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Why do bus bars have voltage ratings?

jameshowison

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Jul 30, 2021
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I think I have a grasp of amperage ratings, but I'm confused about max voltage ratings for bus bars.

Unlike switches/disconnects/fuses I don't think that arcing is an issue for bus bars (or is it?)

I'm confused why wire generally seems to be rated up to something very high (like 600v) but bus bars are often rated much lower (like 50vdc or 32vdc)? Is this generally just a "tested up to" number? Or is there some property that limits this? If there is, why doesn't it apply to wire?

e.g., https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs which has 300V AC/48V DC

compared to

https://www.bluesea.com/products/1990/PowerBar_1000_-_8_3_8in_Terminal_Studs which just says 150V

Or


which shows 50VDC for the bus bar (see p7 of the PDF).

(Overall context is 48v nominal systems, where actual voltages are up around 58v, sometimes!)
 
The Wire insulation is rated at 600 volts. Not the conductor.
 
"
The distance an arc will jump through air is proportional to its voltage.

3000 volts jumps 1 mm.

3,000,000 volts jumps 1 meter

300,000,000 volts jumps 100 meters.

It takes 900 million volts to jump 300 meters. If it jumps more than 300 meter (about 1000 feet) then its got to be bigger proportionately than 900 million volts."

I took that off another web page, I don't know its accuracy, but, I do know its relevance to your question. They have to rate them at something, and I'd say typically 600Volts is the high of what most people would expect.
 
So if this is about protecting against arcing, could there really be sufficient difference between, say, 50v (rated) and 58v (sometimes experienced in 48v nominal systems)? Seems like the differences would need to be in the hundreds of volts.
 
So if this is about protecting against arcing, could there really be sufficient difference between, say, 50v (rated) and 58v (sometimes experienced in 48v nominal systems)? Seems like the differences would need to be in the hundreds of volts.
That depends on how much current is flowing.
 
So if this is about protecting against arcing, could there really be sufficient difference between, say, 50v (rated) and 58v (sometimes experienced in 48v nominal systems)? Seems like the differences would need to be in the hundreds of volts.
I would not worry.
 
So if this is about protecting against arcing, could there really be sufficient difference between, say, 50v (rated) and 58v (sometimes experienced in 48v nominal systems)? Seems like the differences would need to be in the hundreds of volts.
Many times items are rated for listing or insurance reasons… as in, they are TESTED to be safe at the rated voltage… designed for that voltage. I doubt a 48V rated bussbar would be less safe operating at 58 etc Volts but if someone got hurt, or something failed, you couldn’t sue them for damages, as the rating is for only 48V…

Relays and breakers and switches rating is different, they are rated at the voltage, AND amps… and exceeding that can be a bad thing. Arcing, and failure to operate would be a concern.
 
Thanks. Yes, this is this thing I'm trying to understand. If it's just that it was tested at those numbers then what is a reasonable extrapolation.

e.g., if it was amps and we're talking 20% higher (48-->58 amps rather than 48-->58 volts) then I know I have to be concerned, because the heat generation due to resistance is way higher. But reasoning about volts escapes me.

If it's arcing, with switches/fuses etc we are talking really small gaps for the arc to jump across. But with busbars we are talking 3/4 inch or more, across plastic standoffs. It just doesn't seem realistic that arcing could be an issue across these gaps with the move from 48-->58v (whereas moving to 600v or 60,000v yes!). But I don't know and I can't find any resources about it.

If it's not arcing then what?

Hmmm, this is interesting: https://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/ suggesting that voltages above 80vdc are problematic (although these are *much* smaller gaps than any busbar would involve).
 
It seems the busbar people are inventing a problem (arcing) so they can sell you a solution.

You can test a busbar to 170 peak volts by putting a 120vac in series with a 7-1/2 w lamp in series with the bar.

Wear gloves & goggles. See if you can draw an arc to ground.

The lamp limits the current to 60 mA or less if you should somehow draw an arc. Which you will not.:cautious:

However: If you do, today I will have learned something about breakover voltage.
 
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James, I think this is beyond what your going to get, go chase another bone....
 
Thanks. Yes, this is this thing I'm trying to understand. If it's just that it was tested at those numbers then what is a reasonable extrapolation.

e.g., if it was amps and we're talking 20% higher (48-->58 amps rather than 48-->58 volts) then I know I have to be concerned, because the heat generation due to resistance is way higher. But reasoning about volts escapes me.

If it's arcing, with switches/fuses etc we are talking really small gaps for the arc to jump across. But with busbars we are talking 3/4 inch or more, across plastic standoffs. It just doesn't seem realistic that arcing could be an issue across these gaps with the move from 48-->58v (whereas moving to 600v or 60,000v yes!). But I don't know and I can't find any resources about it.

If it's not arcing then what?

Hmmm, this is interesting: https://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/ suggesting that voltages above 80vdc are problematic (although these are *much* smaller gaps than any busbar would involve).
Busbars are not an issue for voltage.
Use whatever is rated high enough for the amps.

PS: don't let them touch each other. lol
 
Busbars are not an issue for voltage.
Use whatever is rated high enough for the amps.

PS: don't let them touch each other. lol
Well, not ALL bussbars…

The bussbars likely being described here are those in a mount with lugs for additional circuits.
The material insulating it, or shielding it from contact may only be pvc, or similar and it may not be suitable for higher voltage…

If just a metal bar connecting stuff… yeah, voltage is irrelevant to a point…
 
Busbars are not an issue for voltage.
Good god are they not....

Stating something so definitive is dangerous, its clear to me the original OP needs someone to do this for them.

If you run a million volts thru any of these bus bars youll have major problems, regardless of the amps. Yes its a extreme, but, none the less true.
 
Good god are they not....

Stating something so definitive is dangerous, its clear to me the original OP needs someone to do this for them.

If you run a million volts thru any of these bus bars youll have major problems, regardless of the amps. Yes its a extreme, but, none the less true.
Not at all.
Voltage ratings have to do with insulation factors.
In an uninsulated bar, the only insulation factor is (air gap) the distance from another conductive object.
 
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