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Servo chopper circuit wire rating

Servo chopper circuit wire rating

Servo chopper circuit wire rating

(OP)
For years I have seen companies using choppers with external resistors to help with servo braking. Recently I can into a situation when I need to do the same. The problem is I notice that the DC voltage on the bus is over 600 volts (750 to 800VDC). 600V is what the standard MTW or THHN wire is rated for, therefore I have investigates several other companies panels in the field, and it looks like they have used 600V rated wire. What and I missing? Shouldn't this be rated for 1000V or more in this application? To add to the issue the panel needs to meet CE spec also. Any help is appreciated.

RE: Servo chopper circuit wire rating

The 600 V is RMS and the DC link voltage is DC. So, the 600 V wire sees around 850 V 100 (or 120 if 60 Hz) times per second. It is rated to withstand that. The continuous 750 - 800 V should not be a problem. But, then again, there's NEC and UL. I do not know what they think about it.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Servo chopper circuit wire rating

(OP)
Thank you for the reply. I was sent this by a friend today, which is supports your reasoning.

UL 508 PRACTICAL APPLICATION GUIDELINES
PAG ID: #14

CLAUSE NUMBER: 21.1.2

CLAUSE HEADING: Internal Wiring - General

OTHER RELEVANT CLAUSES (as applicable):

DESCRIPTION OF ISSUE:
Par. 21.1.2 requires that all internal wiring be rated for the voltage of the circuit in which it is used. This requirement applies to both ac circuits and dc circuits. However, Listed conductors and Recognized Appliance Wiring Material are rated in volts without an indication of whether the voltage rating is rms, peak or dc. How should wiring be selected to comply with 21.1.2 for dc applications?

APPLICATION GUIDELINE:
The marked voltage rating for UL Listed and Recognized wiring should be multiplied by root 2 to determine the peak voltage rating of the conductor. The rated dc voltage shall be less than the calculated peak voltage rating.

RATIONALE:
The voltage rating on Listed and Recognized wire identifies an rms voltage and also covers the peak equivalent voltage. Therefore, for example, wire rated 600 V may be used in circuitry rated up through 600 V ac or 848.5 V peak.

Skogsgurra, I appreciate your help.
 

RE: Servo chopper circuit wire rating

Thanks for the feedback! It is encouraging to see that UL also sometimes is sticking to basic physical laws. I am more used to obscure juridical reasoning from that part.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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