Arc Fault Calculations 1

[ruggedscot]

I see that out american cousins are heavily into arc fault calculations. Is this something that will come to the UK and start to feature alot in our own electrical systems ?

If so then where should I be looking at to try and get a head start and look to start prepreation of a plan of attack to cover what we will be required to cover.

Installation comprises of a few generators of about 1500kVA, 2 transformers 2.5MW some UPS gear and an intensive power delivery distribution system.

Rugged

 

[dpc]

Scotty,

Intepretation in the US is that full PPE is required for voltage test and applying (and I suppose removing) any protective grounds to de-energized equipment even when there is a visible disconnecting means. I have never heard any other interpretation of NFPA 70E or OSHA requirements, although this is often not adhered to in practice.

David,

Yes if the available arc energy exceeds 40 cal/cm2, you're in a Catch-22. As a practical matter, I think a reasonable interpretation would be to wear the 40 cal (or 100 cal) suit and just do it. The other option would be to increase the working distance by using a voltage tester attached to a hotstick. The arc-energy falls off pretty quickly as you increase the working distance. Increasing from 18" to 36" makes a big difference. (Yes, someone still has to open the door, etc...)

A PG&E engineer told me that they have a few old substations in downtown San Fran that they cannot take a clearance on because they don't have a ground set that can withstand the available fault duty.

 

[ruggedscot]

As the system utilises two supplies were having to asses this and try to work out a suitable response. The 'breaker is being used as a switch as well as a protection device. If the utility drops this breaker should open and its partner close allowing the generator source to connect and feed the panel board.

Now you can see where Im coming from, if you are racking this breaker out then there may be a possibility that you have utility power on one set of contacts and the generator source will be present on the other. Energy availiable at this point would be pretty high.

So as a response to this I feel that we need to take adequate protection measures to ensure the safety of the operator during switching operation or racking proceedures on there units. Simply going up and switching without eye protection or hand/arm protection is putting a risk there that can be managed out of the equation.

 

[dpc]

Remote racking devices are available for most metal-clad swgr breakers. You still have to get the thing in place and set up, but operator can be 100 feet away during actual racking operation. This option has been available forever, but not often utilized pre-arc-flash.

 

[Zogzog]

Scotty UK,

Yes, waering a 40cal suit can increase the chance of an accident occuring, your vision is impared and it is difficult to work in. However, as mentioned above you usually are only wearing it for a few minutes and there are cooling options available on the market.

Our course is a 3-4 hour web based program covering the 2004 NFPA 70E requirements.

Scott Peterson
Training Manager
Power Plus Engineering

http://www.epowerplus.com

 

[rbulsara]

A few points:

Current PPE categories are 0-4. This does not mean that there are no arc faults exceeding energy levels of categories 4. It only means that there are no PPE available to protect against hazard above category 4. In fact hazard beyond Category 4 that are not survivable. Beyond that you cannot perform the work live or there are no PPE designed for that.

Also the PPEs when they work as designed only limit the "Burn" injuries to second-degree burns. Second degrees burn are most painful yet curable. 3rd degree burns leaves permanent deformity and beyond that you are dead.

PPE only protects against burns, they are not designed to protect against shrapnel flying out when a arcing faults results in full blast or sound pressure related injuries.

So anyone thinks that just putting on a PPE makes one entirely safe, he/she can't be mislead any further. Nor does it reduce risk of liabilities; injuries or death due to any other reasons but burns.

Rafiq.