Dead break elbows

Is there any reason these days to use dead break connectors? I dont generally do MV, but I have sourced and terminated a few load break elbows, and was wondering if there would ever be a reason to use a dead break.

What got me thinking about this again is I just talked to the Seattle City Light Rep for a job I am doing where I need a disconnect reconnect. 25.5KV comes from a vault in/at the side of the street to the customer vault with 3 X 166KVA 120/208 bank. Rep said this would be difficult to connect because that road (Lake City Way) is all older dead break. This might be interesting.
 

Hv&Lv

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the nice thing though is on some of them you take the probe out, pull off the old elbow, clean it, slide on the new elbow and install the new loadbreak probe. New bushings or junction points and done.
we have swapped them out on a 30 minute outage.
 

paulengr

Senior Member
One big reason is live break elbows are much harder to remove. According to the standard it can take up to 120 pounds to remove and that’s if you can get on it and pull straight off.

Other good things are it’s simple to connect multiple elbows in underground which is what it’s for originally. The shield goes all the way around so very few failures compared to busbar air termination cabinets or mining square connectors or marine pin and sleeve. And if the transformer bushing gets messed up they can be screwed out and replaced. And you can safely test for voltage via the test point. And there are some very cool accessories like test points, stands, junctions, fuses,’and surge arresters.

The downsides are that you MUST have the right elbow if a new one needs to be installed, getting stuck on, often they just don’t have enough current capability to use on the low side, for the 35 kV version there Is a high stress point right by the lug so you need to follow installation instructions to the letter, and at very cold temperatures some of the early ones can arc when removed. But outside of these it drastically reduces removal and installation times for utilities.
 

Hv&Lv

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Are you saying that 600 and 900 amp are ONLY dead break? Breaking 600 amps of MV sounds interesting :cry:
I haven’t ever seen a 600 or 900 amp loadbreak.
Not saying somewhere in the world someone isn’t making one, but I wouldn’t pull it..
 

Hv&Lv

Senior Member
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Engineer/Technician
One big reason is live break elbows are much harder to remove. According to the standard it can take up to 120 pounds to remove and that’s if you can get on it and pull straight off.

Other good things are it’s simple to connect multiple elbows in underground which is what it’s for originally. The shield goes all the way around so very few failures compared to busbar air termination cabinets or mining square connectors or marine pin and sleeve. And if the transformer bushing gets messed up they can be screwed out and replaced. And you can safely test for voltage via the test point. And there are some very cool accessories like test points, stands, junctions, fuses,’and surge arresters.

The downsides are that you MUST have the right elbow if a new one needs to be installed, getting stuck on, often they just don’t have enough current capability to use on the low side, for the 35 kV version there Is a high stress point right by the lug so you need to follow installation instructions to the letter, and at very cold temperatures some of the early ones can arc when removed. But outside of these it drastically reduces removal and installation times for utilities.
Paschen’s law.
Partial vacuum flashover can be extremely scary when it happens to you while pulling off an extremely lightly loaded loadbreak elbow on 25 kV.
They are venting the elbows or bushings now to stop that or attempt to stop it.
heating blankets are a must if doing winter pulling on no load elbows.
 
And correct me if I am wrong, dead brakes are designed to be installed while the power is off, as opposed to live breaks that can be installed on live circuits.
Someone with more MV experience can clarify if I am wrong, but I believe the distinction is load versus no load. I believe a dead break can still be opened when live, just not when under load. Note it's called a "load break elbow" not a "live break elbow".
 

Hv&Lv

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Someone with more MV experience can clarify if I am wrong, but I believe the distinction is load versus no load. I believe a dead break can still be opened when live, just not when under load. Note it's called a "load break elbow" not a "live break elbow".
I wouldn’t make a habit of pulling a deal break elbow.

the distinction is the spring loaded trap door and the ceramic load break section on the end of the probe.

the correct nomenclature is “load break” and “Dead break”
Some call them “non-load break” which is wrong. Dead break are designed to be disconnected de-energized.

The 200 amp dead break doesn’t have to be bolt on, they use a bail to secure them. Pulling them energized can lead to arc flashing because they don’t have the trap door to extinguish the arc. (We won’t talk about how I KNOW that..)
600&900 amp are bolted on and impossible (or should be) to take apart energized.
 

zoeyisagirl

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I wouldn’t make a habit of pulling a deal break elbow.

the distinction is the spring loaded trap door and the ceramic load break section on the end of the probe.

the correct nomenclature is “load break” and “Dead break”
Some call them “non-load break” which is wrong. Dead break are designed to be disconnected de-energized.

The 200 amp dead break doesn’t have to be bolt on, they use a bail to secure them. Pulling them energized can lead to arc flashing because they don’t have the trap door to extinguish the arc. (We won’t talk about how I KNOW that..)
600&900 amp are bolted on and impossible (or should be) to take apart energized.
So nice you are, thank you very much. I am writing a blog related to a product named dead break connector but I don't know what it is. And I can't believe I could acquire answers so quickly as the last discuss was ended in 2020.
 
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