Charlie Palmieri





















CP

I dont even want to think about what would have happened had that gas equipment went.

They are very lucky that when it fell it did not take out that gas meter. or they would have had a bigger fire, Maybe even the whole house

Speculation, of course, but service riser turned to lawn fertilizer may have been from a primary-to-secondary fault in the transformer.

Peeling of the raceway from the building probably saved a “structure
fully involved” report.




[This message has been edited by Bjarney (edited 07-06-2004).]

Yikes what a mess. By the way, Is this the same Charlie Palmieri that is an excellent code instructor here in Mass?

WOW!
Curious about something here... Was the gas service bonded to the EGC? (Or formerly when the panel was actually in place?) This looks like a house, with a 3 phase service? Something you don't see here everyday... People that live here have someone watching over them!

-Randy

I figure first short in riser, then another short in transformer. But is it good for the lawn?

(Sorry, I couldn't resist, I'm sure this scared the people there out of thier minds! They are lucky!)

The occupancy was a commercial motel. The fire department was extremely concerned that the entire area was in peril if the gas touched off. They blocked off a stat highway until the utility was cut, and maintained a considerable distance.

Bumping this up..facinating example of utility fault current damage!

Show this to anyone who douts the power of electricity. Imagine being on the other side of the wall. It also reinforces the point about having proper distance between utilities. This could have been soo much worse if that gas meter was in a worser spot.

Very impressive, I am curious to find out what the fault current was. There is a formula for that in my ohm's law book, that uses length of the wire, size and the voltage to give you potential fault current. I do believe that there is a resistance table for lengths of wire that is needed also.

I used to know that of the top of my head, that's why this site is so great, gives me that continuing education that I need. Sure can't remember it all!

And people wonder why the service disconnect has to be nearest the point of entrance. Think about that service raceway burning up like that inside of the building.
Don

The motel owner is really lucky this time, if the gas service let go, it will go up in a big fireball. By the way, did the cutout on the pole trip?

That sounds rather suspicious!

No...all there would be is a big torch and if the FD applies water to protect the building there would be little additional damage.
Probably not. I watched 30' of 4" rigid with 4 500 kcmil copper inside vaporize and the primay fuse never opened.
Don

[This message has been edited by resqcapt19 (edited 09-15-2006).]

To get the exact fault current available use a loop impedance tester like the MIT 310 from AVO Megger.
It will impose a brief testload on the 230 or 115 Volts mains and calculates the available short circuit current.
Depending upon length and size of cable, condition of connectors etc. it should be less than 0.4 Ohms (in NZ case).
Say 230 volts / 0.4 Ohms = 575 Amps.

It is amazing fire works but quite often the overall resistance may be a few ohms and the fault current may be 200 Amps or so when arcing.

A low resistance fault say 0.02 Ohms will give a large current but not always a hughe arc 11500 Amps initially to blow the fault clear with a lot of damage, then the after arcing will take place with a lower current.

The formula is the standard one

U
____

I * R

Where U or V or E is voltage
I is current
R is total resistance

Powerfactor can be neglected in this case.

Thanks for the refresher RODALCO. Simple ohm's law, less resistance = more current flow. Oh and another thing, those cutouts, fuses...up on the poles. Sounds like they aren't much good for their intended purpose.

Their intended purpose is to protect the utility distribution sytem, not to protect the transformer and its secondary conductors.
Don

Thank you for the information on the cutouts Don. That was something I was never aware of until now. I just "assumed" that the intened purpose was o.c.p for the drop and pole trannie.

I know that old saying about assuming things, I should know better. Maybe if I was a lineman instead of an inside wireman I would have known this? Thanks anyway though.

What are they protecting from?

Larry

To elaborate a bit on what Don said:

Larry, the cutouts are used to help reduce the possibilty of violent failure of a faulted transformer/capacitor, to prevent the primary conductor burning down from a fault, to provide isolation of a faulted tx/cap/feeder; and to provide in most cases a visible means of locating a fault. (Most cutouts drop open or otherwise provide a visual cue that they've opened.)

The cutouts on a transformer are rarely fused to protect the transformer from overloads, even sustained ones. The utility practice is to allow the trans to operate to failure, usually no more than a burnout resulting in primary current in excess of the fuse cutout rating, which then opens. But sometimes the short circuit current available on the primary is very high, or the fuse rating is accidently too high, then the transformer can fail anyway by explosion or fire.

That's why faults like this one and some others we've seen here can happen without taking out a primary fuse/cutout.


[This message has been edited by mxslick (edited 09-18-2006).]

OK, that makes sense to me now.

Thanks

Wow.

I was always taught to assume that service conductors have no overcurrent protection whatsoever. Here is a stark illustration of this fact.

1-Don't you need the transformer impedance to figure out the short circuit amps?

2-The transformer sees this type of short as a load and nothing trips - I think!

Please correct me if I'm wrong
I'm not sure about either of my comments!

Yes, you need to know the transformer rating, transformer impedance and line impedance to figure out the fault current. At higher currents, the transmission cables (especially the poco ones that are undersized by NEC standards) act as resistors, further limiting the fault.

The transformers themselves are stupid- they don't know a fault from a load until they burn up. The fuse on the primary is only slightly smarter, but apparently not quite smart enough in this instance...

[This message has been edited by SteveFehr (edited 11-30-2006).]