Interesting.  The test engineer at the NRTL (not UL) I always work with always 
says we (the lab and the client) must always apply sound engineering judgment 
when applying standards when something isn’t completely clear or 
straightforward in the standard.  And this lab is always making sure their 
reports can withstand the scrutiny of the OSHA auditor.

-Dave


From: Richard Nute [mailto:ri...@ieee.org]
Sent: Thursday, December 07, 2017 6:12 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Pilot rating


According to
https://www.macromatic.com/blog/relays/what-are-pilot-duty-ratings-and-which-macromatic-products-have-them

“A pilot duty rating is a contact rating intended for contacts that control the 
coil of another relay or contactor. These ratings are applicable when 
controlling loads like relay coils, contactor coils, solenoids, and other 
similar inductive loads. Contacts with a pilot duty rating have passed 
standardized testing to prove they can reliably control a pilot duty load. The 
highly inductive nature of pilot duty loads is hard on contacts; controlling 
pilot duty loads using contacts not rated accordingly can cause premature 
failure and improper contact operation.”

Since you are driving a contactor with a solid-state relay, there are no 
physical contacts.  So, it seems to me, the solid-state relay need not have a 
pilot duty rating.  But, the device must withstand the inductive kickback when 
the circuit is opened.  The zener reduces the kickback.  But, there is no 
outward sign when the zener fails open, so the solid-state relay must be 
capable of withstanding the kickback.

UL only applies the standard.  UL folks seldom apply their engineering skills 
to a certification as the EUT must comply with the standard.  Differing from 
the standard requires review by at least one engineer or manager.  You must 
build the case and show the UL folks how the EUT meets the “intent” of the 
standard.

Good luck!
Rich

Ps:  Thanks, John, for the hint of a web search.

From: John Woodgate [mailto:j...@woodjohn.uk]
Sent: Thursday, December 7, 2017 2:00 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Pilot rating


A web search for 'OPTOMOS pilot duty rating' produces useful information, 
including references to UL508. But it seems that these are contact ratings for 
switching inductive loads (other relay coils). Since you have the double zener 
to absorb the inductive kick, you would only need, it seems, the opto to have 
pilot rating if the zener fails open-circuit.

John Woodgate OOO-Own Opinions Only

J M Woodgate and Associates www.woodjohn.uk<http://www.woodjohn.uk>

Rayleigh, Essex UK
On 2017-12-07 21:45, Jon Keeble wrote:
We are getting a somewhat innovative product through UL at the moment.
So there has been quite a lot of discussion and feedback from UL.
But when UL said they thought my little board needed a pilot rating I really 
thought they were joking.

Jon Keeble

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