Double Pole Vs Single pole Breakers

[Craig]

Just had this question pop up on another thread.

What are the advantages/disadvantages of a double pole breaker compared to a single pole breaker for use in our systems.

I have been using double pole breakers because 3 years ago when I searched DC breakers that's what popped up.

 

[Rider]

I've always felt that breaking both legs of a circuit pretty much guarantees there isn't any chance of leaked voltage coming back from the other leg when referenced to ground. Break both legs and you're pretty safe.

 

[BiduleOhm]

What are the advantages/disadvantages of a double pole breaker compared to a single pole breaker for use in our systems.

Pretty much only safety; it is higher for the double pole but it probably cost a bit more.

 

[Xolar]

Nec 2017 is going to require that both positive and negative feeds are opened on the pv input, I am pretty sure it’s been require on ungrounded pv for quite a while as well

 

[John Frum]

I've always felt that breaking both legs of a circuit pretty much guarantees there isn't any chance of leaked voltage coming back from the other leg when referenced to ground. Break both legs and you're pretty safe.

Or in a wheel chair

 

[Bob142]

I've always felt that breaking both legs of a circuit pretty much guarantees there isn't any chance of leaked voltage coming back from the other leg when referenced to ground. Break both legs and you're pretty safe.

Welcome back.

 

[tictag]

I am not a qualified electrician, but I do know that disconnecting both Live and Neutral is mandatory in Caravans here in the UK (I live in a caravan) because it is quite possible that sites (or extension leads, adapters etc) could have the poles crossed meaning that if only the live was switched, a device could still end up being live and, assuming a ground fault (or no ground) potentially electrocute people.

I don't know anything about 'your' NEC but it kinda just makes sense to me to disconnect both.

I think there is also some issue with the earthing of Neutral lines, in that some are earthed locally, others at distribution, which can create potential differences. Not sure about this, just heard about it anecdotally. But another reason to disconnect both.

 

[SolarRat]

Nec 2017 is going to require that both positive and negative feeds are opened on the pv input, I am pretty sure it’s been require on ungrounded pv for quite a while as well

I can see why this may be important as you want to be able to disconnect outside (lightning prone?) devices from finding a path through an inside ground...but I can't think of many other instances in our systems where you would want to disconnect equipment on the ground side, for safety reasons. Of course for 240v split phase...but on DC systems, where? Why?

 

[John Frum]

I am not a qualified electrician, but I do know that disconnecting both Live and Neutral is mandatory in Caravans here in the UK (I live in a caravan)

It may or may not be required in NA but it sure makes sense here also.

 

[John Frum]

I can see why this may be important as you want to be able to disconnect outside (lightning prone?) devices from finding a path through an inside ground...but I can't think of many other instances in our systems where you would want to disconnect equipment on the ground side, for safety reasons. Of course for 240v split phase...but on DC systems, where? Why?

Would an open double pole breaker really help?

 

[Abby Smith]

Double Pole circuit breaker is like having 2 single pole circuit breakers. They are not interchangeable with single pose circuit breakers. Their advantage is that they provide two different circuits.

 

[Craig]

Double Pole circuit breaker is like having 2 single pole circuit breakers. They are not interchangeable with single pose circuit breakers. Their advantage is that they provide two different circuits.

Not necessarily these breakers are made for a positive and a negative input they are somewhat directional as well as tied together.

 

[Abby Smith]

Not necessarily these breakers are made for a positive and a negative input they are somewhat directional as well as tied together.

Are you saying that the outputs are shorted? Do you have a part number of the circuit breaker?

 

[SolarRat]

Double Pole circuit breaker is like having 2 single pole circuit breakers. They are not interchangeable with single pose circuit breakers. Their advantage is that they provide two different circuits.

I would not use a double pole for two seperate circuits. One reason is the mechanical force to keep the breaker closed is double that of a single breaker (harder to trip, i'd assume?). I just don't see the reason to even bother doing it that way?

 

[Craig]

Are you saying that the outputs are shorted? Do you have a part number of the circuit breaker?

I do not necessarily recommend this breaker the switch seams weak but I had it laying around so I could take a picture. Look at its little circuit diagram.

I am sincerely interested in learning the pros and cons of these things.

 

[Rider]

Are you saying that the outputs are shorted?

No. The two halves are mechanically tied together, not electrically.

One reason is the mechanical force to keep the breaker closed is double that of a single breaker (harder to trip, i'd assume?)

I would disagree. Think of the breaker as a mouse trap. Big ol' spring held by a tiny little clip. Once you hit the trigger, it's going to snap. Doesn't matter if there is one side or two, that spring, when trigger point is hit, is going to snap. If you took two separate breakers and tied them physically together, when you reach the rating of one breaker, the spring is strong enough to trip both breakers and stay in spec.

The discussion kind of mixed DC with AC applications. For the purposes of the OP, I'm pretty sure he was only talking about DC, as in the wires coming from the PV panel, as per the other thread he referenced. In that case, using a dual-pole breaker isn't protecting 2 circuits, it's protecting 2 halves of the same circuit, the positive and negative legs.

However, I believe the need for breaker protection on the PV line was moot, as per previous discussions. It would act primarily as a switch. Or did I miss an opposing view?

 

[svetz]

I'm only familiar with them in the U.S. where they're typically used to run two phases of 120V to a 240V AC device. But ultimately, it should be the same electrical footprint as any double-pole switch. That is it open/closes two circuits with a single throw.

So for DC power, where there is no phase change, I imagine it's the same ulterior purpose... some device where you want X watts over two wires that can carry .5 X. That is if one trips, you want the other to trip as it would be hazard for the device to be half-alive (either mechanically as some parts are trying to work, or via fire hazard). I don't see a point for example of putting the +/- battery leads onto a double pole DC breaker, you only need one to trip to break the circuit.

 

[Craig]

No. The two halves are mechanically tied together, not electrically.

I would disagree. Think of the breaker as a mouse trap. Big ol' spring held by a tiny little clip. Once you hit the trigger, it's going to snap. Doesn't matter if there is one side or two, that spring, when trigger point is hit, is going to snap. If you took two separate breakers and tied them physically together, when you reach the rating of one breaker, the spring is strong enough to trip both breakers and stay in spec.

The discussion kind of mixed DC with AC applications. For the purposes of the OP, I'm pretty sure he was only talking about DC, as in the wires coming from the PV panel, as per the other thread he referenced. In that case, using a dual-pole breaker isn't protecting 2 circuits, it's protecting 2 halves of the same circuit, the positive and negative legs.

However, I believe the need for breaker protection on the PV line was moot, as per previous discussions. It would act primarily as a switch. Or did I miss an opposing view?

Yes this is a DC only application.

 

[svetz]

I would not use a double pole for two seperate circuits. One reason is the mechanical force to keep the breaker closed is double that of a single breaker (harder to trip, i'd assume?). I just don't see the reason to even bother doing it that way?

Don't know about double pole DC breakers, but in double pole AC breakers, both trip if either exceeds the rated current for a single leg. That is, a 30 amp double pole breaker isn't 15 amps for each leg, it's 30 amps per leg (same as a switch). Well, if it's UL listed anyway...

 

[Supervstech]

I can see why this may be important as you want to be able to disconnect outside (lightning prone?) devices from finding a path through an inside ground...but I can't think of many other instances in our systems where you would want to disconnect equipment on the ground side, for safety reasons. Of course for 240v split phase...but on DC systems, where? Why?

Ground should NEVER pass through a breaker... grounding, where needed should be a PERMANENT path.
On 240V split phase circuits, each hot leg is fed through a breaker, and the grounding conductor is not broken, and it shouldn’t be.
On DC systems, the ground is not broken. The PV SUPPLY & RETURN path of the circuit should be broken by a breaker, and often the negative side is bonded to ground, or chassis.