This week begins a series of questions regarding interpretations of the intent of the 40 cal/cm^2 reference found in NFPA 70E 130.7(A) Informational Note 3.

Informational Note No. 3: When incident energy exceeds 40 cal/cm2 at the working distance, greater emphasis may be necessary with respect to de-energizing when exposed to electrical hazards.

Here is the scenario:

1) The main service equipment on the secondary side of a utility transformer has a calculated incident energy of 70 cal/cm^2 using a 2 second cut off described by IEEE 1584 for the arc duration.

2) The actual arc duration is quite long based on the characteristics of the upstream utility transformer primary device.

3) Electrical work is required on equipment immediately downstream served by the service equipment.

4) It is desired to establish an electrically safe work condition which requires operating and opening the service equipment.

5) The condition of "Normal Operation" can not be established based on NFPA 70E's definition because the equipment is old and the condition of maintenance is not known.

6) The highest rated PPE that you have available is 40 cal/cm^2 PPE

The service device needed to de-energize a circuit has 70 cal/cm^2. You would:

Operate the device anyway without PPE
Operate the device with 40 cal/cm^2 PPE
Obtain 100 cal/cm^2 PPE to operate the device
Not Operate and Contact the utility to open their primary device
Something else

There will not be a question of the week next week due to the American Thanksgiving Day Holiday.

I picked something else as there may be a way to operate the device either:
1. By increasing the distance by using an insulated stick, for examp, to lower the incident energy to a lower level which would be within the range of a 40 cal suit.
2. Perhaps a remote operator would be possible to achieve the same as #1

If neither of those are a viable option, then I would have the utility open the primary device.

Another angle: Would the Utility company really appreciate anyone chancing it with a known/suspect 'high risk' device, that has the potential to collapse the utility line that it's fed from?

To me, this is a clear situation where there need to be collaboration between the User and the Utility in making the sensible decision - common sense should prevail and effect a planned Utility outage. There is really no excuse for endangering a system, personnel, and equipment in any reckless way, when there is a work around.

There is not a lot of detail here but why would you not operate it (assuming a breaker)? Has it been maintained, are the covers on? For the last 100 years we would not have thought about it and operated it. Just because the there is "this new label" on it does not mean failure is imminent. The question was not - will you open the cover and.....

Is it 70cals only because we did not know the utility information? If I told you that you MAY get in your car and you MAY get in an accident, and you MAY roll-over - would still drive you car??

I am not saying I would be reckless. I would stop and think about the possible risk/hazard for myself and those around me.

Just saying!

In the case of a mechanically operated - customer operated / owned utility disconnect, my recommendation would be to have the disconnect either retrofitted or replaced with an electrically operated device that can be triggered from a distance.

An electrically operated breaker / disconnect can be connected to a mimic panel or SCADA system and operated from a safe distance.

Calling the local utility for a shutdown every time maintenance is required can be an arduous and expensive proposition.

If the breaker / disconnect needs to be racked out and locked, there are multiple remote racking operators available on the market.

The ultimate protection would be associated with an arc flash mitigation system which would drive the IE low enough for safe local operation.

I agree with Barry Donovan that would be an immediate way to handle the situation. However I would like to add that fro a look forward fix - adding a Current Limiting Fuse, a Maintenance switch or an Infrared detection system would also work. Recent working with a very similar situation I was able to model a CLF in ETAP and was very surprised with the impact. I will mention that the situation was 60 calories and I was able to reduce the Hazard Level to a 3.

The motor operator is still the best solution because it gets the operator completely out of Arc Flash Boundary. And I did install one of those recently. I an concerned with mechanical longevity but in this case the breaker is operated often...

I chose have the utility come and open the upstream device.

Even with this option, the "safe working condition" in question may still be of issue. Just because that the utility has eliminated the input, there may be something of back-feeding or storing energy that can still be released.

I would probably follow something along this line.

Pre-work: Research "MAIN" to change or align maintenance tasks to bring up "MAIN" to date for future work while "MAIN" is open for other task (Time may limit this).
1. Isolate the main in question as much as possible, from downstream loads (this may have to be done after step 2 given knowledge of rest of system).
2. Have utility open incoming power.
3. Dress out in 40 Cal suit and test for voltage with ticker (utility can probably help here).
4. Test for voltage with meter if less than 1000V.
5. Open main. Test for absence of power again and lock-out.
6. Perform original desired work.
7. Perform maintenance or re-establish the "MAIN" in good standing for future work.

Once the utility opens their circuit, expect a visit from the local electrical inspector before power can be restored.

If back feeding or cap banks are an issue, you must ground. That's OSHA, not just 70E. Tics are for >1000V. Meters for <=1000 V.With cap banks and MV wiring where induced voltages are not an issue, grounding is not really covered by any standard because the first step is to drain the charge and the discharge rate may have to be controlled to a safe level (eg with a resistor). The second step is the temporary grounding. This detail often gets glossed over because with overhead lines, the issue is induced voltage from nearby energized conductors, lightning, wind (yes, wind), or stupid homeowners hooking up generators without isolation. With primarily industrial sites where wiring is short and not outdoors the issues tend to be cap banks, charge in shielded cables, electrostatic equipment, and again non-isolated generators.

I agree with Wormfood. We do have a few stations in our system that the calculated Hazard is over 40cal/cm^2, in fact 1 is well over 100cal/cm^2. We have the utility open their switch that feeds our system. We have to go through and open all loads and show them where they are locked out, and the utility adds a lock to our lockboxes. Then they go open the feeder switch on their side. The process is reversed when re-energizing. I know it seems like overkill, but even the utility engineer says it isn't worth the risk to our technicians to just open our main breaker. We are all in agreement that now that we know the hazard we need to protect our guys.
Thanks!