Sollatek's American partner is controlteconline.

Timescope

 

Lost neutrals are a rare occurance. If your electrician checked your neutral bar and made sure the wires were tightly bonded you should be OK, I doubt it would happen again.

 

Firstly, broken neutrals are pretty rare and just getting an electrician to inspect your wiring every so often is probably the best choice.

A ferro-resonant transformer should offer reasonable protection against overvoltage. They saturate in normal operation and limit the output voltage by limiting the flux - with constant input frequency you should never be able to get enough voltage out of them to damage anything. On the other hand prolonged overvoltage might damage the transformer but I'd imagine most have a thermal switch for protection.

Some kind of device which monitors line voltage and cuts the power if it exceeds a threshold would be good but I'm not aware of any that are commercially available. You could monitor either live-neutral voltage or neutral-ground voltage.

A neat solution might be to make up a cable with a small 120V light bulb and a pair of 30 Volt back-to-back zeners connected in series between neutral and ground. Plug it into the same power strip as the electronics you want to protect and plug that power strip into a GFCI outlet. When the neutral-ground voltage exceeds 30 Volts (live-neutral > 150 Volts) the bulb will pass enough current to trip the GFCI from live-neutral imbalance. The GFCI might then die due to overvoltage but since it has already opened your expensive electronics is protected.

 

Richard your idea is intriguing. Can you explain in more detail how that would work.
It seems if the neutral disconnects the GFCI has no reference and would never trip?

Secondly, why should voltage on neutral be present if there is no short?

I currently am not using a GFCI on my media circuit. We are only require them in wet locals.

Lastly, I have an emergency generator and they are notorious for Frequency fluctuations. The gen's Freq is dependant on a precise engine speed.Which we all know is hard to maintain with changing loads and tempermental carbs.
Thank you for your help.

 

In my country we have GFCIs (we call them RCDs, for Residual Current Device) where the tripping mechanism is powered solely by the current imbalance and will therefore operate without neutral connected, I am not certain if yours work the same way but in any case you get a kind of pseudo-neutral (of the wrong voltage) from the loads on the other 120V leg - without that you wouldn't have any destructive voltages anyway.

With my suggestion the GFCI is being used as a convenient switching mechanism more than anything else, a similar circuit could be made that switches off a normal relay but this method mechanically latches, and requires much less electronics knowledge.

Neutral is normally the same voltage as ground (within a few volts) - neutral and ground are connected at the utility transformer. The two 120V legs are therefore both 120V from ground as well as 120V from neutral. When your neutral becomes disconnected it drifts in voltage towards the most heavily loaded phase, so it might be 200v from the least loaded phase and 40V from the other - that 200V is the cause of your damage. But in doing so it is also 80V from the midpoint of the two phases, and therefore 80V from ground.

With 30V zeners the circuit I suggested will conduct when the peak neutral-ground voltage exceeds 30V, the rms in that case would be about 20V and therefore this corresponds to your loads seeing about 140V (not 150V - small correction from my previous post). A small light bulb is used rather than a resistor because 1) they are readily available with the required voltage rating 2) can safely dissipate the power if the GFCI does not trip for some reason and 3) have a low resistance when cold and therefore a negligible effect on tripping voltage.

Regarding your emergency generator, you would really need to determine the amount by which the frequency fluctuates (by measuring either engine speed or power frequency) before we can say if a ferro-resonant voltage stabiliser would be useful.

 

Richard,
I appreciate your detailed advice.

I will connect the two diodes in series and insert in series between the lamp and the neutral line.As seen in the diagram.

Is there a way to test it?

My generator will fluctuate between 58 and 62. If the gen becomes overloaded it could maintain around 55Hz until the overload is gone.

 

Richard,
I appreciate your detailed advice.

I will connect the two diodes in series and insert in series between the lamp and the neutral line.As seen in the diagram.

Is there a way to test it?

My generator will fluctuate between 58 and 62. If the gen becomes overloaded it could maintain around 55Hz until the overload is gone.

You need to flip one of your zeners. They need to have either their anodes connected together, or their cathodes connected together (note Richard said back-to-back).

 

Ron,

Thank you. I wonder why the GFCI would burn? Will it not just trip?
Also, by changing the value on the Zener can I get it to trip closer to the 120? Or would changing the bulb watts make a difference.

 

Richard,
Thought you would be interested in this. It is a variation of your idea.

I wonder if most of this can be contained on a micro controller

 

andersonmilltexas
Using zeners of a different voltage would be the best way to change the tripping characteristics. The wattage of the light bulb will have only a marginal effect and I would suggest using a small night-light bulb of around 5 Watts. With that bulb the worst-case current if the GFCI doesn't trip is 5/120 = 42mA, but the cold resistance will be only a few hundred ohms ( http://forums.x10.com/index.php?topic=18816.5;wap2 ) so it will only make a volt or two difference to the tripping threshold.

Your zeners should be rated such that they don't burn up if the GFCI doesn't trip (we expect it to, but don't want to create a fire hazard if it's faulty). Each one will dissipate 0.5*0.042*30 (for 30V zeners) = 1.3W, I would use zeners rated for roughly twice this.

Ron,
That's an interesting cicuit you have posted, that one monitors for excessive live-ground voltage which is useful but wouldn't detect an overvoltage due to lost neutral. It could be modified to separate the voltage being monitored from the tripping current.

It could be done with a microcontroller but I suspect that between powering the microcontroller and providing the tripping current the circuit wouldn't get any simpler. It would however allow you to program some time dependant tripping characteristic which would be a nice feature to have.

 

andersonmilltexas
Using zeners of a different voltage would be the best way to change the tripping characteristics. The wattage of the light bulb will have only a marginal effect and I would suggest using a small night-light bulb of around 5 Watts. With that bulb the worst-case current if the GFCI doesn't trip is 5/120 = 42mA, but the cold resistance will be only a few hundred ohms ( http://forums.x10.com/index.php?topic=18816.5;wap2 ) so it will only make a volt or two difference to the tripping threshold.

Your zeners should be rated such that they don't burn up if the GFCI doesn't trip (we expect it to, but don't want to create a fire hazard if it's faulty). Each one will dissipate 0.5*0.042*30 (for 30V zeners) = 1.3W, I would use zeners rated for roughly twice this.

Ron,
That's an interesting cicuit you have posted, that one monitors for excessive live-ground voltage which is useful but wouldn't detect an overvoltage due to lost neutral. It could be modified to separate the voltage being monitored from the tripping current.

It could be done with a microcontroller but I suspect that between powering the microcontroller and providing the tripping current the circuit wouldn't get any simpler. It would however allow you to program some time dependant tripping characteristic which would be a nice feature to have.

'Twas not I who posted it.

 

'Twas not I who posted it.

Oops.

 

I went to buy the parts needed to create the project idea suggested by Richard.CS.

While at my local electric supply house, a Leviton Rep was visiting and over heard my plans.

He suggested that they make a product that would solve this solution.

So, I thought I would run this by everyone before making a move.

Please see the attached brochure from Leviton. This item would supposedly cut all circuits in the event of an open neutral.

This is a different approach then what Richard.CS suggested. Richards solution would cut power if there was an overvoltage versus this cutting power if neutral was open.

What do you all think. Use both solutions together or does Levitons product just marketing hype.

 

Just noticed this thread. I didn't see it mentioned, but a loose neutral at the power pole transformer will also cause the branch over-voltage problem. It happened to my parents' farm house. Kept blowing bulbs in certain rooms. Finally Dad happened to notice arcing at the pole during a wind storm. Electrician tightened it, and no more problems.

Ken

 

If Levitons product does what it says then it should offer the protection you need. Internally I imagine it has something very similar to the circuit I proposed.

You should note though that a lost neutral on a 110V-only part of the circuit (which is what their advert seems to be considering) results in the neutral swinging up towards the live (so they have similar voltages), and probably reaching it or almost so. That's different from the fault you experienced where the neutral broke in a split-phase 220V part of the circuit and the neutral was pulled down away from the 110V leg where the damage occurred, towards the other 110V leg.

If, as I suspect, that device just monitors neutral-ground voltage it should work for either type of fault. But it is possible that it looks for low live-neutral voltage in which case it might not trip on a lost neutral in the 220V panel. If the Levitons product is reasonably priced I would buy one and test it, and if it doesn't work return it as not-fit-for-purpose.

To test I would build a simple 220V split-phase circuit with two 110V light bulbs (of different wattages). If you build the attached circuit and connect the Leviton device to the right hand side it should trip when the switch is opened simulating a broken neutral. It should also trip with the 100W and 40W lightbulbs reversed (that's actually the damaging way). Note that all points on that circuit are dangerous to touch when powered, but if it's made with standard mains lamp holders and switches everything should be safely insulated. Do not connect anything to the outlet of the trip being tested. To estimate the tripping voltage you could try different wattage lamps, maybe a 60W and a 40W, or a 100W and 120W - it's the ratio between the two that matters and if you find some combination that trips and some that doesn't (two identical lamps almost certainly wont trip it) we can work out the worst case voltage your load sees before it trips (or you can measure it directly as the voltage across the smaller bulb with the switch open).

It is possible it won't trip without a load connected, if it doesn't then use something cheap like another light bulb, but this will affect the calculation or tripping voltage. And beware that once you open the switch you'll be over-volting the lower wattage light bulb moderately - it should survive it for a few minutes but close the switch or power down once you have your answer about the trip.

 

Richard,

Thank you very much for the schematic-it makes a big difference.

I suppose the safest way would be to cut up an old 240V Dryer Plug and splice the ends to a Light switch placed in a plastic work box. Use a standard duplex outlet for the two desk lamps.

Richard- since I am disconnecting neutral only at the outlet,there is no way this will affect other outlets in my home? I assume since they are still getting neutral to panel.

It is actually disconnecting neutral from both legs , so why not be able to lower volts on one leg as the other increases in volts---similar to my situation.

 

If you use a duplex outlet then you could just use two desk lamps plugged into the two outlets*, one via the device you're testing. Then it just becomes a 240V dryer plug to duplex 120V outlet with a switched neutral. Breaking the neutral in that lead is not dangerous to the rest of the house but may damage the loads on the duplex outlet (the two cheap lightbulbs) - that's the idea - it replicates the fault condition for that outlet only.

When the trip you're testing is on the side with the higher wattage bulb it will see low volts with the switch open. When it's on the side with the low wattage bulb it will see high volts. Because of the unequal loading on the two legs the voltage seen by one side goes up and that by the other side goes down - really this is the neutral voltage moving towards the most-loaded leg.

This does mean that the trip sees a higher than normal voltage during one test. It will likely trip anyway but it is possible that the high voltage may cause damage like you mentioned happening to your other GFCIs - that depends entirely on its internal construction. It's probably acceptable if the trip is sacrificial when it's protecting expensive electronics but it does make it a potentially destructive test so do the one where the trip sees low voltage first. I would disappointed if a device designed to protect from lost-neutral couldn't survive 240V just fine, but it is possible if the manufacturer was a cutting corners.


*I'm assuming this is the type of outlet where the two outlets are on different 120V legs, I believe this is the common type of duplex outlet in your country.

 

No. In the US, a receptical is always run as two loads on the same 120V phase unless you break off the little connector and run the wiring yourself or demand the electrician do that.

ps, In general, I disagree with all this complication. I had an illegal splice in my neutral and lost a few devices, but after I repaired the illegal splice, everything is good, like several million other houses in the US.

 

No. In the US, a receptical is always run as two loads on the same 120V phase unless you break off the little connector and run the wiring yourself or demand the electrician do that.

In that case either that "little connector" needs breaking off or two seperate outlets should be used.

ps, In general, I disagree with all this complication. I had an illegal splice in my neutral and lost a few devices, but after I repaired the illegal splice, everything is good, like several million other houses in the US.

I agree that lost neutrals are probably quite rare, but they can be very destructive. It happens in the UK three-phase system occasionally causing 240V loads to receive 400V. In the US split-phase system the worst case voltage in the event of neutral failure is 2*normal rather than (√3)*normal and there are more places where such a fault can occur because split-phase is used domestically.

If you only lost a few devices I would guess that either your splice was just high-resistance rather than open, or the loads are unusually well balanced in your house. It also seems from the OP's experience that many 120V appliances don't fail gracefully with overvoltage, it would be nice if they just stopped working rather than potentially starting a fire.

 

I am pretty diligent about what is going on in my house and this happen to me.

My neurtral bus bar is made of 4 sections screwed together. One of the mounting screws came loose. It was the one that held the main neutral to the other bus bar.

Anyhow, curious about one thing. My 3000.00 plasma did not smoke.

Are these units designed with power supplies made to accept upto 240 volts and freq between 50 and 60? I am guessing this because it would simplify manufacturing to different countries. I wouls also assume it is done automatically as the volts are recieved the PS determines which way to go.
In any event that is my guess. what do ya think? as far asd #12's response I appreceiate your input but there is more to it.
#1. I find out learning new thing about electronics fasinating
#2. I would sleep better if just the large toys had protection
#3. It would be fun to assemble something like this.
#4. I am really interested in how it works.

Oh one last note. Why is my laser printer leaking a clear oily substance after the rogue neutral attack? The printer despite the profuse smoke seems to be working. Are there redundant parts in these? Or shall I expect erratich or short lived behavior with this leaking thing ma jiggy?