Dave, et al,
Being able to argue the imposition of requirements requires
several things. The requirements should be soundly technically based, cynical
Rich already addressed one case showing deficiencies. Since the application
description doesn’t seem to cover the situation at hand each party must have a
good grasp as to the basis for the requirement and bring that into the analysis
of the present situation while coming to agreement between the two parties.
Each party has to work to understand the concerns of the other in the
negotiation. Generally, to get a timely solution, a small adhoc team will
gather on each side and the negotiations will get underway (anyone remember
when we used to conduct these by telex or fax?). The final agreement should
bring the parties together in understanding the requirements and agreeing on
the implementation details. The really disruptive technology changes that
don’t fit the mold well are pushed back up to the standards development groups
and a modification to the requirements haggled out there (you don’t want to
watch sausage being made); this level of change takes eons on the
manufacturer’s timescale.
My experience is that there are weaknesses at each step of the
way. Agreement is usually a compromise for both sides. Hopefully the solution
will withstand the test of time with regard to adequacy in the application,
else the manufacturer is drawn into a failing product, perhaps even a recall.
The test house might get criticized over a decision but they carry hardly no
responsibility in the product failure and subsequent consequences.
Good solutions built along the way work to smooth the
technology disruptions as they are shared (each test house has a scheme for
sharing info among their far flung groups) and implemented along the way to
changing the requirements.
Dave’s comments seem to be more the rule than the exception in
my experience.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
<mailto:[email protected]> [email protected]
From: Nyffenegger, Dave [mailto:[email protected]]
Sent: Thursday, December 7, 2017 6:31 PM
To: [email protected]
Subject: Re: [PSES] Pilot rating
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:[email protected]]
Sent: Thursday, December 07, 2017 6:12 PM
To: [email protected] <mailto:[email protected]>
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:[email protected]]
Sent: Thursday, December 7, 2017 2:00 PM
To: [email protected] <mailto:[email protected]>
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:[email protected]
<mailto:[email protected]> ]
Sent: Thursday, December 7, 2017 12:29 PM
To: [email protected] <mailto:[email protected]>
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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