Broken neutral on utility pole

[jokirk]

I am looking for some recommendations on a residential over-voltage protection device. (Not just a surge protector) I have recently experienced for the 3rd time in 10 years, a broken neutral line on the utility pole feeding my house. This usually happens when the bare neutral is weakened by squirrels chewing on it (according to the power company) and then a limb will fall on the line and break the wire. When this happens, 240V goes through everything in my house until either something fries and trips a circuit breaker or I discover it and shut off the main breaker. It has happened to some of my neighbors as well. The utility company doesn't seem to mind that it happens but I think my insurance company, like me, is getting tired of it. Any recommendations? I would like to have something that I can install at the meter base or at the main 200A distribution panel.

-Just curious, have any of you run into this situation before?

[ February 20, 2005, 10:21 PM: Message edited by: jokirk ]

[hurk27]

Jokirk

I have seen where this has happened and houses that had multiple TVSS units on both legs of a service seemed to protect it.
We had a case about little over a year ago that a high voltage line was knocked down into a medium voltage line and it took almost 15 seconds before the utility's breakers open the circuit. Which is an eternity by the speed of electrons go. That morning we received almost 80 calls ranging from small fires to all electronics in a house smoking. After responding to almost all these calls I made some mental notes:
1. One surge device on one circuit on one leg of service = a loss of all electronics and the surge device blew open.
2. two surge device's on the same circuit would open that circuit OPCD and protect the equipment on that circuit. If they were on different circuits but still on the same leg of the service they would sometimes open the main OCPD device but not always protect the equipment on the other leg.
3. If two or more surge devices was on different circuits with two or more being on each leg of the service almost all cause the main OCPD to open and they had no damage to any electronic equipment.
In the case of the small fires that was reported, it was when the home only had one surge suppressor or had two with one on a circuit but each circuit was on a different leg of the service. No OCPD's opened and the MOV's in the unit over heated and burned through the plastic case of the unit and burned the carpeting. Luckily the carpet was treated with flame retardant and no fire resulted.

Now I don't guarantee that a TVSS unit can protect in a neutral loss, and or even in a over-voltage situation as above that happened in our area. But it could be a good system that could be developed to use this technology to maybe create a device to do just this?

The down side of this is as you place more and more MOV's on circuits they use more and more stand by current and actuly waste energy by just sitting there. So they will add to your electric bill.

After the above experience I do suggest that all plug in surge devices be placed on a non-flammable surface to prevent the failure of the MOV's from igniting anything that can cause a fire.

I have at my own house at least three units on different circuits on each leg of the service. That is a total of six units. also I have line conditioners on all my computers (5) that are capable of adjusting the line input voltage from 50 vac to 250 vac and the output stays at 120 vac. I went through the overvoltage event above without one loss of any equipment. Both the 100 amp main out on the pole and the 200 amp main in my trailer both opened as did the circuit breakers that the TVSS units was on. But all equipment was OK and the two computers that did stay online (one that monitors my electric and one that does weather) kept on working on UPS power. The electric monitor computer recorded a 1830/915 volt spike that lasted 14.89 seconds @ 5:07a.m. febuary, 7, 2003 The 1830 volts was line to line. I don't know how accurate the pickup probes are as they are for a HP quad trace scope 10 to 1 reduction but they are fairly accruate at 240 volts. The current on both ungrounded legs of the service went off scale @ about 10k amps. Which was the max range I had it set at. So it was above that before the OCPD's opened. Which only lasted about 3 cycles in which the main opened. The voltage monitor is tapped before the main at the service with a 10 amp breaker tap panel. The software is for the HP scope.

[pierre]

Wayne
Your suggestion of placing the TVSS on a surface that is at least fire retardant is a good idea. I have these all over my house (on the carpet) and will now place something under them. I too have seen the damage and potential fire starting these can cause when damaged. It is funny how we don't always think of our own situations when we are on jobsites.

[dereckbc]

Jokirk and Wayne, FWIW a TVSS is not designed nor is it capble of over voltage protection from a lost neutral. It is designed for very short (less than a milli-second) transients.

Wayne sorry to re-direct, I just do not want anybody to come off with the impression a TVSS is for over voltage protection. The only devices I know that can do that effectively are very high-end UPS and ferro-resonant isolation transformers. Not likely to find either one in a residence.

[rattus]

One could utilize some sort of "crowbar" circuit which senses sustained high voltage and places a controlled short between hot and neutral in order to trip the breaker. Might not save the electronics, but it should prevent a fire.

I doubt though that such a device is available, and if you build your own, it might not be legal. So don't go out and do this without approval from the authorities.

Back to basics though, a good ground to the neutral bus is your simplest and perhaps best protection. I have seen open neutrals which caused no damage to anything, not even a popped light bulb. The neutral was grounded to a copper cold-water pipe.

[dereckbc]

Originally posted by rattus:

a good ground to the neutral bus is your simplest and perhaps best protection. I have seen open neutrals which caused no damage to anything, not even a popped light bulb. The neutral was grounded to a copper cold-water pipe.

Please define a good ground. Metallic water pipes are becoming very rare now days. A good argument can be made that a metallic water pipe shared with you neighbor on the same transformer is dangerous to local water utility and plumbers. I am not trying to pick on you, but IMO is a false assumption.

[kilewatt2002]

Here in Wash.state (the wet spot) we have rodent & tree intrusion on our overhead lines. Years back, a company in Moses Lake Wash designed a piece of equipment they called a "K-Bar". Check into that if you can find the company.( I dont remember who it was ). I Installed one of these units & the produvt worked perfectly If you dont have any luck locating this thing contact me. I'LL go where I installed it & see what I can find for you. Glenn

e-mail adress removed by moderator...please use the PM function for private contacts.

[ February 21, 2005, 01:04 PM: Message edited by: don_resqcapt19 ]

[jokirk]

Thanks for the info guys.
I have been doing a little more research on this open neutral subject and it seems that possibly an AFCI might help out with the open neutral. From what I have read on an article by Mike Holt, "an AFCI will protect against the arc caused by an open grounded (neutral) service conductor. What will happen is that the electronic sensing element of the AFCI will be destroyed from over voltage!"
However, I don't know if the AFCI will respond fast enough in this certain circumstance to save any electronics. As far as surge protectors go, they won't help. As dereckbc stated, "a TVSS is not designed nor is it capable of over voltage protection from a lost neutral." I had several of these devices connected to different TV's, computers etc. They didn't help at all. In fact, one of them died as well. At a cost of $30-$40 each for an AFCI, I would like to get a warm and fuzzy that they will help before going to buy them.
Anyone like to comment on this application?

[ February 21, 2005, 01:08 PM: Message edited by: jokirk ]

[don_resqcapt19]

AFCIs are not fail safe. If the electronics are damaged, the breaker does not trip, it just acts like a standard breaker.
Don

[dereckbc]

jokirk, the only fail safe method I know of would be very expensive. That would be one of the isolation transformer offered by high end A/V manufactures. The ones I am thinking of are 240 input/120 output. No grounded circuit required to operate.