of the A phase neutral is cross connected to the feed end of the B phase neutral.
Then B to C and C to A.
Each neutral should spend an equal distance with each phase, or as near to equal as possible.
The neutrals must be isolated from each other and from ground at each transition.
That will allow the induced voltages to cancel out and with the induced voltages cancelled, there will be no induced current.
There are multiple transitions from underground to overhead and back again. The overhead only has a single neutral to connect to. So, on a terminal pole there isn't a separate Feed/Load concentric. (Overhead is single MCM phase conductors whereas the underground is Parrell MCM) What would the overhead static ground/grounded side of surge arrestors/terminal pole ground, connect to? The Concentrics are also bonded to the manhole grounds in each MH. Are you saying all these should be disconnected?

As for ground currents:
1. That is too much ground current to be reasonable. Agreed, we have had many splices blow up at the concentric snap ring and melted insulation from the jumper wires to prove that.




2. You have a textbook case for circulating currents from induced shield voltages. I don't disagree, but is there a possible solution other than a complete redesign of the existing system?

I really appreciate all the input. Step one:
Interrupt the current.
At every access point, the concentric conductors should be grounded on the outgoing cables and insulated on the incoming cables.
A concentric wrap on a multi conductor cable may be a concentric neutral.
A concentric wrap on a single conductor cable is an equipment grounding conductor.
The concentric wrap may only be used to ground equipment that does not have the neutral bonded to the equipment.
When the concentric conductors are not used or can not be used for equipment grounding they should be treated as a shield and grounded at the feed end and isolated/insulated at the load end.
It is good practice and safer to treat each individual section independently and ground and isolate at each manhole or transition.

Step two:
Provide a neutral.
Is a neutral needed?
If all of your loads are line to line, you may not need a neutral.
If you do need a neutral there are several possibilities;
a) Run neutral cables with the phase cables. In some instances this is the easiest solution, but in your case this may be the most difficult and expensive.

b) Install an artificial neutral. This may be a zig-zag transformer or a small wye delta bank.
The zig-zag may be a special order. You may be able to use distribution transformers in wye/delta connection to develop an artificial neutral.
The size of the artificial neutral should be the greater of;
​i) Adequate to carry the greatest possible neutral load current.
​ii) Adequate to withstand fault current until the protection clears. This may be mitigeted by resistance grounding.

c) install a ground grid including consideration of a buried conductor encircling the buildings that are fed from the circuit.
This should be about three feet from the outer walls.

My first choice would be option b), artificial neutrals.

Note. Some literature designates the concentric conductors as a concentric neutral. Some literature designates the same construction as an equipment grounding conductor.
In the instances where the literature calls the concentric conductors a concentric neutral; Do you believe everything that a salesman tells you?
If so, this may not be the only disappointment in your life. grin
Comparing a four conductor cable, a three conductor cable, a two conductor cable and a single conductor cable,
When all phases of a circuit are inside the concentric conductors, the concentric conductors may be used as a concentric neutral (Ampacity permitting).
With a single conductor cable, even though the construction is similar to multi conductor cables, the concentric conductors may be used for equipment bonding but not as a neutral conductor.
Don't believe everything that the sales brochure tells you.

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Ohm's law
Not just a good idea;
It's the LAW!