NEC, I disagree.

[David Weiszbrod]

I ran across a discussion about voltage ratings on single, double and three pole breakers used in a 240V open delta service. Article 230.85 says a breaker with a 120/240 volt rating cannot be used on a 208 volt phase. It describes the rating as the limit of voltage to ground. The breaker does not connect to ground except when its a GFCI and I am excluding the GFCI in the post. While the insulated case does touch grounded parts of the panel the voltage highest potential is between the poles of two adjacent phases. In the case of a two or three pole breaker the voltage potential between the poles within the breaker is 240 volts which is greater than 208V. If it's not safe on 208v then it's not safe on 240v.

Designed insulation voltage must include current interruption voltage. Contact voltages on inductive loads can be in thousands of volts but are usually short lived. On a two or three pole the first pole to open will have 240 volts plus inductive EMF across it. The action of one pole is connected to the other pole(s) to completely disconnect the circuit.

I contend that the 120/240 means (either/or) not exclusive or. A Siemens Q120 breaker has a rating of 120/240V. Does that mean it's suitable for European panels? I yes why not US?
What are your thoughts?

David

 

[LarryFine]

Welcome to the forum.

The lower voltage covers line-to-ground faults, while the higher voltage covers line-to-line faults.

The former requires one pole to interrupt the current, while the latter allows two poles to share it.

 

[David Weiszbrod]

The short of my post is Article 230.85 prohibits using a 2 pole breaker (marked 120v/240v) on a high leg. I don't see the hazard!
1/3 of the stabs in the panel are high leg. I need to use them where possible.

Do you think there is a hazard?

 

[augie47]

2 pole straight rated breakers are available albeit at a higher cost.
Why not use them and avoid any possibility of a problem.

 

[LarryFine]

Do you think there is a hazard?

That is a side debate with many NEC rules.

 

[electrofelon]

The short of my post is Article 230.85 prohibits using a 2 pole breaker (marked 120v/240v) on a high leg. I don't see the hazard!
1/3 of the stabs in the panel are high leg. I need to use them where possible.

Do you think there is a hazard?

I think the hazard is minimal to nonexistent. I do a lot of work in an area with tons of high leg delta services and I have NEVER seen the proper 2 pole breaker used when connected to a high leg. for siemens, it would be a Q220R for the "Straight" rated 2 pole 20 amp breaker.

P.S. My attorney has advised me to say the following: Nothing in the post should be construed that I have ever used the improper circuit breaker in such an application nor am advising anyone do so. Always follow the code for safety and liability reasons. May cause cancer in California.

 

[jim dungar]

A standard breaker has internal construction, such as insulation, for 120V to ground. When used on a 208V to ground application, there is a good possibility that the breaker will not clear the fault cleanly and safely.

Luckily most of the misapplied breakers have never been called on to to interrupt a large enough fault that they have failed.

Manufacturers make these special breakers in order to pass UL tests, not because marketing says they should.

 

[LarryFine]

And, it's possible that it's cheaper for the manufacturers to make all breakers capable of the higher voltage, and merely charge more for the higher-rated-labeled ones.

 

[don_resqcapt19]

I think the hazard is minimal to nonexistent. I do a lot of work in an area with tons of high leg delta services and I have NEVER seen the proper 2 pole breaker used when connected to a high leg. for siemens, it would be a Q220R for the "Straight" rated 2 pole 20 amp breaker.

P.S. My attorney has advised me to say the following: Nothing in the post should be construed that I have ever used the improper circuit breaker in such an application nor am advising anyone do so. Always follow the code for safety and liability reasons. May cause cancer in California.

But have you ever seen a fault from the high leg to ground on one of those breakers? That is where is a possible issue as the current from a 208 v line to ground fault will be much higher than from a 120 v line to ground fault. Where there is a line to line short circuit both poles act to interrupt the current flow

 

[electrofelon]

But have you ever seen a fault from the high leg to ground on one of those breakers? That is where is a possible issue as the current from a 208 v line to ground fault will be much higher than from a 120 v line to ground fault. Where there is a line to line short circuit both poles act to interrupt the current flow

I dont recall ever seeing a high leg to ground fault on one of those. But I agree that would be the issue. Its kinda like AIC and under-dutied equipment, its just quite rare to have issues due to so many factors having to align and happen. Dont get me wrong, I am not saying to use equipment that is not rated for the task, just that I dont find it to be as significant an issue as inspectors and plan reviewers make it out to be with it being the primary thing they check - that and grounding of course, and dont get me started on that

Curious, do you see the correct breaker for this application used where you are?

 

[don_resqcapt19]

I dont recall ever seeing a high leg to ground fault on one of those. But I agree that would be the issue. Its kinda like AIC and under-dutied equipment, its just quite rare to have issues due to so many factors having to align and happen. Dont get me wrong, I am not saying to use equipment that is not rated for the task, just that I dont find it to be as significant an issue as inspectors and plan reviewers make it out to be with it being the primary thing they check - that and grounding of course, and dont get me started on that

Curious, do you see the correct breaker for this application used where you are?

It is very rare to even see a 4 wire delta around here....been decades since I worked on one and that was long before I knew about the slash rating issue.

 

[LarryFine]

I, on the other hand, have been playing with them since I was a helper, which means 50+ years, so they're just another common system to me. I knew how to recognize them and what to check for.

We have a lot of older commercial buildings with them, many of which are conversions. A friend of mine grew up in a home with a high leg and a separate disconnect just for the A/C compressor.

Here's a high-leg open delta that supplies one of my favorite Waffle Houses. This one was obviously built new this way, and it's relatively older than most of the buildings around it:

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.

www.google.com

 

[electrofelon]

I, on the other hand, have been playing with them since I was a helper, which means 50+ years, so they're just another common system to me. I knew how to recognize them and what to check for.

We have a lot of older commercial buildings with them, many of which are conversions. A friend of mine grew up in a home with a high leg and a separate disconnect just for the A/C compressor.

Larry have you ever seen the correct 2 pole. breaker connected to the high leg used?

 

[LarryFine]

Larry have you ever seen the correct 2 pole. breaker connected to the high leg used?

Yes, but only when I was doing the work, because I was aware of it. I believe they cost more.

I have never thought to check an existing installation. I certainly will next time, and get a pic.

 

[electrofelon]

Yes, but only when I was doing the work, because I was aware of it. I believe they cost more.

I have never thought to check an existing installation. I certainly will next time, and get a pic.

Last I got one, it was a Siemens and was $95. 50% More than a three-pole.

 

[ActionDave]

It's cheaper to buy a three pole beaker and only use two of the poles.

 

[electrofelon]

It's cheaper to buy a three pole beaker and only use two of the poles.

If we are talking a true panelboard, the nice thing about Siemens is their standard 277/480 breaker (BQD) has the same bus mounting as their 240V bolt on breakers, and I think even one of those in a two pole is cheaper than the straight rated 240 version. Bonus: if you are feeling like a real renegade, you can get a single pole and connect it to the high leg to run something 208 to neutral

 

[LarryFine]

Bonus: if you are feeling like a real renegade, you can get a single pole and connect it to the high leg to run something 208 to neutral

Well, yes and no.

 

[TX+ MASTER#4544]

2023 NEC
Section 240.85 explains the applications and the slash rating for circuit breakers and the I Note for corner grounded delta systems.

Thanks for reading.
TX+MASTER#4544

 

[don_resqcapt19]

2023 NEC
Section 240.85 explains the applications and the slash rating for circuit breakers and the I Note for corner grounded delta systems.

Thanks for reading.
TX+MASTER#4544

that was covered in post 1 of this thread