open service neutral

[petersonra]

Today's email from Mike Holt discussed open service neutrals. he indicated there is no way to determine if the neutral is open to protect one's self against this problem.

I am not all that sure he is correct on this.

If one were to measure the difference in current flow through the two hot lines and compare it to the neutral current, any significant difference would indicate an open neutral.

Or is this too simple?

It would seem like an enterprising manufacturer could adapt simple and inexpensive existing GFCI technology to detect such a condition.

Why not a more or less standard 2 pole GFCI breaker but with the trip point kicked up enough to eliminate nusiance trips.

 

[ron]

Re: open service neutral

I posted a comment regarding the addition of an over/under voltage relay to trip a shunt trip on the main CB. Unfortunately, until it was mass produced for the residential market, it would be costly.

 

[charlie tuna]

Re: open service neutral

or possibly when this occurs a voltage would build up on the main ground conductor and the technology of the simple tick tracer could provide a warning signal to the homeowner?

 

[tx2step]

Re: open service neutral

Originally posted by ron:
I posted a comment regarding the addition of an over/under voltage relay to trip a shunt trip on the main CB. Unfortunately, until it was mass produced for the residential market, it would be costly.

How about instead of a shunt trip main, your O/UV relay tripped a simple alarm? The alarm cover could tell the HO to turn off all 120V loads and call an electrician.

 

[don_resqcapt19]

Re: open service neutral

Bob,
Any GFCI type device would have to have a much higher set point. In areas that have common metal undergroung water piping systems, it is not unusual to find 25% or more of the grounded conductor current on the water pipe, even when there are no problems with the grounded conductor.
Don

 

[hardworkingstiff]

Re: open service neutral

Originally posted by petersonra:

If one were to measure the difference in current flow through the two hot lines and compare it to the neutral current, any significant difference would indicate an open neutral.

I think it would indicate a problem with the neutral. I could be the neutral has developed a high resistance but not necessarily be open. Anyway, I think your idea has merit.

 

[charlie b]

Re: open service neutral

Originally posted by petersonra:If one were to measure the difference in current flow through the two hot lines and compare it to the neutral current, any significant difference would indicate an open neutral.

OK. I'll admit my idiocy. If you suspect the neutral is open, how are you going to measure neutral current? You must be talking about two or more different points within the distribution system, but I can't see what you mean.

 

[physis]

Re: open service neutral

 

[apauling]

Re: open service neutral

Controlling current flow in microprocessors is "relatively" easy, and i do not understand why it could not be implemented for 120v breakers, or for the neutral bar.

The problem with lost neutrals comes from the current flowing in reverse thru the neutral bar (and also thru the breaker). Why can't a higher amp device be developed? My understanding is that in 120v condition, current only flows in one direction, thus 60 hertz as opposed to 120 hertz (2 peaks), why coil ballasts hum at 60 hertz, not 120. The charge changes on the hot, but no current flows.

If the device is too costly for use in each breaker, it could be saved for use with circuits with expensive electronic equipment, as opposed to circuits with an alarm clock.

It would also be easy to add an alarm to this circuitry. if this idea were developed, and homeowners were more aware of this problem, the local poco's would be more inclined to take care of their connections, as the lawsuits would "bloom".

I don't understand the electrical theory enough to either posit this idea or disbelieve its implementability. But I know that in computers this limitation is used all over the place. if it were added as a trip device to breakers, even if expensive at first, all the computer professionals in non-site transformed services would be interested. Once that first wave of technology is crossed, they would be cheaper.

This area is not a strong point for me and I apologize if i seem a little "duncey" here.

paul

 

[jim dungar]

Re: open service neutral

No answer can really be given until the problem is correctly identified.

Do you want to sense an open neutral:
1) On the utility side of a properly bonded service entrance?
or
2) Between the utility meter and the neutral/ground bonding point in a properly grounded service?
or
3) At the neutral/ground bonding point on a properly grounded system
or
4) Any where on a service bonded improperly (at multiple points) on the load side
or
???

[ July 26, 2005, 03:59 PM: Message edited by: jim dungar ]

 

[beanland]

Re: open service neutral

When a utility service neutral breaks, the 240V remains constant but the 120V legs go up/down. If a utility primary neutral breaks, the entire service voltage can go up or down but the 1:1 relationship between legs remains. An overvoltage and undervoltage sensor with inverse time delay characteristic is needed on each side of 120/240V service. It seems feasible to add voltage montitoring to the microprocessor in an AFCI and implement OV/UV protection at a reasonable cost. The need is to have an AFCI manufacturer put the effort (cost) into programming the microprocessor.