Why are devices allowed to use the EGC as a current carrying conductor?

[Tester101]

I was recently going to install a Lutron Maestro Occupancy Sensor (MS-OPS2), but I noticed in the installation instructions that it said the device wouldn't work without an equipment grounding conductor connected. This seemed strange to me, so I did a bit of research. I found that the device actually uses the grounding conductor as a grounded conductor, so it can have constant power. It only seems to be a small amount of current, as this document says you should be able to connect 20 devices before tripping a GFCI at 4-6mA.

But why is this allowed at all? Why are devices allowed to intentionally create ground faults? Shouldn't a normally non-current-carrying conductor, normally not carry current?

 

[GoldDigger]

I was recently going to install a Lutron Maestro Occupancy Sensor (MS-OPS2), but I noticed in the installation instructions that it said the device wouldn't work without an equipment grounding conductor connected. This seemed strange to me, so I did a bit of research. I found that the device actually uses the grounding conductor as a grounded conductor, so it can have constant power. It only seems to be a small amount of current, as this document says you should be able to connect 20 devices before tripping a GFCI at 4-6mA.

But why is this allowed at all? Why are devices allowed to intentionally create ground faults? Shouldn't a normally non-current-carrying conductor, normally not carry current?

A normally non-current-carrying conductor should not be expected to carry normal current, regardless of how small. But at the same time there are designs that rely on it and have realllllllllly low current drain.
This a long story of conflict between the UL which approves the devices and NEC which essentially prohibits them. The partial resolution depends on the recent NEC provisions requiring a grounded conductor to be present (or easily pullable) at every box that contains a light switch.

 

[cadpoint]

A few plus years ago a Lutron "person" spoke/ posted on this exact subject. Maybe they can re-post their own article or the OP can research it.

 

[Dennis Alwon]

I thought with the new code the use of the equipment grounding conductor would not be allowed. I have seen other manufacturers do the same - I started a thread on it. Here it is

 

[GoldDigger]

I thought with the new code the use of the equipment grounding conductor would not be allowed. I have seen other manufacturers do the same - I started a thread on it. Here it is

My impression is that with the changes made in NEC 2011 in effect, the current devices which use the EGC as a return path for control current will be grandfathered in their UL listing for some length of time (possibly forever) but no new lighting control or presence sensor devices will be approved by UL unless they use the neutral instead.
It is a chicken/egg thing and we are still in a transition.
If that impression is not correct, please give the right explanation. Thanks.

 

[kwired]

My impression is that with the changes made in NEC 2011 in effect, the current devices which use the EGC as a return path for control current will be grandfathered in their UL listing for some length of time (possibly forever) but no new lighting control or presence sensor devices will be approved by UL unless they use the neutral instead.
It is a chicken/egg thing and we are still in a transition.
If that impression is not correct, please give the right explanation. Thanks.

That is kind of my thoughts. They probably stop making them rely on the EGC as part of the circuit at some point if they want them to have a valid listing, but I don't know when that point is.