Proper procedures/safety for flipping a 300a 480v breaker

[QualC45]

We have 2 48 module sensor classic racks. Whenever we have to replace to modules we would just pull them straight out while it was live (the manual recommended killing main power, but not required. It was entirely clear how to kill power so we never did)
When someone can to service our system and we talked to them they said ETC now says to kill power no matter what after someone died replacing a module with power on (it arced and killed them)

So we have a 300a 480v breaker on the same panel as the 2000a main coming in.


Do we need to get an arc flash hazard rating assessment and the appropriate PPE for the category?

Do we need an energized work permit?

Is there anything else we're supposed to do/should be aware of?

Also: at what point does this start to come into play? I assume you don't need this to flip a 120v 20a so at what point does this come into play?

 

[TJCornish]

The NFPA/OSHA rules are not always clear, as arc flash hazard calculation depends on a number of factors not easy to look up in a table. Here's an OSHA note where case 2 relates to your situation: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=25973

You should have breakers downstream of your transformer, though, so there should be no reason to turn off a 480v breaker to shut down the dimmer rack.

 

[QualC45]

The NFPA/OSHA rules are not always clear, as arc flash hazard calculation depends on a number of factors not easy to look up in a table. Here's an OSHA note where case 2 relates to your situation: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=25973

You should have breakers downstream of your transformer, though, so there should be no reason to turn off a 480v breaker to shut down the dimmer rack.

The transformer feeds directly into the dimmer rack with no panels between it

 

[rsmentele]

The transformer feeds directly into the dimmer rack with no panels between it

This is not all that uncommon. There are certain classes of flash and shock hazard and I do not know what class switching that breaker would fall under, but it might be a 0 or a 1. I will let someone else speak to that. As far as physical procedure, always turn your body away from the breaker and if possible, use your non-dominant hand to physically do the switching. this will protect your body from any potential arc damage. Again, I will let someone else speak as the the proper PPE required. Also, most of our industry will fall under the NFPA 70E

 

[JD]

Arc flash in this type of application would indeed be a very very rare occurrence, but the results can be deadly. Non-fault disconnect is not usually the problem, but re-energizing when there is a fault in place (screw drive left across rails in rack, etc) can be like a bomb going off. Circuit breakers are generally designed to contain/withstand this condition, but as with everything, sometimes they don't. Rules can get tricky to interpret. If the front of the panel was off, then the answer would be that full protection is required. Closed panel, permanent install, and things lighten up a bit. Generally, protection becomes important once you have exceeded the 200 amp level and once you have made the jump from 120/208 to 480 volts.
To be safe, there are four areas which may dictate protection; House rules, Local jurisdiction, OSHA requirements, and the NEC. (Feel free to correct me on the NEC as chapter and verse don't come to mind.)

 

[DavidNorth]

I agree with above postings as far as liability, safety and process come in to play. Do please follow rsmentele and JD. Also consider talking to your insurance representative and building representative.

A clarification: no one has died working with a Sensor rack. ETC changed their handling of electrical safety issues once we got a question from a facility asking us which level of PPE they needed to be wearing when replacing a module under live power. After that, we changed a lot of things in training, manuals, manufacturing processes and customer education. All of this has helped improve safety at ETC and with our product users.

Let us know if you have more questions!

David

 

[Dionysus]

In reality:

• Never stand in front of the enclosure when throwing a breaker/switch. (if there is an arc-flash you want to be as safe as possible)
• Wear eye/full face protection whenever you can, if not turn your face away from the enclosure before throwing.
• Whenever possible don't work live. (does not apply here)
• Whenever possible ensure when switching off (open) there is as little load as possible, same as on (close)
• Whenever possible obtain, make, or ask for an arc-flash assessment, etc. In some situations you'll find stickers and other documentation that will give you exact information on level of PPE required, and how "dangerous" an arc flash could be.
• Proper Gloves are never a bad idea, and I am not talking about work gloves.
• the Minimum level of PPE for arc flash technically includes: Proper work clothing which may be IFR or FR treated or simply cotton, etc (no polyester etc) with NO metal parts in direct contact with skin (zippers, buttons) as these will quickly conduct heat and cause burns, along with eye protection, hard hat and proper safety footwear.

Anyone often operating switchgear, breakers or working inside large enclosures should get their Arc-Flash training (I got mine many years ago... should renew actually, not that Ive had an employer in a while who cares at all). This will help answer such questions. But it really only gives you an overview of how the assessment is made.

I've worked inside 600A 600V, 800A 600V, 200A 347V, etc and larger switches and enclosures LIVE before MANY times.

I still remember checking the fuses in a 800A 600V disconnect live for the first time (could NOT turn it off), I was TERRIFIED (I think I should be) as there was very little room between me and a printing press. I tell you those probes moved SLOWLY and DELIBERATELY! Should I mention it was the middle of the night (I was woken up) in the middle of a thunderstorm with hail making all KINDS of noise? Turns out the fuses were good (THANK GOD) and a tap on a transformer outside had come off during the storm. Thankfully it turned into the utility's problem then and we just needed to assist. And yes we did end up turning the disconnect off after shutting everything fed from it down.

Just be careful, and take a second to THINK before you throw switches, especially big honking ones with lots of potential energy behind them. IS there an obstruction (was someone an idiot and store stuff right there)? If this blows will a big sheet of metal slam into me? Will I easily get burned? etc.

 

[SteveB]

Confused by this.

I have never heard of nor seen recommended the need to wear full arc flash protection while throwing on/off any breaker, if it's an entirely enclosed panel. Standing off to the side I can see, but if the panel is closed up, do they still recommend protection ?

 

[BillConnerFASTC]

480 directly into a sensor rack - in Maryland? No disconnect between transformer and rack? All seems strange.

 

[QualC45]

480 directly into a sensor rack - in Maryland? No disconnect between transformer and rack? All seems strange.

Correct. The breaker feeds the transformer with conduit running directly to the two racks


Reading through and looking at everything, table 130.7(c)(9)(a) only applies <600v if there's less than 25000a short circuit current availble, in our case it's on the same bus bar as a 2000A breaker where our main feed comes in and probably has ~100ka+ fault current possible

We're likely going to try and get a breaker between the transformer and dimmer racks

 

[BillConnerFASTC]

Correct. The breaker feeds the transformer with conduit running directly to the two racks


Reading through and looking at everything, table 130.7(c)(9)(a) only applies <600v if there's less than 25000a short circuit current availble, in our case it's on the same bus bar as a 2000A breaker where our main feed comes in and probably has ~100ka+ fault current possible

We're likely going to try and get a breaker between the transformer and dimmer racks

A simple disconnect may be less expensive and perfectly adequate.

 

[Dionysus]

A simple disconnect may be less expensive and perfectly adequate.

I agree you should have a "disconnecting means" nearby, depending on AHJ rules and other things of course. But a disconnecting means does not require a breaker, just a regular disconnect "switch".

As for arc-flash, yes there are situations where you would require higher levels of protection even with a closed enclosure but they are pretty much non-existent in "this field". Youtube videos are find-able with enclosure fronts flying off and all sorts of nasty awfulness.

 

[Amiers]

If I were to throw a breaker that flashed I wouldn't want to lose an arm from standing to the side of it, I would take my chances of taking a cover in the face and hope for the best.

Knock on wood that day never happens. It gives me chills just thinking about it.

 

[RickR]

If I were to throw a breaker that flashed I wouldn't want to lose an arm from standing to the side of it, I would take my chances of taking a cover in the face and hope for the best.

That which can blind you might only leave a scar on your arm.
That which will take off your arm may well take off your head.

 

[Moose Hatrack]

In lighter news about disconnects, not an arc-flash situation, but... An electrician working on a UPS distribution panel in our data room found the 3 pole breaker he just installed tough to turn on. He pushed so hard that, when it did flip, his hand kept going and shut OFF the breaker on the other side of the panel. A rack full of mission critical database servers sat down pretty hard.

 

[Dionysus]

That which can blind you might only leave a scar on your arm.
That which will take off your arm may well take off your head.

My thoughts exactly, and why Arc-Flash certification training tells you to "NEVER stand in front". Id rather break my arm than DIE or at least be laid up in hospital with serious blunt force trauma and third degree electrical burns. NOT FUN.

Than again as stated, in typical situations in this industry chances of severe issues like we are discussing are rare if not of very low probability (don't care to say impossible, as there is often SOME chance)...