Single phase appliance on a 3 phase panel?

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ActionDave said:
Both are saying it is ok to use the high leg in the panel for any single phase 240V loads that don't need a neutral. Both would agree that a straight rated breaker is required for any two pole breaker that uses the high leg.

One option that hasn't been mentioned is to use a three pole breaker provided there is room in the panel. They are less expensive than straight rated breakers.
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So a three pole breaker, but only using the two phases that are not the high leg?
 
If you had 3 full slots to utilize for my scenario, then we are back to square one and would just use the two legs that weren't high leg and just use a slash rated breaker. Lol, this sounds like a Seinfeld episode.

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wondervamp said:
After rereading, I see they agree. I'm just really trying get the lowdown on this for the sake of doing my part to keep the phases in balance.

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Yeah that can be a bit hard to do with the high leg delta. Most times all the single phase loads are pretty low. They supply a small office, break room, small water heater, shop receptacles. and lighting.

Really balancing single phase loads on 3 phase is kind of a crap shoot anyway. My buddy has a little commercial building with a 120/208 wye. Building has a laundromat, tanning salon and coffee shop in it. The current on the phases loosely follows the time of day, but depending on day of the week also. Thank god the tanning beds are 3 phase, those things are power hogs
 
Joethemechanic said:
Yeah that can be a bit hard to do with the high leg delta. Most times all the single phase loads are pretty low. They supply a small office, break room, small water heater, shop receptacles. and lighting.

Really balancing single phase loads on 3 phase is kind of a crap shoot anyway. My buddy has a little commercial building with a 120/208 wye. Building has a laundromat, tanning salon and coffee shop in it. The current on the phases loosely follows the time of day, but depending on day of the week also. Thank god the tanning beds are 3 phase, those things are power hogs
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Many high leg deltas around here are not designed to have the phase loads balanced. The often use a larger transformer to feed the A and C phases to permit larger 120 volt line to neutral loads.
All of them I have worked on had much higher line to neutral loads than three phase loads.
 
don_resqcapt19 said:
Pretty sure it has to do with the heat energy at the contacts. With a properly applied 120/240 volt slash rated breaker, the breaker contacts will only see heat energy of the fault current times 120 volts because only one contact sees the fault for a ground fault and the two contacts are essentially in series for a line to line fault. With a high leg fault the heat energy would be 173% higher.
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So it seems like a higher AIC rating would get you a straight rating too, but that doesn't seem to be the case - unless some breakers are actually the same but the mfg puts a different label and price on it.
 
don_resqcapt19 said:
Many high leg deltas around here are not designed to have the phase loads balanced. The often use a larger transformer to feed the A and C phases to permit larger 120 volt line to neutral loads.
All of them I have worked on had much higher line to neutral loads than three phase loads.
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Most around here are repair garages, welding shops, small machine shops. A 60 amp sub panel is more than enough for the 120/240 single phase loads. Air compressors, machine tools, electric welders etc. are the larger loads. PP&L doesn't offer it for new customers now if 3 primary phases are available.

Now you can only get 120/208 unless you want 480. It's a bit of a pia because most of the used equipment on the market is made 240/480.

  1. Three Phase, 4 Wire, 240 Volt, Delta Service:
    Three phase, 4 wire (grounded neutral), 240 Volt delta connected service is only allowed by special permission where two phase distribution is available. If three phase distribution is available, wye connected service must be taken.
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Rule 2

Rule 2
www.pplelectric.com www.pplelectric.com
 
The issue with slash rated breakers is the withstand capability under fault conditions. Phase to ground faults put the highest physical stress on multi pole breakers, because all of the mechanical forces are exerted onto one pole. So in a slash rated breaker, the ENERGY in the fault is never based on more than 120V, so it has lower mechanical stresses. If there is a fault from the High leg, the energy and stresses will be based on 208V, so the slash rated breaker may not hold together. If there is never a fault, you may never know that the breaker is different. But breakers have to be made for the worst case scenario.
 
Jraef said:
The issue with slash rated breakers is the withstand capability under fault conditions. Phase to ground faults put the highest physical stress on multi pole breakers, because all of the mechanical forces are exerted onto one pole. So in a slash rated breaker, the ENERGY in the fault is never based on more than 120V, so it has lower mechanical stresses. If there is a fault from the High leg, the energy and stresses will be based on 208V, so the slash rated breaker may not hold together. If there is never a fault, you may never know that the breaker is different. But breakers have to be made for the worst case scenario.
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So why can't say a 22 or 65 kaic slash rated breaker be straight rated at 10k or something?🤔
 
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