5 homes burn after POCO connects power after hurricane

[electricblue]

So here in Florida after the hurricane the neighborhood I'm working in. The POCO fired the tranny back up before the grounded conductor was connected or something along those lines( not sure what the whole story is). 5 homes caught on fire, one a complete loss. So I'm wondering how this can be prevented. I see it from time to time on a service call where the cable has carried the current and burnt cable jacks and such. I'm think a ground fault main would prevent this. Thoughts?

 

[Ponchik]

It could be the neutral was not connected before they energized the transformer, then again a loose or a disconnected neutral causing a whole house fire??? I don't know.

Here the POCO usually will turn the main breaker OFF before connecting the over head service and will check for proper voltage before engaging the meter. And they will not turn the main breaker back ON.

 

[ramsy]

So here in Florida after the hurricane the neighborhood I'm working in. The POCO fired the tranny back up before the grounded conductor was connected..

Primary distribution voltage may have blew up houses if a secondary transformer was shorted, or got crossed with grounded conductor?

 

[topgone]

Short circuits do not cause fires most of the time. Fuses and breakers blow when things get shorted. What starts fires in homes are loosened connections that do not get noticed, getting temps higher than normal which could ignite materials in the vicinity.

My first job as a lineman involved clearing feeders after typhoons. The POCO which Im working with has a strict instruction never to go beyond the meters! That said, whatever happens after energization of the cleared feeders, we don't feel responsible,imo.

 

[GoldDigger]

Short circuits do not cause fires most of the time. Fuses and breakers blow when things get shorted. What starts fires in homes are loosened connections that do not get noticed, getting temps higher than normal which could ignite materials in the vicinity.

My first job as a lineman involved clearing feeders after typhoons. The POCO which Im working with has a strict instruction never to go beyond the meters! That said, whatever happens after energization of the cleared feeders, we don't feel responsible,imo.

But a lost/unconnected neutral can send enough current through a powered on device to cause it to burn. For a small to medium load this would not even need to draw a maximum current from the branch circuit, let alone enough to blow a breaker.

The only protection against that is to make sure the main is open at all connected buildings before energizing the service transformer.

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[Ingenieur]

Were the 5 homes the ONLY ones on the xfmr?

how would i flow with no neutral?
I suppose you could get 240 across 120'devices

 

[gadfly56]

Were the 5 homes the ONLY ones on the xfmr?

how would i flow with no neutral?
I suppose you could get 240 across 120'devices

Exactly. If the loads on each leg are balanced, no problem. If not - BRBQ time.

 

[electricblue]

http://www.tampabay.com/news/public...of-collapses-after-attic-catches-fire/2337840

 

[electricblue]

Were the 5 homes the ONLY ones on the xfmr?

how would i flow with no neutral?
I suppose you could get 240 across 120'devices

Most likely

 

[Ponchik]

But a lost/unconnected neutral can send enough current through a powered on device to cause it to burn. For a small to medium load this would not even need to draw a maximum current from the branch circuit, let alone enough to blow a breaker.

The only protection against that is to make sure the main is open at all connected buildings before energizing the service transformer.

Sent from my XT1585 using Tapatalk

Hence the reason our POCO (PG&E) will not turn ON the main breaker and will not even energize the meter if the reading are not correct at the meter jaw.

 

[ramsy]

..how would i flow with no neutral?

1) Telephone & cable, bonded to PoCo ground, carry open-neutral current back to service-neutral via building main bonding.
This un-fused structured cable is not designed to carry building power, and doing so with open neutrals can ignite buildings.

2) Water/gas lines, and re-enforced concrete provide neutral return paths to PoCo thru Main bonding and earth, but are less a fire hazard than
a shock hazard to plumbers, and expendable laborers, if contained without legal recourse against unauthorized or unqualified access to building services.

 

[ramsy]

I suppose you could get 240 across 120'devices

Multi-wire branch circuits (MWBC) share the same neutral to get multiple L-N circuits on different phase conductors.

A completely open-service return prohibits L-N voltage, but shared neutrals find higher-Z Line-Line paths thru appliance loads. Although listed appliances are destructively tested to fail harmlessly open, long before they catch fire.

Some high-voltage distribution systems use "Single Wire Earth Return" (SWER), including the Los Angeles Dpt. of Water & Power at 5.8kv. If high-voltage systems can feed multiple transformers, the same way MWBC's feed L-N outlets on different phase conductors, then an open-ground at distribution voltage can find a higher-Z Line-Line path thru buildings.

The 5 homes that burned in Florida may not be related to inside wiring, if the PoCo fired up a transformer without a line-side ground connection.

 

[ramsy]

Edit time expired:
"The 5 homes that burned in Florida may not be related to inside wiring, if the PoCo fired up a transformer without a primary ground connection."

 

[Strathead]

But a lost/unconnected neutral can send enough current through a powered on device to cause it to burn. For a small to medium load this would not even need to draw a maximum current from the branch circuit, let alone enough to blow a breaker.

The only protection against that is to make sure the main is open at all connected buildings before energizing the service transformer.

Sent from my XT1585 using Tapatalk

But for it to happen to five houses on the same transformer?

 

[Ponchik]

Some high-voltage distribution systems use "Single Wire Earth Return" (SWER), including the Los Angeles Dpt. of Water & Power at 5.8kv. If high-voltage systems can feed multiple transformers, the same way MWBC's feed L-N outlets on different phase conductors, then an open-ground at distribution voltage can find a higher-Z Line-Line path thru buildings.

The 5 homes that burned in Florida may not be related to inside wiring, if the PoCo fired up a transformer without a line-side ground connection.

So a SWER works the same concept as our basic MWBC but utility higher voltage uses the earth as the grounded conductor?

 

[ramsy]

So a SWER works the same concept as our basic MWBC but utility higher voltage uses the earth as the grounded conductor?

Larger SWER systems with 2 or 3 legs of phase conductors may be similar to our basic MWBC, but perhaps not with a single leg.

Seems to me any distribution system using a primary ground to divide voltage, which can break open, offers primary voltage to any connected secondary grounds or buildings offering a return path, which is different from a shorted transformer.

 

[Jim1959]

Hence the reason our POCO (PG&E) will not turn ON the main breaker and will not even energize the meter if the reading are not correct at the meter jaw.

This can however be deceiving, the voltage may read fine without a load, but if there is a neutral issue, it won't become apparent until the system is loaded.

 

[topgone]

This can however be deceiving, the voltage may read fine without a load, but if there is a neutral issue, it won't become apparent until the system is loaded.

If that's the case, the PoCo has nothing to do with the incident. Anything beyond the service meter is HO's responsibility.

 

[GoldDigger]

If that's the case, the PoCo has nothing to do with the incident. Anything beyond the service meter is HO's responsibility.

Note that we said that is might read fine at the meter, not that it was fine at the meter. If the POCO neutral is missing between transformer and service point, any resulting damage is their responsibility. If the neutral problem is downstream of the service point, then the HO may be on the hook, although it would mean that POCO restored service to a damaged building wiring system.

 

[rlundsrud]

I wonder if someone mixed up a hot with the grounded conductor. I find it hard to believe that 5 separate structures caught fire because of an open neutral.