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Joined: Aug 2005
Posts: 250
T
Member
Yup I'm not getting involved in any letters. I agreed to move any breakers off the hot leg and replace any currently bad contactors with whatever he supplies. He's paying cash, no receipt and I'm never coming back. I told him this and hes fine with it.

Thanks guys


Shake n Bake
Joined: May 2005
Posts: 984
G
Member
If they're powering something using the high leg that could be the problem. Single-phase loads can't be fed by the high leg and the neutral.

That voltage will read 208V on a meter but that's just a mathematical coincidence; you can't put any load on that or you're going to have nothing but trouble. All you have available to you with that type of system is 240V-3phase and 2 places that you can get 120V-1phase from.

Also, the total of the single phase loads is limited to 5% of the transformer rating or you'll start getting overheating problems in the transformer ahead of the Service.


Ghost307
Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
Originally Posted by Trick440
The contactor went to shut off and only 1 leg shut off, leaving the high leg energized and killing the ballast.? Idk.


You don't understand high-leg 240/120V 3-phase 4-wire systems.

When you have 2-wire loads connected to 240/120V, the troubleshooting, and potential problems, are no different than any other 240V system. If you routinely hold hold one meter probe to ground, or neutral, the 'low leg' will be about 120V and the high-leg about 208V. It is straight math, if the high leg is not 208V, then the low leg is not 120V.

So, if one contact stayed closed, then one ballast wire would still be energized. At worst, the ballast would see 208V to ground, which is exactly the same voltage it sees when it is operating. How is this a problem?

The biggest issue is when the equipment uses a neutral connection. Unless you know the internal wiring of the equipment, do not wire it to a high-leg.

Bad contactor contacts can lead to abnormal currents. Abnormal currents can lead to device failure.

Joined: Jul 2004
Posts: 9,669
Likes: 6
G
Member
This whole thread confuses me. If the ballasts are plugged 240 and the building is 208 wye, where is the 240 coming from?
Aren't ballast 2 wire (single phase) loads anyway? If one leg was open, no current should flow no matter what the voltage is.
If this is really high leg delta, 240v between legs, you really have to be careful with single phase loads. They should never be on the orange (high)leg even if they are line to line 240v. If they are not perfectly balanced, you will get into trouble. That leg will drift around, depending on the load. We used to have that problem in computer rooms and the only fix, if you are not going to be scrupulous about load balance is to get the PoCo to drop in that missing 3d transformer. At that point they will want to hook you up wye anyway. I have really only seen one place with center tapped delta and 3 transformers (behind the Hogs Breath in Key West). I assume they grew into it.


Greg Fretwell
Joined: Apr 2002
Posts: 7,283
Likes: 3
Member
Greg:
I've been scratching my head since page 1.

I used to do a lot of lighting maintenance in the day, both site lighting and interior. HID, fluorescent, etc.

Lots of contactors, both 'real' lighting contactors, and fabricated panels with definite purpose contactors. Never came upon anything like this.

Funny red leg though....one of my guys connected a 120 volt, single receptacle for a bottle type water cooler to the red leg. It took 3 coolers until someone said..."hmmmm"



John
Joined: Nov 2002
Posts: 791
W
Member
Originally Posted by gfretwell
...
If this is really high leg delta, 240v between legs, you really have to be careful with single phase loads. They should never be on the orange (high)leg even if they are line to line 240v. If they are not perfectly balanced, you will get into trouble. That leg will drift around, depending on the load. ...


Will this still be a problem if you somehow determine which of the 120V lines and the high leg the 2nd transformer is connected to? Idea being that your 240V load would be seen only by the 2nd transformer. Also this assumes that voltage drops in the wiring are minimal.

Joined: May 2005
Posts: 984
G
Member
Yes.
Any time that you try to put a single phase load on the high leg you're asking for trouble.


Ghost307
Joined: Jul 2004
Posts: 9,669
Likes: 6
G
Member
All single phase loads, line to line or line to neutral should be on the "big" transformer, the one that is center tapped. The only exception would be if there are 3 transformers on the pole and that is rare.
Usually red leg delta is done with 2 transformers and if the load is not very well balanced, you will drag that 3d leg around and upset the 240/240/240 relationship.

If your distribution looks like this, be careful with your load balance
[Linked Image from gfretwell.com]


Greg Fretwell
Joined: Jul 2004
Posts: 9,669
Likes: 6
G
Member
Just as gee whiz info, these are the transformers behind the Hogs Breath in Key West. The first thing that got my attention was that one was bigger than the other two and then I look at how they were connected. The fatter one is center tapped. This is the only time I have seen red leg delta using 3 transformers. My guess is the 3 bars it serves, does have a significant amount of single phase load and they fixed the balance problems or the load problem by dropping in the 3d transformer.

[Linked Image from gfretwell.com]


Greg Fretwell
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