brake resistor wiring

[petersonra]

Just curious what you guys think.

480V drives have well above 600VDC on the DC bus where a brake resistor is often connected.

yet it is pretty much universal to use 600V insulation on this wiring.

why is this OK?

 

[GoldDigger]

Just curious what you guys think.

480V drives have well above 600VDC on the DC bus where a brake resistor is often connected.

yet it is pretty much universal to use 600V insulation on this wiring.

why is this OK?

As long as the DC does not go above the rectified/peak voltage corresponding to 600 V AC, I do not see this as a problem. But since the braking EMF will be some unspecified amount higher that would be exceeding the insulation rating. Although it would probably be within the insulations safety factor.
What do the installation instructions for the braking resistor kit say? And is it part of the VFD or connected by building wiring?
Maybe we should be being PV wire rated at 1000V for all such installations.

BTW, that DC is with respect to ground, not just "phase to phase", which makes it even worse.

Tapatalk...

 

[petersonra]

I seem to recall hunting this down once and finding some UL statement that it was OK, but it just bugs me.

the answer seems to be that 480V is 678V P-P, so that is what the DC bus voltage max can be, so that makes it OK.

 

[Besoeker]

Just curious what you guys think.

480V drives have well above 600VDC on the DC bus where a brake resistor is often connected.

yet it is pretty much universal to use 600V insulation on this wiring.

why is this OK?

The peak of 480Vac is about 680V.
If the insulation is good for that it is good for 600Vdc.

 

[Besoeker]

BTW, that DC is with respect to ground, ...

It's from the AC source so no different WRT ground than that is.