high-current single-pole breakers.

pharkusOctober 15, 2010

Alright, someone just handed me a single-pole 40A breaker... and the only thing that comes to mind is: WHY?

We can't legally install a 40A general-use circuit. What real-world large load would I ever use one of these for? Once you need more than a 20A circuit @ 120, why wouldn't the manufacturer have just gone to 240?

The breaker I've been handed is a quite-antique wadsworth, the kind whose handle SLIDES, so I will accept that its use is equally-archaic, but it still eludes me... and I've seen a 30A single-pole QO before, so apparently they're still around...

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"We can't legally install a 40A general-use circuit. "

Not all circuits are general use.

While most larger loads ARE 240 V, there are all sorts of weird things hanging around.

    Bookmark   October 15, 2010 at 1:46PM
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Ron Natalie

I've seen 30A single poles used all the time usually feeding L5-30R's. We used them extensively for larger computer servers. I've got one (I didn't install it) feeding my airplane hangar and I've seen them used for boat/mobile home hookups.

You're right, I've never seen a 40A single pole used to my recollection.

    Bookmark   October 15, 2010 at 4:24PM
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The only place I have seen 125V circuits above 30A is shore power for marine service. 125V, 50A was at one time fairly common.

    Bookmark   October 15, 2010 at 5:27PM
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I was looking for a partial enumeration of the "all sorts of weird things." :)

boats and RVs... didn't think of those... Airplane hangar? Is it feeding lights and one or more receptacles directly? Is that legal?

That's a BIG computer server!

    Bookmark   October 15, 2010 at 8:20PM
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cool! i dont know what it would be used for, but it is different. You could always use it to control a qo 2 space panel wita 2 20a berakers and recs, but you could just use a double pole cb with 12-3G

    Bookmark   October 16, 2010 at 12:12AM
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Racks of communications gear sometimes get up well past 30 amps @120 V.

They are not plugged, but hard wired.

Additional over-current protection is built into the rack of equipment.

While running a multi-wire circuit could be used, it adds additional issues with leakage currents between the equipment running on the separate legs.

It is easier to just keep everything on a single 120 V leg.

    Bookmark   October 16, 2010 at 9:20AM
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A couple of years ago I put in an off-grid solar power system for my sister. The inverter produces 4000W continuous and 8000W surge of 120V power. That is, it's a single pole system and no 240V is available anywhere in the system.

The AC panel "main breaker" is 70A. The breaker feeding her barn/utility building is 50A, the feed to the guest cottage is 40A, and the feed to the pump house is 25A -- all single pole. Had to order them on the 'net since the big box stores and electrical supply houses I checked didn't stock anything larger than 30A.

    Bookmark   October 16, 2010 at 8:22PM
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Griswold Family Christmas lighting project? :-)

    Bookmark   October 17, 2010 at 11:26AM
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There are plugs and receptacles available in very large ratings that are seldom seen in a residential setting.

    Bookmark   October 17, 2010 at 11:32AM
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Ron Natalie

The airplane hangar has a separate circuit for the lighting. The 30A circuit feeds a single L5-30R. I don't know the intended use, but that's what the hangar comes with for power. I've got a small breakout box that plugs into it that I run the block heater and a few tools off of.

    Bookmark   October 17, 2010 at 12:09PM
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