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Zinsco breakers: slims vs standard, single vs 2 pole, 120 vs 240

Zinsco breakers: slims vs standard, single vs 2 pole, 120 vs 240

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Old 06-30-20, 02:19 PM
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Exclamation Zinsco breakers: slims vs standard, single vs 2 pole, 120 vs 240

We have a Zinsco style panel. We’re replacing it in a few months, but in the meantime it’s all we have to provide power to our trailer while we build a tiny house. Until we’ve finished all the house wiring and the panel for the house itself, we won’t know for sure what to replace the crappy old Zinsco panel with, so replacing it now would be foolish. Here is the existing breaker in the panel:


30 amp breaker from side angle

The slim style circuit breaker for the 30 amp 120v circuit the trailer is on has been getting hot and shutting off when the trailer AC is running, and arcing where the breaker connects to the bus. The bus is basically solid, but the surface is a bit rough from arcing between breaker and bus. For reference, rough means similar to medium to fine sandpaper, not raised lumps or craters. I’m thinking that replacing the existing breaker with a Standard width breaker (like this) will double the contact surface where the breaker clips onto the bus, and eliminate our breaker problems. But nobody carries it locally, so I can’t actually examine one to be sure it’s what we need. I’m hoping I can get the clarification I need here. There is a pic of the existing 30 amp slim breaker, one of the whole breaker, one showing the single wire that it connects to. Here’s what I think I need to know before ordering the part; please use “Explain Like I’m Five” language, because I’m just not going to understand if you use vernacular like “plug in” and “feed through”:

- The 2-pole standard appears to be a lot wider that the single pole slim. Will the metal clip contact area where the breaker connects to the bus be twice as wide as the single, and will that translate to doubling the width/size of the metal, current carrying contact area, thereby spreading out the connection surface area and reducing the possibility of arcing and heat buildup compared to the slim, single pole breaker? And if so, will that still be true if there’s only a single wire connected to the breaker? As in, is the area where the breaker clips to the bus split into two sections, with only one being used per wire? Here is a close up pic of the bottom of the existing breaker, you can see the one wire that connects the breaker to the outlet:




- I’m very confused about how the same breaker can be 120 or 240 volt. The guy at the local building supply place said that requires 2 wires connected to the breaker, and since we only have a single wire going to the outlet that the trailer is plugged into, that should not be an issue. But since very expensive **** will happen if I wire this for 240 by accident, I want to be sure I don’t do that.

- Do I even need a 2-pole breaker? I’m looking at that because it seems to be the widest, and therefore has the widest contact patch to spread out the conductive and heat load, and minimize heat buildup. From the pics I’ve seen online, the difference in width between the standard single pole 30 amp and the “new” slim style single pole 30 amp is not very much. Also the specs I’ve been able to find say the two-pole standard width can carry 13,000 watts, but the slim single poles can’t handle nearly as much load. Should I be searching for a single pole that is as wide a Standard two-pole breaker? If so, how do I do that.

- Again, the same guy at the building supply place said you need to cut the “bridge” between the two toggles on the Standard Width, 2-pole breaker in order for it to be 120 volt, otherwise it’s 240 volt? A short explanation of how one of these breakers gets configured to 120V vs 240V might help me, I tend to understand things better if I know a little of the underlying principles.


Any help will be greatly appreciated, most especially by my daughter in law, who is dealing with a toddler and a 6 month old in the 100 degree heat we often get here. The kids don't seem to care about the heat at all, but we adults need the AC when we're chasing the little demons around.
 
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Old 06-30-20, 03:08 PM
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The slim style circuit breaker for the 30 amp 120v circuit the trailer is on has been getting hot and shutting off when the trailer AC is running, and arcing where the breaker connects to the bus. The bus is basically solid, but the surface is a bit rough from arcing between breaker and bus.
That 30 amp breaker looks full size to me and it is a replacement breaker by UBI from Connecticut electric and not an original Zinsco breaker. Arcing at the aluminum bus is what happens to this style breaker and once the arcing starts the damage is done. Replacing the breaker might buy you a little bit more time, but moving the breaker to a space where the bus isn't pitted would help a lot more.


I’m thinking that replacing the existing breaker with a Standard width breaker (like this) will double the contact surface where the breaker clips onto the bus, and eliminate our breaker problems.
The 30 amp breaker is a single pole breaker and can provide 120 volts. The breaker you propose to replace it with is a 2 pole breaker which is used for 240 volt circuits because each pole connects to a different bus bar. The voltage across the two bus bars is 240 volts, you do not get 240 volts on a single wire. Changing to the 2 pole breaker really doesn't accomplish anything. The contact surfaces to the bus bars is the same.


Do I even need a 2-pole breaker?
I would say no. Evidently from your description and pictures the trailer only has 30 amp 120 volt feed.


Again, the same guy at the building supply place said you need to cut the “bridge” between the two toggles on the Standard Width, 2-pole breaker in order for it to be 120 volt, otherwise it’s 240 volt? A short explanation of how one of these breakers gets configured to 120V vs 240V might help me, I tend to understand things better if I know a little of the underlying principles.
As before, the 2 pole breaker is for 240 volt circuits and you need a 1 pole breaker so don't buy the 2 pole. If the 2 pole is all you can find it will work, but you only connect the feeder wire to one terminal. No need to cut the "Bridge" between the two handles as the other side of the breaker isn't used.

The 1 pole breaker has a contact and connects two only one of the vertical bus bars and from that bar it delivers 120 volts to the screw terminal where the wire terminates. The 2 pole breaker has contacts that connect to both vertical bus bars and thus provides 240 volts across the two terminals on the breaker where two wires in a 240 volt circuit would be terminated.

What are the other breakers in the Zinsco panel for, what do they feed? Where is this panel located?
 
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Old 06-30-20, 04:26 PM
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What are the other breakers in the Zinsco panel for, what do they feed? Where is this panel located?
The panel is on a short pole outside the shed where to water pump is. The other breakers are for the pump, and some outlets in the shed that only have a freezer, a couple of small lamps, and the internet modem and router. Nothing heavy duty besides the pump.

Yes, the trailer has a 30 amp plug. I was hoping to get a breaker where the contact that slips onto the upper bus is wider than the one we have now. I know there's new replacement breakers that are "slim style" and "Standard" width, and it seems like the standard ones are a tad wider. But without going into the store and eyeballing both, I can't be sure.

I know this may sound crazy, but can I reverse the lower clip on the 30 amp 2 pole so that it's in the upper slot, then run the second wire from the bottom to the same outlet, which should still be 120V because both are connected to the upper bus only? Jeez, just writing it makes me think that's not an option. I'm really just hoping for a breaker with a wider contact surface, to spread out the current and the heat buildup. If we were far enough along on the house build, we'd just replace that zinsco monster. But with the building inspectors here, we're afraid that they would look at it now and say "go ahead and put in that new panel", then come back after we've finished the house electrical stuff and say "hey, that panel isn't enough, you need to replace it". They have literally done this already with the house plans and the build; we've installed stuff according to the written and signed off plans, and had them tell us the code had changed and now we need to replace everything. Costing us about $2500 to replace what the plans told us to get in the first place.
 
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Old 07-05-20, 09:47 AM
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I'm really just hoping for a breaker with a wider contact surface, to spread out the current and the heat buildup.
You are out of luck with that hope. Regardless of which breaker you buy, they all have the same contact surfaces.
 
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