Hi-pot test of a circuit with a diode

[jim hardy]

Industrial electrical symbols are a little different from pure electronics or telephone industry.

Working in the power plant where the equipment is so diverse, one runs across a lot of different drawing 'dialects'. In the sixties and seventies it seemed every manufacturer had his own drafting standards . One quickly became "multilingual".
Some instruction manuals were almost works of art. Now that it's mostly CAD there's a lot less individuality. I never did adjust to the European drawings, though.

Letters A and B referring to a contact mean Normally Open and Normally Closed, respectively. Mnemonic is "A = Alike" for NO, B = Backward" for NC. Letter C means a SPDT contact, one each NO and NC with common flapper.
So when i said "B contacts" earlier i was referring to the diagonal slash, as explained in Don's sketch above.
The contact's name should include the same identifier as the contactor to which it is mechanically slaved, but those are hidden by the note on OP's drawing . Probably they're C1 and C2.

There are standard device numbers too - http://en.wikipedia.org/wiki/ANSI_device_numbersold jim

 

[bramdam]

Sorry I am late to this. You have found the heater and it is after the auxiliary contactor, either C1AUX or C2AUX, not sure which one is our heater. My guess is the heater is after the NO contact for what I have been told there is a selector switch that allows the heater to be turned on or off.

It sounds like the way they test could definitely be the source of the sporadic failures of the diode. Those diodes are definitely not the most robust elements and when we buy them in the tens of thousands some are bad coming out of the box.

At this time, I see a couple of different options:
1) Try to get them to change their test methods by either removing our heater from this hi-pot test (since we hi-pot the heater prior to shipping and before the diode is put in, or by tying the two leads of the heater together prior to shocking their system.
2) Re-design the heater by either including some type of surge protector in parallel with the diode or removing the diode completely. Both will be hard. The UL is one thing but to get the heater to mimic the current limitation caused by the diode may not be possible.

Thanks for taking this issue on gentlemen.

 

[jim hardy]

This 1kv zener diode would survive the hi-pot, but the leakage it allows might cause the unit to fail its insulation test.

http://www.vishay.com/docs/88554/byv26dgp.pdf

12 cents at Digikey if you want t try a couple.

 

[bramdam]

Jim,
I laid out four options to resolve this issue and they chose to re-evaluate their hi-pot testing procedure. In the meantime they will tie the leads of our heater together, after the contactor, to avoid presenting a voltage differential across it. I could not get one to fail testing it this way at our shop. They too are weary of changing the part at this time so did not bite on putting a surge device in parallel.

 

[berkeman]

In the meantime they will tie the leads of our heater together, after the contactor, to avoid presenting a voltage differential across it. I could not get one to fail testing it this way at our shop.

Hey, that's great news!

 

[jim hardy]

Jim,
I laid out four options to resolve this issue and they chose to re-evaluate their hi-pot testing procedure. In the meantime they will tie the leads of our heater together, after the contactor, to avoid presenting a voltage differential across it. I could not get one to fail testing it this way at our shop. They too are weary of changing the part at this time so did not bite on putting a surge device in parallel.

understand. Your fix will work.

(Just for your bag of tricks) That 1KV zener should halve the heater power for you , just like the diode you're using. It'd survive the hi-pot too.


glad you got a path to success !

old jim