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Discussion Starter #1
I am going to have a 312v (more when fully charged) system that is
capable of drawing around 300amps.
So my question is can I use a Square D I-Line thermo-magnetic 3 pole
circuit breaker rated 350amps at 600v AC or 250v DC and wire it up so
that 2 of the poles are in series to increase it's rated voltage?

Thanks,
--
Tehben
'90 Toyota 4x4 Pickup
'hElix EV'
Website: www.helixev.com
evalbum: http://www.austinev.org/evalbum/1225

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Discussion Starter #4
Travis Gintz wrote:

> I just re-read what you said.
>
> you CANNOT increase the rated current just because you put
> them in series. Put the 2 poles in PARALLEL.

Hmmm... maybe you re-read the wrong post? ;^>

> On 10/31/07, Tehben Dean <[email protected]> wrote:
> > I am going to have a 312v (more when fully charged)
> > system that is capable of drawing around 300amps.
> > So my question is can I use a Square D I-Line
> > thermo-magnetic 3 pole circuit breaker rated 350amps
> > at 600v AC or 250v DC and wire it up so that 2 of the
> > poles are in series to increase it's rated voltage?

Yes, or more preciely, most probably ;^>

Check the Square-D literature to see if they include connection diagrams for this sort of application. I have seen diagrams from breaker manufacturers depicting their recommended connections when wiring poles in series to increase the voltage rating (or to acieve the stated DC voltage rating).

This is where you need to check the fine print carefully; sometimes the DC rating is specified assuming that the poles are already wired in series (i.e. the DC rating might be 125VDC for a single pole, but the datasheet lists 250VDC with a footnote referring you to an appropriate connection diagram showing 2 poles wired in series to achieve this maximum rating).

A couple things to point out:

- most EVs with breakers use a Heinneman (sp?) magnetic-hydraulic breaker; i.e. one without a thermal trip mechanism. The magnetic trip feature responds to peak current, not average (the hydraulic feature provided the delay characteristic). A thermal-magnetic breaker can trip at well under the rated current if it is enclosed such that it heats up, etc. as the thermal trip mechanism will respond to average current while the magnetic trip provides a faster response to brief/sudden peaks.

- with the magnetic-hydraulic breakers, one can easily use a breaker rated for a lower current than the peak that the system is capable of. For instance, I use a 250A breaker and pull 450A through it routinely and it has never tripped. A 350A breaker would normally be overkill for a 300A peak system, but due to yours including the thermal trip, it might still nuisance trip on you.

Hope this helps,

Roger.

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Discussion Starter #6
Hello Tehben,

It may work, it both breaker contacts open exactly at the same time. If one
contact opens a hair sooner then the other, then that one contact that is
still close, acts like a extension of the conductor and you may have only a
600 VAC- 250 VDC breaker.

I have temporary wire up breakers this way to keep some critical items
running until we can get a replacement.

Roland


----- Original Message -----
From: "Tehben Dean" <[email protected]>
To: "EV mail list" <[email protected]>
Sent: Wednesday, October 31, 2007 2:22 PM
Subject: [EVDL] 3 pole circuit breaker


> I am going to have a 312v (more when fully charged) system that is
> capable of drawing around 300amps.
> So my question is can I use a Square D I-Line thermo-magnetic 3 pole
> circuit breaker rated 350amps at 600v AC or 250v DC and wire it up so
> that 2 of the poles are in series to increase it's rated voltage?
>
> Thanks,
> --
> Tehben
> '90 Toyota 4x4 Pickup
> 'hElix EV'
> Website: www.helixev.com
> evalbum: http://www.austinev.org/evalbum/1225
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Discussion Starter #7
Travis Gintz wrote:

> But even then, 250A is nominal... and likely derated. Its
> likely got a much higher instantious current rating.... Call
> a local engineerinf firm and ask them... couldn't hurt.

Travis, Tehban described his breaker as 350A/600VAC and as having a 250VDC rating.

This makes it a 350A/250VDC breaker for sure, and if the ratings do not already assume multiple poles wired in series to achieve the 250VDC rating, then he is most likely able to wire two poles in series for a 350A/500VDC capable breaker.

The interrupt ratings are usually lower for DC than AC, but this will be spelled out in the datasheet (and it is usually something like 10,000-20,000A (or more) on AC and 5,000-10,000A on DC, so quite adequate for the perhaps 3000A short circuit available from a stack of group31 or smaller AGMs.

The manufacturer should also provide trip curves for the breaker, and these will show how the trip current varies with time. Be aware, however, that these curves will make some assumptions abou thow the breaker is mounted and cooled, etc., and so if the breaker is not mounted in a standard panel and does not cool as effectively as assumed in the trip curves, your mileage may vary. Specifically, if the breaker has a thermal trip feature and does not have the same cooling as the manufacturer assumes, then you could find that it heats up enough during normal driving (100-200A?) that it will trip when subsequently asked to carry 300A.

Cheers,

Roger.

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Discussion Starter #8
> Travis, Tehban described his breaker as 350A/600VAC and as having a 250VDC rating.

I read it wrong, I thought he wanted to increase the current rating...
oops... I see now that its a 250VDC at 350A and he wants 500VDC at
350A

> and if the ratings do not already assume multiple poles wired in series to achieve the 250VDC rating, then he is most likely able to wire two poles in series for a 350A/500VDC capable breaker.

I see where you're going. He's going to need the datasheet to see if
that is allowable

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Discussion Starter #10
Tehben Dean wrote:

> I looked on their website and this is all I found:
> Question: Are LH/LHL 2 pole breakers rated for use at 250 Vdc?
> Answer: Yes, 2 pole breakers are good for 50 kA at 250v DC. Three
> pole breakers can also be used .
>
> The breaker I was looking at is a 3 pole LH36350.
>
> It actually says this on the case: For 250volt DC service use
> outside poles only.

I'm afraid that this reads to me as stating that you require 2 poles in series to achieve the 250VDC rating. If each pole were rated 250VDC, then the statement would not have been that 2 pole and 3-pole breakers can be used for 250VDC service.

The use of the two outside poles of a 3-pole breaker is something I have seen in manufacturer connection diagrams as well. These diagrams are useful to refer to since the manufacturer may also want the poles "looped" to ensure that the load connected to the appropriate side of *both* poles.

Cheers,

Roger.

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