wrote:

| My error here, you need to get your magic 480 to jump two breaker
| contacts, if one of your sources (utility or genset) is set to run your
| load. You're still welcomed to point out where UL says that snap in
| circuit breakers can't handle those voltages.

UL is not saying they can't. I believe that in general they will be able
to withstand even the 480. I do know UL tests for at least double voltage
and that is probably good enough for this scenario. But if double is all
they do _and_ if manufacturers get lax enough, the low end of tolerances
could end up with a breaker with a couple gaps that could arc over at 480
in a situation like this.

What I'd like to see is for the _rating_ to be double that of the expected
usage, much like we use 600 volt insulation system wiring for 120/240 volt
circuits in homes. Maybe they are doing this and just aren't saying so.
But if a device is rated for 480 it would be tested for 960 to at least
provide for a very good margin for a lot of unusual circumstance that in
rare corner of corner cases could lead to a breakdown. I would just like
to see them cite the rating as 480 in some way so I could be more confident.

--
|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 on July 8, 2008, 12:53 am

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wrote:
| phil-news-nospam@ipal.net wrote:
|> On Mon, 7 Jul 2008 20:12:00 +0000 (UTC) Cydrome Leader
|>
|> | Where do you keep coming up with 480 volts? Nobody in the US, where UL
|> | listed items are key has 240 volts from neutral coming into their home.
|>
|> In an open circut situation, the voltage that applies is the full voltage
|> of the circuit, not the voltage to ground. For example you have a 240 volt
|> applicance (or for simpler case, consider a 240 volt light bulb) on its
|> own circuit. When the two pole breaker is OPEN, the voltage potential
|> across BOTH poles is the full 240 volts. That is a series circuit that
|> involves an open gap, the resistance of the branch circuit wiring to the
|> load, the load impedance itself (in non-operating condition, such as a
|> cold light bulb), the return wiring of the branch circuit, and the open
|> gap on the other pole. If you measure the voltage across the terminals
|> of ONE of the poles of the OPEN breaker, you can get anywhere up to the
|> full 240 volts. This will be the gap breakdown voltage.
|>
|> Yes, it is 120 volts relative to ground. But the question is what is
|> relative between the two terminals of the open gap. That is 240 volts.
|
| you use tandem breakers for 240 volt split phase service. There is never
| 240 to ground or neutral.

I never said there was. The open gap is NOT "to ground" or "to neutral".

|> | Split 240 service is 120 volts to neutral x2. A 240 volt breaker can
|> | handle that, even if you have 120 volts from the utility and generator
|> | cranking out another 120 volts, out of phase. There's no 480 volts
|> | anywhere.
|>
|> Replace the load in the above scenario with a 240 volt source phased to
|> add the voltages in the circuit loop and you will have an open gap voltage
|> that could add up to as much as 480 volts for the same reasons the case
|> with just a load could add up to 240 volts. But in this case, it can be
|> worse because there is no actual load in series to limit the current to
|> a low value. The limit would be somewhat greater than the available fault
|> current of the generator (which might not be much for most home generators
|> but would be more than most loads).
|>
|> If the gaps do break down from the 480 volts open circuit potential, and
|> if the arc is sustained in both, this will give a voltage relative to
|> ground of just 120 volts, possibly reduced further by the high current
|> and the arc voltage drop. But it is a 480 volt open circuit potential
|> that has to be considered at both gaps
|
| If you start to do stupid things like disconnect your neutrals (so you can
| pretend you have 240 or 480 volts) you stand a great chance of destroying
| half your loads to begin with, with or without a generator or interlocks
| of any sort.

You would not get 480 volts from a single supply source by disconnecting
the neutral. Even with two supplies out of phase forming a 480 volt loop,
the loads themselves are not going to see that 480 because they will be
in parallel with the sources, not in series with the loop.

| Let's pretend you did just that, you've got split phase 240 into your
| already half burned out home, and some generator out back supplying the
| same, and you removed all your neutrals and grounds.
|
| you have 4 circuit breaker air gaps to jump with 480 volts. Are you now
| going to state that circuit breakers in the US arc over at 120 volts?

First of all, you only have 2 gaps to deal with because ONE of the source
breakers is closed while the other is open. You still have to deal with
the full _potential_ for air breakdown purposes because of even a tiny bit
of capacitive coupling in the "other" one. Once one of them gets an arc
to come across, its impedance changes to become the arc voltage drop
divided by the instantaneous surge current. If the other gap does not
also arc over at this time, the arc may well just extinguish and just be
a transient event. But if they both arc over (and that is the risk), then
you can have all that current flow come across. Hopefully the breakers on
the other source will now open and extinguish their own arcs in the act
and then it will be harder to fault when there are 4 gaps.

BTW, I hope you have not doubled bonded the neutral to ground.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by Neon John on July 7, 2008, 8:56 pm

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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.

>Where do you keep coming up with 480 volts? Nobody in the US, where UL

>listed items are key has 240 volts from neutral coming into their home.

>Split 240 service is 120 volts to neutral x2. A 240 volt breaker can

>handle that, even if you have 120 volts from the utility and generator

>cranking out another 120 volts, out of phase. There's no 480 volts

>anywhere.

The 480 volts across the breaker occurs when the generator on one side and the
utility on the other are 180 deg out of phase. It's meaningless, other than
to give people like Phil something to demonstrate their ignorance with.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
The secret to creativity is knowing how to hide your sources -Albert Einstein

Posted by on July 8, 2008, 1:08 am

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| 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.

|>
|>Where do you keep coming up with 480 volts? Nobody in the US, where UL
|>listed items are key has 240 volts from neutral coming into their home.
|>
|>Split 240 service is 120 volts to neutral x2. A 240 volt breaker can
|>handle that, even if you have 120 volts from the utility and generator
|>cranking out another 120 volts, out of phase. There's no 480 volts
|>anywhere.
|
| The 480 volts across the breaker occurs when the generator on one side and the
| utility on the other are 180 deg out of phase. It's meaningless, other than
| to give people like Phil something to demonstrate their ignorance with.

Someone with specific technical knowledge of any error I've made would be
able to point exactly to it. You have not. I remember Matthew L. Martin
over in the TV groups who make such accurations against me and several other
people for a few years and never, ever, pointed at anything specific to say
that was in error. That's why I get the impression you might be cast from
the same mold. Mr. Martin regularly and frequently twisted what people said
to give himself the opportunity to make a personal attack on someone.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by stu on July 8, 2008, 3:03 am

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> | 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?

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.

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