Working distance from energized 15 kv shielded cable

[bayoubare]

Are there any guidelines for minimum clearances required for working near an energized 15 KV shielded cable?

 

[Marmite]

Not that I'm aware of. It would be subject to a site specific risk assessment and production of detailed method statements. It all depends on what "work" is.
Regards
Marmite

 

[PHovnanian]

Its primarily a function of arc flash protection and what sort of PPE you have available. Depending on the jurisdiction involved, there are working rules (OSHA, Labor and Industries, etc.) that regulate work methods and protective equipment.

 

[Zogzog]

One reference is the NFPA 70E that lists insulated cable examination >1kV in the task tables, depends if it is open area or confined space like a manhole, both required voltage rated gloves.

Open area = HRC 2
Manhole = HRC 4

 

[electricpete]

If you are working along the length of the shielded cable (not at the terminations), then wouldn't there be no restrictions? (other than don't cut into the cable).

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(2B)+(2B)' ?

 

[rasevskii]

Not mentioned is what is the environment: Is the cable in a tray and a new cable is being pulled in along it, or is it a direct buried cable in trench and some excavation or cable pulling is to be done adjacent to it, etc. Is it a relatively new XLPE or PVC insulated cable, or a very old lead covered oil/paper insulated cable...

The basic rule is never to move, touch, or otherwise jostle an energized HV cable at all, a fault might occur resulting in injury or fire. The protections may claar the fault, but the protection only limits the arcing damage at the point of the fault which may well still injure any person close by.

The safe procedure is to de-energize the adjacent cable if work has to be done immediately next to it.

rasevskii

 

[bayoubare]

We are working in the back of 12 year old switchgear; the cables are good condition, 12 year old clx with EPR insulation.
There are two breakers behind the rear door of the switchgear, one on top of the other separated by a metal plate. We would be working on the bottom cubical which is de-energized and grounded. Both cables enter the bottom of the bottom cubical. One cable lands on the bottom de-energized bus, the other cable will remain energized. As the cable enters the bottom of the cubical it passes through a TMC connector and through a break out boot. The tape shield remains on and a 3m re-jacketing kit installed on the individual conductors. The clearance from the nearest energized exposed conductor is 4 feet the available fault energy is 8.1 cal at 36 inches. We would have to touch and possibly gently move the energized conductor to access the de - energized buss so the de-energized cable can be isolated for testing.

 

[rasevskii]

Not a good idea, IMHO. It is a close and confined space, and a fault at that point would be severe, likely with injury if not worse. It seems like very badly designed HV switchgear that one circuit passes through the cubicle of another circuit.

If there were full metal barriers between the circuits throughout, it might br safe, but there are no such barriers as I understand it.
Do not move or touch the energized cable, I would say.

Get an outage to be able to do the work safely.

The opinion of Zogzog (our metalclad switchgear expert) is needed.

Perhaps you can send a photo or state the mfr. of the gear.

rasevskii

 

[rasevskii]

In fact if you are in a position to refuse the work, you should do so, if an outage cannot be had. It is better to have a dispute with the owner, or your boss or supervisor than to be dead, or have someone else dead on your account. Then remove yourself from the site, and let them get someone else to do it.

After an accident has occurred. the whole scene changes. Police, authorities and inspectors are called in and the site is shut down. Legalities go on forever after.

I was once on a site where the chief engineer himself was electrocuted on an old 60KV installation, no correct safety procedures were used and no grounding was applied. The site was shutdown for weeks, and we all had to attend the funeral afterward.

rasevskii

 

[jimioy]

Slow down boys! Stop...and read NFPA 70E! This is how you get dead. You need a coordination study done to determine available fault current, to get an energy incident rating (cal), which then is used to determine what hazard risk category (1-4), which determines your PPE. You need to have a hot work permit which states why equipment cannot be de-energized and get a signature on it from someone with a lot to lose if someone gets hurt (this usually gets the power off to do the work - and it's the law). You really need to read 70E and take a class or two before getting to much farther along.

Jimi Young - civilian
184th CES/Electrical Shop
Ks Air Nat'l Guard
McConnell AFB, KS

 

[rasevskii]

for jimioy:

Good reference. NFPA70E should clearly stop the work that bayoubare is considering. In view also that it is evidently a confined-space situation.

Not only is it a clearance issue from live parts, but moving the existing cable under HV is the real common-electrical-sense risk factor. IMHO an outage is mandatory.

Where can we download a FREE copy of NFPA70E? It seems to be behind a paywall everywhere. I am in Europe.

rasevskii

 

[bayoubare]

I guess this is where I am getting confused. The restricted approach distance from an exposed live conductor was 2.2 feet. The only exposed conductor is in the cubicle above which is 4- 5 feet in a straight line but there is a metal plate between the cubicles. There is an energized conductor but it is not exposed. From some of the responses, I get the feeling that NFPA70E restriction distance should be applied to all energized conductors . If that is true the in some cases an unqualified worker would have to remain over 20 feet from conduit or CLX cable because they are energized that don’t sound right. NFPA 70E states distance from exposed energized conductor not energized conductor.
jimioy--- Why would you call for an energized work permit? The prohibited approach is 7.2 inches from an exposed energized conductor and it would clearly not fall in to that. I would not normaly get an energized work permit unless I crossed the prohibited aproach distance of an exposed energized conductor.

 

[rasevskii]

for bayoubare:

Obviously you have the NFPA 70E, I do not have it.

Common electrical sense would dictate not to move the energized cable, even if it shielded/screened. A fault might occur inside the cable insulation (brittleness) while your men are inside the panel space. The fault would lkely be a ground fault between the conductor and screen. The fault current is at first determined by the grounding method of the system (there are several threads about this on this forum), and therefore the related arc flash energy.

Even though the NFPA may indicate that you are a safe distance from the energized parts (the metal panel in between), in my opinion it would be unsafe, should a fault occur inside the energized cable as mentioned above, because you have had to move it out of the way to get access.

During work mistakes can happen, tools can fall or someone sticks their arm out too far by accident...

If I understand the physical layout of the panel correctly, an
outage has to be gotten to be absolutely safe.

Furthermore, even if you have de-energized the offending cable, and moved it, it might fail due to the above reasons when it is re-energized.

rasevskii

 

[bayoubare]

Furthermore, even if you have de-energized the offending cable, and moved it, it might fail due to the above reasons when it is re-energized.

rasevskii-- you do not ever recommend test a cable ? Even if the entire switchgear is de-enegized a cable must be moved to be tested. Using your logic that may cause a fault when it is re-energized so it should not be done?

 

[rasevskii]

Yes, in fact it could fault after you have re-energized it, if you had moved it for testing. That is not impossible, but unlikely. It could fault even if you had never moved it, upon re-energization.

If the cable is landed on a set of porcelain bushings, rather than the frequent arrangement of a set of epoxy CTs, you can test it without disconnection. Assuming that you have racked out the breaker.

I really don't understand why you are not asking for an outage to be safe.

rasevskii

 

[bayoubare]

I am just trying to understand the risk. I have not found anyone that would refuse to move or be afraid to touch or be around a SO cable that would power you typical 480vac portable equipment such as a welding machine. Such equipment may have an arc flash level of 40- 100 cal. per centimeters squared. Nor is any one afraid of a 60,000 volt spark plug. There is high voltage but limited amount of energy. Why are we so afraid of a 8 cal hazard at 13,000 volts?
I have seen people around tray cable and cable in conduit and CLX, I have never heard anyone say that there should be a limited approach boundary to it. We routinely collect data from transformers such as tank pressure liquid level, temperature and load tap changer position. I have seen catastrophic transformer failures that have resulted in a fire and explosion. In these failures anyone standing around them would have surely been killed. Should we de-energize transformers before collecting the temperature data?

 

[rasevskii]

My good friend, Mr. bayoubare, I wish you a long and successful career in the electrical business. Just don't keep moving energized HV cables around because they are in the way of something else.

You are stuck with some badly designed equipment.

Read the advice of jimioy.

Here it is morning and the sun is shining.

I am signing off from this thread.

Others will continue??

rasevskii

 

[electricpete]

I am not intending to argue one way or the other. I am curious to explore whether we can separate opinions from requirements. Obviously a final decision rests with qualified people on-site following local requirements and if there remains uncertainty, you can't go wrong erring on side of personal safety.

I googled "Personal Protective Equipment" "shielded cable" and came up with something

stonewaterconsulting.com/ELECTRICAL-SAFETY042810doc.pdf

4.1.11. All taped or compound insulated bus, connections, terminations, non-shielded cable in non-metallic duct or shielded cable where the ground attachment is not visible shall be considered as un-insulated or exposed

Note this appears to be a proposed company safety guideline developed by a contractor. In other parts of the document, NFPA 70E is referenced.

One might conclude they are suggesting to treat the shielded cable as if it is exposed for purposes of arc-flash hazard analysis IF the shield ground attachment is not visible, and presumably that implies the same author would treat it as a grounded part if the shield ground attachment is visible.

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(2B)+(2B)' ?

 

[electricpete]

note the above document just posted to introduce another opinion.... it is certainly not anything resembling a standard or requirement.

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(2B)+(2B)' ?

 

[bayoubare]

Thanks electricpete ---- I agree with you, I am curious to explore requirements. I can argue both sides however I am looking for the requirements, which appears to be hard to find any clear cut. Thanks again.