Tapping Transformer Secondary with HMCP's/Motor Starters

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MrJLH

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CO
If a transformer without secondary protection (primary only) were to be tapped with six combination motors starters with HMCP's would each tap still require an additional OCP for each individual feeder?

Ran into a similar installation like this but instead of fused disconnects the HMCPs/Starters are tapped directly off the transformer secondary with a tap scheme similar as pictured off the transformer secondary .

Thanks

Transformer Secondary Example.jpg
 

david luchini

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Unless it was a supervised industrial installation, which might permit such an installation, there would need to be an ocpd between the #4/0 and the #6 conductors.
 

kwired

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What exactly is the secondary voltage? If it were two wire - two wire single phase or delta-delta three wire, the secondary conductors can be considered to be protected by the primary device and you don't have a "feeder tap/transormer secondary tap" that 240.21 would apply to.

If secondary has a neutral, you are out of luck and can't tap the tap.
 

david luchini

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What exactly is the secondary voltage? If it were two wire - two wire single phase or delta-delta three wire, the secondary conductors can be considered to be protected by the primary device and you don't have a "feeder tap/transormer secondary tap" that 240.21 would apply to.

I don't believe that that is correct. The 3 wire Delta secondary conductors can be protected by an ocpd located on the primary side of the transformer per 240.21(C)(1).

240.21 says that a conductor protected in accordance with 240.21(A) through (H) shall not supply another conductor except through an ocpd.
 
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kwired

Electron manager
Location
NE Nebraska
I don't believe that that is correct. The 3 wire Delta secondary conductors can be protected by an ocpd located on the primary side of the transformer per 240.21(C)(1).

240.21 says that a conductor protected in accordance with 240.21(A) through (H) shall not supply another conductor except through an ocpd.
240.21 doesn't allow it per what you mentioned, but I think 240.4(F) does allow it, must comply with 450.3 and have device sized in accordance with primary to secondary voltage ratio.
 

david luchini

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240.21 doesn't allow it per what you mentioned, but I think 240.4(F) does allow it, must comply with 450.3 and have device sized in accordance with primary to secondary voltage ratio.

240.21 is clear that the #4/0 can't supply the #6 except through an ocpd.
 

kwired

Electron manager
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240.21 is clear that the #4/0 can't supply the #6 except through an ocpd.
And 240.4(F) is clear that in such situation that conductor is considered protected and therefore is not a tap conductor.

We essentially have a feeder with a transformer within the feeder. The primary overcurrent protection is the feeder protection If it is a 1:2 voltage ratio then the primary conductor ampacity to secondary conductor ampacity is also 1:2, and the primary OCPD still protects the secondary conductor.
 

david luchini

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And 240.4(F) is clear that in such situation that conductor is considered protected and therefore is not a tap conductor.

We essentially have a feeder with a transformer within the feeder. The primary overcurrent protection is the feeder protection If it is a 1:2 voltage ratio then the primary conductor ampacity to secondary conductor ampacity is also 1:2, and the primary OCPD still protects the secondary conductor.

The transformer secondary conductor is not a tap conductor, regardless of whether it is a delta-delta or delta-wye transformer. It is a transformer secondary conductor.

240.4(F) says that the transformer secondary conductors for a 3 wire delta secondary can be considered as protected by the primary OCPD if certain conditions are met. It doesn't say anything about connecting another conductor to the secondary conductor.

240.21 says that conductors shall have overcurrent protection AT THE POINT they receive their supply, EXCEPT as specified in 240.21(A) through (H). The EXCEPTION in 240.21(C)(1) permits the 3 wire delta secondary conductors to have their protection at other than the point that they receive their supply. 240.21 also says that Conductors supplies under the provisions of 240.21(A) through (H) SHALL NOT supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

SHALL NOT makes it perfectly clear that the #4/0 conductors cannot supply the #6 conductors directly. Nothing in 240.4(F) changes that.

(And that is not even taking into consideration that the #4/0 conductors in the image don't comply with 240.4(F) or 240.21(C)(1)).
 

MrJLH

Senior Member
Location
CO
What exactly is the secondary voltage? If it were two wire - two wire single phase or delta-delta three wire, the secondary conductors can be considered to be protected by the primary device and you don't have a "feeder tap/transormer secondary tap" that 240.21 would apply to.

If secondary has a neutral, you are out of luck and can't tap the tap.

The overall scheme is a ungrounded delta-delta 12.47kV Primary 480V secondary
 

kwired

Electron manager
Location
NE Nebraska
The transformer secondary conductor is not a tap conductor, regardless of whether it is a delta-delta or delta-wye transformer. It is a transformer secondary conductor.

240.4(F) says that the transformer secondary conductors for a 3 wire delta secondary can be considered as protected by the primary OCPD if certain conditions are met. It doesn't say anything about connecting another conductor to the secondary conductor.

240.21 says that conductors shall have overcurrent protection AT THE POINT they receive their supply, EXCEPT as specified in 240.21(A) through (H). The EXCEPTION in 240.21(C)(1) permits the 3 wire delta secondary conductors to have their protection at other than the point that they receive their supply. 240.21 also says that Conductors supplies under the provisions of 240.21(A) through (H) SHALL NOT supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

SHALL NOT makes it perfectly clear that the #4/0 conductors cannot supply the #6 conductors directly. Nothing in 240.4(F) changes that.

(And that is not even taking into consideration that the #4/0 conductors in the image don't comply with 240.4(F) or 240.21(C)(1)).
If the conductor is protected at or below it's ampacity it is no different than a feeder or branch circuit conductor. 240.4(F) says it is protected if the conditions mentioned are applied.

Transformer secondary conductors may not be called "taps" but are treated in almost same way as feeder taps as the overcurrent protection of either is at the load end of the conductor rather than the supply end. 240.4(F) is saying under certain situations this protection is on the supply side which makes it no different than a feeder or a branch circuit conductor - whichever applies depends on what is supplied.
 

david luchini

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If the conductor is protected at or below it's ampacity it is no different than a feeder or branch circuit conductor. 240.4(F) says it is protected if the conditions mentioned are applied.

Whether or not the conductor is protected at or below it's ampacity is irrelevant to supplying another conductor from it.

240.21 says that conductors must have overcurrent protection AT THE POINT where the conductors receive their supply EXCEPT as specified in 240.21(A) through (H). The transformer secondary conductors DO NOT have overcurrent protection at the point they receive their supply. The have overcurrent protection on the transformer primary AS SPECIFIED in 240.21(C).

240.21 also says that conductors supplied under the provision of 240.21(A) through (H) SHALL NOT supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

In the image, the #4/0 conductors CANNOT directly supply the #6 conductors (even if the #4/0 were properly protected). To do so would be a VIOLATION of 240.21.

I don't know how else to say the same thing. You can't use 240.4(F) as an excuse to violate 240.21.

240.4(F) is saying under certain situations this protection is on the supply side which makes it no different than a feeder or a branch circuit conductor - whichever applies depends on what is supplied.

240.4(F) doesn't say any such thing. Transformer secondary conductors are already feeder conductors (or possibly branch circuit conductors) by definition. Also, 240.21 makes no reference to 240.4(F).
 

kwired

Electron manager
Location
NE Nebraska
Whether or not the conductor is protected at or below it's ampacity is irrelevant to supplying another conductor from it.

240.21 says that conductors must have overcurrent protection AT THE POINT where the conductors receive their supply EXCEPT as specified in 240.21(A) through (H). The transformer secondary conductors DO NOT have overcurrent protection at the point they receive their supply. The have overcurrent protection on the transformer primary AS SPECIFIED in 240.21(C).

240.21 also says that conductors supplied under the provision of 240.21(A) through (H) SHALL NOT supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

In the image, the #4/0 conductors CANNOT directly supply the #6 conductors (even if the #4/0 were properly protected). To do so would be a VIOLATION of 240.21.

I don't know how else to say the same thing. You can't use 240.4(F) as an excuse to violate 240.21.



240.4(F) doesn't say any such thing. Transformer secondary conductors are already feeder conductors (or possibly branch circuit conductors) by definition. Also, 240.21 makes no reference to 240.4(F).
And they are already protected, making them no different than feeder or branch circuit conductors. 240.21 doesn't need to reference 240.4(F). 240.21 (before you get to part (A) says conductors must be protected at the point which they receive their supply. 240.4(F) is saying that protection is there if the conditions are applied.
 

david luchini

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And they are already protected, making them no different than feeder or branch circuit conductors. 240.21 doesn't need to reference 240.4(F). 240.21 (before you get to part (A) says conductors must be protected at the point which they receive their supply. 240.4(F) is saying that protection is there if the conditions are applied.

You are ignoring half of what the first sentence of 240.21 says.

I suggest you compare 240.21(C)(1) to 240.4(F).

The secondary conductors do not have overcurrent protection at the point the receive their supply. As such, they cannot supply another conductor except through an overcurrent device. You can't ignore a Code section because it doesn't suit you.
 

kwired

Electron manager
Location
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You are ignoring half of what the first sentence of 240.21 says.

I suggest you compare 240.21(C)(1) to 240.4(F).

The secondary conductors do not have overcurrent protection at the point the receive their supply. As such, they cannot supply another conductor except through an overcurrent device. You can't ignore a Code section because it doesn't suit you.
Sorry but I don't feel I am ignoring anything or making it suit my beliefs, it is how I see it, I can just as easily say you are doing what you accuse me of.

They are no longer "secondary conductors" because of 240.4(F) allowances, they do have overcurrent protection.


How do you get overcurent on conductors in question without tripping the OCPD, unless there is some catastrophic failure in the transformer, which likely trips primary protection anyway? A multiwire secondary is different, you can unbalance it and have high secondary current on only a portion of he secondary and not be enough primary current to trip primary device.

You are going to have to come up with something more black and white to convince me otherwise.
 

david luchini

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Sorry but I don't feel I am ignoring anything or making it suit my beliefs, it is how I see it, I can just as easily say you are doing what you accuse me of.

I'm not sure how you would accuse me of ignoring Code sections when I'm not ignoring any of the Code sections.

They are no longer "secondary conductors" because of 240.4(F) allowances, they do have overcurrent protection.

I find quite a bit of irony when you say "you don't feel you are making the code suit your beliefs" and "conductors connected to a transformer secondary are no longer transformer secondary conductors", in the same post.

You are going to have to come up with something more black and white to convince me otherwise.

I don't know what would be more black and white than the words "shall not supply another conductor"...literally in black and white...in the NEC.

But let's try this. Some simple yes/no question directed towards the application of the Code:

Question #1: Are the #4/0 conductors in the image supplied by the secondary side of the transformer?
 

MrJLH

Senior Member
Location
CO
I'm not sure how you would accuse me of ignoring Code sections when I'm not ignoring any of the Code sections.



I find quite a bit of irony when you say "you don't feel you are making the code suit your beliefs" and "conductors connected to a transformer secondary are no longer transformer secondary conductors", in the same post.



I don't know what would be more black and white than the words "shall not supply another conductor"...literally in black and white...in the NEC.

But let's try this. Some simple yes/no question directed towards the application of the Code:

Question #1: Are the #4/0 conductors in the image supplied by the secondary side of the transformer?


No I was just trying to use the figure pictorially. I don't have fused disconnect I have HMCPs.

Which is my problem in understanding this setup with using HMCPs "tapped" off a transformer.
 

david luchini

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Which is my problem in understanding this setup with using HMCPs "tapped" off a transformer.

You can't tap the transformer secondary conductors. You would need an ocpd between the secondary conductors and the taps.
I think the hmcp's would be allowed under 430.28.
 
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