occupancy sensor safety

[lzielk]

My question is about a Hubble LHMTS1-G-WH wall mounted sensor. I installed this unit on a 277 volt system and it is rated for that. The problem is after wiring it and properly grounding it. I found the yolk to ground to be live. I got a shock trying to mount it to the box. and it measured 277 volts to ground.
I followed up with a call to the manufacturer where I was told that this condition is normal and that the instructions clearly state not to install on a live circuit and that once mounted to the box it would no longer be a shock hazzard. I was wondering if this condition meets the rules of the NEC. thanks for any and all input

 

[luckylerado]

My question is about a Hubble LHMTS1-G-WH wall mounted sensor. I installed this unit on a 277 volt system and it is rated for that. The problem is after wiring it and properly grounding it. I found the yolk to ground to be live. I got a shock trying to mount it to the box. and it measured 277 volts to ground.
I followed up with a call to the manufacturer where I was told that this condition is normal and that the instructions clearly state not to install on a live circuit and that once mounted to the box it would no longer be a shock hazzard. I was wondering if this condition meets the rules of the NEC. thanks for any and all input

That sounds awfully fishy to me. What if it were a plastic box?? Is there a neutral connection?? Was the device grounded? If the yoke is grounded and the box is properly grounded how would there be a shock??

 

[iwire]

It is the truth and the reason the NEC now requires neutrals at many switch locations.

 

[lzielk]

It was properly grounded with a green wire from the yoke to the metal box and there was still a difference in potential but I am told that it is safe as there would be voltage but very limited power and to avoid it you would need the neutral

 

[GoldDigger]

It was properly grounded with a green wire from the yoke to the metal box and there was still a difference in potential but I am told that it is safe as there would be voltage but very limited power and to avoid it you would need the neutral

If the potential from yoke to ground was more than a volt or two and existed while the green wire was connected to the box it suggests that the box is not grounded.

 

[luckylerado]

... it suggests that the box is not grounded.

And is therefore unsafe regardless of what some flunky at Hubble is telling you.

 

[iwire]

If the potential from yoke to ground was more than a volt or two and existed while the green wire was connected to the box it suggests that the box is not grounded.

Actually it says nothing about the box grounding it suggests the green jumper between the device and the box is not connected to the yoke.

 

[steve66]

It is the truth and the reason the NEC now requires neutrals at many switch locations.

My thought exactly. The sensor probably doesn't have a neutral wire, so it is using the ground as a return path to run its power supply.

The sensor greatly limits the current flowing to ground. If the installer had touched a wire connected directly to 277 V (and not through the sensors current limiting power supply), he would have gotten a much worse shock.

Its not a good idea to install any devices (especially 277V) with the power applied.

My understanding is that 277 Volts can be a really bad shock.

 

[don_resqcapt19]

And is therefore unsafe regardless of what some flunky at Hubble is telling you.

While I agree this is a safety hazard, the UL standard permits these types of devices to use the EGC as the grounded conductor to power the electronics in the occupancy device. The standard say that each such device can draw up to 0.5 mA of current via the EGC. If the equipment grounding conductor is not connected, there is a shock hazard.

This is the very reason the code now requires a neutral conductor to switch boxes as iwire pointed out.

The next code and the new UL standards for these types of devices will not permit new devices to use the ECG as the grounded conductor.

 

[steve66]

While I agree this is a safety hazard, the UL standard permits these types of devices to use the EGC as the grounded conductor to power the electronics in the occupancy device. The standard say that each such device can draw up to 0.5 mA of current via the EGC. If the equipment grounding conductor is not connected, there is a shock hazard.

So the installer would have received a maximum of 0.5 mA shock current if his hand completed the circuit between the device yoke and the grounded box.

I'm sure someone could feel that shock, but its roughly only 1/10 of the current that a GFCI receptacle would trip at. And once the device is properly installed, I don't think its much of a shock hazard at all.

 

[iwire]

So the installer would have received a maximum of 0.5 mA shock current if his hand completed the circuit between the device yoke and the grounded box.

I'm sure someone could feel that shock, but its roughly only 1/10 of the current that a GFCI receptacle would trip at. And once the device is properly installed, I don't think its much of a shock hazard at all.

Now picture your electrician working on an EGC at a panel with a number of these units connected to that EGC.

IMO EGC are not live conductors I am required to deenergize before working with them yet these devices do make the EGCs live conductors.

 

[don_resqcapt19]

So the installer would have received a maximum of 0.5 mA shock current if his hand completed the circuit between the device yoke and the grounded box.

I'm sure someone could feel that shock, but its roughly only 1/10 of the current that a GFCI receptacle would trip at. And once the device is properly installed, I don't think its much of a shock hazard at all.

While the shock itself may not be a serious hazard, the physical reaction to that shock maybe.

 

[steve66]

Now picture your electrician working on an EGC at a panel with a number of these units connected to that EGC.

IMO EGC are not live conductors I am required to deenergize before working with them yet these devices do make the EGCs live conductors.

While the shock itself may not be a serious hazard, the physical reaction to that shock maybe.

I should have qualified that by saying "not much of a shock hazard to the end user." I wasn't trying to say that the new rule is unnecessary or overkill.