Ran into something today.....

[stevephillips]

Was called to a church because light bulbs were burning out very fast. I show up and start asking my basic questions, (new problem, old problem, any new work, bad smells, etc..) They decided to demonstrate by putting a 75 watt incan in a lamp and turning it on. It burned out in about 1 second with a bright flash. Plugged into that same outlet was a computer, and some other officey equipment.

Went outside to get my fluke and looked up the pole and saw 2 pots, one big and one small. Hrmmm, open high leg maybe? Well, long story short, the buildings service is high leg delta. Outlet was putting out 208 volts.

Upon asking more questions, and speaking with the resident electrical "expert", the office needed more circuits so he added them. He found that every third slot was free and decided to use those.

The scary part, its been like this for over 2 years. The reason the computers didn't burn up is because they had universal power supplies (100-250 volt, 50-60hz) so 208 was right in the range. Its a good thing they never plugged a space heater.

I never could convince the resident "expert" that 240 phase to phase, 120 phase A and C to ground and 208 phase B to ground was normal. I ended up installing a sub panel with all the new circuits added to it.

Thought you guys might find this interesting.

 

[ActionDave]

I went on a call where an regular 120V recpt was tied to the high leg by a fella who was smart enough to do it on purpose. He rigged it up to run a small kiln.

When he moved out the landlord's cleaning crew moved in and smoked two vacuum cleaners.

 

[fmtjfw]

What out;et should he have used?

What out;et should he have used?

For 208V should you use the standard 240V 2/G NEMA 6-14R or 6-20R? or a depopulated 120/208V w/o/G 18-15?

My guess would be the 6-15R

 

[euboss]

You should NEVER connect a single phase load to the high leg of any open delta service. It is not designed for this application. I have seen refrigeration service men connect a compressor to the high leg because there were no open 2 pole spaces in the panel. Scary huh?:happysad:

 

[Jljohnson]

The issue with doing it "on purpose" regardless of the receptacle type used, is that the single pole breaker will ONLY be rated for 120 volts, not 208.

 

[stevephillips]

You should NEVER connect a single phase load to the high leg of any open delta service. It is not designed for this application. I have seen refrigeration service men connect a compressor to the high leg because there were no open 2 pole spaces in the panel. Scary huh?:happysad:

Just out of curiosity, why? (From an engineering standpoint)

I fully understand that the breaker would be seeing 208 as opposed to 120 like it was designed, but beside that, is there any real reason? What if a breaker rated for 277 was used? Only curious.

I am thinking of 208 loads such as kilns and maybe some motors. Again, only curious.

 

[texie]

Was called to a church because light bulbs were burning out very fast. I show up and start asking my basic questions, (new problem, old problem, any new work, bad smells, etc..) They decided to demonstrate by putting a 75 watt incan in a lamp and turning it on. It burned out in about 1 second with a bright flash. Plugged into that same outlet was a computer, and some other officey equipment.

Went outside to get my fluke and looked up the pole and saw 2 pots, one big and one small. Hrmmm, open high leg maybe? Well, long story short, the buildings service is high leg delta. Outlet was putting out 208 volts.

Upon asking more questions, and speaking with the resident electrical "expert", the office needed more circuits so he added them. He found that every third slot was free and decided to use those.

The scary part, its been like this for over 2 years. The reason the computers didn't burn up is because they had universal power supplies (100-250 volt, 50-60hz) so 208 was right in the range. Its a good thing they never plugged a space heater.

I never could convince the resident "expert" that 240 phase to phase, 120 phase A and C to ground and 208 phase B to ground was normal. I ended up installing a sub panel with all the new circuits added to it.

Thought you guys might find this interesting.

I once sent a lessor experienced electricain out to a tanning salon to add a circuit for another tanning bed. Well, as you can guess what the system was, it was an expensive mistake.

 

[kwired]

Just out of curiosity, why? (From an engineering standpoint)

I fully understand that the breaker would be seeing 208 as opposed to 120 like it was designed, but beside that, is there any real reason? What if a breaker rated for 277 was used? Only curious.

I am thinking of 208 loads such as kilns and maybe some motors. Again, only curious.

I don't see any problem with the load if you were to do this. If the breaker was rated 277 you would have a different panel type than what is commonly used. Multipole breakers would be rated 277/480 or just 480. That same rule applies to 480 volt delta systems - if voltage to ground is more than 277, a 277/480 rated breaker can not be used.

 

[zbang]

I once sent a lessor experienced electricain out to a tanning salon to add a circuit for another tanning bed. Well, as you can guess what the system was, it was an expensive mistake.

Please don't take this the wrong way, but don't these people have voltmeters? I can't see ever walking away from a job without actually testing the work. I mean, I've made some really dumb mistakes, but caught them when I checked the work. Or is the problem a lack of knowledge about things like high-leg systems?

"every third space was free", I like that. He never stopped to wonder why they were free....

 

[kwired]

Please don't take this the wrong way, but don't these people have voltmeters? I can't see ever walking away from a job without actually testing the work. I mean, I've made some really dumb mistakes, but caught them when I checked the work. Or is the problem a lack of knowledge about things like high-leg systems?

"every third space was free", I like that. He never stopped to wonder why they were free....

Guys that never run into such systems, sometimes have no idea what it even is. Guys that are in areas where they are common are often suprised when a system is 120/208 supplied by the utility. 120/208 derived from a 480 volt system is common pretty much anywhere if there is a 480 volt system from utility, but 120/208 for a smaller service where there is mostly single phase services in the area, like an old downtown district, is not so common around here anyway.

 

[broadgage]

The connection of significant load between the high leg and the neutral of a delta service is unwise.

Firstly the load current passes through two transformer windings, with voltage drop in each. Therefore the voltage may drop on load by a larger than expected figure.

Secondly, because the load current passes through two windings and causes heating in each, it is possible to overload the transformer despite the total KVA load being no more than the transformer bank rating.

I would not worry about loads that are a small percentace of the service capacity, but for large loads, no way.
And why would you need to ? 2 wire 208 volt loads are very rare.
Most are heating or cooking appliances that are dual rated for 208 and 240, and will perform better on 240.
3 phase 3 wire or 3 phase 4 wire 208 volt loads need a suitable 3 phase 120/208 volt service, not high leg delta.

If for some reason a small load is connected between the high leg and the neutral, then make certain that the breaker and any outlet is suitable for this application.

Rough service 130 volt lamps will survive 208 volts for an hour or two and will be very bright indeed for this short life.
I have heard of "red neck" photographers using this trick to obtain a very bright short term light for photographic purposes.

 

[zbang]

Guys that never run into such systems, sometimes have no idea what it even is. Guys that are in areas where they are common are often suprised when a system is 120/208 supplied by the utility.

Sure, but don't "they" even check the new outlets when they're installed? Seems kinda sloppy to install a new breaker, wire a receptacle, and not poke a meter in to see if it's live (or try all the switches of a 3/4/4/3 lighting setup). Ought to be easy telling the difference between 120 and 208. I suppose there are people that like to learn new things and some that won't bother, and not everyone is willing to say "how strange" and check things out.

 

[kwired]

Sure, but don't "they" even check the new outlets when they're installed? Seems kinda sloppy to install a new breaker, wire a receptacle, and not poke a meter in to see if it's live (or try all the switches of a 3/4/4/3 lighting setup). Ought to be easy telling the difference between 120 and 208. I suppose there are people that like to learn new things and some that won't bother, and not everyone is willing to say "how strange" and check things out.

I can't really speak for those that don't check it out after wiring it up. I can't say that I check everything myself every time, but kind of make it my own policy to check voltage, operation, rotation, things of that nature before leaving something I just connected.

One time had to fix a whole bunch of area lights at a cattle feed yard. POCO had underground primary line feeding the service, three phase conductors were buried but they only used two lines and connected the transformers open delta. It was some old underground and when one line went bad they would switch over to the unused line and repair the bad one at their own convenience. (This line has since been replaced but was the practice at the time to just swap underground lines when one went bad) Well one time when needing to swap lines the guys got it up and running and checked rotation at the mains before turning them on. Rotation was correct - but nobody thought to make sure high leg was in right position --OOPS! POCO paid for all the resulting repairs.

Another time at a local school building an elevator was being added. Building was supplied with high leg delta. Big city electrical contractor was contracted by elevator installers to run feed to supply elevator. They moved some items around in switchgear to get what they needed installed. The company I worked for did most of work needed, and service calls for this school, so we get a call saying a lot of items in cafeteria were not working. Come to find out when they moved items around in switchgear high leg supplying feeder to cafeteria area ended up in different position. Another OOPS! That contractor (or at least guys on job, I was pretty new in field at time but knew what a high leg delta was) acted like they never heard of such a thing. My boss and I both felt maybe they should stay away from wiring in rural areas and small towns as those systems are everywhere.