High Voltage Cable rated DC only?

[overkill94]

I did an inspection on an amplifier that steps up the voltage from 220 V to 4200 Volts AC which is rectified to DC immediately after being stepped up. To connect the secondary of the transformer to the rectifier, they're using AWM style 3239 (http://iq.ul.com/awm/stylepage.aspx?Style=3239) which shows that it's rated for maximum 60kV DC. I flagged it as a discrepancy since the style page seems to indicate that it should only be used in DC applications, otherwise they would've just said 60kV without the "DC" qualifier. Is this the correct interpretation or should all conductors be assumed to handle AC and DC voltages?

 

[GoldDigger]

They may have listed 60kV DC to indicate that the highest allowed voltage is that exact number while 60kV AC (RMS) would correspond to an even higher peak voltage.
Or (less likely) there may be something about the insulation which would not hold up well to changing voltages.
But in that case it should not be OK for pulsed or switched DC either.

For lower voltages, like 300 or 600 volts, NEC/UL consider that the nominal voltage is either AC RMS or DC, but at high voltages the cost requires more exact characterization.

mobile

 

[Ingenieur]

the original date is 1969
looks like it was approved for HV TV power supply use

I read it that it was approved for DC, not that it is not approved for AC use
ie, they only sought DC approval, not AC

is there a mfg and pn on the cable?

 

[Jraef]

Look at the last sentence in that UL sheet. Using it for anything other than its intended (in this case highly specialized) use will be a violation of 110.3

 

[overkill94]

Look at the last sentence in that UL sheet. Using it for anything other than its intended (in this case highly specialized) use will be a violation of 110.3

It does say "or where the acceptability has been determined by Underwriters Laboratories." and they sent me this blurb from the manufacturer's information:

• HVSR lead wire may be used in TV receivers, stoves, heaters, furnaces, dryers, signs, lighting fixtures, and high temperature electronic devices.

They're saying the transformer is considered a high temperature electronic device which I suppose is true. My main question is the suitability for AC applications.

 

[Ingenieur]

It does say "or where the acceptability has been determined by Underwriters Laboratories." and they sent me this blurb from the manufacturer's information:

• HVSR lead wire may be used in TV receivers, stoves, heaters, furnaces, dryers, signs, lighting fixtures, and high temperature electronic devices.

They're saying the transformer is considered a high temperature electronic device which I suppose is true. My main question is the suitability for AC applications.

I guess listing wise it may be iffy

but technically is it an issue? rated to 60 kv(dc) and is operated at only 4.2 kv(ac)
with dc it is continuously stressed, with ac stressed/relaxed (at zero crossing)
safety issue? imho, no

judgment call, that's why they pay you the big bucks

 

[overkill94]

I guess listing wise it may be iffy

but technically is it an issue? rated to 60 kv(dc) and is operated at only 4.2 kv(ac)
with dc it is continuously stressed, with ac stressed/relaxed (at zero crossing)
safety issue? imho, no

judgment call, that's why they pay you the big bucks

Ha! I don't inspect a whole lot of high voltage equipment so I'm trying to be a bit more cautious. Especially since it's AWM which has even more specific restrictions than a normal UL-listed wire.

I've requested the manufacturer's information so I can call them directly, hopefully they can provide more test data from their UL file.

 

[overkill94]

I did some digging on the AWM ULiQ and found some styles that had ratings for AC and DC high voltages, which leads me to believe the listing is exclusive to AC or DC unless stated otherwise. If anyone has anything from the UL style guide or something that says different, that would be helpful.

 

[junkhound]

I did an inspection on an amplifier that steps up the voltage from 220 V to 4200 Volts AC which is rectified to DC immediately after being stepped up. To connect the secondary of the transformer to the rectifier, they're using AWM style 3239 (http://iq.ul.com/awm/stylepage.aspx?Style=3239) which shows that it's rated for maximum 60kV DC. I flagged it as a discrepancy since the style page seems to indicate that it should only be used in DC applications, otherwise they would've just said 60kV without the "DC" qualifier. Is this the correct interpretation or should all conductors be assumed to handle AC and DC voltages?

DC rated does NOT mean it is good for that voltage ac peak.

google "partial discharge' and 'paschen curve' for details. At even 4.2kV ac a 60 kV dc rated cable may fail - what happens is the capacitive current that flows at ac can breakdown small air gaps (partial discharge) which etches the insulation away over time and the insulation fails. For dc, the small airgaps only breakdown when the power is turned on and off, not every half cycle like ac.

 

[Ingenieur]

I did some digging on the AWM ULiQ and found some styles that had ratings for AC and DC high voltages, which leads me to believe the listing is exclusive to AC or DC unless stated otherwise. If anyone has anything from the UL style guide or something that says different, that would be helpful.

I did the same for that style
looked at data sheets for 1/2 dozen different mfgs
some listed v dc, some v ac/dc, some v only