Protection for lost neutral (help)

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petersonra said:
It is something that could probably be detected and the main CB tripped if it is detected.

Whether it is worth doing is something else.
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I am pretty sure there are overvoltage and undervoltage relays, I know there are undervoltage ones, but sometimes the simple solution is best. Run two neutrals.
 
over/under voltage relay

over/under voltage relay

If you lose the neutral generally you will get a higher or lower voltage from hot to neutral, due to loads now in series. You could use line voltage monitors from each hot to neutral then a shunt trip breaker.
 
Strathead said:
I am pretty sure there are overvoltage and undervoltage relays, I know there are undervoltage ones, but sometimes the simple solution is best. Run two neutrals.
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Hello, what do you mean with run two neutrals?
I'm supposing that the lost neutral is outside the house.
Thanks
 
just the cowboy said:
If you lose the neutral generally you will get a higher or lower voltage from hot to neutral, due to loads now in series. You could use line voltage monitors from each hot to neutral then a shunt trip breaker.
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Hello, Im wondering if the CB works in the case of loss neutral, do you have any experience on this.
Thanks in advance
 
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ramironchis said:
Hello, Im wondering if the CB works in the case of loss neutral, this because the CB as i see the problem going to be in serie with the circuit, do you have any experience on this.
Thanks in advance
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A circuit breaker, even a GFCI or AFCI breaker, will not detect a lost neutral. What it will detect is if the overvoltage on one side of the line blows up equipment which pulls enough current in the process to trip the overload function of the breaker. But IHMO that would be very unlikely.
 
ramironchis said:
Any one could help me? I need to know if there is any protection for this fault.
Thanks in advance.
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I think you need to provide much more info.

Are you asking about branch circuit, feeder or distribution work?

What voltage level?

What is the specific application?

What is the specific concern?
 
ramironchis said:
Any one could help me? I need to know if there is any protection for this fault.
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ramiron -
It would help if we could narrow this down a bit. One could fill a large library with books and papers about protective relaying, reliability of grounded systems, and Reliability Centered Maintenance.

I will start by guessing:
1. The systems in question are 1 phase and residential.
2. The single phase systems are 120/240V.​

If this is not so - forget the rest. But tell us what systems you are trying to protect.

First:
Are the L-O-N failures on the utility side of the main disconnect or on the house side of the main disconnect? (Answered: Line side of main - ice)

There are other failure modes that are very difficult to protect against:
1. Multi-wire branch circuits losing the neutral conductor.
2. 120/240 appliances​
Suggest saving these for a later discussion if you have an interest.

edit to add: I'm a slow poster. Some already answered

ice
 
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iceworm said:
ramiron -
It would help if we could narrow this down a bit. One could fill a large library with books and papers about protective relaying, reliability of grounded systems, and Reliability Centered Maintenance.

I will start by guessing:
1. The systems in question are 1 phase and residential.
2. The single phase systems are 120/240V.
​

If this is not so - forget the rest. But tell us what systems you are trying to protect.

First:
Are the L-O-N failures on the utility side of the main disconnect or on the house side of the main disconnect? (Answered: Line side of main - ice)

There are other failure modes that are very difficult to protect against:
1. Multi-wire branch circuits losing the neutral conductor.
2. 120/240 appliances​
Suggest saving these for a later discussion if you have an interest.

edit to add: I'm a slow poster. Some already answered

ice
Click to expand...

iwire said:
I think you need to provide much more info.

Are you asking about branch circuit, feeder or distribution work?

What voltage level?

What is the specific application?

What is the specific concern?
Click to expand...

Sorry for poor information...

1. The systems in question are 1 phase and residential.
2. The single phase systems are 120/240V.​

If we lost the neutral we gonna have something like this:

3wire3.jpg

The circuit I want to protect is a home installation, we have only 120v equipment, I'm from Ecuador so I don't speak English very well, If I'm not wrong I want protection for the feeder (I need a breaker for the whole installation).

If you interest over here we don't use any especial protection, we only use QO CB, we don't use AFCI, GFCI, overload breakers, so I'm trying to investigate the best way to have a house fully protected as I go on many questions appear and Is kind of difficult for me find answers over here, so any commentaries or bibliography you can give me gonna help me a lot.
thanks in advance


The image I attached I copied from another forum, and I think it was made for roger.
 
I was thinking of a basic relay with a 120vac coil wired L-N. Should you loose a N the relay coil drops out closing a contact which intern trips a shunt trip in the breaker. But, that's not reliable because it is oosible for the open neutral to be back feed from 120v L-N loads depending upon which line you use to energize the relay with. There would be a chance that the voltage may be greater than 120v tword The 240v L-L voltage depending upon the connected loads.
Also, the ST in the beaker should be energized by the L-L 240v as that doesn't depend on the neutral.
 
Great for detecting voltage problems which result from a lost neutral. But not the lost neutral itself in the absence of a load, and an unbalanced load at that.

Maybe something which injects a current pulse in the way a GFCI device checks for an open neutral?


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GoldDigger said:
Great for detecting voltage problems which result from a lost neutral. But not the lost neutral itself in the absence of a load, and an unbalanced load at that.

...
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Say what???

In the absence of a load, an unbalanced condition does not, cannot exist. Also, with no load, what needs protecting???
 
Smart $ said:
Perhaps this...

http://ecmweb.com/power-quality-archive/power-quality-relay-breaks-low-cost-barrier
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Perhaps
It would take two - one for each side of the 120VAC. The alarm contacts go open circuit, so one would have to make up a circuit (interposing relay and power source) to shunt trip a CB and get a shunt trip CB.

The thresholds are pre-set, however one of the settings is 10% (plus or minus) so that is pretty good.

A shunt trip QO 2pole 100A lists for $400. Add $550 for the monitors. Add additional $xx for the control relay/power source.

Ouch!

ice
 
iceworm said:
...

Ouch!
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Yep...

Wasn't making a recommendation. Just ran across the article and thought I would post it. Wouldn't necessarily require two, as over voltage on one side would be indicative of under voltage on the other. Granted, two would be better.

Using over/under voltage monitoring relays would likely be less costly.

Effectiveness vs. cost comparison is the big ?.
 
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Smart $ said:
Say what???

In the absence of a load, an unbalanced condition does not, cannot exist. Also, with no load, what needs protecting???
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True, but just as a ground detector is used in an ungrounded system to immediately detect an unintended ground even though there is no fault current at that point, to be most useful a lost neutral detector should alarm when the neutral is lost, not when it starts to cause damage and the system must be shut down.
Otherwise, as has been said, all that is really needed is over and under voltage detection, not anything specific to a lost neutral.
 
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