Voltage Sensor with dry contact (no physical wire contact)

[crsimmons]

We are needing to sense voltage on some 500mcm cables off several large breakers. Do you know of a voltage switch with a dry contact that actuates when voltage is present? The voltage range is 120v to 240v.


We are guessing there is something available out there that operates the same way a non-contact "tick-tracer" type pen voltage tester works. But, it would have a dry contact like a current switch does.


We cannot put a small #14 wire under the same lug of the breaker as the 500mcm cable according to the NEC or we would use a pilot relay.


Or, we would use a current switch in this application but, at times there is no load present on the bus duct the breaker is serving. We are trying to prove that voltage is present off the breakers (which do not have auxiliary contacts).


Any information, advise or help would be appreciated.

Thank you,
Chris Simmons

 

[jim dungar]

We cannot put a small #14 wire under the same lug of the breaker as the 500mcm cable according to the NEC or we would use a pilot relay.

But you may be able to drill and tap a screw hole to allow you to use mount your #14 conductor.

http://static.schneider-electric.us/assets/digest/sd17603.pdf
page 3-17

 

[kwired]

We are needing to sense voltage on some 500mcm cables off several large breakers. Do you know of a voltage switch with a dry contact that actuates when voltage is present? The voltage range is 120v to 240v.


We are guessing there is something available out there that operates the same way a non-contact "tick-tracer" type pen voltage tester works. But, it would have a dry contact like a current switch does.


We cannot put a small #14 wire under the same lug of the breaker as the 500mcm cable according to the NEC or we would use a pilot relay.


Or, we would use a current switch in this application but, at times there is no load present on the bus duct the breaker is serving. We are trying to prove that voltage is present off the breakers (which do not have auxiliary contacts).


Any information, advise or help would be appreciated.

Thank you,
Chris Simmons

I myself would be more comfortable with something that measures actual voltage even if it created extra hurdles to install it. The non contact voltage detectors are not all that consistently reliable IMO. I'm sure they can make better versions but it is still nothing more than something that detects capacitive coupling, change the "capacitor" in any way and you change the range of the unit.

 

[petersonra]

isn't the #14 wire now a tap conductor? I guess it is OK as long as you follow the tap rules.

many circuit breakers can have small terminals installed on them for this purpose. I have used them on Sq D breakers. I don't know if they are available on all breakers. I don't think they are on Siemens.

there are also connectors that can be tapped onto the big wires and a smaller conductor can be spliced in.

 

[crsimmons]

Alternative Solution

Alternative Solution

Jim,

Thank you for the advise. I believe you are correct on the tap rule. However, I'm not sure if there is a lug adapter for the GE breakers that are in that switch gear.

Maybe I can tap a flat surface on the lug face if there is enough room? I could probably put a small 8/32 somewhere on there that would accommodate a #14 stakon lug.

Thank you again for your response and advise,

Chris Simmons

 

[crsimmons]

Control Wire Tap

Control Wire Tap

The length of the #14 wire to the relay from the breaker will easily be within the tap rule max length. Would I need to put a 15amp in-line fuse in it though to protect the #14?

Anyone's thoughts on this?

Thank you,
Chris Simmons

 

[Smart $]

But you may be able to drill and tap a screw hole to allow you to use mount your #14 conductor.

...

....

Maybe I can tap a flat surface on the lug face if there is enough room? I could probably put a small 8/32 somewhere on there that would accommodate a #14 stakon lug.

...

Field drilling and tapping breaker lugs would likely void the listing.

You didn't give any model info.

Ge does have means for some breakers...

https://www.google.com/search?q=GE+...1&sourceid=chrome&espvd=215&es_sm=93&ie=UTF-8

 

[kwired]

The length of the #14 wire to the relay from the breaker will easily be within the tap rule max length. Would I need to put a 15amp in-line fuse in it though to protect the #14?

Anyone's thoughts on this?

Thank you,
Chris Simmons

I'd say 725.45 is what likely applies. In particular subpart (C):

(C) Branch-Circuit Taps. Class 1 circuit conductors 14 AWG and larger that are tapped from the load side of the overcurrent protective device(s) of a controlled light and power circuit shall require only short-circuit and ground-fault protection and shall be permitted to be protected by the branch-circuit overcurrent protective device(s) where the rating of the protective device(s) is not more than 300 percent of the ampacity of the Class 1 circuit conductor.

If the overcurrent device were no more than 300% the conductor size no additional protection is necessary.

But if you had a listed piece of equipment with same thing already installed in it they very well may not include any overcurrent protection. I see this on pump panels all the time - up to 200 amps overcurrent device - control circuit directly tapped with no overcurrent protection using 14 AWG conductors. If I tried to field assemble the same thing I would have to have additional overcurrent protection on the control circuit.

 

[jim dungar]

Field drilling and tapping breaker lugs would likely void the listing.

The listing says the equipment left the factory is a manner that met the standards under which it was built
Only the AHJ can decide if this type of modification negatively impacts the ability of the equipment continue to meet the standards it was listed under. As often as I see drilling and tapping of busbars, I would think this type of action would be accepted quite commonly.

 

[iwire]

Jim beat me too it while I was looking for the text.

An authorized use of the UL Mark is the manufacturer's declaration that the product was originally manufactured in accordance with the applicable requirements when it was shipped from the factory. When a UL-Listed product is modified after it leaves the factory, UL is unable to determine if the product continues to comply with the safety requirements used to certify the product without investigating the modified product. UL can neither indicate that such modifications nullify the UL Mark, nor that the product continues to meet UL's safety requirements, unless the field modifications have been specifically investigated by UL. It is the responsibility of the authority having jurisdiction (AHJ) to determine the acceptability of the modification, or if the modifications are significant enough to require one of UL's Field Engineering Services members to evaluate the modified product. UL can assist the AHJ in making this determination.

http://www.ul.com/global/eng/pages/...ctrical/fieldcertification/fieldmodification/

 

[iwire]

I'd say 725.45 is what likely applies. In particular subpart (C):

How did you determine this is a branch circuit and not a feeder?

 

[kwired]

How did you determine this is a branch circuit and not a feeder?

Ok maybe it is not a branch circuit. If that is so, the rules for tapping a feeder are even more restrictive and in subpart (B):

(B) Feeder Taps. Class 1 circuit conductors shall be permitted to be tapped, without overcurrent protection at the tap, where the overcurrent device protecting the circuit conductor is sized to protect the tap conductor.

So the 300 percent part is missing and the tapped conductors must be protected at their ampacity.

 

[Smart $]

The listing says the equipment left the factory is a manner that met the standards under which it was built
Only the AHJ can decide if this type of modification negatively impacts the ability of the equipment continue to meet the standards it was listed under. As often as I see drilling and tapping of busbars, I would think this type of action would be accepted quite commonly.

Jim beat me too it while I was looking for the text.



http://www.ul.com/global/eng/pages/...ctrical/fieldcertification/fieldmodification/

I am well aware of such. The intention of my statement was to incite the response that it did. :happyyes:

 

[Smart $]

Ok maybe it is not a branch circuit. If that is so, the rules for tapping a feeder are even more restrictive and in subpart (B):

So the 300 percent part is missing and the tapped conductors must be protected at their ampacity.

We've not yet established it'll be a Class 1 circuit... but I will say it is a quite reasonable assumption.

However, if we don't stipulate it as a Class 1 circuit, it is entirely possible no overcurrent protection will be required. For example, with 240.21(B)(1)(1)(b), note the qualifying condition is either device or ocpd. Say the tap supplies an incandescent pilot lamp as the device mounted in the same enclosure. IMO, it would be rather moot to fuse the tap circuit.

 

[iwire]

I am well aware of such. The intention of my statement was to incite the response that it did. :happyyes:

So that tells us what about you?

It tells me to ignore future posts of yours.

 

[petersonra]

put a fuses in and be done with it.

then you will not have to worry about it.

the scheduled shutdown to do the work is going to cost 100X what the fuses will cost.

 

[Smart $]

So that tells us what about you?

I don't know. I can make assumptions based on my experience and thoughts, yet I realize its pointless. People will think what they think... so I make no attempt to elicit any particular opinion from others.

It tells me to ignore future posts of yours.

Your prerogative. Just exemplifies that people will think what they think regardless of my intentions. I could elaborate on the whole thought process that went into my posts. It may or may not sway your opinion... but that too would be pointless. I could elaborate on why it would be pointless... but that too would be pointless. Do you see a pattern evolving here?

 

[GoldDigger]

Point taken.

Sent from my XT1080 using Tapatalk

 

[crsimmons]

Many Thanks to Everyone

Many Thanks to Everyone

Wow!

I am very grateful for all the responses. And, the VERY useful code sections in case I need to argue this installation with the AHJ.

The device we are going to use on the two #14 wires is a Veris RIB relay (coil rating 240v). The N.O. dry contact on that RIB, we are going to use to drive a little 24v (in the field located) LED that will indicate that the bus duct the 500mcm cables are supplying is hot.

And like was indicated in petersonra's post, the cost for the inline fuses will be minimal for the shutdown.

I believe I will have to place on the switch gear afterwards though, that another power source is present (maybe a plaque?) even though it will be 24v. We are going to use a 120v circuits with a step down transformer to 24v to power the (6) LEDs that will be mounted in the field close to the corresponding bus ducts. The dry contacts on the Veris RIB will switch them on and off when voltage is present on the various buses. And, we will be installing a little test button to prove the LEDs are functioning.

Again, thanks to everyone for their knowledge and advise. All of your inputs have solidified my resolve that I will be installing this correctly.

Thank you,
Chris Simmons

 

[kwired]

With all the equipment you have connected I think you probably have an art 725 application.

If all you had were a volt meter or a simple indicator lamp, maybe a neon indicator, that connects directly to the lines I have to question whether or not 725 would apply, after all it is not controlling anything just indicating voltage. I know I would connect a voltmeter or neon indicator (and likely have done so before) without any additional overcurrent protection, unless someone can quote a code section that prohibits this.

ETA: I can't think of any installations where I have added such instrumentation where the proper overcurrent protection was already there or maybe I was covered by 725.45(C) and the 300% allowed there anyway. The only one that comes to mind was installing some blown fuse indicators - that was so long ago I don't recall exactly what was done. I do know they were essentially neon indicators installed across some 600 amp fuses but can not recall if any supplemental overcurrent was used. I also feel even supplemental overcurrent were used it seems to be somewhat pointless IMO, as long as leads are kept short and the indicator is mounted in/on the enclosure containing the fuses it is monitoring.