240.21(c)(4)

Status
Not open for further replies.
jim dungar said:
You literally cannot terminate directly to "listed" fuses, so we must infer the intent of the code when it tells us to do so. You can only terminate to fuse holders or disconnect switches with integral fuse holders.
Click to expand...

Can you terminate on a disconnect first and then route to an adjacent set of fuse (holders)? Would that meet 240.21(C)(4)? I'd say not. But it would be OK to terminate to a set of fuse (holders) first and then to an adjacent disconnect. So why would it be OK to terminate on the switch part of a fused disconnect first. It doesn't comply with the language of the code.

jim dungar said:
If 240.21(C)(4) is applicable only if you terminate on the fuses, then it can never be applied on circuits greater than 150V to ground.
Click to expand...

Nonsense. 240.21(C)(4) can be applied to circuits greater than 150V to ground by simply using a c/b instead of a set of fuses.
 
david luchini said:
But it would be OK to terminate to a set of fuse (holders) first and then to an adjacent disconnect.
Click to expand...
Not if the system is above 150V to ground.


So why would it be OK to terminate on the switch part of a fused disconnect first. It doesn't comply with the language of the code.
Click to expand...
How does a switch with integral fuse holders not comply? After all, it is a single device holding a single set of fuses.
 
Our wonderfull nec is full of articles related to one single installation. In this case where fuses are used, we must apply another article along with 240.21c.4. That would be 240.40. After that,rating of the enclosure, bending radius and so on must also apply as well.

In the one line, show the incoming feed going top side of the enclosure feeding the disconnect with fuses. 240.21C4(2) allows it and 240.40 requires it.

Rick
 
jim dungar said:
How does a switch with integral fuse holders not comply? After all, it is a single device holding a single set of fuses.
Click to expand...

Because the conductors would then terminate at the disconnecting means rather than at the OCPD. 240.21(C)(4) requires that they terminate at a single OCPD.

If you used a fused switch as the service disconnecting means, would it be OK to land at the fuses first (assuming less than 150V to ground?)
 
david luchini said:
If you used a fused switch as the service disconnecting means, would it be OK to land at the fuses first (assuming less than 150V to ground?)
Click to expand...
Not according to 404.6(C), based on the "Listed" construction of normal devices.

Using your strict interpretation of 240.21(C)(4) requiring termination only to the actual OCPD, you would also not be allowed to install any device that uses an external overcurrent relay fed by CTs, like a MV breaker.
 
jim dungar said:
Not according to 404.6(C), based on the "Listed" construction of normal devices.
Click to expand...

Then would a separate set of fuses be allowed to be installed before a disconnect switch at a service?


jim dungar said:
Using your strict interpretation of 240.21(C)(4) requiring termination only to the actual OCPD, you would also not be allowed to install any device that uses an external overcurrent relay fed by CTs, like a MV breaker.
Click to expand...

Why would I want to use a MV breaker on a system rated 600 Volts or less? 240.21(C)(4) does not apply to systems over 600V.
 
Last edited:
I am leaning towards David's point of view, if only because I, for one, should not be circumventing "Charlie's Rule." ;) I think it makes more sense to land on the switch, and I know there is no physical difference in the way the two configurations would operate (i.e., in terms of providing overcurrent protection). I also think the words, as written, don't allow it. That is why I asked the question.

To address one of David's earlier points, I think that if the fuses and the switch were in separate, adjacent enclosures, then it would not be acceptable to terminate on the switch. The difference is that this configuration brings another conductor into play. The tap rules address the tap conductor, but do not deal with conductors beyond the first point of connection.

I think I need to present this to the AHJ. There should be some room for the AHJ to conclude that terminating on the switch is equivalent to terminating on the fuse (holders).

Many thanks for the assistance, everyone. :D
 
I've got to agree with Jim and Larry on this one. I don't see any problem with terminating to the switch side of a fused disconnect. Otherwise, one could also argue that with a circuit breaker you are terminating on the LUG, and not the breaker itself. Using that logic, there wouldn't be any way to use this paragraph.

Sometimes it seems pretty clear that the intent of a particular paragraph is not the same as its literal iinterpretation. In these cases, I think we should be following the intent - we interpert the rule the way the people who wrote it intended it to be used. That's what lawyers do when they cite precedents in courtroom cases.

If we insist on following the literal interpertation of every word, we are going to wind up with some funny rules, no matter how careful the writers try to be. And that's not going to benefit anyone.

I think the "EMT through framing members poll" was another example of this. The "literal interpertation" people were on one side of the fence, and the "intent" people were on the other side.

Steve
 
david luchini said:
Why would I want to use a MV breaker on a system rated 600 Volts or less? 240.21(C)(4) does not apply to systems over 600V.
Click to expand...
I said a device that used a set of CT's and a relay as outlined in UL Category PAQX, a MV breaker was referred to as an easily identifiable example of that type of construction.
 
charlie b said:
I am leaning towards David's point of view, if only because I, for one, should not be circumventing "Charlie's Rule." ;) I think it makes more sense to land on the switch, and I know there is no physical difference in the way the two configurations would operate (i.e., in terms of providing overcurrent protection). I also think the words, as written, don't allow it. That is why I asked the question.
Click to expand...

Charlie,

What voltage is this system?
 
LarryFine said:
I consider a fused switch to be a single device.
Click to expand...

I'd consider a fused switch to be a single OCPD that is an integral part of a disconnecting means, as permitted by 240.21(C)(4)(3). But the conductors are still required by (C)(4)(2) to terminate at the OCPD and not the disconnecting means.
 
jim dungar said:
I said a device that used a set of CT's and a relay as outlined in UL Category PAQX, a MV breaker was referred to as an easily identifiable example of that type of construction.
Click to expand...

In that case, my clear interpretation of 240.21(C)(4) would allow that. A circuit breaker is a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent...

240.15 says that a combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit, and that an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. So the CT's, relay and a device to open the circuit, that you describe, is "a circuit breaker." It would be acceptable per 240.21(C)(4)(2).

A single manual disconnecting means, however, even when in the same enclosure with fuses, is NOT capable of opening a circuit automatically on a predetermined overcurrent.
 
david luchini said:
But the conductors are still required by (C)(4)(2) to terminate at the OCPD and not the disconnecting means.
Click to expand...


I don't think "terminated" means what you are taking it to mean.

In this case, I think terminated simply means that all the current through the tap conductors runs through the set of fuses.

For example, if I had a tap of 3/0 wire, couldn't I splice a larger wire in the middle of that tap, as long as the entire run ends in a proper overcurrent device?? Or would you say that isn't allowed because the 3/0 doesn't terminate directly on the fuses??

As long as all the pieces are rated to carry the same current that the tap conductor is rated for, and as long as those pieces are simply passing the power (as opposed to being a load), I think it would comply.
 
steve66 said:
I don't think "terminated" means what you are taking it to mean.

In this case, I think terminated simply means that all the current through the tap conductors runs through the set of fuses.

For example, if I had a tap of 3/0 wire, couldn't I splice a larger wire in the middle of that tap, as long as the entire run ends in a proper overcurrent device?? Or would you say that isn't allowed because the 3/0 doesn't terminate directly on the fuses??

As long as all the pieces are rated to carry the same current that the tap conductor is rated for, and as long as those pieces are simply passing the power (as opposed to being a load), I think it would comply.
Click to expand...

I'm taking "terminate" as to mean where the conductors end, not how they are connected. Per 240.21(C) and 240.21(C)(4), the transformer secondary conductors would "originate" at the transformer secondary and "terminate" at a single circuit breaker or single set of fuses.
 
charlie b said:
480 volts.
Click to expand...
Then you must have 'blades' on the supply side of your fuses per 240.40, end of discussion as to location.

Now, if you will not allow the conductors to terminate on a disconnect with integral fuse holders, then you may not use any of the following 'tap rules' above 150V L-G:
240.21(B)(1)(1)(b)
240.21(B)(2)(1)(b)
240.21(B)(4)(4)
240.21(B)(5)(2)
240.21(C)(2)(1)(b)
240.21(C)(4)(2)
240.21(C)(6)(2)
 
jim dungar said:
Then you must have 'blades' on the supply side of your fuses per 240.40, end of discussion as to location.
Click to expand...

No, then you must have a circuit breaker rather than fuses.

jim dungar said:
Now, if you will not allow the conductors to terminate on a disconnect with integral fuse holders, then you may not use any of the following 'tap rules' above 150V L-G:
240.21(B)(1)(1)(b)
240.21(B)(2)(1)(b)
240.21(B)(4)(4)
240.21(B)(5)(2)
240.21(C)(2)(1)(b)
240.21(C)(4)(2)
240.21(C)(6)(2)
Click to expand...

Wrong again, you may use any of those 'tap rules' above 150V L-G by using a circuit breaker instead of fuses.

(And (B)(1)(1)(b) and (C)(2)(1)(b) both allow termination at a "device" rather than OCPD.)
 
Status
Not open for further replies.
Top