NEC Rules for 600VDC Electrical System

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juanhorta

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Hi, I wanted to know if there is any restriction or rules when installing a Variable Frequency Drive, which will be powered using 750VDC (Voc) open circuit voltage. This means that the operating voltage will be about 600-620. or 480VAC. Is there any special regulations, equipment requirements as far as wires, conduits, disconnects? Does UL1741 have any regulations about this?

Thank you

Juan
 
You pose an interesting question. I am surprised no one has chosen to answer. The DC bus voltage on a 480V drive will exceed the insulation limits of common wire (600V).

Seems to me there is some dispensation somewhere about using 600V rated wire in these cases.

<added>
I wonder what this actually means.

UL508a
29.1.2 All internal wiring shall have insulation rated for the voltage involved.
Exception: The voltage rating of conductors connected to a dc circuit, such as a dc bus or dc motor
circuits supplied from power conversion equipment, shall be the peak equivalence of the rms voltage
(rated voltage of the conductor multiplied by the square root of 2) marked on the conductor.
Click to expand...
 
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We use VFD rated shielded cable. Voltage is handled, nasty signals are shielded. Wouldn't do it any other way; fixing noise problems caused by improper use of wire/cable takes just too much time.
 
kc8dxx said:
We use VFD rated shielded cable. Voltage is handled, nasty signals are shielded. Wouldn't do it any other way; fixing noise problems caused by improper use of wire/cable takes just too much time.
Click to expand...

I haven't had all that much trouble with VFDs creating noise problems. I still think that cabling is a good idea. Even if you use SO cord, it is better than wire.
 
MLO cable is rated at 2KV and is very flexible. It is often used as a DC link between motor drives set up as input converter/ output inverter design.
 
Ul Thnn 600v

Ul Thnn 600v

Thank you petersonra, for getting back to me. I guess not that many people know about the subjet...either do I by the way. Based on your comments below, what should I do in order apply 600VDC to a 480VAC VFD and not being in violation of NEC.
The UL508a quote...mentions about internal wiring...is this wiring inside the drive? Inside a cabinet? I know NEC does not apply for wires runs inside a cabinet of short length.
In my case, the wire run I am reffering to are over 50 Ft through conduit. What kind of wire should I use in these cases if a UL THNN 600V rated wire is not good enough? What should I use for the Disconnects? I hope I am following you.

Thank you!

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You pose an interesting question. I am surprised no one has chosen to answer. The DC bus voltage on a 480V drive will exceed the insulation limits of common wire (600V).

Seems to me there is some dispensation somewhere about using 600V rated wire in these cases.

<added>
I wonder what this actually means.


Quote:
UL508a
29.1.2 All internal wiring shall have insulation rated for the voltage involved.
Exception: The voltage rating of conductors connected to a dc circuit, such as a dc bus or dc motor
circuits supplied from power conversion equipment, shall be the peak equivalence of the rms voltage
(rated voltage of the conductor multiplied by the square root of 2) marked on the conductor.
 
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