Re: Broken neutral on utility pole
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.
