4 wire delta

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lapseofmind

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So, I was going through the electrical system at the shop I work at(I honestly had nothing better to do) to better familiarize myself with things and found that their service is a 4 wire delta, 3 phase 120/240. I've only read about these, albeit briefly, during my apprenticeship and was wondering just how common(or better yet rare) are these systems?

It seems to work pretty well for what they have. It supplies all their 120 needs while also running their 230v welding machines and other heavy equipment(shears, mills, lathes, press breaks, etc).
 
As long as all of the supply equipment (POCO) is properly sized, it is a very satisfactory solution to the problem of both 120V and three phase 240V loads.
But some POCOs apparently are not offering them to new services and to a non electrician or an electrician who has not worked with them before, the high leg can be dangerous. It also requires non-slash-rated-breakers for three pole loads connected to the high leg.

Tapatalk!
 
It is definitely an interesting setup. The warehouse is pretty old and as far as I know has always been used as a fabrication shop. Now I know the high leg holds the higher voltage but can you tell me why it is more dangerous(besides the higher voltage)? Just so I know.

I haven't opened up the gear, nor do I ever intend to unless absolutely necessary.
 
lapseofmind said:
It is definitely an interesting setup. The warehouse is pretty old and as far as I know has always been used as a fabrication shop. Now I know the high leg holds the higher voltage but can you tell me why it is more dangerous(besides the higher voltage)? Just so I know.

I haven't opened up the gear, nor do I ever intend to unless absolutely necessary.
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The high leg to ground or neutral is 208V (approx). Someone not familiar with it could get hurt or cause serious problems.
The main problem occurs if someone were to run a single phase 120V circuit and unknowingly use the leg that had the 208V on it. If a 120V load were plugged into it, it will probably fry whatever is plugged into it because you would have 208V instead of 120V.
 
lapseofmind said:
It is definitely an interesting setup. The warehouse is pretty old and as far as I know has always been used as a fabrication shop. Now I know the high leg holds the higher voltage but can you tell me why it is more dangerous(besides the higher voltage)? Just so I know.

I haven't opened up the gear, nor do I ever intend to unless absolutely necessary.
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nothing more dangerous about it - especially when you ask for anything besides the high leg. Take away the high leg and you are left with a 120/240 single phase setup.
 
Well, so far it's been pretty dangerous there but I've been cleaning the place up. The welders dealt with 80v running across almost every piece of around them, I got shocked testing amp draw on the motor for a shear, the horizontal mill had exposed wiring from the oil pump in the reservoir, etc. Quite a bit of work but a good learning experience for someone like me.
 
lapseofmind said:
Well, so far it's been pretty dangerous there but I've been cleaning the place up. The welders dealt with 80v running across almost every piece of around them, I got shocked testing amp draw on the motor for a shear, the horizontal mill had exposed wiring from the oil pump in the reservoir, etc. Quite a bit of work but a good learning experience for someone like me.
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the fact you have 4 wire delta system had nothing to do with any of those problems, if it did it was installer's incompetence and not because it is a delta system.
 
kwired said:
the fact you have 4 wire delta system had nothing to do with any of those problems, if it did it was installer's incompetence and not because it is a delta system.
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well yeah, I figured that. I was just putting in those extra dangers I'm forced to deal with. Whoever wired this place up originally either wasn't an electrician, was really lazy or just plain incompetent.
 
The system is very common here.
We usually set up an equipment panel for the three phase loads and from that, feed a second panel with only single phase for lighting and receptacle loads.
This kinda mitigates the risk of someone unknowing getting into the high leg.
 
jrannis said:
The system is very common here.
We usually set up an equipment panel for the three phase loads and from that, feed a second panel with only single phase for lighting and receptacle loads.
This kinda mitigates the risk of someone unknowing getting into the high leg.
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Do you just send a 120V single phase line to the 120V panel, or do you send 240V over to help balance the load. Also, if the high leg was on B phase, do you use a 3-pole breaker and only connect two wires, A-C to feed the other panel?
 
Yes, you send 120/240 three wire to the panel. That way you can use standard panel and breakers and run MWBCs.
Also you can supply 240 loads that also need 120.
You can use a two pole breaker to feed the sub as long as you put it in the right place and label it not to be moved.
With a three pole breaker, you still need to install it in the right place so that the lead you leave open is the high leg. :)

Tapatalk!
 
GoldDigger said:
Yes, you send 120/240 three wire to the panel. That way you can use standard panel and breakers and run MWBCs.
Also you can supply 240 loads that also need 120.
You can use a two pole breaker to feed the sub as long as you put it in the right place and label it not to be moved.
With a three pole breaker, you still need to install it in the right place so that the lead you leave open is the high leg. :)

Tapatalk!
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Thanks for that! But I was asking Jrannis specifically how they did it!:D:slaphead:

I used to use a 3-pole breaker with only two leads (leaving out the high leg), that way I know the high leg wasn't going to the sub.

Unless someone moved the breaker!:cry::)
 
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Little Bill said:
Thanks for that! But I was asking Jrannis specifically how they did it!:D:slaphead:

I used to use a 3-pole breaker with only two leads (leaving out the high leg), that way I know the high leg wasn't going to the sub.

Unless someone moved the breaker!:cry::)
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Big cost difference between 2 pole and 3 pole. I say let those that don't know any better to learn the hard way not to mess with it:happyyes:
 
ActionDave said:
As long as you use A and C what else is there to worry about.
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Yeah I am missing any advantage gained by a 3 pole breaker.

Not a common system around me, in 30 years doing electrical I think I have only seen a high leg once or twice.

Not even an option for new services.
 
iwire said:
Yeah I am missing any advantage gained by a 3 pole breaker.

Not a common system around me, in 30 years doing electrical I think I have only seen a high leg once or twice.

Not even an option for new services.
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Kind of a fun thing about being in a big country. High legs are not the most common service to find but not a rare bird by any stretch.

Most any one here can tell you a story about the first time he needed to run a new circuit and found a panel with a whole bunch of empty spaces......
 
Around here, we run into neighborhoods that had it run to residences.
One 3 pole breaker for the A/C.
The stinger only fed this breaker, not the buss.
Made me scratch my head the first time I ran into it.
 
wirebender said:
Around here, we run into neighborhoods that had it run to residences.
One 3 pole breaker for the A/C.
The stinger only fed this breaker, not the buss.
Made me scratch my head the first time I ran into it.
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That be called a "delta breaker"

Little Bill said:
Someone sliding the 3-pole breaker up/down only 1 or 2 SP spaces and not re-landing the wires!
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2 pole or 3 pole doesn't matter, if you are moving things around you need to pay attention to where the high leg ends up especially if line to neutral loads are involved. I like it when someone messes up here, you can explain to them what happened and they still give you that clueless look, even an occasional electrical professional still has no clue.
 
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