|
|> | On Mon, 7 Jul 2008 20:12:00 +0000 (UTC), Cydrome Leader
|> |
|> |
|> |>> Then it needs to be specifically RATED at that double voltage ... 480
| volts!
|> |>> It needs to SAY that so people know what they are getting.
|> |
|> | No they don't. Anyone skilled in the craft knows what the ratings mean.
| Both
|> | UL and the NEC take that into account. I can see how you'd be confused,
|> | though.
|>
|> Ratings that say 240 volts mean 240 volts. What is added to that is the
|> base knowledge from limited existing documents that in most cases UL tests
|> at double the voltage relative to the expected rating. That's just on the
|> hairy edge for the generator/utility loop. They will probably hold
| because
|> if it passes at a test of 480, it probably passes at a but more than that.
|> The problem is tolerances. You can lose your margin above 480 with sloppy
|> manufacturing tolerances.
|>
| No, ratings that say 240 volts means "240V + whatever safety margin was
| decided on". Not "241V = failure". I assume when they wrote the test specs
| they thought about the possibility of 480V(of course I could be wrong). The
| only test spec I can remember is the primary-earth breakdown voltage for the
| 240V transformers I used to make, it was around 3kV. Are you saying they
| should be rated at 3kV but everyone should know only to use it on 240V?

When the rating says 240 volts, that is the _design_ parameter. While you
can know that it will withstand a lot more than 240 volts, it is not correct
for the expected design voltage to take advantage of that margin. That margin
is for the unexpected things.

If you are talking about a distribution transformer that is stepping 2400 volts
or something down to 240 volts, it will have a number of parameters that are
intended for its usage. But tests will go above that. When you get into MV
and the higher ends of it, this tends to not be as much as double for some
reason. Neverthless, it is wrong to use the voltage they test at as if it is
the design rating. I don't know what the design rating for whatever transformer
you made is. But I'm sure testing procedures added a margin over that and that
this margin was NOT so you could design it into a system that was intentionally
running it above the rated voltage.

| You don't know the test voltage. How can you say "You can lose your margin
| above 480 with sloppy manufacturing tolerances." when you don't even know
| what the margin is? It could be anything. If you find out that the (I guess
| its called the isolation voltage) test spec is less than say 600V then maybe
| you have something to worry about.

I can say that because I don't actually need to know the test voltage in order
to do the right thing ... which is to never, ever, design it into a system
where any design voltage applies will be above the _rated_ voltage. It is the
_rated_ voltage that I design to, not the _test_ voltage. So I do not need to
know the test voltage to do the design right; I only need to know the rated
voltage. Testing procedures will choose a test voltage as a means to ensure
the device is safe under circumstances I can't control in my design, such as
the manufacturing tolerances of the devices I would use.

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|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
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| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by stu on July 10, 2008, 9:14 pm

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> I can say that because I don't actually need to know the test voltage in

order

> to do the right thing ... which is to never, ever, design it into a system

> where any design voltage applies will be above the _rated_ voltage. It is

the

> _rated_ voltage that I design to, not the _test_ voltage. So I do not

need to

> know the test voltage to do the design right; I only need to know the

rated

> voltage.

So your car has 14V bulbs and relays? :)

Posted by on July 10, 2008, 10:16 pm

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|> I can say that because I don't actually need to know the test voltage in
| order
|> to do the right thing ... which is to never, ever, design it into a system
|> where any design voltage applies will be above the _rated_ voltage. It is
| the
|> _rated_ voltage that I design to, not the _test_ voltage. So I do not
| need to
|> know the test voltage to do the design right; I only need to know the
| rated
|> voltage.
| So your car has 14V bulbs and relays? :)

I'm not talking about cars. I'm talking about a home with a generator in
the system separated from a live utility by a single main breaker.

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|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
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| Usenet from these places, find another Usenet provider ASAP. |
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Posted by Cydrome Leader on July 10, 2008, 10:21 pm

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phil-news-nospam@ipal.net wrote:

> |> I can say that because I don't actually need to know the test voltage in

> | order

> |> to do the right thing ... which is to never, ever, design it into a system

> |> where any design voltage applies will be above the _rated_ voltage. It is

> | the

> |> _rated_ voltage that I design to, not the _test_ voltage. So I do not

> | need to

> |> know the test voltage to do the design right; I only need to know the

> | rated

> |> voltage.

> | So your car has 14V bulbs and relays? :)

> I'm not talking about cars. I'm talking about a home with a generator in

> the system separated from a live utility by a single main breaker.

So now it's a single breaker between the utility and the generator?

Is this home attached directly (no circuits breakers at all) to the
utility?

Posted by on July 11, 2008, 5:25 pm

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On Fri, 11 Jul 2008 02:21:14 +0000 (UTC) Cydrome Leader
| phil-news-nospam@ipal.net wrote:
|> |> I can say that because I don't actually need to know the test voltage in
|> | order
|> |> to do the right thing ... which is to never, ever, design it into a system
|> |> where any design voltage applies will be above the _rated_ voltage. It is
|> | the
|> |> _rated_ voltage that I design to, not the _test_ voltage. So I do not
|> | need to
|> |> know the test voltage to do the design right; I only need to know the
|> | rated
|> |> voltage.
|> | So your car has 14V bulbs and relays? :)
|>
|> I'm not talking about cars. I'm talking about a home with a generator in
|> the system separated from a live utility by a single main breaker.
|
| So now it's a single breaker between the utility and the generator?

It always has been. This is a case where the breaker supplying generator power
into the panel bus is in a closed state. So that breaker is not counted as a
breaker with a voltage across it.

| Is this home attached directly (no circuits breakers at all) to the
| utility?

There is a main breaker between the utility and the panel bus which is in an
open state when the generator breaker is closed.

The same situation exists when the main (utility) breaker is closed and the
generator breaker is open, when the generator is operating. But in this case
the series voltage potential exists across the poles of the generator breaker
that is open.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
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