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Thread: 120/240v breakers in delta high-leg panel. Violation?

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    120/240v breakers in delta high-leg panel. Violation?

    Hello,
    Would slash rated (120/240v) breakers not be allowed on the "B" or HIGH leg of the 240v Delta system since there is more than 120v line to ground/grounded conductor.
    I don't recall seeing anything but slash rated breakers on the high leg delta system (not that I have checked every breaker to verify).
    My questions:
    Does the code require straight 240v breakers for a 2-pole, 240v load (no slash rated 120/240)?
    Are 120/240v breakers unsafe if used on the high-leg system?

    Thanks a lot!
    DX

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    Quote Originally Posted by dxco View Post
    Hello,
    Would slash rated (120/240v) breakers not be allowed on the "B" or HIGH leg of the 240v Delta system since there is more than 120v line to ground/grounded conductor.1
    I don't recall seeing anything but slash rated breakers on the high leg delta system (not that I have checked every breaker to verify).
    My questions:
    Does the code require straight 240v breakers for a 2-pole, 240v load (no slash rated 120/240)?2
    Are 120/240v breakers unsafe if used on the high-leg system?3

    Thanks a lot!
    DX
    1: Yes, slash rated breakers would not be allowed to connect to the B phase wire, for exactly the reason you specify. Same for any phase combination on a corner grounded delta.
    2: If the load is connected line-to-line on a center grounded wye, or A to C on high leg system, slash rated is fine.
    If the load is connected line to line on a corner grounded delta, no, regardless of which two phase wires are used.
    3: Those slash rated breakers meed the code requirement in the situation you describe as long as they connect only to the A and C phase buses. That way they can serve either an MWBC, single 120V loads or a simple line-to-line 240V load which is no more than 120V to ground on either end.
    Are they safe? Sure, except to the extent that they serve as a bad example for somebody who later connects to the B phase for any reason.
    The most safe and understandable design would run only A and C and the neutral to a single-phase 120/240 3-wire panel for all 120V and 240V single phase loads and run A, B and C to a separate three phase panel for three phase loads only and using only full rated breakers.
    Last edited by GoldDigger; 10-14-13 at 04:31 PM.

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    Quote Originally Posted by dxco View Post
    Hello,
    Would slash rated (120/240v) breakers not be allowed on the "B" or HIGH leg of the 240v Delta system since there is more than 120v line to ground/grounded conductor.
    I don't recall seeing anything but slash rated breakers on the high leg delta system (not that I have checked every breaker to verify).
    My questions:
    Does the code require straight 240v breakers for a 2-pole, 240v load (no slash rated 120/240)?
    Are 120/240v breakers unsafe if used on the high-leg system?

    Thanks a lot!
    DX
    Anything that connects to the HIGH leg must be rated straight 240. Those breakers are not commonly stocked by most suppliers in the two pole versions. If you look at your three pole breakers they are rated 240 volts and not 120/240, so you never have that issue with a three pole breaker. You also will not find a single pole rated for more than 120, other than those designed for 277 volts in other series made for 277/480 purposes.

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    See 240.85 2011 NEC.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Thank you, and...

    Quote Originally Posted by GoldDigger View Post
    3: Those slash rated breakers meed the code requirement in the situation you describe as long as they connect only to the A and C phase buses. That way they can serve either an MWBC, single 120V loads or a simple line-to-line 240V load which is no more than 120V to ground on either end.
    Are they safe? Sure, except to the extent that they serve as a bad example for somebody who later connects to the B phase for any reason.
    The most safe and understandable design would run only A and C and the neutral to a single-phase 120/240 3-wire panel for all 120V and 240V single phase loads and run A, B and C to a separate three phase panel for three phase loads only and using only full rated breakers.
    Thank for the quick and informative replies. My understanding was correct but I needed confirmation.
    I agree that the best installation would call for a single phase sub with A, C & Neutral for the 120 & 240v loads -That way there is no chance of somebody coming along later and running a new 120v branch circuit using the high leg!
    But - If we are talking about a substantial load (mostly 240v lighting) wouldn't balancing the system be an issue?
    I'm thinking of installing all of the 240v loads in a 3ph panel (using ALL straight 240v breakers rather than a few slash-rated on the A to C loads)
    and a small sub for the 120s because I do like the idea of keeping any neutral-connected load out of the panel.

    One more thing: I had asked about the safety of slash rated breakers when misused by installing on the "B" leg. Other than setting a bad example, and that the installation would not be compliant, I'm curious as to the consequences. Or maybe a better question is, "what is the difference between slash rated and straight 240v breakers?
    Maybe the insulation rating is different.
    It seems to me that everything inside the breaker would be of the same spec's: The thermal and magnetic tripping properties would be exactly the same so there's really nothing left but the insulation and heat dissipation which might cost another 2 cents worth of plastic!
    Nothing logical warrants the huge difference in price between a slash and straight rated breaker.
    If anyone has any theory or knowledge about the actual difference in the breaker I'd be interested to hear.

    Thanks again for all who replied. DX

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    Quote Originally Posted by dxco View Post
    Thank for the quick and informative replies. My understanding was correct but I needed confirmation.
    I agree that the best installation would call for a single phase sub with A, C & Neutral for the 120 & 240v loads -That way there is no chance of somebody coming along later and running a new 120v branch circuit using the high leg!
    But - If we are talking about a substantial load (mostly 240v lighting) wouldn't balancing the system be an issue?
    Yes, which is why a typical high-leg delta is fed by POCO using a single large pot for A/C and either a single smaller pot for an open delta or two smaller pots for a closed delta.

    Quote Originally Posted by dxco View Post
    One more thing: I had asked about the safety of slash rated breakers when misused by installing on the "B" leg. Other than setting a bad example, and that the installation would not be compliant, I'm curious as to the consequences. Or maybe a better question is, "what is the difference between slash rated and straight 240v breakers?
    Maybe the insulation rating is different.
    The breaker has to be insulated from breakdown to the grounded parts of the metal panel that it is installed into as well as the operator touching the handle or front face of the breaker. Also the actual contacts of the breaker must be able to open against the full 240 volt applied voltage rather than just the lower line to ground voltage as would be the case in a phase to ground short. And the breaker must handle the resulting arc which would have a potential of more than 120 volts to other parts within that section of the housing as well as just withstanding creepage voltages between stationary parts. Depending on the breaker design, this may or may not be a practical problem.

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    Quote Originally Posted by dxco View Post
    I'm thinking of installing all of the 240v loads in a 3ph panel (using ALL straight 240v breakers rather than a few slash-rated on the A to C loads) and a small sub for the 120s because I do like the idea of keeping any neutral-connected load out of the panel.
    Just because you can, doesn't mean you should.

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    In the few times I've had to install anything delta; we've always used 480 pannels

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