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Posted by Cydrome Leader on July 8, 2008, 12:22 am
Please log in for more thread options > 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.
>
>> | 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.
>
> 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?
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.
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