No secondary over current protection?

Status
Not open for further replies.
iwire said:
My confusion comes from the fact the label states that only one phase to midtap = 120.
Click to expand...

Maybe the label is implying that the 120V is single phase, not that its 120V from only one point. Not sure why they would put that on the label as its pretty obvious, but who knows.

I'm also curious why the mid tap X4 is not diagrammatically equidistant from it's adjacent taps, since after all it is 120V to both of the adjacent taps. I'm no transformer expert, maybe GE has their reasons...
 
Pierre, it appears to me Bob's post #14 confirms that this is the case (high-leg). Looking at his diagram I think confirms it also. I'm lost when it comes to "phase angles" etc., but looking at the X2 windings in the chart seems to confirm the readings he has.
The wording on the label (1 phase to midtap) might be a bit deceiving, but the diagram shows it fairly well, IMHO.
 
Last edited:
DetroitEE said:
I'm also curious why the mid tap X4 is not diagrammatically equidistant from it's adjacent taps, since after all it is 120V to both of the adjacent taps. I'm no transformer expert, maybe GE has their reasons...
Click to expand...

Maybe there is not 120 to both adjacent taps, I really have no clue.:confused:

I wish I could have taken some measurements but the unit was locked off. :)
 
iwire said:
My confusion comes from the fact the label states that only one phase to midtap = 120.
Click to expand...
No, the label says that for 120V you use the midtap point of X4. This tap is midway between X1 and X3 therefore both 'phase' X1 and X3 to X4 will provide 120V single phase. X4 is not midway from X2 to anywhere so that voltage is not defined, per the namplate (it will always be a nominal 208V on a 240/120 transformer).
 
DetroitEE said:
I'm also curious why the mid tap X4 is not diagrammatically equidistant from it's adjacent taps, since after all it is 120V to both of the adjacent taps. I'm no transformer expert, maybe GE has their reasons...
Click to expand...
It is shown correctly. It is midway between X1 and the jumper to X3.
 
augie47 said:
In my opinion, In that there is a XO tap, the supply meets the requirements of 250.20(B) and should be grounded. ....
Click to expand...
I'm looking at a 2005:
250.20.B.1 does not apply. One of the ungrounded conductors exceeds 150V

As for 250.20.B.3. It is not dependent on if there is an X0, but rather if, "the midpoint of one phase winding is used as a circuit conductor". As I understood Bob to say - it isn't used.

cf
 
Cold Fusion said:
I'm looking at a 2005:
250.20.B.1 does not apply. One of the ungrounded conductors exceeds 150V

As for 250.20.B.3. It is not dependent on if there is an X0, but rather if, "the midpoint of one phase winding is used as a circuit conductor". As I understood Bob to say - it isn't used.

cf
Click to expand...

Another day where I learned something on the Forum. When I read 250.20(B)(1) I didn't catch then point you noted. Wow!
Bob's pomit on turns ration and 210.10 would still be reason for OCP, I believe.
 
If the midspan of the said transformer is not grounded, then there is no midspan tapped delta 4 wire, it is simply an ungrounded delta system.

If the midspan is grounded, and the grounded conductor is not used, it is still grounded, and the system does fit 250.20(B)(3)

That would be the similar to a 208Y/120V system, with all 3phase loads not requiring a neutral/grounded conductor.
 
Pierre C Belarge said:
If the midspan of the said transformer is not grounded, then there is no midspan tapped delta 4 wire, it is simply an ungrounded delta system.

If the midspan is grounded, and the grounded conductor is not used, it is still grounded, and the system does fit 250.20(B)(3)

That would be the similar to a 208Y/120V system, with all 3phase loads not requiring a neutral/grounded conductor.
Click to expand...

Do I have my thinking correct now that I have read your post & Cold Fusions's post ?
From 250.21(B), If we have a midspan tapped 4 wire secondary, then we can choose to ignore the XO terminal and simply have a delta system.
If we have a 208Y/120 secondary, since the system "can be grounded" and meet 250.21(B) we would need to ground XO (and bond, etc)
If XO is used on either system, we have a grounded system.
 
iwire said:
Are we looking at the same label? :confused::confused:

I admit I have no clue and you are far more experienced.:) But I don't seem to be seeing what you do.:confused:
Click to expand...

The label shows:
Primary (H) 480 VOLTS (LINE - LINE)
Secondary (X) 240 VOLTS (LINE - LINE)

It does not say what exact connections are LINE, but from reading the diagrams or maybe past experience, you determined that the 480V connections were H1, H2, H3 and the 240V ones were X1, X2, X3.

The label also says 120 VOLTS (1PH - MIDTAP), but again it does not identify the connections. From reading either the pictorial or wiring diagrams, it can be determined that X4 is the only MIDTAP location and it occurs between the X1 and X3 connections.

So 120V is available from any 1PH (X1 or X3) to its midtap (X4), and 240V is available from any line to line (X1-X2, X2-X3, X3-X1, and X1-X2-X3).
 
Wow! Jim has the right of it.

Physically present:
240Vac ph-ph X1-X2; X2-X3; X3-X1
120Vac ph-0 X1-X4; X4-X3
208Vac High Leg ph-0 X2-X4 (Not used for power)

Three phase 240Vac loads use X1 & X2 & X3
Certain loads such as heaters may use X1-X2-X3; X2-X3-X1; X3-X1-X2
Single phase 240Vac loads use X1-X2; X2-X3; X3-X1
Single phase 120Vac loads use X1-X4; X4-X3

Load balancing should be done across all phases.
Loads between X1-X2; X2-X3; X3-X1 should be balanced.
Loads between X1-X4; X4-X3 should be balanced.

Midtap is X4 not X0; this is a delta so there is no X0. Only Wye has an X0.

Labeling states only that you can get 240Vac using ph-ph and you can get 120Vac using ph-midtap. It assumes you understand that means X1 or X3 to X4 from the drawing.

If X4 is unconnected this transformer reverts to an ungrounded delta that qualifies for 240.21(C)(1) with no secondary OCPD.

Primary only OCPD protects the secondary conductors under 25 ft in length but does not protect equipment. Read especially 240.21(C)(6) about ampacity of secondary conductors and how this must terminate at OCPDs.
 
iwire said:
... 480 volt panel > 45 amp breaker > 30 kva transformer > 8 AWG > non fused 60 amp disconnect > 175? 8 AWG > 60 amp receptacle > 60 amp plug > 75? 8/4 rubber cord > refrigeration unit. ...
Click to expand...

Oh BTW, your secondaries are too long (25' limit) and you are missing the terminating OCPDs for the run per 240.21(C)(6)
 
The secondary is a typical hi-leg Delta, just like the POCO supplies.

iwire said:
My confusion comes from the fact the label states that only one phase to midtap = 120.
Click to expand...
Note that the label doesn't show 240v three times either, but we know it's available.

DetroitEE said:
I'm also curious why the mid tap X4 is not diagrammatically equidistant from it's adjacent taps, since after all it is 120V to both of the adjacent taps.
Click to expand...
It's just because they happen to use an odd number of loops in the winding drawing. I don't believe anything can be deduced from the as-drawn off-center tap.

If there are both 120v and 240v available, the tap must be centered in actuality.
 
As it happens I had to send a guy out to that building on a service call. :cool: Sometime luck is with me.

The unit should be on now and I asked him to grab the voltage readings for me.
 
pfalcon said:
If X4 is unconnected this transformer reverts to an ungrounded delta that qualifies for 240.21(C)(1) with no secondary OCPD.

.
Click to expand...
240,21(C)1 says for single voltages only. The tag on the transformer states (2) voltages. If this was a single voltage out i would agree.

Rick
 
iwire said:
My confusion comes from the fact the label states that only one phase to midtap = 120.
Click to expand...
You need read that as "single phase", not as "one phase".
Without a connection to x4, you would not need protection for the secondary conductors, but they would have to be 90 amp conductors based on the primary OCPD being sized at 45 amps.
 
don_resqcapt19 said:
Without a connection to x4, you would not need protection for the secondary conductors, but they would have to be 90 amp conductors based on the primary OCPD being sized at 45 amps.
Click to expand...

Don, If it went that route wouldn't ground fault indicators be needed?

Could I supply a 60 amp receptacle without OCP?
 
Status
Not open for further replies.
Top