Chris,
Per your description, your Current Transformer is in a safety circuit. The
fact that "normally" you do not have high voltages on the primary side does
not cut it. (Besides, what is "high" voltage???) You have several choices
(in order of what my preference would be, and money being no object!).
However, if I misunderstood you, and your transformer is NOT in a safety
circuit, then all you need to do is to prove to UL that this is the case;--
it should be obvious from your schematics.
1. Since the transformer manufacturer already is using a UL
coordinated/approved insulation system, it would not take much more money
for him to submit this particular transformer to UL. Your company probably
should pay for the UL submittal costs, but the manufacturer should pay for
UL factory inspections. This way, you are off the hook when he changes
construction;-- he has to maintain compliance at all costs, and you don't
need to know the details as to how he does this.
2. If the manufacturer is very stubborn for some reason, and does not
want to do the above, tell him you will submit the transformer, however, you
will need complete construction details that he will have to provide you.
Since this is a custom design, he should not mind this. Thus, you pay
directly to UL for this evaluation. However, you also designate the
manufacturing location the address of your vendor, not your own. (This is
not the same as split inspection.) Here, you have more of a headache: you
pay for UL factory inspections;-- whenever anything is wrong UL writes you
letters about it, since you are the listee and applicant. Thus, you know
every time your vendor trips up. Be sure to tell him that now you will
have this knowledge!
3. You submit this transformer to UL as described in 2 above, but do
not designate the vendor as the manufacturing location. Now you have a
very big headache. Whenever the vendor changes construction, you don't
know anything about this, and then you get a spiffy UL field inspector who
demands that you saw the transformer in half so that he can measure the
spacings and count the number of windings! (Don't ever fall for this!
You need a laboratory special saw to do this correctly.) I would never
never choose this last option!
Thus, number 1 is your best choice even if your company has to pay up-front
costs for the UL evaluation-- after all, it is a custom design! However,
you save money and time down the road. I hope I have given you some
justifications for your decision.
Tania Grant, [email protected]
Lucent Technologies, Switching Solutions Group
Intelligent Network and Messaging Solutions
-----Original Message-----
From: Chris Wells [mailto:[email protected]]
Sent: Wednesday, November 15, 2000 5:20 PM
To: 'emc-pstc'
Subject: UL rec. needed on custom transformer ???
Question - What is the simplest, least expensive, way to define an
isolation transformer used in a UL508 (or similar standard) recognized
product? The transformer is a custom design made by a magnetics vendor for
use in our industrial products.
The product is manufactured under a UL coordinated insulation system or
recipe.
Do I need the manufacture to obtain a UL construction file?
I am concerned about managing our UL inspections since I can not prove the
construction at our sight.
What is the best way to handle the inspection issues?
I run into this issue with some of our switch mode power supply isolation
transformers. Typically these have a construction file. But I have been
told that I don't always need to do this.
I am confused!
Details -
My latest application is a Current Transformer used in power distributions
systems.
A power main transformer steps down the supply current to 0-5 Amp and then
the CT in my product steps this down again to mA range for measurement
purposes. These CTs in my product become referenced safety barriers in the
UL product file but do not normally have high voltages on the primary. My
magnetics vendor says I do not need the construction file but I do not see
how I can get a split inspection with UL inspecting the CT at the vendor,
with out this.
Is there another way?
Guidance on this topic would be most appreciated.
Thank you
Chris Wells
Senior Des Eng.
[email protected] <mailto:[email protected]>
Cutler-Hammer
412 490 6862
-------------------------------------------
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
To cancel your subscription, send mail to:
[email protected]
with the single line:
unsubscribe emc-pstc
For help, send mail to the list administrators:
Jim Bacher: [email protected]
Michael Garretson: [email protected]
For policy questions, send mail to:
Richard Nute: [email protected]
