Arc flash concern at 240v ?

[ritelec]

Hello
started looking at extra high voltage lines and arcing on you tube. Started looking into arc fault experiments at 480v. Flash. Burns. Explosions. Scary stuff.
I have not been around that voltage in a few years and if I do go around it again will be extra cautious and observe better safety techniques than I did.

My question is. What type of arc fault dangers are around 240 v single phase systems.

I'm sure there has to be something but is it as dramatic ? That 480v was intense.

If 240 v was half as intense it would still be a terrible thing to be caught up in it

 

[iwire]

240 can still have huge arc fault potential. It just depends on the source and the distance from it.

In a home with a small transformer supplying it via long and relitivly small conductors not a big issue.

In commercial close to a good sized transfirmer you could have some very high fault current

 

[Sahib]

Per IEEE 1584, ?Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply.? This is about the incident energy exposure possible under these conditions during testing. It means no need to calculate incident energy on equipment under 240V fed from a transformer of size below 125 kVA, because the available fault current is not high enough to sustain an Arc-Flash and release significant energy.

 

[iwire]

Per IEEE 1584, ?Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply.? This is about the incident energy exposure possible under these conditions during testing. It means no need to calculate incident energy on equipment under 240V fed from a transformer of size below 125 kVA, because the available fault current is not high enough to sustain an Arc-Flash and release significant energy.

IEEE is a standard, not a code, not a rule, not a law.

I believe the NEC requires the calculations to be performed.

110.9 Interrupting Rating. Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.

You would have to calculate the fault current to know if the equipment is sufficiently rated.

 

[Sahib]

You would have to calculate the fault current to know if the equipment is sufficiently rated.

Yes.You would have to calculate the fault current to know if the equipment is sufficiently rated. But arc flash study is not necessary for equipment as stated in my last post.

 

[iwire]

Yes.You would have to calculate the fault current to know if the equipment is sufficiently rated. But arc flash study is not necessary for equipment as stated in my last post.

Maybe for those located outside the US but good luck with that if you move over here.


http://www.wendelcompanies.com/files/pdf/ENG_Arc_Flash.pdf

 

[ritelec]

Thank you

I checked the link. Any suggestions where to go to figure out calculations for the degree of arc flash danger?

In the ceu it was mentioned how the degree is lessened as you go further from the source but that was all that was said about it. No I can't say that. They said you had to get the starting arc fault current from the utility company. They also mentioned that the utilities are installing larger transformers notifying landlords as by law they have to but not telling them that they need to be re calculated and possibly have all there equipment changed.

I went to a on line arc fault calculator but it's still a bit foreign to me.

Anything about calculating or posting arc fault in one or two family residence ( I guess except for the little red sticker of a guy getting blown up that you where supposed to stick on the cover that I haven't seen in years )

 

[Fulthrotl]

Thank you

I checked the link. Any suggestions where to go to figure out calculations for the degree of arc flash danger?

In the ceu it was mentioned how the degree is lessened as you go further from the source but that was all that was said about it. No I can't say that. They said you had to get the starting arc fault current from the utility company. They also mentioned that the utilities are installing larger transformers notifying landlords as by law they have to but not telling them that they need to be re calculated and possibly have all there equipment changed.

I went to a on line arc fault calculator but it's still a bit foreign to me.

Anything about calculating or posting arc fault in one or two family residence ( I guess except for the little red sticker of a guy getting blown up that you where supposed to stick on the cover that I haven't seen in years )

short of getting the current rating from the poco, there is little you can do
to calculate this. residential services, there is a smaller can feeding a number
of occupancies, usually. this cuts the Ka-Wham factor a lot.

a lot of stuff we run across in the general world doesn't have an arc flash sticker
on the panel. since i've been self employed, since 2005, i've yet to see one in any
situation, anywhere, there is a PPE sticker on the panel.

you look at what the POCO shows up wearing when they pull and set meters,
it's an approved face shield, and FR shirt, with 1KV gloves. a good starting point.
you should have that on your truck, period. good for about 7 calories or so.

i ended up needing a bunny suit, so my decision was based on what i'd been told
at arc flash class with LADWP... 40 calories is the practical limit of functionality,
as the blast from something bigger, the explosion will probably kill you. suits go
up to 100 calorie. they usually have blowers on the back to force air in, so you can
stand to work in them.

so, i bought a 40 calorie suit, and 15KV gloves, good for 40 calories. the gloves are
unsuitable for anything requiring manual dexterity. put a set of gloves and outers on,
and try to figure out which one is your thumb. but it's good for closing and opening
overcurrent. i'll use 1KV gloves if i need more dexterity.

is this approved means and methods? nope. but it's what i do personally. operating
without employees means i can apply common sense, if i have any. it's my ass i'm
directly affecting.

a full on 40 cal suit is about $1,500 or so.

 

[ritelec]

Thanks for that...

Yep those gloves, seems more dangerous trying to use them than not.

Actually got a pair from a utility worker 1990ish..
Kept them on the truck (or in shed and on truck over years of self employed or employed) and went to use them and well, the rubber disintegrated .. now they are glorified leather gloves for digging.

https://www.youtube.com/watch?v=xvC4ha1EuAM

 

[ritelec]

terrible

https://www.youtube.com/watch?v=hfnEuRA7-vo

 

[meternerd]

[you look at what the POCO shows up wearing when they pull and set meters,
it's an approved face shield, and FR shirt, with 1KV gloves. a good starting point.
you should have that on your truck, period. good for about 7 calories or so.] QUOTE

Been in the POCO business for 40+ years. Arc flash is relatively new. Back in the day, we wore leather gloves, mostly to keep from getting cut if we broke the glass cover installing a meter. But after having seen first hand arcs and molten metal from a fault ahead of the main breaker, I'm a believer! Arc flash can be huge if the fault current is high. Most utilities have multiple customers on one transformer. That means a large transformer associated with relatively short secondary runs. Fault currents can be in the tens of thousands of amps. I've seen a meter panel nearly vaporized and the transformer fuse didn't blow. Primary fuses are for protecting the transformer, not the load, so they are sized pretty high. Bad news during a fault. Face shield, FR shirt and rubber/leather gloves is a minimum for us. A meter puller (plastic cylinder that snaps over the meter) when pulling is a good idea, too. 480V is a full 40 cal suit.

 

[iwire]

Most utilities have multiple customers on one transformer. That means a large transformer associated with relatively short secondary runs.

This is opposite what I would expect.

In my area a group of homes or small businesses is usally supplied by a single, undersized (by NEC standards) transformer and relatively long and undersized conductors. This makes the fault current low at most of these installations.

 

[Sahib]

In my area a group of homes or small businesses is usally supplied by a single, undersized (by NEC standards) transformer and relatively long and undersized conductors. This makes the fault current low at most of these installations.

To expect service entrance equipment, having 0 category arc flash hazard label due to undersized (by NEC standards) transformer and relatively long and undersized conductors and other favorable factors, would have downstream equipment also of 0 category is a misconception. Those equipment could have even 2 or 3 category.

 

[iwire]

To expect service entrance equipment, having 0 category arc flash hazard label due to undersized (by NEC standards) transformer and relatively long and undersized conductors and other favorable factors, would have downstream equipment also of 0 category is a misconception. Those equipment could have even 2 or 3 category.

:lol:

 

[kwired]

Even a 5 or 10 KVA 240 volt secondary transformer has enough output energy that it is easy to see (with little sophistication of experimental controls) that one would at least want to be wearing safety glasses when working in vicinity of energized components supplied by it. Isn't that an arc flash hazard? How much burn potential is there may be more complicated to determine but there is some easily identifiable dangers there.

 

[Sahib]

:lol:

Naughty.

 

[meternerd]

This is opposite what I would expect.

In my area a group of homes or small businesses is usally supplied by a single, undersized (by NEC standards) transformer and relatively long and undersized conductors. This makes the fault current low at most of these installations.

Kind of an old post, but I just read it again. Our philosophy is to avoid customer complaints (yeah, right...) as much as possible. One common complaint is flickering lights. Usually caused by other customers on the same transformer kicking on high starting loads or a heavily loaded transformer supplying low voltage. We decided to upsize transformers and limit secondary runs to help. A typical residential is 25 to 50 KVA. Not much more expensive. We are a resort community, so many second homeowners only come up on weekends and holidays. All is fine during the week when loads are low, but on 4th of July or over Christmas, low voltage can be a problem. As I said, available fault currents can be VERY high, so we take appropriate precautions. Plan for the worst and hope for the best.