Zero Voltage Verification: >50 V or <50 V ?

[domenicod]

We have some magnets connected to a 500 V dc power supply. The magnets have exposed power leads and they cannot be accessed while in operation. We plan to install on each magnet a UL Listed Universal Power Alert device UPA-100 (http://www.alliedelec.com/Images/Products/Datasheets/BM/ATC/ATC_Industrial-Control_9930006.pdf) that indicates if the voltage is less than 27 V.
When we want to perform maintenance on these magnets we shut off the power supply, apply Lock and Tag and perform a Zero Voltage verification required by NFPA 70E since the equipment operates at >50 V. If the UL Listed UPA-100 indicates <27 V we can do the zero voltage verification with minimal training and PPE.

Question: if the UL Listed UPA-100 indicates <27 V, can we consider the equipment as if it operates at <50 V so that we are not required to perform the zero voltage verification?

 

[richxtlc]

If you read the information page referenced is says that isolation and de-energization shall be verified by the qualified employee. To me that means you verify the zero energy state.

 

[domenicod]

My question was: can I use the UPA-100 to show that the voltage is less than 50 V?
If OSHA 1910.147 and NFPA70E allow such a use then I can skip the zero voltage verification because the system has < 50 V.

 

[jeremysterling]

When I check for voltage, I test my VOM on a known live source, then test the equipment to be maintenanced, then retest my VOM again.

I am not sure your UPA-100 can safely perform this function. If the UPA-100 fails, the maintenance worker will be unaware of dangerous voltage present.

 

[richxtlc]

The statement of circuits are not considered dangerous if <50 volts is for systems that operate at <50 volts. There is a caviat, for high energy <50 volt systems. Your system operates at 500 volts and therefore is not in this category. The zero energy state is for zero energy not <27 volts. You must verify with voltage rated equipment using the live-dead-live method.