No secondary over current protection?

[iwire]

I have an installation that I feel is in violation of a number of NEC sections and would like some other peoples thoughts as well

Here is the set up.

A 45 amp 3 pole breaker supplies the primary side of a 30 KVA 480 delta transformer , the secondary is three phase 240 phase to phase and 120 one phase to midtap. No 120 volt loads are being supplied. From the secondary side, 8 AWGs supply a non fused disconnect right beside the transformer from there 8 AWG is run about a 150? ? 200? to a 60 amp receptacle that in turn supplies a mobile freezer unit.

Here is sort of a one line of it.

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.

Here is what I come up with. Primary side is OK secondary side not so good.

240.21(C) (The installation does not meet any of the options)

210.21(B)(1) (There is no over current protection protecting the receptacle)

It seems to me there could be other violations as well. Any thoughts are appreciated.

 

[iwire]

Here is some more info from the transfomer.

 

[Pierre C Belarge]

I agree with the two sections you have posted.
What kind of wiring method is this installed in?

Since the requirements of 240.21(C) have not been followed, I believe you can also cite 240.4.

I wonder, is the transformer secondary grounded?

Even though there are no secondary neutral loads, is the grounded conductor run to the unfused disconnect?
How was/if is the transformer to first disconnect wired?

How about the identification of the highleg?

 

[RUWired]

I would check the load and make sure it does not exceed 80% of the branch circuit rating.(210.23(A)1 once the secondary protection has been established.

Rick

 

[iwire]

I agree with the two sections you have posted.
What kind of wiring method is this installed in?

A bit of everything, FMC / EMT / PVC / RMC / XHHW-2

Since the requirements of 240.21(C) have not been followed, I believe you can also cite 240.4.

I wonder, is the transformer secondary grounded?

I did not open the cover but it looked like they did a fine job of grounding the trranas to building steel.

The actual installation looks very well done and professional.

Even though there are no secondary neutral loads, is the grounded conductor run to the unfused disconnect?

No just an EGC.

How was/if is the transformer to first disconnect wired?

FMC

How about the identification of the highleg?

I don't think there is a high leg, I think there would be two 'high legs' but I am not real strong on transfomers.

 

[iwire]

I would check the load and make sure it does not exceed 80% of the branch circuit rating.(210.23(A)1 once the secondary protection has been established.

Rick

The load is approxmatly 24 amps @ 230 volt.

 

[Pierre C Belarge]

A midspan tap delta has 2 legs at 120 to ground and 1 leg at 208 to ground. See 110.15 for the identification requirement.

 

[pfalcon]

Did they use X4 and ground the secondary mid-tap?

Without X4, wouldn't this qualify to 240.21(C)(1)?
Would be: three-phase delta-delta with three-wire (single-voltage) secondary.

 

[iwire]

A midspan tap delta has 2 legs at 120 to ground and 1 leg at 208 to ground. See 110.15 for the identification requirement.

I do not believe that describes this tranformer.

I think this trans has:

240 phase to phase

1 phase 120 VAC to ground

2 phases greater than 120 to ground.

 

[iwire]

2 phases greater than 120 to ground.

Or less than 120 to ground, this where I get weak.

 

[pfalcon]

A midspan tap delta has 2 legs at 120 to ground and 1 leg at 208 to ground. See 110.15 for the identification requirement.

Or less than 120 to ground, this where I get weak.

X1 to X4 = 120V
X3 to X4 = 120V
X2 to X4 = 208V high leg
Provided X4 is used.

 

[jim dungar]

I do not believe that describes this tranformer.

I think this trans has:

240 phase to phase

1 phase 120 VAC to ground

2 phases greater than 120 to ground.

According to the laws of physics, the secondary voltages are:
X1-X2 = 240V
X2-X3 = 240V
X3-X1 = 240V
X1-X4 = 120V
X2-X4 = 208V
X3-X4 = 120V

X4-G is installation dependent. there is nothing on the nameplate that indicates what must be done with this terminal.

Because at least one secondary voltage will be >150V it can be argued that this transformer can be wired as an 240V un-grounded or 240V corner grounded. And as pfalcon said, if the X4 terminal is not used in the system (i.e. not connected to ground) you could consider this a single voltage secondary.

 

[DetroitEE]

Based on the diagram shown on the xfmr label, doesn't this look like it accurately describes the configuration? http://en.wikipedia.org/wiki/File:CenterTappedTransformer.svg

I could be wrong here, but at a glance it seems like the configuration matches up.

 

[iwire]

According to the laws of physics, the secondary voltages are:
X1-X2 = 240V
X2-X3 = 240V
X3-X1 = 240V
X1-X4 = 120V
X2-X4 = 208V
X3-X4 = 120V

That is interesting as the label seems to violate the laws of physics.

120 volts (1 PH to MIDTAP)

 

[augie47]

In my opinion, In that there is a XO tap, the supply meets the requirements of 250.20(B) and should be grounded. Also, with the XO, it does not meet the "no secondary" protection clause of 240.4(E).
It is debatable, I guess, if one could choose to ignore XO since it is not needed.
If you do look at it as a delta-delta situation, the the transformer secondary conducts would be considered protected by the primary. Then it would come down to the load supplied as to if overcurrent was required. So many items (motors, appliances, etc) have overcurrent rules which must be addressed.
In addition to all of the above 210.10(C) requires OCP for equipment.
In summary, with an XO, I think you must treat it as a non delta-delta system, and if you choose to ignore XO then only the conductors would be considered to be protected, not the equipment.

 

[iwire]

If you do look at it as a delta-delta situation, the the transformer secondary conducts would be considered protected by the primary.

I agree it could but that would have to be based on the turns ration and while I don't know it I figure 8 AWGs are not large enough and neither is the receptacle.

 

[augie47]

You are correct, I missed that..must be getting old . In this situation you would need OCP for the #8s based on the ampacity and turns ratio, in addition you would need OCP based on 210.10

 

[jim dungar]

That is interesting as the label seems to violate the laws of physics.

120 volts (1 PH to MIDTAP)

X1-X4 = 120V
X3-X4 = 120V

Where is the confusion? The fact that X2-X4 = 208V?

The label shows this as a delta transformer. This transformer does not have an X0, (a neutral point), it has a midtap X4 instead.

 

[iwire]

Where is the confusion?

My confusion comes from the fact the label states that only one phase to midtap = 120.

 

[Pierre C Belarge]

My understanding of a midspan tapped 240V, 3 phase delta system is for the midspan to have 120V between 2 legs, the 3rd leg will have 208V to ground.

120V X 1.732 = 208V

So as per the label, there are 2 legs with the 120V and 1 leg with the 208V to ground.

I have spent some time in the documentation I have, and that is pretty consistant.

But...manufacurers come up with new stuff all the time.

If you can, find out if in fact there is not a 208V highleg on the secondary side.