The ultimate issue is what safety issue occurs if the contactor fails to open 
or close when it is supposed to?  If there is no safety consequence, then the 
contactor control is functional, not a safeguard.  If there is a safety 
consequence, then the circuits controlling the contactor constitute a safeguard 
and must be “reliable,”  and must meet the intent of the standard.

 

Not so cynical Rich

 

 

From: Jon Keeble [mailto:j...@wattwatchers.com.au] 
Sent: Thursday, December 7, 2017 12:29 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Pilot rating

 

I am using a Panasonic AQH3213A PhotoMOS optical isolator to control a small 
contactor.

 

At 110VAC the contactor coil draws 30mArms.

The coil contacts are wired to a PCB via a terminal block plug and socket.

 

On the PCB is a series 10ohm fusible resistor, and a SMBJ400AC bidirectional 
zener.

 

When the switch opens at peak current (42mA) there is 0.1J of energy in the 
coil that gets absorbed by the zener.

 

The zener 

* clamps at a voltage way below the voltage rating of the optoMOS switch.

* is rated at 600W for 8.3msec and is subject to only 13W for a similar period.

 

The UL test engineer says that the optoMOS should be "pilot duty" rated (the 
part I am using does have this rating).

 

Does anyone know what triggers the requirement for a "pilot duty" rating?

Is this defined in a standard somewhere?

 

This useful link identifies "contact rating codes"

https://na.industrial.panasonic.com/blog/what-pilot-duty-rating-how-it-obtained

 

The lowest rating E300 is for 110V 1.8A (make) 0.3A (break)

 

Technically speaking, my switch is not connected to the contactor .. there is a 
two-component network in between

Does UL have the capacity or procedures in place to understand and accept a 
circtuit analysis that shows my circuit as safe?

 

Jon Keeble

 

Wattwatchers.

 

 

 

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