Parallel path's??

[don_resqcapt19]

Mark,
That is correct and rules are not permitted to be in a definiton per the NEC Style Manual, however if you use the EGC for some other purpose it is no longer an EGC, so you would have to provide another EGC.

 

[K8MHZ]

however if you use the EGC for some other purpose it is no longer an EGC, so you would have to provide another EGC.

As per what article?

I sure can't find one that makes such a statement.

There are several that could be construed to make such an inference, but as far as I can see, so long as there is *no objectionable current* there is no violation. It seems to me that the NEC has not defined such a phrase, but UL has, and as such, these switches seem to be legal.

As with any law, if it is not specifically prohibited, it is allowed.

 

[crossman]

Just to play along:

I suppose those switches can't be connected to multi-wire branch cirucits.

210.4(C) says MWBCs can only supply line-to-neutral loads. It doesn't say they can supply line-to-equipment ground loads.

Of course, Ex2 may negate my above comment considering that MWBCs must now originate from a 3-pole breaker or from breakers with an approved handle tie.

 

[K8MHZ]

Just to play along:

I suppose those switches can't be connected to multi-wire branch cirucits.

210.4(C) says MWBCs can only supply line-to-neutral loads. It doesn't say they can supply line-to-equipment ground loads.

Of course, Ex2 may negate my above comment considering that MWBCs must now originate from a 3-pole breaker or from breakers with an approved handle tie.

You may have a point there. 210.4 does, by implication, indicate that SWBCs *can* supply line to equipment ground loads, does it not?

 

[crossman]

Yeah, I am laughing right now!:grin: The whole thing is absurd! Intellectually and going with principle, my brain is saying "you can't use an equipment ground to intentionally carry normal current". But the practical side of me is saying "So what, no big deal."

 

[K8MHZ]

"So what, no big deal."

Exactly, so long as it doesn't carry an 'objectionable current'.

All we need now is a definition!

:smile:

 

[76nemo]

What the???

What the???

Boy, now I am confused, like that's something new, eh?
The diagram shows the switch grounded. If the grounding is the return, what happens in the event of fault current:-?

 

[K8MHZ]

Boy, now I am confused, like that's something new, eh?
The diagram shows the switch grounded. If the grounding is the return, what happens in the event of fault current:-?

Bye, buy, switch??

 

[don_resqcapt19]

Mark,
If the conductor in question no longer meets the definition of EGC, how is it still an EGC? As far as the objectionable current, that is very subjective, and to me any current other than fault current on the EGC is objectionable. In this case I don't think it is a big safety issue. It is just a major mistake on the part of UL, one they would like to have a "redo" on.

 

[76nemo]

Don?

Don?

If the switch doesn't have the grounded and grounding bonded, (illegal), at the switch, how does the UL see this as permissable?
This scenario is totally new to me, one I have never heard of. If the switch is grounded to the box, and the grounding is the return path, than how can this be deemed safe? Are these switches only listed to be used in plastic boxes???

 

[K8MHZ]

If the switch is grounded to the box, and the grounding is the return path, than how can this be deemed safe?

The amount of leakage current is less than a micro amp, about the same (or less ) than a DVOM supplies on the 'ohms' setting.

The assumption of safety seems to be based upon the nearly immeasurable amount of current in question.

 

[don_resqcapt19]

Yes, I think it is "safe", but UL rules and standards do not change the NEC rules.

 

[GMc]

Mark,
It is just a major mistake on the part of UL, one they would like to have a "redo" on.

So it's not as easy to just reverse their mistake? Bunch of red tape involved I guess.

If the switch doesn't have the grounded and grounding bonded, (illegal), at the switch, how does the UL see this as permissable?
This scenario is totally new to me, one I have never heard of. If the switch is grounded to the box, and the grounding is the return path, than how can this be deemed safe? Are these switches only listed to be used in plastic boxes???

The UL would probably think it was ok to rob a bank as long as you just took a little.

I don't think they were designed to be used in plastic boxes. The Manufacturers designed them to capture the commercial market. They know that there is no neutral at the switch locations. They didn't want the commercial market to have to hire us to pull a neutral down to the switch. Then they got the UL to list the product. Wa-La, big bucks for them. They made big bucks just from our Facility.

Yes, I think it is "safe", but UL rules and standards do not change the NEC rules.

I agree 100% they should not be allowed.

Thanks for all the responses,
Gary

 

[winnie]

Yes, I think it is "safe", but UL rules and standards do not change the NEC rules.

I agree 100% they should not be allowed.

Playing devil's advocate here, but why should these devices be prohibited, rather than changing the NEC rules to permit them? In other words, make it explicit that for switch loops the EGC is permitted to carry <5uA of current to power these types of switches?

-Jon

 

[cschmid]

Why would want to set the precedence on a situation like this and encourage a higher level of manufacturing and design in this area..why encourage bad behavior..nip it in the bu--before it becomes a real problem..

Also if you design it to use the ECG then what prohibits it from failing to the EGC and allowing a shock current on the ECG, which in turn energizes every thing bonded to it..even if it is temporary it is a shock current non the less..

 

[winnie]

I tend to agree, however just to keep things in perspective: for a 120V switch loop run on 12-2 MC cable, I would expect about 1uA of leakage to ground per _foot_ of switch loop cable, simply because of capacitive coupling between the ungrounded conductors and the jacket.

-Jon

 

[Smart $]

I tend to agree, however just to keep things in perspective: for a 120V switch loop run on 12-2 MC cable, I would expect about 1uA of leakage to ground per _foot_ of switch loop cable, simply because of capacitive coupling between the ungrounded conductors and the jacket.

I agree. I assume it's a commonplace occurrence, but most never considered to check it, especially at that low of current level.

 

[K8MHZ]

Playing devil's advocate here, but why should these devices be prohibited, rather than changing the NEC rules to permit them? In other words, make it explicit that for switch loops the EGC is permitted to carry <5uA of current to power these types of switches?

-Jon

Why not just get the UL and the NEC to agree? The UL allows 500 micro amps (1/2 a milli-amp) which is a nearly negligible amount of current.

Yeah, I know, I am dreaming, right???

 

[mivey]

bud-nippin

bud-nippin

Why would want to set the precedence on a situation like this and encourage a higher level of manufacturing and design in this area..why encourage bad behavior..nip it in the bu--before it becomes a real problem..

Also if you design it to use the ECG then what prohibits it from failing to the EGC and allowing a shock current on the ECG, which in turn energizes every thing bonded to it..even if it is temporary it is a shock current non the less..

"...you'll find that every one of 'em is in favor of bud-nippin'... Only one way to take care of it."-BF

 

[cschmid]

"...you'll find that every one of 'em is in favor of bud-nippin'... Only one way to take care of it."-BF

That bud nippin that will get you in trouble..:grin:

Yep only one way, not to install them..

I will now read the directions better..I had a lutron switch like that, an occupancy sensor I believe and I could not get it to work correctly..It was in and old install area not a good enough ground..two wire setup and box in plaster wall no ground to speak of..I now know why it did not work right..did not spend much time on it loosing proposition..junk and run..