This is my first post. We are a medium sized manufacturing plant.

We will be having our annual power outage to do scheduled maintenance on 4kv switch gear and 4kv/480v transformers. Part of our preparation for conducting the maintenance is hanging grounds. In discussions with others, and trying to make real sense out of 70E, I am trying to define what we are really accomplishing when hanging grounds.

Consider this scenario. A qualified worker is instructed to hang grounds on the line side of a 4kv disconnect feeding a 4kv/480v transformer. The 4kv breaker that feeds the disconnect has been opened, racked out and locked out. The breaker on the transformer's secondary has been opened, racked out and removed. The disconnect has been opened and verified visually by looking at the blades. A non-contact voltage test has been preformed. It is now time to hang the grounds. The qualified worker is instructed to wear PPE rated for the electrical and arc flash hazard.

Now comes a question from the qualified worker. Where is the Electrically Energized Work Permit that allows me to cross the Prohibited Approach Boundary, or is this actually a way to conduct a contact voltage test and no EEWP is needed, or is the PPE just for the appearance of safety?

I am not saying that grounds should not be hung, if for no other reason than dangers involved when TR testing the transformers. What I am wondering is what the act of actually hanging the grounds accomplishes: ensuring that the bus does not become energized or ensuring the buss is not presently energized? And I wonder what 70E says about PPE when hanging grounds.

There is an old saying for MV work, "If it isn't grounded, it isn't dead". After your voltage check you should still treat the equipment energized until grounds are installed, we use shotgun sticks to install grounds (And PPE).

Grounds have 3 functions:
-Dissapate and stored energy that may still be present in the system
-Provide a low impedence path to trip the OCPD if the system is ebergized or becomes energized during work (Must be rated for systemn fault surrent to ensure this happens)
-Provide a zone of equalized pontential should the system become energized so anything you touch will be at the same potential

Zog:

Thanks for the reply. "If it isn't grounded, it isn't dead." I like that.

As far as 70E is concerned, do you see the act of hanging grounds as live work requiring a EEWP, or voltage testing not requiring a EEWP, or something else?

One discussion I had was about the use of a contact voltage tester. The person that I talked to felt that it was dangerous to use one with MV, but had to admit that doing so with grounds was even more dangerous. Not every place can be grounded with shotguns. This particular person felt it was necessary to wear PPE for hanging grounds, but not for removing them. So I had to consider his view of grounds was really a way to conduct a contact voltage test.

Until the grounds are installed I would still consider it energized (And wear PPE), but IMO would not require an EEWP if it is just the process of establishing an electrically safe working condition (Article 120 clarifies this). Isolate, LOTO, Verify de-energized, apply grounds.

An EEWP is required when working on equipment that has not been placed in a safe working condition so I suppose I can see an arguement to require an EEWP, if that is how your safety department views it I would create a "standing EEWP" for that process.

Here is a great video on the subject
[media=youtube]hG2p9N1MHlk[/media]

If you run the calculations on MV work typically at the standard work distance when working from a hot stick, you are outside the arc flash hazard boundary. Second, 70E is really poor when it comes to MV work. Fuse cutouts are clearly a disconnect device as are saddles and jumpers for overhead work but a reading of 70E the way it is written suggests that this is considered energized work in spite of the fact that hot line clamps and disconnects are the disconnect method that you use for this type of equipment.

Second, read up carefully on equipotential grounding. It is a fascinating subject in the fact that you come away from it realizing that grounded is not dead in all cases except at the point where it is grounded.

Third, another glaring problem with 70E is that it fails to recognize that there are actually 4 different work methods (as laid out in IEEE 516): de-energized work, live line bare hands, glove work, and insulated tool work. The first three are covered more or less, but the last one is in no way whatsoever really addressed, except as a very vague footnote in the shock table for <300 volts that is not explained anywhere else. Let's face it, wearing insulated gloves and attempting to use small screwdrivers to handle PLC wiring is extremely difficult at best and is kind of forced on us even if the circuit itself is dead due to proximity of other energized circuits (inside the limited approach boundary). If one were to use an insulated screwdriver which is insulated to prevent both shock and arc flash (phsae to phase short) regardless of the almost nonexistent arc flash hazard in the first place, then this can clearly be done safely and filling out an EEWP becomes a sillly exercise. What am I going to say for justification? Well, how about "the risk due to arc flash from operating the circuit breaker to de-energize the equipment is greater than the risk of shock or arc flash from working while energized'."

Until the grounds are applied the equipment is still considered energized, after application of grounds the equipment is considered electrically safe. In many cases the grounds are removed and test applied to the equipment, the grounds are removed without gloves as it has been proven electrically safe. Reapplication of grounds would require the use of gloves ot insure that there is no residual energy residing in the equipment.

The National Electric Safety Code has some more information on the grounding of medium voltage. one needs the proverbial 10 foot pole, actually the line man generally use one long enough to stand on the grand. First step is to use a voltmeter mounted on the pole or other instruments to detect the presence of voltage. then the grounds are applied using the hot stick. As stated this is best done from the ground with the proper equipment. I suggest, you have someone who has done it before show you how. Also buy Mcgraw Hills line and cableman book and it shows how it is done. Just like soling an airplane, first fly with an instructor until he says you are ready to do it. This is not a job to make any kind of error on,

Might want to have a look at : ASTM F855 - 09 Standard Specifications for Temporary Protective Grounds to Be Used on De-energized Electric Power Lines and Equipment. Safety grounds are required to keep the voltage at the point of contact below 100 Volts in the advent power were to be returned to the equipment. They are required to maintain integrity for the duration of the fault and stay in place until the protective devices operate. I've seen many cases whese safety grounds are undersized or the attachement point cannot take the fault current. Over 42 KA manufacturers i'm familiar with require socket and ball arrangements to meet ASTM F855 requirements. Until the grounds are installed equipment must be treated with the same respect as you would live energised equipment.

Have to disagree here. Just because it's "grounded" doesn't mean that a potential can't exist, thus the reason for the test for absence of ground. You MAY have drained the residual stored energy in capacitors as well as in the cabling itself (impressed voltage from hi potting for instance) but it does not prove it's "dead". In fact in HV systems when you do equipotential grounding, you can only ensure that things are "grounded" within a short distance of a point. Two-point grounding has been conclusively shown not to work that well. And worse, the ground man is actually in more danger than the line man. AEP did some testing on this and it's pretty clear from their tests that grounding is not absence of voltage with HV systems.

Just ran into this with BRAND NEW GE 480 V breakers. The screws holding the fixed part of the shutters were too long. It was an outright manufacturer design defect. They will probably respond though just about 2 days before hell freezes over. Shutters are one of those items that almost everyone removes though because for the improved safety they give you, they also jeopardize the most dangerous part of a draw out breaker design (inserting it into the cell). It is possible to make a safe shutter but every one I've seen is a very weak/cheap design that increases the hazard of inserting the cell.





Earlier in the text (used to be section 110) they clearly state that even if "working live" rules do not apply, you still have to deal with the hazards. This means for instance that even if you don't need an EEWP and you are working on a de energized line, if you have a hot phase right next to it you may want still need PPE.




70E falls apart for overhead work. For instance it has the line telling you to use a disconnect to open/close circuits. But hot taps (saddles, jumpers, etc.) are the standard method for overhead switchgear. Also the distances in IEEE 1584 are totally inappropriate for shotguns and you should not use the tables. Use the tables in NESC (which contains the proper rules for overhead work) if you must use a table or else calculate it yourself with IEEE 1584 using the actual distance you are standing at the end of a hot stick. In our case on 22.9 kV in the main sub area (highest cal/cm^2) it drops to 0.8 cal/cm^2 with an 8 foot distance.




MV systems MAY carry energy on them even if disconnected for a variety of reasons. Examples are lightning, generators being connected that you don't know about and can't control, inductive coupling, stored charges in the insulation or capacitors on the line, capacitive coupling, or even conduction through the ground. These are all still factors even at LV but they are much more pronounced (and a safety concern) at 1 kV and above.

Please note that both NFPA 70 and 70E are very good for the interior work in the usual industrial plant, While OSHA and building departments accept and enforce them, the best guide for medium voltage work and for larger substations is the National Electrical Safety code, which covers utility lines and The National Electrical Safety code covers both installation and work rules. It is usually enforced by the State utility commissions and is published BU the IEEE. Of course there is one state, (name Withhold to protect the guilty.) that requires that communication utilities use an edition at least 12 years old and the Electric utilities use the latest edition. Of course they use the same pole and i suppose the conflicts get resolved in the field.