208 volts single pole usage ?

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Stevenfyeager

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United States, Indiana
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electrical contractor
In an old 3 phase panel, 120/208, every third space is 208 v to ground. These spaces are not being used, blanked off, probably for good reason. This museum used to be an auto body shop. What kind of machine or appliance runs on a single pole 208 v ? Thank you.
 
zbang said:
Sounds like a 240/120v high-leg delta panel; you only use that 3rd leg for 3-phase loads. (Check the phase-to-phase voltage, expect it to be 240v.) Pretty common for old installations.
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208 volt lighting, single phase 208 motors, etc., need slash rated breakers I think I recall.
 
The company I used to work for had a maintenance contract with an apartment complex whos service carried a "High Leg". The load centers were configured as a split-buss system with the high leg on the secondary buss. The high leg is normally used for the electric heating systems, air conditioning systems. And maybe the electric range and water heater?
 
PhenixFord said:
The company I used to work for had a maintenance contract with an apartment complex whos service carried a "High Leg". The load centers were configured as a split-buss system with the high leg on the secondary buss. The high leg is normally used for the electric heating systems, air conditioning systems. And maybe the electric range and water heater?
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I would hate to put a new electric range on that. There’s always the possibility of getting the clock or other 120 V stuff on the range hooked to the wrong leg
 
A slash rated breaker could not be used on the high leg as the voltage exceeds the lower voltage of the 120/240V rating, a 277V breaker could be used but I don't think the high leg is intended for a line to neutral load.
 
Stevenfyeager said:
In an old 3 phase panel, 120/208, every third space is 208 v to ground. These spaces are not being used, blanked off, probably for good reason. This museum used to be an auto body shop. What kind of machine or appliance runs on a single pole 208 v ? Thank you.
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As was mentioned, you don't have a 120V/208V service. You have a 240V/120V 3ø with a high leg, most likely an Open Delta. The "every 3rd space" would be the high leg and would be around 208V. Nothing really runs on the single 208V leg, it is part of the 3ø. Voltage between any two of the three legs would be 240V. Voltage between two of the legs measured to ground/neutral would be 120V each, and the other "high" leg would be 208V to ground/neutral.

The reason every 3rd space is blanked off is so someone doesn't try to run a single pole circuit thinking it is 120V when it's really 208V. It will ruin most 120V equipment to get 208V through it. Voltage wise, some equipment will run on the 208V single pole but it wouldn't be compliant to do so. You won't find a single pole breaker rated for that voltage that isn't slash rated.
 
Hv&Lv said:
I would hate to put a new electric range on that. There’s always the possibility of getting the clock or other 120 V stuff on the range hooked to the wrong leg
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I suppose, at least in my case, the confusion is somewhat mitigated by the split-phase panel board. And that the high leg is intended for dedicated circuits. Not 100% sure that the Range was on the service? If it was, I'm sure that it was designed for the voltage.
 
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PhenixFord said:
I suppose, at least in my case, the confusion is somewhat mitigated by the split-phase panel board. And that the high leg is intended for dedicated circuits. Not 100% sure that the Range was on the service? If it was, I'm sure that it was designed for the voltage.
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There is not (usually) a dedicated circuit for a high leg, just that it serve a 3ø load or a 2-pole single ø load. Maybe dedicated in the sense that they serve no loads that might include 120V circuits along with 2-pole, such as the already mentioned stove. But normally the caution is to stay away from it for 120V loads in general.
 
Feeding 240 volt 1 phase loads connected to high leg on a high leg service is often done as long as the breakers are properly rated. However, feeding 120/240 1 phase loads, such as a range, that require a neutral should not be done as you can never be sure that the load equipment won't get 120 volt loads connected to the high leg.
 
Little Bill said:
There is not (usually) a dedicated circuit for a high leg,
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I was referring to "dedicated" as in a: Service for a heating unit or Service for a water heater. More specifically as in "dedicated" to it's intended purpose.

The Split Phase Panels that I referenced earlier have (2) sets of main lugs. Note that this experience was back in the early 1980's and was my first exposure to High Leg Services. And the complex was well established in the community (possibly built in the late 60's / early 70's). My memory has somewhat faded over the years. But I do recall that the 1st set of ML's only contained the 120v/ 240v service conductors supplying the convenience loads. . And probably only contained about 12 circuit spaces. The 2nd set of ML's carried the High Leg and also only carried about 12 circuit spaces. What I cant remember is, if it were (Phase - Neutral) or (Phase - one of the other phases) connected to this set of ML's? Certainly, the High Leg buss only supplied the utilities for the apartment.
 
texie said:
However, feeding 120/240 1 phase loads, such as a range, that require a neutral should not be done as you can never be sure that the load equipment won't get 120 volt loads connected to the high leg.
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Most of my experience was with servicing these systems well before a range required a neutral. I haven't seen any other service's of this type in quite a while.
 
texie said:
Feeding 240 volt 1 phase loads connected to high leg on a high leg service is often done as long as the breakers are properly rated. However, feeding 120/240 1 phase loads, such as a range, that require a neutral should not be done as you can never be sure that the load equipment won't get 120 volt loads connected to the high leg.
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That is a good point I never thought of. Probably many have learned the hard way about the "bastard leg" as it's called around here.
 
Most common on 240/120 3 phase high-leg deltas is not to use the wild leg for anything but 2 or 3 pole loads. And there is no such thing as a 208 volt rated single pole circuit breaker.
 
Beaches EE said:
Most common on 240/120 3 phase high-leg deltas is not to use the wild leg for anything but 2 or 3 pole loads. And there is no such thing as a 208 volt rated single pole circuit breaker.
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So what Texie was saying if you use it on a 2 pole appliance that has a neutral you might burn out the controls or anything that is 120 volt, although I thought some appliances had a transformer to get the 120.
 
If the appliance or other load is anything but 240 volt without a neutral then it's best to not use the wild leg for one of the poles, yes.
 
PhenixFord said:
Most of my experience was with servicing these systems well before a range required a neutral. I haven't seen any other service's of this type in quite a while.
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Hmm, I've never seen a range without a three wire plug, until 4 wire range plugs came out. So if you mean "required a neutral" as a 4 wire plug, that's wrong, as the three wire plug had two hots and a neutral. It was the true equipment ground that was missing.
 
No matter how you slice it, don't use the "high leg" for single phase loads; just don't. If you have a 208/240v load, use the two main legs for 240v; if you must have 208v for some equipment, use a buck transformer.

Jreaf- I tend to agree, but SDSs could fight for the title.
 
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