3phase Parallel Feeders only 5wires??

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JohnJK

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I ran across an old Square D panel that is rated @ 600A, 3Ph, 240V, it has twin sets of vertical bus bar, the feeders terminate on the bottom in this order ABC-CBA with a bar connecting the two C phase termination lugs but there are only 5 wires, what gives? Anyone ran across this? Look at this pic, most of the wiring is old TW, Panel might be from the 50/60's.
3ph 5wire.jpg
 
Intentional reduced capacity of the high leg? I assume originally (or currently since I can't see how much the high leg bus is skipped from this picture) most of the panel was feeding 120 volt loads and very few 240 1 phase or 3 phase loads where expected. Now I won't speak on the code compliance but I've seen it so much I know it certainly was common practice at some point. Almost every time i see this it was a terrible place for a delta...
 
TexasMaster said:
Intentional reduced capacity of the high leg? I assume originally (or currently since I can't see how much the high leg bus is skipped from this picture) most of the panel was feeding 120 volt loads and very few 240 1 phase or 3 phase loads where expected. Now I won't speak on the code compliance but I've seen it so much I know it certainly was common practice at some point. Almost every time i see this it was a terrible place for a delta...
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I would tend to agree with you. The center phase is bussed for only those bottom few breakers. Since this appears to be nippled to another enclosure, I would guess the neutral is in another nipple :)
 
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Dennis Alwon said:
Looks like a single phase bus on the left and a 3 phase bus on the right... Never seen one
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look closer to the bus, both sides look like three phase to me. The full exposed bus on each side only hits every third breaker space, if one side were for single phase only it would hit every other space, you just can not see enough of the other remaining buses because they are covered by the breakers.


My guess is also reduced capacity high leg. I will bet there is no reduced overcurrent device protecting it though - seldom is when you run into that.

Neutral - likely does enter through a different nipple - seen that many times and especially on installations roughly same age looking as this install.
 
Dennis Alwon said:
Looks like a single phase bus on the left and a 3 phase bus on the right... Never seen one
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Dennis, I assure you both sides of the bussing bars are 3phase. I haven't figured this one out yet, the Panel cover is like 6foot tall and weighs a ton, it has the old clips you rotate that never rotate properly so its a back breaking experience to take off. When I get about half a day of down time I'm going to explore greater into this. Its got me miffed.
 
TexasMaster said:
Intentional reduced capacity of the high leg? I assume originally (or currently since I can't see how much the high leg bus is skipped from this picture) most of the panel was feeding 120 volt loads and very few 240 1 phase or 3 phase loads where expected. Now I won't speak on the code compliance but I've seen it so much I know it certainly was common practice at some point. Almost every time i see this it was a terrible place for a delta...
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Since the feed to the high leg bus is identical to the others except for the jumper and the single wire, I would have to agree that they just sized the high leg feed smaller than the other two because most of the load was on the 120/240 leg and pot.
If this were a connection directly from the incoming service wires, I would say that it would be up to POCO to protect the high leg phase wire at whatever size was dropped and whatever the high leg pot (assuming open delta) could handle.
If this is a subpanel and feeder situation, then it is quite possible that the upstream OCPD is not correct for the wire size, making that wire a tap conductor. Now look at what the load on that phase (among other things) is to see whether or not it is a legal tap. :)

There is also a possibility that, way back when, this panel was wired up with no neutral feed and a raceway EGC, turned into a raceway neutral for the sake of line to neutral loads.
Or there may be only line to line loads but with unbalanced loads on the phases so that the line current in C is lower.

Note that the NEC currently requires that the high leg be landed on the B phase. :(
 
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kwired said:
look closer to the bus, both sides look like three phase to me. The full exposed bus on each side only hits every third breaker space, if one side were for single phase only it would hit every other space, you just can not see enough of the other remaining buses because they are covered by the breakers.


My guess is also reduced capacity high leg. I will bet there is no reduced overcurrent device protecting it though - seldom is when you run into that.

Neutral - likely does enter through a different nipple - seen that many times and especially on installations roughly same age looking as this install.
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Kwired, yes you are right both sides are 3phase. I haven't gotten to the bottom of this issue yet. I need to trace back the feeders and see where they originate. Note this is a commercial kitchen occupancy.
 
If it is a high leg delta panel is it possible that the two hot conductors on the left are feed through to a single phase panel with the non-highleg conductors for only single phase loads? also why we don't see a service neutral in this panel? also note the amount of smaller conductors feeding through this panel to the panel on the left, it looks like they brought the service feed into the panel on the left dropped off the neutral then continued with the three legs but then fed the single phase panel off the feed through lugs back into the other panel???

I'm just guessing at it, but you knew that already LOL
 
The double row bus bars were used in 400A and 600A, NQO and NQOB panels up to the early 80's. They were designed to allow large ampacity breakers without loosing useable space, due to the old 42ckt limit.

The Q1 family of breakers (70A and larger) looked like double wide QO breakers. When Q1 breakers were installed in these double row interiors they only took the space of a QO. The 'inside' portion of the bus bars was never intended to be used as space for QO breakers, although I have seen several instances where it was.

With the advent of the larger ampacity (70A and larger) QO breakers the Q1 family of breakers was obsoleted, thus removing the need for double row NQO/NQOB panels.
 
TexasMaster said:
"Commercial kitchen"... "240 3 phase"... I'm even more convinced its a cheaped out high leg.
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I see absolutely nothing wrong with the bussing in the OP picture. Everything appears to be standard construction. The factory jumpers between the (2) A and (2) B lugs is just not visible in this picture. I see room for at least 3 3-pole breakers on each side of the panel.

The bus connection finger for A and B phase are not visible, as they are covered by branch breakers.
Yes, this could be a 240/120V wild leg system, but that is not readily apparent. In these panels you could reconfigure the phasing of the branch breakers so it was easy to create a panel where only a few breaker positions were 3-phase while the rest were 1-phase.

Now field wiring is an entirely different issue. I have seen reduced capacity high leg conductors. I have also seen the second set of lugs used for sub-feeding a 1-phase only panel next to the primary 3-phase panel.
 
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induced current

induced current

I am curious as too whether an induced current could occur in the nipple as the high leg isn't pulled for the left group and there are all three legs in the right group with no nuetral. Any thoughts?

Bob
 
rlundsrud said:
I am curious as too whether an induced current could occur in the nipple as the high leg isn't pulled for the left group and there are all three legs in the right group with no nuetral. Any thoughts?

Bob
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Most likely those lugs are tied together by the bus making it essentially one bus per phase, you just have two lugs per phase to land parallel conductors, but even if not this would not be an issue with the high leg, what is an issue is wherever the neutral enters (assuming there is one entering elsewhere) it should be in the same raceway as the ungrounded conductors to prevent induced currents in the raceway.

You can kind of tell in the photo there is a connecting bar between the center two lugs, the connection between other phases is not in plain sight in the photo. ETA: look at the labels below the lugs, center ones both are "C" phase.

I seriously doubt the bottom breaker on each side is a main for each side, that style would have only been 100 amp max, and it sure looks like they intended to be able to handle at least 200 amps if each side is independent of the other. There also would about have to be a conductor from the outsides running either to the main lugs or to the bus and the back of the breaker would connect to the other (bus or lugs).
 
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kwired said:
I seriously doubt the bottom breaker on each side is a main for each side, that style would have only been 100 amp max, and it sure looks like they intended to be able to handle at least 200 amps if each side is independent of the other. There also would about have to be a conductor from the outsides running either to the main lugs or to the bus and the back of the breaker would connect to the other (bus or lugs).
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There are not two independent rows of bussing. This is a panelboard with parallel bus bars. This was normal construction for Square D back when they regularly used the Q1 family of breakers (circuits #21 and #22 which do not have load wires). I sold many of these.

There are clearly three sets of 3-phase connectors on each side. You can not see them as they are behind the breakers, all that is visible are the normal 'bolt-on' screws.

When these panels were built, the neutral bar was on the panel end opposite the incoming lugs, therefore it is not visible in the OP picture.
 
jim dungar said:
I see absolutely nothing wrong with the bussing in the OP picture. Everything appears to be standard construction. The factory jumpers between the (2) A and (2) B lugs is just not visible in this picture. I see room for at least 3 3-pole breakers on each side of the panel.

The bus connection finger for A and B phase are not visible, as they are covered by branch breakers.
Yes, this could be a 240/120V wild leg system, but that is not readily apparent. In these panels you could reconfigure the phasing of the branch breakers so it was easy to create a panel where only a few breaker positions were 3-phase while the rest were 1-phase.

Now field wiring is an entirely different issue. I have seen reduced capacity high leg conductors. I have also seen the second set of lugs used for sub-feeding a 1-phase only panel next to the primary 3-phase panel.
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I kind of quit speculating if it was or wasn't a delta at the op's "240 3 phase". Am I wrong? All I'm saying is in my experience this system in this type of application commonly comes with wasted spaces and unbalanced loads.
 
TexasMaster said:
I kind of quit speculating if it was or wasn't a delta at the op's "240 3 phase". Am I wrong? All I'm saying is in my experience this system in this type of application commonly comes with wasted spaces and unbalanced loads.
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Sorry I reread, op is stating the rating of the panel. Still someone put 1/2 the wire in for one phase and I can only think of one reason.
 
TexasMaster said:
I kind of quit speculating if it was or wasn't a delta at the op's "240 3 phase". Am I wrong? All I'm saying is in my experience this system in this type of application commonly comes with wasted spaces and unbalanced loads.
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Unbalanced loads yes.
Wasted space, depends on the panel. Ordering inexpensive panels with fixed bus connections 'wastes' every 3rd space. Panelboards with adjustable connections, like in the OP, can be configured as a mix of 3-phase and 1-phase only spaces.
 
jim dungar said:
There are not two independent rows of bussing. This is a panelboard with parallel bus bars.
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Maybe I wasn't all that clear, but that is what I was trying to say this likely is. I have seen a few similar panels around. Square D is and has been fairly common around this area.

TexasMaster said:
I kind of quit speculating if it was or wasn't a delta at the op's "240 3 phase". Am I wrong? All I'm saying is in my experience this system in this type of application commonly comes with wasted spaces and unbalanced loads.
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Depends on the application. If limited three phase loads - more chance of wasted spaces. If majority of load is three phase motors, load is pretty balanced.

If majority of load is 120 volt loads - one should consider 208/120 wye system if possible.
 
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