Working distance from energized 15 kv shielded cable
Working distance from energized 15 kv shielded cable
(OP)
Are there any guidelines for minimum clearances required for working near an energized 15 KV shielded cable?
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Working distance from energized 15 kv shielded cable
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RE: Working distance from energized 15 kv shielded cable
Regards
Marmite
RE: Working distance from energized 15 kv shielded cable
RE: Working distance from energized 15 kv shielded cable
Open area = HRC 2
Manhole = HRC 4
RE: Working distance from energized 15 kv shielded cable
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(2B)+(2B)' ?
RE: Working distance from energized 15 kv shielded 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
RE: Working distance from energized 15 kv shielded cable
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.
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
Jimi Young - civilian
184th CES/Electrical Shop
Ks Air Nat'l Guard
McConnell AFB, KS
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
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.
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
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?
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
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?
RE: Working distance from energized 15 kv shielded cable
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
RE: Working distance from energized 15 kv shielded cable
I googled "Personal Protective Equipment" "shielded cable" and came up with something
stonewaterconsulting.com/ELECTRICAL-SAFETY042810doc.pdf
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)' ?
RE: Working distance from energized 15 kv shielded cable
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(2B)+(2B)' ?
RE: Working distance from energized 15 kv shielded cable
RE: Working distance from energized 15 kv shielded cable
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If we learn from our mistakes I'm getting a great education!
RE: Working distance from energized 15 kv shielded cable
Triton-Industries.com
BrahmanSystems.com
RE: Working distance from energized 15 kv shielded cable
RE: Working distance from energized 15 kv shielded cable
you are correct, a cable moved/tested whilst de-energised might well develop a fault when re-energised but the big (and probably life saving) difference is that when I re-energise a cable I can be in a different room whereas to move an energised cable as you are suggesting I'd have to be in the same compartment
Turning it off gets my vote too