Tandem Breakers.

[LarryFine]

I'll volunteer.

 

[Jraef]

The issue is slash-rated vs straight rated breakers.

A slash rating, such as 120/240V, means it's rated for 240V between any pair of conductors in the system, and not more than 120V to ground on the particular circuit where it's used. What you need for using on an ungrounded system, are straight-rated breakers, that are rated for the full 240V, regardless of where ground is within that range. An ungrounded system may generally be in a metastable state of being 120V to ground, but there's no guarantee that it remains that way. It could have a single line-to-ground fault, that goes undetected.

The majority of 1-pole breakers in general, are slash-rated. This is likely the case for tandem breakers as well.

I think this is the issue. It's not "ungrounded" systems, it is 240/120 3 phase 4 wire DELTA systems, where the B phase to ground is 208V potential. Single pole plug-in breakers, and by virtue of the fact that they use a single pole connection, Tandems, are only rated for maximum 120V reference to ground, so cannot be plugged into B phase on a 4 wire Delta panel.

When you have that kind of system, the breakers that plug into the B phase must be "fully rated" for 240V, not "slash rated" as in 120/240V. For most brands, there are 2 pole fully rated 240V options, but for single pole, no, which will mean having to use a 480V rated breaker like an I-Line Square D if you want a single pole plug-in.

 

[Jraef]

I'll volunteer.

View attachment 2576036

You had to dig deep into the archives for that reference eh? Think about it, Mathew Broderick played a "teenager" in that movie, even though he was 21 at the time, but he is now old enough to collect Social Security!

 

[Carultch]

You had to dig deep into the archives for that reference eh? Think about it, Mathew Broderick played a "teenager" in that movie, even though he was 21 at the time, but he is now old enough to collect Social Security!

That's from the movie, War Games.

 

[kwired]

When you have that kind of system, the breakers that plug into the B phase must be "fully rated" for 240V, not "slash rated" as in 120/240V. For most brands, there are 2 pole fully rated 240V options, but for single pole, no, which will mean having to use a 480V rated breaker like an I-Line Square D if you want a single pole plug-in.

In the Square D lineup there is the NF panels that have 277 volt rated single pole breakers and 277/480 volt rated two and three pole breakers.

If you have any version of 480 volt delta you do have to use the I-Line series to get a straight 480 volt rated breaker NF doesn't have that rating.

I am not all that familiar with other brands, especially for over 240 volts as have not been around all that many others very often. But I do believe there are some others that have a line similar to the Square D NF line that are likely 277 for single poles and 277/480 for two and three pole, but need to go to some other line if you need straight 480 rating.

 

[electrofelon]

In the Square D lineup there is the NF panels that have 277 volt rated single pole breakers and 277/480 volt rated two and three pole breakers.

If you have any version of 480 volt delta you do have to use the I-Line series to get a straight 480 volt rated breaker NF doesn't have that rating.

I am not all that familiar with other brands, especially for over 240 volts as have not been around all that many others very often. But I do believe there are some others that have a line similar to the Square D NF line that are likely 277 for single poles and 277/480 for two and three pole, but need to go to some other line if you need straight 480 rating.

Siemens is nice because their standard buss provision accepts both the 240V BL breakers and the 277/480 BQD breakers so you can mix and match. If you need a fully rated 480V or 600V breaker however, you will need to go to their xGB provision which is different.